the methods and compositions described herein utilize laboratory techniques well known to skilled artisans , and can be found in laboratory manuals such as sambrook , j ., et al ., molecular cloning : a laboratory manual , 3rd ed . cold spring harbor laboratory press , cold spring harbor , n . y ., 2001 ; spector , d . l . et al ., cells : a laboratory manual , cold spring harbor laboratory press , cold spring harbor , n . y ., 1998 : nagy , a ., manipulating the mouse embryo : a laboratory manual ( third edition ), cold spring harbor , ny , 2003 and harlow , e ., using antibodies : a laboratory manual , cold spring harbor laboratory press , cold spring harbor , n . y ., 1999 . methods of administration of pharmaceuticals and dosage regimes , can be determined according to standard principles of pharmacology well known skilled artisans , using methods provided by standard reference texts such as remington : the science and practice of pharmacy ( alfonso r . gennaro ed . 19th ed . 1995 ); hardman , j . g ., et al ., goodman & amp ; gilman &# 39 ; s the pharmacological basis of therapeutics , ninth edition . mcgraw - hill , 1996 ; and rowe , r . c ., et al ., handbook of pharmaceutical excipients , fourth edition , pharmaceutical press , 2003 . as used in the present description and the appended claims , the singular forms “ a ”, “ an ” and “ the ” are intended to include the plural forms as well , unless the context indicates otherwise . a 12 month - long nmn administration study using wild - type mice under a regular chow - fed condition was conducted . nmn was administered through drinking water , and two doses of nmn , 100 and 300 mg / kg body weight / day , were tested . the stability of nmn was examined in drinking water and found that nmn was stable in solution . no significant degradation was observed at room temperature . water intake was also monitored very carefully , and the water intake did not change significantly through the experimental period . to assess beneficial and possible adverse effects of nmn , a variety of physiological parameters were periodically monitored , including body weight , body temperature , food and water intake , fed and fasted blood glucose levels , fed and fasted plasma lipid panels , and glucose and insulin tolerance , in nmn - administered and control mice . blood chemistry , blood cell counts , urine strip test , and other physiological tests including physical activity test were also checked . based on all these assessments , no adverse effects , such as malnutrition , or signs of toxicity were observed in either of the 100 mg / kg or 300 mg / kg groups . two groups of wild - type c57bl / 6 mice at ˜ 2 months of age were fed a high fat diet ( hfd ) containing 42 % of the total calories from fat ( td88137 ; harlan taklad ). nmn at a dose of 300 mg / kg / day began to be administered through drinking water to one of the hfd - fed groups after 4 months of hfd feeding . the control group was fed a regular chow . after 8 months of hfd feeding with or without 4 months of nmn treatment , the contextual fear conditioning test , a sensitive test to examine the memory function that involves the hippocampus , was conducted for mice in these three groups . mice were maintained on a regular chow ad libitum on a 12 hr light / dark cycle ( lights on from 6 am to 6 pm ). namptflox / flox mice ( rongvaux et al , 2008 ), in which exons 5 and 6 of the nampt gene are flanked by loxp sites , were crossed to nestin - creert2 mice ( lagace et al , 2007 ) to generate nampt flox /+; cre double heterozygous mice . double heterozygous mice were bred to namptflox / flox mice to obtain namptflox / flox ; cre mutant mice ( inspc - nampt - ko mice ) in the expected mendelian ratio . to trace the progeny of adult nspcs and to confirm the specificity and magnitude of the recombination induced by tamoxifen injection , inspc - nampt - ko and nestin - creert2 mice were crossed to a reporter mouse strain that expresses a loxp - flanked stop cassette that prevents transcription of the downstream enhanced green fluorescent protein [ zsgreen1 ; jackson laboratories # 7906 ( madisen et al , 2010 )]. recombination pcr on hippocampal extracts of tamoxifen or vehicle treated mice showed successful deletion upon treatment with tamoxifen ( fig2 c ) tamoxifen injections were performed as described previously ( lagace et al , 2007 ). briefly , inspc - nampt - ko mice ( 5 - 7 weeks old ) were administered tamoxifen ( tam , sigma t5648 ) at 180 mg / kg / d for 5 days ( d , intraperitoneally ; dissolved in 10 % etoh / 90 % sunflower oil ), a protocol that produces maximal recombination with minimal lethality ( 5 %) ( lagace et al , 2007 ). 5 ′- bromodeoxyuridine ( brdu , sigma , b9285 ) was diluted in sterile saline and administered by intraperitoneal injections ( 100 mg / kg body weight ). for analysis of the cumulative effects of loss of nampt , mice were given brdu twice a day for 2 days and sacrificed the following day or 28 days later . for analysis of the effect of loss of nampt on adult nsc differentiation and postnatal oligodendrocyte differentiation , mice were given brdu twice a day for 1 day and sacrificed 2 days later . demyelination was induced by feeding 6 to 8 - week - old mice a diet containing 0 . 2 % cuprizone ( bis - cyclohexanone oxaldihydrazone ; sigma c9012 ) mixed into a ground standard rodent chow for 4 to 5 weeks ( harlan laboratories , td . 01453 ). to allow recovery from cuprizone treatment , food was replaced with standard chow for an additional 1 week . this protocol has been shown to successfully demyelinate and remyelinate the hippocampus ( skripuletz et al , 2011 ). all tissue sections were and cells incubated in blocking / permeabilization solution containing 10 % normal goat serum , 1 % bsa , and 0 . 3 % triton - x in pbs for 45 to 60 min prior to 24 or 48 h of incubation with primary antibodies in 5 % normal goat serum and 0 . 1 % triton - x in pbs at 4 ° c . at the concentrations listed below . alexa627 , alexa488 , or cy3 conjugated - secondary antibodies diluted in 2 % normal goat serum , 1 % bsa , and 0 . 1 % triton - x in pbs were added for 2 h at room temperature . nuclei were stained with 4 , 6 - diamidino - 2 - phenylindole ( sigma ) for 10 min at room temperature . cells were harvested by fixation with 4 % paraformaldehyde in pbs ( 15 min ). mice were anesthetized by i . p . injection of ketamine and xylazine , and perfused transcardially through left ventricle with cold 0 . 1 m phosphate buffer at ph 7 . 4 followed by a phosphate - buffered solution of 4 % paraformaldehyde ( pfa ). brains were postfixed with 4 % pfa overnight and placed into 15 % sucrose followed by 30 % sucrose , frozen , and stored at − 80 ° c . until use . coronal sections ( 30 μm ) were made by cryostat in a 1 in 8 series and stored at − 30 ° c . in cryoprotectant until use . to remove any endogenous peroxidase activity , all sections were incubated with 3 % h2o2 for 10 min . tissue sections used to assess brdu incorporation were treated before the immunostaining procedure with 50 % formamide in 2 × saline / sodium citrate ( ssc ) at 65 ° c . for 2 h , 2n hcl for 30 min at 37 ° c ., 0 . 1 m borate ph 8 . 5 , and then washed twice with pbs before proceeding with the staining protocol . tissue sections not used to assess brdu incorporation were either incubated in 50 % formamide in 2 × saline / sodium citrate ( ssc ) at 65 ° c . for 2 h or 10 mm citrate buffer at 65 ° c . for 1 h before proceeding with the staining protocol . detection of dcx , nestin , nampt , and apc was performed using the tsa - plus fluorescein kit ( perkinelmer ). for tissue sections , high - magnification ( 20 ×, 0 . 8dicii or 40 × oil 1 . 3dicii ) microscopic imaging was performed using a zeiss axioimage . z1 . images were taken in z - stacks of 1 μm steps through the range of tissue section immunoreactivity . for the dorsolateral corner of the svz , images were taken from bregma 1 . 10 to − 0 . 10 mm . for the corpus callosum , images were taken from bregma − 1 . 06 to − 2 . 54 mm . for the dentate gyrus , images were taken from bregma − 1 . 34 to − 3 . 64 mm . quantification was performed blinded to genotype on 3 - 8 tissue sections per animal . cell densities were estimated by the number of immunoreactive cells divided by the area of the structure , measured with imagej . verification of colocalization was achieved by importing stacks of z images into imagej and performing 3d rendering . for cells , 10 or 20 × microscopic imaging was performed using a zeiss axioimage . z1 . quantification was performed blinded to genotype on 2 to 3 fields of view per sample and treatment , from 3 to 9 independent samples . nad + levels were determined using an hplc system ( shimadzu ) with a supelco lc - 18 - t column ( 15 cm × 4 . 6 cm ; sigma ), as described previously ( yoshino et al , 2011 ). for individual genes , raw microarray data were subjected to z score transformation , and z ratios were calculated as described previously ( cheadle et al , 2003 ). subsequent analysis and parametric analysis of gene set enrichment ( page ) analysis was performed as previously described ( yoshino et al , 2011 ). the microarray data used in this study has been deposited into the ncbi geo database ( geo accession number ( gse49784 ). protein extracts ( 15 - 50 μg ) from mouse hippocampi or neurospheres were prepared as previously described ( yoshino et al , 2011 ). total rna was extracted from the hippocampus using an rneasy ® kit ( qiagen ®) and reverse - transcribed into cdna with a high capacity cdna reverse transcription kit ( applied biosystems ). quantitative real - time rt - pcr was conducted with the taqman ® fast universal pcr master mix ( applied biosystems ) and appropriate taqman ® primers for each gene with the geneamp ® 7500 ( applied biosystems ) fast sequence detection system . relative expression levels were calculated for each gene by normalizing to gapdh levels and then to a control . primary antibodies and their uses or cell type specificities ( see von bohlen und halbach , 2011 ): actin : normalization , wb 1 : 4000 cpo1 , sigma ; gapdh : normalization , wb 1 : 4000 6c5 millipore cb1001 ; nampt : ihc 1 : 1000 ; wb 1 : 3000 alexis biochemicals alx - 804 - 717 - c100 ; pdgfrα : oligodendrocyte precursor cells , if 1 : 500 apa5 bd biosciences ; olig2 : all oligodendrocyte lineage cells . ihc 1 : 500 , if 1 : 1000 ; millipore ; o4 : immature oligodendrocytes , if 1 : 1000 millipore , mab345 ; apc : oligodendrocytes , ihc 1 : 1000 millipore cc - 1 op80 ; mbp : mature oligodendrocytes , ic 1 : 1000 millipore mab386 ; ki67 : proliferating cells , ihc , if 1 : 500 ; wb 1 : 3000 abcam ab66155 ; pcna : proliferating cells , wb 1 : 2000 ; pc 10 cell signaling # 2586 ; 5 - bromo - 2 ′- deoxyuridine ( brdu ): a thymine analog that incorporates into the dna of cells in s phase , ihc 1 : 500 ; obt0030 accurate ; activated caspase 3 : apoptosis , ihc , if 1 : 500 : cell signaling # 9661 ; lc3b : autophagy , wb 1 : 1000 ; novus nb600 - 1384 ; tunel : cell death , roche in situ cell death detection kit 11 684 795 910 ; dcx : newly born neurons , ihc 1 : 1000 ; cell signaling # 4604 ; neun : mature neurons , ihc , 1 : 500 , millipore , mab377 ; nestin : nspcs , ihc , if 1 : 1000 , millipore mab353 ; sox2 : nspcs , ihc , if 1 : 500 ; wb 1 : 2000 ; millipore ab5603 ; gfap : nspcs and astrocytes , ihc , if 1 : 1000 ; millipore mab360 ; secondary antibodies : jackson immunoresearch anti - rat , anti - rabbit , anti - mouse cy3 ( 1 : 400 ), alexa fluor488 ® ( 1 : 200 ), and alexa fluor647 ® ( 1 : 200 ) ( life technologies corporation ). anti - rabbit , anti - mouse horseradish peroxidase ( invitrogen ). fk866 ( hasmann & amp ; schemainda , 2003 ) ( sigma f8557 ), ex527 ( peck et al ., 2010 ) ( cayman chemical 10009798 ), and agk2 ( outeiro et al , 2007 ) ( sigma a8231 ) were dissolved in dmso and used to inhibit nampt , sirt1 , and sirt2 respectively . neurosphere cultures and culture media were prepared as described by dasgupta & amp ; gutmann , 2005 and lu & amp ; ramanan , 2012 with the following minor modifications . briefly , postnatal hippocampi were dissected in hibernate - a ® ( invitrogen , a12475 - 01 ) and trypsinized at 37 ° c . for 7 m . cells were mechanically dissociated by pipetting and pelleted by centrifugation ( 1700 rpm , 7 min ). dissociation medium ( 0 . 1 % sodium bicarbonate , 15 mm hepes , 0 . 5 % glucose in hbss ) was used to wash the cells before they were resuspended in growth medium . growth medium consisted of dmem : f12 ( 1 : 1 , invitrogen 11966 - 025 and 21700 - 075 , respectively ), b27 ( invitrogen , 17504 - 044 ), n2 ( invitrogen , 17502 - 048 ), pen / strep ( invitrogen ), epidermal growth factor ( egf , 20 ng / ml , sigma , e4127 ), fibroblast growth factor ( fgf , 10 ng / ml , r & amp ; d systems , 233 - fb ), and heparin ( sigma ). cultures were maintained at 37 ° c . with 5 % co2 , and passaged twice before use in experiments . three to nine independent samples , each in 1 to 3 replicates , from at least two different litters , were used in all experiments . neurospheres were cultured in the physiological glucose level of 5 mm ( dienel & amp ; cruz , 2006 ), which has been previously shown to have no negative consequences on nspc proliferation , differentiation , or death ( fu et al , 2006 ; gao & amp ; gao , 2007 ). neurospheres derived from nampt flox / flox mice were infected with ad5 cre recombinase - or b - galactosidase - expressing ( lacz , control ) adenoviruses at an moi of 100 . all assessments were performed at least 6 days post infection . neurospheres derived from nampt flox / flox mice were dissociated by trypsin digestion and seeded at similar cell densities in 24 - well plates with fresh growth medium . every 24 hours , neurospheres from triplicate wells were collected , dissociated , and counted on a hemocytometer using 0 . 2 % trypan blue exclusion to distinguish viable cells . for analysis of neurosphere diameter , the largest neurosphere in each well was imaged ( 20 × objective ) and the diameter was calculated using imagej . for secondary neurosphere analysis , the total number of neurospheres in each well was counted at 7 days post - plating . three to five days after their first passage , neurospheres were trypsinized , washed with dissociation medium , and plated at 150 , 000 cells per well in 24 - well plates in differentiation medium [ growth medium without fgf and egf and with bdnf ( 5 ng / ml , peprotech , 450 - 02 ) on glass coverslips coated with poly - d - lysine ( 50 ug / ml ; sigma ) and laminin ( 20 ug / ml ; bd biosciences )]. 6 - well plates were coated with poly - d - lysine ( 20 ug / ml ) and laminin ( 10 ug / ml ). to enrich for oligodendrocytes , pdgfαα ( 10 ng / ml , peprotech 100 - 13a ) was added to neurospheres at passage 2 and pdgfαα ( 2 . 5 ng / ml ) and 3 , 3 -, 5 - triiodo - l - thyronine ( t3 , 40 ng / ml , sigma t4397 ) were added to differentiation medium . the percentage of oligodendrocyte precursor cells ( opcs ) generated was analyzed after 2 d of differentiation , and the percentage of differentiated oligodendrocytes was analyzed after 6 - 7 d of differentiation . differences between two groups were assessed using the student &# 39 ; s unpaired t - test . comparisons among several groups were performed using one - way anova with the tukey - kramer post hoc test except for fig1 j and fig2 d - e , in which the games - howell post - hoc test and the fisher lsd posthoc test were used , respectively . p values & lt ; 0 . 050 were considered statistically significant . a 12 month - long nmn administration study using wild - type mice under a regular chow - fed condition was conducted . nmn was administered through drinking water , and two doses of nmn , 100 and 300 mg / kg body weight / day , were tested . the stability of nmn was examined in drinking water and found that nmn was stable in solution . no significant degradation was observed at room temperature . water intake was also monitored very carefully , and the water intake did not change significantly through the experimental period . to assess beneficial and possible adverse effects of nmn , a variety of physiological parameters were periodically monitored , including body weight , body temperature , food and water intake , fed and fasted blood glucose levels , fed and fasted plasma lipid panels , and glucose and insulin tolerance , in nmn - administered and control mice . blood chemistry , blood cell counts , urine strip test , and other physiological tests including physical activity test were also checked . based on all these assessments , no adverse effects , such as malnutrition , or signs of toxicity were observed in either of the 100 mg / kg or 300 mg / kg groups . the present teachings including descriptions provided in the examples that are not intended to limit the scope of any claim or aspect . unless specifically presented in the past tense , an example can be a prophetic or an actual example . the following non - limiting examples are provided to further illustrate the present teachings . those of skill in the art , in light of the present disclosure , will appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the present teachings . this example illustrates a suppressive effect of nmn on age - associated body weight increase . in these experiments , nmn was administered to mice at a dosage rate of 100 mg / kg per day or 300 mg / kg per day . nmn demonstrated a suppressive effect on age - associated body weight increase in a 12 month - long nmn administration study . ( see methods : administration of nmn through drinking water and determination of nmn stability and toxicity ) in these experiments , nmn demonstrated a suppressive effect on age - associated body weight increase ( fig2 ). the results were analyzed with two - way ranova and one - way ranova with the unweighted linear term . all values are presented as mean ± sem ( n = 15 , 14 , and 14 for control , 100 , and 300 mg / kg nmn - administered groups ). average body weights in each group are shown through 0 - 12 months . there was a statistically highly significant interaction between time and group ( p & lt ; 0 . 001 from the two - way ranova ), and linear dose - dependent effects were statistically significant at all time points through 4 - 12 months ( p & lt ; 0 . 05 from one - way ranova with the unweighted linear term ). the average percent body weight reduction normalized to control mice were 4 % and 9 % in 100 and 300 mg / kg groups , respectively . this suppressive effect of nmn on age - associated body weight increase was further recognized by calculating body weight gains in each group ( fig3 ) in fig3 , average body weight gains in each group are shown through 0 - 12 months . the results were analyzed with two - way ranova and one - way ranova with the unweighted linear term . all values are presented as mean ± sem ( n = 15 , 14 , and 14 for control , 100 , and 300 mg / kg nmn - administered groups ). the interaction between time and group was statistically highly significant ( p & lt ; 0 . 001 from the two - way ranova ), and the linear dose - dependent effects were significant at all points through 2 - 12 months ( p & lt ; 0 . 01 from the one - way ranova with the unweighted linear term ). the average numbers of percent body weight gain suppression normalized to control mice were 12 % and 30 % in 100 and 300 mg / kg groups , respectively . taken together , these results from this 12 month - long nmn administration study demonstrate that nmn can suppress age - associated body weight increase in a dose - dependent manner , without showing any serious side effects during the entire experimental period . these results demonstrate that nmn can be used for the treatment , reduction or prevention of age - associated obesity . this example illustrates an enhancement of energy metabolism over age with nmn administration . in this long - term nmn administration study ( see methods ; administration of nmn through drinking water and determination of nmn stability and toxicity ), the inventors measured oxygen consumption , energy expenditure , and respiratory quotient for control , mice administered 100 mg / kg nmn per day and mice administered 300 mg / kg nmn per day at the 12 month time point by using the oxymax lab animal monitoring system ( columbus instruments , columbus , ohio ). fig4 shows oxygen consumption in control , 100 and 300 mg / kg nmn - administered mice . the data were analyzed by witcoxon signed ranks test . all values are presented as mean ± sem ( n = 5 in each group ). *** p & lt ; 0 . 001 . as illustrated in fig4 , oxygen consumption significantly increased in both 100 mg / kg and 300 mg / kg groups when examined at times 0 through 27 ( p & lt ; 0 . 001 , wilcoxon signed ranks test ). energy expenditure measurements also showed significant increases in both 100 mg / kg and 300 mg / kg groups through 24 hours ( p & lt ; 0 . 001 , wilcoxon signed ranks test ) ( fig5 ). energy expenditure in control , 100 and 300 mg / kg nmn - administered mice is presented in fig5 . the data were analyzed by wilcoxon signed ranks test . all values are presented as mean ± sem ( n = 5 in each group ). *** p & lt ; 0 . 001 . respiratory quotient in control , 100 and 300 mg / kg nmn - administered mice are presented in fig6 . the data were analyzed by wilcoxon signed ranks test . all values are presented as mean ± sem ( n = 5 in each group ). *** p & lt ; 0 . 001 . respiratory quotient significantly decreased in both groups ( p & lt ; 0 . 001 , wilcoxon signed ranks test ) ( fig6 ). without being limited by theory , these results suggest that nmn increases energy expenditure by switching their main energy source from glucose to fatty acids , thereby increasing fatty acid oxidation . without being limited by theory , this phenomenon could provide an explanation for the suppressive effect of nmn on age - associated body weight increase . this example illustrates a suppressive effect of nmn on age - associated increases in blood lipid levels . blood levels of cholesterol , triglycerides , and free fatty acids are shown over 12 months in the control and the 100 and 300 mg / kg nmn - administered cohorts in fig7 a - c . the results were analyzed with two - way ranova and one - way ranova . all values are presented as mean ± sem ( n = 25 for each group ). blood levels of cholesterol , triglycerides , and free fatty acids are shown over 12 months in the control and the 100 and 300 mg / kg nmn - administered cohorts . the results were analyzed with two - way ranova and one - way ranova . all values are presented as mean ± sem ( n = 25 for each group ). in the control cohort of a long - term nmn study ( see methods ; administration of nmn through drinking water and determination of nmn stability and toxicity ), blood levels of cholesterol showed steady increases over time , whereas blood levels of triglycerides and free fatty acids ( ffas ) peaked at the 6 - month time point and then decreased . however , in both 100 and 300 mg / kg groups , these age - associated increases in cholesterol and free fatty acids tended to be suppressed ( fig7 a - c ). in particular , the interaction between time and group was statistically highly significant for ffas ( p = 0 . 003 from the two - way ranova ), and the 300 mg / kg group did not show any statistically significant increase over time , whereas the control and the 100 mg / kg groups did show statistically significant increases over 12 months and the first 6 months , respectively ( p & lt ; 0 . 05 from tests of within - subjects effects in the one - way ranova ). all values are presented as mean ± sem ( n = 25 for each group ). although the average level of free fatty acids at the 0 - month time point in the 300 mg / kg group was significantly higher than those in the other two groups , nmn at the dose of 300 mg / kg suppressed age - associated increases in blood levels of ffas , particularly at the 6 - month time point ( p & lt ; 0 . 05 from the one - way anova with the dunnett t3 post - hoc test ). therefore , nmn is capable of suppressing age - associated increases in blood lipid levels , particularly blood ffa levels . without being limited by theory , since nmn has an effect of suppressing age - associated body weight increase , it was hypothesized that nmn &# 39 ; s effect on blood lipid levels could be due to the reduction in body weight . to address this possibility , lipid levels were compared among individual mice whose average body weights were matched through control and experimental cohorts . body weight - matched blood levels of cholesterol , triglycerides , and free fatty acids are shown over 12 months in the control and the 100 and 300 mg / kg nmn - administered cohorts in fig8 a - c . the results were analyzed with two - way ranova and one - way ranova . all values are presented as mean ± sem ( n = 10 - 15 for each group ). after matching body weight , blood cholesterol levels became very similar through control and experimental groups , whereas ffa levels were still lower in 100 and 300 mg / kg groups compared to those in the control group ( fig8 a - c ). even after body weight match , the interaction between time and group was still statistically highly significant for ffas ( p = 0 . 007 from the two - way ranova ), and again , the 300 mg / kg group did not show any statistically significant increases over time , whereas the control and the 100 mg / kg groups showed significant increases over time ( p & lt ; 0 . 01 from tests of within - subjects effects in the one - way ranova ). blood ffa levels tended to be lower in the 100 mg / kg and 300 mg / kg groups compared to those in the control group after the 6 - month time point , although the differences did not reach statistical significance ( fig8 c ). all values are presented as mean ± sem ( n = 10 - 15 for each group ). these findings indicate that nmn has the effect of suppressing the age - associated increase in blood ffa levels , independent of the reduction in body weight . without being limited by theory , the effect of nmn on blood cholesterol levels may be secondary to the effect of suppressing age - associated body weight increase . it has been reported that chronic treatment with nicotinic acid tends to increase blood ffa levels , whereas it lowers total cholesterol and triglyceride levels ( wang , w ., et al ., am . j . phyisol . endocrinol . metab . 279 , e50 - e59 , 2000 ). as shown herein , nmn has a capability of suppressing the age - associated increase in blood ffa levels , which distinguishes nmn from nicotinic acid . nmn is also able to reduce cholesterol levels through the suppression of age - associated body weight increase . whereas chronic administration of nicotinic acid can cause skeletal muscle insulin resistance ( fraterrigo , g ., et al . cardiorenal . med . 2 , 211 - 217 , 2012 ), nmn does not show any adverse effect on glucose metabolism . therefore . nmn administration can be an effective intervention to suppress age - associated increases in blood lipid levels . this example illustrates that administration of nmn enhances insulin sensitivity in old individuals . in these investigations , insulin sensitivity , assessed by the insulin tolerance test , showed significant differences among the control and the 100 mg / kg and 300 mg / kg nmn - administered groups after the 12 - month time point . ( see methods ; administration of nmn through drinking water and determination of nmn stability and toxicity ). as illustrated in fig9 a - b , insulin tolerance results from body weight - matched mice in the control and the 100 and 300 mg / kg nmn - administered groups at the 12 - month time point are presented . blood glucose levels ( fig9 a ) and percent glucose changes ( fig9 b ) after insulin injection are shown . the results were analyzed with two - way ranova and one - way anova . all values are presented as mean ± sem ( n = 10 - 15 for each group ). in these experiments , the last measured time point when mice reached 17 month - old , the nmn - administered , body weight - matched mice showed significantly enhanced insulin sensitivity compared to the body weight - matched control group ( fig9 a ). there was a statistically significant interaction between time and group ( p = 0 . 023 from the greenhouse - geisser test in two - way ranova ), and the linear dose - dependent effects were statistically significant or close to significance at the 30 - min and 45 - min time points , respectively ( p = 0 . 026 and p = 0 . 061 in the one - way anova with unweighted linear term ). the results were analyzed with two - way ranova and one - way anova . all values are presented as mean ± sem ( n = 10 - 15 for each group ). this enhanced insulin sensitivity in the 100 mg / kg and 300 mg / kg groups was recognized further when plotting percent glucose changes ( fig9 b ), although the interaction between time and group did not reach statistical significance in this assessment ( p = 0 . 091 from the greenhouse - geisser test in two - way ranova ). long - term nmn administration can enhance insulin sensitivity in old mice , indicating that nmn administration is an effective anti - aging intervention to maintain better insulin sensitivity in the elderly . this example illustrates improvement of memory function under a high - fat diet ( hfd ) by administration of nmn . ( see methods ; memory function study ) fig1 illustrates freezing responses of regular chow - fed control , hfd - fed , and hfd - fed , nmn - treated mice in contextual and cued fear conditioning tests on day 1 , day 2 and day 3 . nmn was administered at the dose of 300 mg / kg / day for 4 months . on day 1 of the study , mice were given an auditory cue and then a mild electric foot shock , and a time of freezing was analyzed individually . on day 2 , the trained mice were placed into a training chamber with no tone cues , and their freezing responses were evaluated . on day 3 , cued fear conditioning , which does not involve the hippocampus , was tested by giving the same tone cue used in the conditioning session ( day 1 ) and analyzing their freezing responses . hfd - fed mice showed an impairment of contextual fear conditioning on day 2 compared to regular chow - fed control mice but did not show any defect in the conditioning session on day 1 and the cued fear conditioning test on day 3 ( fig1 ), demonstrating that hfd specifically impairs the hippocampus - dependent memory function . nmn - treated , hfd - fed mice demonstrated freezing responses indistinguishable from those of regular chow - fed control mice in the contextual fear conditioning test on day 2 . their freezing responses did not differ from those of control mice on both day 1 and day 3 . these results demonstrate that the 4 - month administration of nmn in mice can restore the normal hippocampus - dependent memory function even under a hfd - fed condition . nmn was administered at the dose of 300 mg / kg / day for 4 months . the results were analyzed by one - way anova with unweighted quadratic term . all values are presented as mean ± sem ( n = 17 , 15 , and 12 for regular chow - fed control , hfd - fed , and hfd - fed , nmn - treated mice , respectively ). ** p & lt ; 0 . 01 ; * p & lt ; 0 . 05 . these results demonstrate that the 4 - month administration of nmn in mice can restore the normal hippocampus - dependent memory function even under a hfd - fed condition . this example illustrates the improvement of retinal photoreceptor cell function over age . in the long - term nmn administration study ( see methods : administration of nmn through drinking water and determination of nmn stability and toxicity ), retinal function was evaluated by fundus biomicroscopy and electroretinography ( erg ). fig1 illustrates fundus biomicroscopy images from control and nmn - administered mice . for each group , five mice were examined , and two representative images are shown . intraretinal whitish deposits were reduced dramatically in nmn - administered mice . on fundus biomicroscopy , all five control mice at 18 months of age showed many intraretinal whitish deposits , whereas two and four each out of five mice at 100 mg / kg and 300 mg / kg doses , respectively , showed dramatic reductions in these deposits , suggesting that age - associated pathological changes in the retina are suppressed by nmn ( fig1 ). fig1 a - c illustrates electroretinograms from control and nmn - administered mice . amplitudes of scotopic a and b ( fig1 a , fig1 b ) and photopic b ( fig1 c ) waves over each stimulus range are shown . consistently , in the erg analysis , there was a significant interaction between stimulus and group ( p = 0 . 009 from the two - way ranova ) for the scotopic a wave , and nmn - administered mice showed significantly higher amplitudes at 0 and 5 db ( p = 0 . 035 and 0 . 022 for the 300 mg / kg group at 0 and 5 db , respectively ; p = 0 . 009 for the 100 mg / kg group at 5 db from the dunnett t3 test in the one - way ranova within groups ), demonstrating that nmn is able to improve rod cell function in aged mice ( fig1 a ). the data were analyzed with the two - way repeated anova . all values are presented as mean ± sem . * p ≦ 0 . 05 ; p ≦ 0 . 01 . although there were no significant interactions between stimulus and group for the scotopic b and photopic b waves , there appeared to be a trend of improvement for the photopic b wave , which represents cone cell function , through an entire range of stimulus in both 100 and 300 mg / kg groups ( fig1 b and 12c ). the data were analyzed with the two - way repeated anova . all values are presented as mean ± sem . * p ≦ 0 . 05 : p ≦ 0 . 01 . taken together , these findings indicate that nmn is able to improve the retinal photoreceptor cell function in aged mice . the present inventors assessed the physiological importance of nampt - mediated nad biosynthesis in the retina by generating rod cell - and cone cell - specific nampt knockout mice . on fundus biomicroscopy , cone cell - specific nampt knockout mice had an atrophic appearance at the optic nerve head , intraretinal whitish deposits , and perivascular sheathing , while littermate control animals were normal . erg demonstrated a significant and dramatic decrease in the scotopic b and photopic b wave amplitudes as compared to the littermate control mice . the scotopic a wave amplitudes in the cone cell - specific nampt knockout mice were significantly decreased but to a lesser extent than the photopic b wave responses . furthermore , rod cell - specific nampt knockout mice exhibited total retinal degeneration . both a and b wave erg responses were completely depressed as characterized by a total lack of response to all stimuli . additionally , the treatment of the mouse photoreceptor - derived 661w cone cell line with fk866 , a potent nampt inhibitor , led them to apoptotic cell death . adding nmn to the culture media successfully rescued 661w cells from fk866 - mediated cell death , suggesting that nad deficiency causes the observed cell death . these results indicate that inhibition of nampt - mediated nad biosynthesis by genetic and pharmacologic means leads to photoreceptor cell death and eventually retinal degeneration . nmn administration is an effective intervention to treat / prevent retinal degeneration . this example illustrates the improvement of tear production over age using modified schirmer testing . in this long - term nmn administration study ( see methods ; administration of nmn through drinking water and determination of nmn stability and toxicity ), tear production was assessed in control and nmn - administered mice with modified schirmer &# 39 ; s test . all values are presented as mean ± sem . ** p ≦ 0 . 01 . nmn increased tear production in a dose - dependent manner in 18 month - old mice ( fig1 ). the tear production observed in the 300 mg / kg group was comparable to the maximal tear production through the mouse lifespan . these findings indicate that nmn administration is able to increase tear production significantly in aged mice , providing an effective intervention to protect eye function from dry eye diseases . this example illustrates that hippocampal nad + levels and nampt expression decline with age . the inventors hypothesized that aging may reduce nampt - mediated nad + biosynthesis in the brain , particularly in the hippocampus , affecting the function of nspcs . the inventors first measured nad + levels in hippocampi isolated from 1 , 3 - 4 , 6 , and 10 - 12 month - old c57bl6 mice . fig1 a - e illustrates hippocampal nad + levels and nampt expression declining with age . fig1 a illustrates nad + biosynthesis from nicotinamide . nicotinamide phosphoribosyltransferase ( nampt ) converts nicotinamide and 5 ′- phosphoribosyl - 1 - pyrophosphate ( prpp ) to nicotinamide mononucleotide ( nmn ). nicotinamide / nicotinic acid mononucleotide adenylyltransferase ( nmnat ) converts nmn and adenosine - 5 ′- triphosphate ( atp ) to nad +. while nad + is commonly used in redox reactions , cells primarily require nad + as a co - substrate for several families of enzymes , one of which is the sirtuin family of protein deacetylases . the sirtuin family includes sirt1 and sirt2 , which cleave nad + at its glycosidic bond , releasing adp - ribose ( stein & amp ; imai , 2012 ). inhibitors used in subsequent experiments is indicated . fig1 b illustrates hplc analysis of nad + levels in hippocampal extracts ( 1 month , n = 5 ; 3 - 4 months , n = 16 ; 6 months , n = 10 ; 10 - 12 months , n = 28 ). c - d ) quantification of immunofluorescence for nampt in the subgranular zone ( sgz ). measurement of thresholded levels of nampt immunoreactivity ( fig1 c ) and the number of highly immunoreactive nampt + cells ( fig1 d ) along the sgz ( n = 5 ). fig1 e shows representative images of immunofluorescence for dapi ( original blue ) and nampt ( original red ) in the sgz in young ( 6 months old ) and old ( 18 months old ) mice . scale bars denote 20 μm . data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . nad + levels gradually decreased with age , reaching 63 % in 10 - 12 month - old mice compared to that of 1 month - old mice ( fig1 b ). consistent with this finding , quantifying nampt immunoreactivity in the sgz of the dg by both a thresholded level of nampt intensity as well as a count of the number of thresholded nampt + cells demonstrated that 18 month - old mice exhibit 52 - 66 % of the nampt immunoreactivity present in 6 month - old mice ( fig1 c - e ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . without being limited by theory , these results suggest that nampt - mediated nad + biosynthesis in the hippocampus declines with age at a time course similar to that of nspc proliferation . this example illustrates that nampt is expressed in a subpopulation of sgz nspcs . nampt has been reported as predominantly expressed in hippocampal neurons but not in stellate astrocytes ( wang et al , 2011a ; zhang et al , 2010 ). consistent with this finding , immunohistochemistry for nampt and cell type specific markers revealed almost all neun + neurons in the granule layer of the ix ) expressed nampt , while almost no s100β + glial cells did ( fig2 a - e ). however , the inventors also noticed that many nampt immunoreactive cells along the sgz of the dg did not express neun ( fig2 b - 22e ). the inventors performed co - immunohistochemistry for nspc markers ( sox2 +, radial gfap +), and found that a significant population of nspcs expressed nampt ( fig2 a - b 0 ). fig2 illustrates that nampt is expressed in a subpopulation of sgz nspcs . a - c ) representative images of immunofluorescence for dapi ( original blue ), nampt ( original red ), and nspc markers ( sox2 , gfap , and nestingfp 3 days post tamoxifen injection ; original green ) in the sgz . dotted lines denote the sgz . single arrows indicate examples of colocalization . double arrows indicate examples of non - colocalization . scale bars denote 10 μm . d ) quantification of the percentages of nspc marker - positive cells in the sgz that also express nampt in 3 to 6 month old mice . at least 350 cells from 7 - 14 mice were assessed per group . e ) a representative immunoblot and quantification of immunoblots for nampt normalized by actin in neurospheres cultured from postnatal mice ( n = 6 independent samples , 16 replicates ), as well as hippocampal tissue extracts ( hc ) isolated from either postnatal ( n = 12 ) or adult mice ( n = 12 ). f ) nampt immunoreactivity was thresholded and the number of highly immunoreactive nampt + cells along the sgz was assessed for colocalization with the neuronal marker neun or the nspc marker sox2 in the subgranular zone ( sgz , n = 5 ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 ( fig1 a - b ). to assess in vivo colocalization between nampt and nestin , the inventors crossed mice expressing cre recombinase under the nestin promoter ( nestin - creert2 ) to a gfp reporter mouse strain that expresses a loxp - flanked stop cassette that prevents transcription of the downstream enhanced gfp ( see methods ), generating inspc - gfp mice . nampt also colocalized with gfp driven by the nestin promoter ( nestingfp , fig1 c ). quantification of these observations revealed that along the sgz , 32 % of sox2 + cells , 55 % of radial gfap + cells , and 78 % of nestingfp + cells expressed nampt ( fig1 d , and table 1 ). additionally , ki67 + and olig2 + cells along the sgz also expressed nampt ( table 2 , fig2 h - 22i ). separate from sgz - localized cell populations , 3 ± 1 % of nestingfp + cells had extremely strong gfp expression , were localized to the granule layer , and expressed neun , likely due to residual creert2 protein left in the progeny of previously differentiated nspcs . data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . *** p & lt ; 0 . 001 . to confirm that nampt is highly expressed in nspcs , the inventors cultured nspcs from the hippocampi of postnatal pups as neurospheres . neurospheres showed 22 or 32 % higher expression levels of nampt than did whole hippocampal extracts taken from postnatal ( p12 ) or adult mice ( 2 . 5 - 4 . 5 months ), respectively ( fig1 e ), indicating that nspcs have higher expression levels of nampt compared to other hippocampal cell types . without being limited by theory , these results suggest that nampt is expressed in a large subpopulation of nspcs . the inventors thresholded nampt immunoreactivity , and assessed the thresholded nampt + cells for colocalization with the neuronal marker neun and the nspc marker sox2 to determine which cell populations lose nampt expression with age . with age , the percentage of intensely nampt immunoreactive cells that colocalized with neun increased slightly , whereas the percentage of intensely nampt immunoreactive cells that colocalized with sox2 decreased from 21 % to 4 % ( fig1 f ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . similarly , in the sgz , the percentage of neun + that expressed nampt increased with age , while the percentage of sox2 + cells that expressed nampt decreased ( fig2 e , table 2 ). thus , at least part of the decrease in nampt expression in the sgz with age is due to loss of sox2 + nspcs . this example illustrates that adult nspc - specific deletion of nampt impairs nspc self - renewal in vivo . the inventors investigated whether inactivating nampt specifically in adult nspcs could recapitulate age - associated phenotypic changes in nspc functionality in vivo . the inventors generated adult nspc - specific inducible nampt knockout mice by crossing nampt flox / flox mice ( rongvaux et al ., 2008 ) with nestin - creert2 mice ( inspc - nampt - ko mice ). to trace the progeny of adult nspcs in which nampt was inactivated and to confirm the specificity and magnitude of the deletion induced by tamoxifen , the inventors also crossed inspc - nampt - ko mice to the aforementioned inspc - gfp mice . after tamoxifen injection , these mice expressed nestingfp in the sgz and svz but not in non - neurogenic regions of the brain such as the corpus callosum or cortex fig2 a - b ). immunohistochemistry and recombination pcr for nestingfp confirmed that there was undetectable recombination present in vehicle injected mice . the ˜ 350 base pair band confirms the deletion of exons 5 and 6 . the 1 , 800 base pair band corresponds to a nampt gene with a full - length exon 5 to 6 sequence . ( fig2 a , 23c ) to verify that the nestingfp + population consisted of nspcs , the inventors co - stained for the nspc markers sox2 and gfap . 61 % of sox2 + cells and 34 % of radial gfap + cells co - expressed nestingfp 7 days post tamoxifen ( fig2 d ). the inventors also verified nampt deletion efficiency by quantifying the percentage of nestingfp + cells that expressed nampt 3 and 7 days post tamoxifen injection . at 3 days post tamoxifen injection , the percentage of nestingfp + cells that expressed nampt in inspc - nampt - ko mice was 40 % less than littermate controls , and at 7 days post tamoxifen injection , the percentage of nestingfp + cells that expressed nampt was reduced by 62 % ( fig2 e ). to assess the cumulative effect of loss of nampt on nspc proliferation , the inventors deleted nampt in inspc - nampt - ko mice at 6 weeks of age with 3 rounds of 5 consecutive days of tamoxifen injections , separated by 6 weeks ( fig1 a ). parametric analysis of gene enrichment ( page ) was conducted based on microarray analyses . see the methods section . data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . the inventors then assessed control and inspc - nampt - ko mice for the expression of lineage specific markers by immunohistochemistry ( fig1 c ). in inspc - nampt - ko mice , the inventors found that the nestin + nspc pool was decreased by 49 % in the dg ( fig1 c ). incorporation of brdu and the population of proliferating cells [ ki67 + ( von bohlen und halbach , 2011 )] were also decreased by 22 % and 35 %, respectively ( fig1 d - 16e . consistent with this defect in the nspc pool and proliferation , the pool of newborn neurons [ doublecortin , dcx +, ( von bohlen und halbach , 2011 )] was also significantly decreased by 26 % ( fig1 f - 16g ). in contrast , the inventors did not observe any significant difference in the maturation of newborn neurons ( fig2 f ). immature cells had no or horizontal projections . mature cells had vertical projections spanning the granule cell layer . nspc / daughter cell survival was accessed by immunostaining for activated caspase 3 . only rare activated caspase 3 + cells were observed in both neurogenic and non - neurogenic regions of the brain ( fig2 a - 23b ), and these activated caspase 3 + cells were never observed in gfp + cells in inspc - nampt - ko dg , without being limited by theory , providing evidence against a potential contribution of cell death to the observed effects . to assess the acute effect of loss of nampt on nspc fate decisions , the inventors induced deletion of nampt at 6 weeks of age with 4 total tamoxifen injections followed by sacrifice 72 hours after the first injection ( fig1 h ). to facilitate assessment of differentiation , dividing cells were labeled by injecting the mice with brdu concurrently with the first day of tamoxifen treatment . 4 total tam injections ( 2 injections on the first day coupled with brdu at 100 mg / kg body weight as well as 2 total injections on the subsequent 2 days ). inspc - nampt - ko mice displayed significantly reduced levels of colocalization of brdu with radial nestin + cells ( fig1 i ), without being limited by theory , suggesting decreased self - renewal decisions . however , inspc - nampt - ko mice exhibited normal levels of brdu colocalization with neuronal ( dcx +), astrocytic ( gfap +) and oligodendrocytic ( olig2 +) markers , indicating that alterations in differentiated cell lineage decisions were undetectable under basal conditions . without being limited by theory , the lack of increase in colocalization of brdu with cell type specific markers may imply that a larger percentage of brdu + cells have failed to differentiate in inspc - nampt - ko mice . inspc - nampt - ko nspcs could have stalled during differentiation after losing nestin expression . the inventors hypothesized that systemic administration of nmn may be able to correct age - associated defects in nspc functionality . intraperitoneal injection of nmn ( 500 mg / kg body weight ) increased hippocampal nad + levels 34 to 39 % within 15 minutes , suggesting that nmn can cross the blood - brain barrier ( fig2 g ). to see if nmn supplementation can maintain nspc proliferation and self - renewal with age , the inventors treated 6 month - old mice with nmn at the daily dose of 100 or 300 mg / kg body weight in their drinking water until 18 months of age . the number of nestin + cells along the sgz was significantly lower in the 18 month - old control mice relative to 6 month - old mice , as previously reported ( encinas et al , 2011 ) ( fig1 j ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . mice treated with 300 mg / kg body weight nmn showed improved maintenance of the type 1 ( radial nestin +) population with age . however , the population of proliferating cells ( ki67 +) remained similar to controls ( fig2 h ). the population of newborn neurons ( dcx +) trended to increase ( fig2 ). quantification of ki67 +( h ) and dcx +( 1 ) cells in the dg per unit area of the dg ( n = 5 ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . without being limited by theory , it is possible that nmn administration maintains the nspc pool by preventing the age - associated increase in terminal fate decisions . this example illustrates that inhibition of nampt in nspcs in vitro impairs nad + biosynthesis and proliferation . the inventors hypothesized whether nampt mediates nspc - specific nad + biosynthesis by using hippocampal neurospheres as the in vitro nspc culture model . neurospheres were treated with a highly specific nampt inhibitor , fk866 , at a dosage and duration ( 10 nm , 48 hours ) that has little to no effect on cellular viability ( hasmann & amp ; schemainda , 2003 ). fk866 reduced nad + levels in neurospheres to 4 % of controls , a decrease completely rescued by concurrent nmn treatment ( fig1 a and 24a ), suggesting that , without being limited by theory , nampt activity is the predominant source of nad + biosynthesis in nspcs . the inventors investigated how inhibition of nampt affects neurosphere proliferation . consistent with the decreases in the nspc pool and in nspc proliferation in inspc - nampt - ko mice , fk866 reduced nspc number by 61 % after 48 hours , but not 24 hours , of treatment ( fig1 b - c and fig2 b ). to distinguish whether this decrease in cell number was due to an inhibition of proliferation or enhancement of death , the inventors analyzed the protein levels of markers of proliferation , apoptosis , and autophagy . expression of the proliferation markers ki67 and pcna decreased 87 % and 43 % respectively ( fig2 c - 24e ), whereas levels of activated caspase 3 were only slightly increased and levels of the autophagy marker , glycosylated lc3b , were unchanged . consistent with these observations , parametric analysis of gene set enrichment ( page ) of a microarray performed on neurospheres treated with fk866 showed that out of the top 50 downregulated pathways , 13 of them were related to the cell cycle , while none of the top 50 upregulated pathways were involved in cell death table 3 , fig2 f - g ). parametric analysis of gene enrichment ( page ) was conducted based on microarray analyses . see the methods section . analysis of specific gene changes by qrt - pcr revealed that cyclins e and a , the two cyclins required for cellular progression from g1 to s , as well as their upstream transcriptional regulator e2f1 ( wong et al , 2011 ), were the primary cell cycle factors affected by this treatment ( fig1 e ). these alterations in gene expression indicated that reducing nampt activity stalls nspcs at g0 / g1 . supporting this notion . facs analysis of neurospheres demonstrated that fk866 treatment increased the proportion of nspcs in g0 / g1 and decreased the proportion in s phase ( fig1 f ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . to assess the effect of chronic nampt ablation on nspc functionality , the inventors genetically ablated nampt by infecting neurospheres from nampt flox / flox mice with cre recombinase - or lacz - expressing ( control ) adenoviruses . neurospheres infected with cre recombinase ( nampt ad - cre ) at passage 1 exhibited a 94 % reduction in nampt mrna expression 3 days post deletion , and the corresponding decreases in nampt protein expression and nad + levels appeared 6 days post deletion ( fig2 a - 25e ). analyses were conducted after passage 2 , at 6 or more days post infection . data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . eight days post deletion , nspcs exhibited a 73 % reduction in nad + levels that was rescued by concurrent nmn administration , and without being limited by theory , further supporting the notion that nampt activity is the predominant source of nspcs nad + levels ( fig1 a ). neurospheres were isolated from namptflox / flox mice and infected with a cre - recombinase expressing adenovirus ( nampt ad - cre ) or a control adenovirus expressing lacz ( nampt ad - lacz ). like fk866 - treated cultures , proliferating nampt ad - cre infected nspcs displayed reduced cell number ( fig1 b ). nampt ad - cre nspcs were unable to increase their cell number between 24 and 144 hours of culture . in contrast , nampt ad - lacz infected cells were able to exponentially increase their cell number over 13 - fold in this time frame . consistent with this finding , nampt ad - cre infected nspcs also showed a 49 % reduction in diameter relative to nampt ad - lacz infected nspcs , indicative of reduced proliferation ( fig1 c - d ). since nspc self - renewal decisions can also contribute to cell number , the inventors assessed secondary neurosphere formation , an assay that quantifies the ability of neurosphere inhabitant cells to reformulate neurospheres upon dissociation . nampt ad - cre infected cells generated 63 % fewer secondary neurospheres than did nampt ad - lacz infected cells ( fig1 e ). nampt ad - lacz and nampt ad - cre nspcs exhibited no difference in the percentages of tunel - or activated caspase 3 - positive cells as well as no difference in activated caspase3 immunoreactivity as detected by immunoblotting , without being limited by theory , indicating that the observed phenotypes upon loss of nampt are not primarily due to cell death ( fig2 e - f ). as a positive control for activated caspase 3 immunoreactivity , indicated samples were treated with staurosporine ( 1 mm ) ( n = 6 ). to see if nampt ad - cre infected neurospheres could be reactivated to proliferate , the inventors plated equal numbers of nampt ad - lacz and nampt ad - cre cells after the second passage and cultured them in the presence or the absence of nmn . nmn treatment was able to fully reactivate the proliferative potential of nampt ad - cre cells ( fig1 f - g ). collectively , without being limited by theory , these results suggest that nampt - mediated nad + biosynthesis plays a role for nspcs to successfully progress through the cell cycle . whereas the inventors did not observe a difference in nspc fate decisions in the neurogenic environment of the sgz in vivo , the inventors detected a decrease in self - renewal decisions . to see if this would occur in the absence of the influences of the sgz niche , the inventors differentiated dissociated neurospheres and assessed the proportion of resulting cell types by immunofluorescence after 6 to 7 days of differentiation induced by removal of growth factors ( fig1 h , fig2 g ). differentiated nampt ad - cre nspcs exhibited a 90 % reduction in oligodendrocytes ( fig1 i ). in contrast , nampt ad - cre infected nspcs exhibited no change in the generation of gfap cells ( fig1 j ). genetic knockdown of nampt also significantly but more mildly decreased the generation of neurons ( by 43 % β - iii - tubulin +, fig1 k ). thus , the decrease in oligodendrocytes was not due to an increase in neuronal fate . as gfap can recognize both nspcs and mature astrocytes , the inventors employed nestin and s100β to distinguish whether the decrease in oligodendrocytes we observed upon nampt knockdown was due to a cell fate choice in these directions . while there was no detectable change in the generation of s100β + mature astrocytes in nampt ad - cre cultures , there was a 4 - fold increase in the percentage of nestin + cells ( 6 % in nampt ad - lacz cells ; 23 % in nampt ad - cre cells ), without being limited by theory , suggesting quiescence rather than precocious astrocytic differentiation ( fig1 l ). all of these effects were rescued by treatment with nmn . the inventors also observed a mild increase in tunel + cell death under these conditions ( 33 % increase relative to nampt ad - lacz cells ). *, ^, and # indicate statistical significance between nampt ad - lacz and nampt ad - cre , nampt ad - lacz and nampt ad - lacz + nmn , and nampt ad - cre and nampt ad - cre + nmn , respectively . data are presented as mean ± s . e . m . * p & lt ;: 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ;: 0 . 001 . ( fig1 a - l ) together , without being limited by theory , these data suggest that genetic knockdown of nampt prevents the successful differentiation of oligodendrocytes from nspcs , potentially due to quiescence as indicated by a retention of nspc characteristics . this example illustrates that genetic knockdown of nampt impairs opc formation in vitro . since differentiation using a nonspecific lineage differentiation protocol ( by removal of growth factors ) revealed a specific requirement for nampt in the successful generation of o4 + immature oligodendrocytes , the inventors next asked which stage ( s ) of nspc differentiation into oligodendrocytes depends on nampt by employing a differentiation protocol that promotes the oligodendrocyte lineage ( fig1 a , fig2 a ). neurospheres were isolated from namptflox / flox mice and infected with a cre - recombinase expressing adenovirus ( nampt ad - cre ) or a control adenovirus expressing lacz ( nampt ad - lacz ). as previously observed using a nonspecific lineage differentiation protocol , the proportion of o4 + intermediate oligodendrocytes was dramatically decreased in nampt ad - cre cultures at 6 - 7 days post differentiation ( fig1 ). the inventors observed that ablation of nampt resulted in a decreased pool of opcs ( pdgfrα +), but an increased pool of nestin + nspcs . the proportion of gfap + astrocytes / nspcs also mildly increased . to investigate whether the depletion of the opc population was preexisting to or induced upon differentiation , the inventors assessed the opc population present during proliferation . dissociated neurospheres were cultured in proliferation media containing pdgfαα . ( fig2 b ) and after 2 days of differentiation ( fig1 c ), a time point that enriches for opcs as assessed by immunofluorescence . both of these time points also showed loss of opcs ( pdgfrα +, olig2 +). these results support that , without being limited by theory , nampt is plays a role for nspcs to differentiate into opcs . the inventors observed that sirt2 was upregulated during oligodendrocyte differentiation in vitro and expressed in the sgz in nampt + cells and nestingfp + nspcs ( fig2 c ). the inventors acutely treated nspcs with the selective inhibitor of sirt2 , agk2 , or the sirt1 inhibitor , ex527 . whereas both inhibitors acutely suppressed oligodendrocyte formation ( o4 +, fig1 d ), neither chronic ablation of sirt2 in the nspcs isolated from sirt2 −/− mice nor cre adenovirus mediated knockdown of sirt1 in sirt1 flox / flox derived neurospheres affected oligodendrogenesis ( pdgfrα +, olig2 +, o4 +), except that sirt1 deficiency affected the production of o4 + intermediate oligodendrocytes ( fig1 e ). the inventors generated sirt1 / sirt2 - double knockout ( sirt1 / 2 dko ) neurospheres . consistent with the inhibitor studies ( fig1 d ), dissociated sirt1 / 2 dko neurospheres were unable to form oligodendrocyte lineage cells upon differentiation ( fig1 e ). to assess the role of sirt1 and sirt2 downstream of nampt activity , the inventors examined the expression of genes associated with opc formation in nampt ad - cre neurospheres , sirt1 / 2 dko neurospheres , and their respective controls . dissociated nampt ad - cre and sirt1 / 2 dko neurospheres showed similar decreases in the mrna expression of pdgfrα , sox10 , nkx2 . 2 after 2 days of differentiation ( fig1 f - g ). dissociated nampt ad - cre and sirt1 / 2 dko neurospheres respectively exhibited similar increases in the expression of p21 ( cdkn1a ). olig1 expression showed no change or slight reduction by these genetic ablations , potentially due to its lesser expression in nspcs relative to olig2 ( ligon et al ., 2007 ) and predominant roles in oligodendrocyte maturation and remyelination rather than specification . neither cre mediated knockdown of sirt1 in neurospheres nor neurospheres cultured from whole - body sirt1 −/− or sirt2 −/− mice exhibited defects in proliferation ( fig2 g - j ). data are presented as mean ± s . e . m . * p & lt ; 0 . 05 . ** p & lt ; 0 . 01 . *** p & lt ; 0 . 001 . the inventors conclude that sirt1 and sirt2 can redundantly mediate nspc differentiation into opcs . this example illustrates adult nspc - specific deletion of nampt impairs nspc differentiation in response to insult in vivo . the inventors observed nampt ablation on nspc differentiation into opcs in vitro , but not oligodendrogenesis in the sgz of inspc - nampt - ko mice in vivo ( fig1 i ). the inventors assessed the percentage of nestingfp + cells that expressed olig2 in the svzs of inspc - gfp and inspc - nampt - ko mice ( fig2 a ). inspc - nampt - ko mice showed a lower percentage of oligodendrocytes generated from adult nspcs . the inventors employed the cuprizone model of demyelination and remyelination . specifically , the inventors fed 6 - to 9 - week - old inspc - nampt - ko and littermate control mice ( inspc - gfp ) a diet containing 0 . 2 % cuprizone for 4 - 5 weeks , inducing deletion of nampt in the adult nestin + population the week before starting the cuprizone diet ( fig2 b ) ( skripuletz et al ., 2011 ). to ensure that analysis of progeny of adult nestin + cells , all mice in our cohort expressed cre recombinase under the inducible nestin promoter ( nestin - creert2 ) ( lagace et al ., 2007 ) and the aforementioned cre recombinase responsive gfp reporter transgene . the analysis focus was on lineage tracer marked ( nestingfp +) cells . cuprizone feeding did not alter the total number of nestingfp + cells present in the inspc - gfp dg ( fig2 a - c ), suggesting , without being limited by theory , that nspc proliferation was unaltered . data are presented as mean ± s . e . m . *, ^ p & lt ; 0 . 05 . **, ^^ p & lt ; 0 . 01 . ***, ^^^ p & lt ; 0 . 001 . cuprizone fed mice exhibited an increased percentage of nestingfp + cells that co - localized with the nspc markers nestin + ( from 13 to 35 %) and gfap + ( from 19 to 41 %), suggesting that , without being limited by theory , cuprizone treatment prevented sgz nspcs from terminally differentiating and instead resulted in their retention of nspc characteristics , which could occur through increased self - renewal decisions and / or quiescence ( fig2 d - e ). the inventors next assessed colocalization between nestingfp and oligodendrocyte specific markers , sox10 and apc . however , the sgz did not substantially produce oligodendrocytes even in response to demyelination ( fig2 f - g therefore , without being limited by theory , sgz nspcs do not appear to be the main mediators of short - term remyelination in the hippocampus . the inventors assessed the fate decisions of migratory cells derived from the adult nestin + population in the subcallosal zone of the corpus callosum ( fig2 a ). in the inspc - gfp cc , virtually no nestingfp + or nestin + cells were seen in regular chow fed mice ( fig2 c - d , fig2 a ). there were no differences in the number of nestingfp + cells in the cc between control and inspc - nampt - ko mice , suggesting , without being limited by theory , that loss of nampt neither affected insult - induced nspc : proliferation or migration . in the inspc - gfp cc , cuprizone feeding significantly increased the percentage of nestingfp + nestin + cells ( from 3 to 41 %) but decreased the nestingfp + gfap + ( from 60 to 24 %) double positive cells , suggesting , without being limited by theory , increased self - renewal fate decisions at the expense of astrocytic fate decisions ( fig2 e - g ). in control mice , cuprizone feeding also increased the number of nestingfp + sox10 + ( from 2 to 16 %) and nestingfp + apc + ( from 0 to 4 %) double positive cells , suggesting increased oligodendrocyte lineage fate decisions ( fig2 h - i ). in contrast , the nestingfp + cells in the inspc - nampt - ko cc showed significantly less colocalization with nestin , sox10 , and ape and more colocalization with gfap ( fig2 f - i ). interestingly , nampt was only expressed in the cc upon insult ( fig2 j , fig2 i ). moreover , nampt colocalized with markers of nspcs ( sox2 , fig2 h ) and oligodendrocytes ( olig2 , fig2 j ). these results suggest , without being limited by theory , that nampt is specifically expressed in sgz / svz derived remyelinating nspcs and plays a role in oligodendrogenesis in response to insult . this example illustrates a model for the role of nampt - mediated nad biosynthesis in nspcs without being limited by theory . nampt - mediated nad + biosynthesis promotes nspc self - renewal , proliferation and differentiation into oligodendrocytes . while the mechanism by which nampt promotes self - renewal and proliferation remains unidentified , nampt - mediated nad + biosynthesis activates sirt1 and sirt2 to promote nspc oligodendrocyte lineage fate decisions by a mechanism involving transcriptional downregulation of pdgfrα , sox10 , and nkx2 . 2 and transcriptional upregulation of p21 ( cdkn1a ). sirt1 and sirt2 may act via an effect on olig2 activity . ( fig2 ) the inventors showed that the nspc pool decreased with age and that long - term nmn administration was able to maintain the nspc pool . the inventors assert that a higher dosage of nmn can be used to promote nspc proliferation . intraperitoneal injection of nmn substantially increases hippocampal nad + levels within 15 minutes ( fig2 g ), without being limited by theory , suggests that nmn can cross the blood - brain barrier . as e2f1 - deficient mice have significantly reduced hippocampal nspc death ( cooper - kuhn et al , 2002 ), without being limited by theory , the observed decrease in e2f1 upon inhibition of nampt may explain this phenomenon ( fig1 e ). the inventors also observed that loss of nampt activity specifically downregulated cyclin e and a expression . e - type cyclins regulate g1 progression . the inventors observed downregulation of e2f1 expression , which transcriptionally regulates cyclin e , therefore , without being limited by theory , it is likely that the downregulation of e2f1 contributes to the downregulation of cyclin e . the inventors also observed upregulation of p21 upon loss of nampt . thus , the upregulation of p21 that we see upon loss of nampt , without being limited by theory , may also contribute to the downregulation of e2f / cyclin e activity . as cyclin a expression is induced after e2f and cyclin e ( wong et al , 2011 ), the changes in cyclin a levels are likely downstream of both the aforementioned changes . while we have linked nampt to the e2f / cyclin e pathway , connecting mediator ( s ) remain unclear . the inventors found neither sirt1 nor sirt2 to be downstream of the effect of nampt - mediated nad + biosynthesis on proliferation . while it is possible that sirt1 / 2 function redundantly to mediate nspc proliferation , the relatively low expression of sirt2 in nspcs ( fig2 g ) makes this possibility unlikely , without being limited by theory . the present inventors revealed that ablation of nampt specifically reduced the proportion of nspc - generated pdgfrα + opcs as well as the transcription of pdgfrα , sox10 , and nkx2 . 2 but upregulated the expression of p21 . the results showed that in neurospheres , treatment with nmn rescued defects in oligodendrogenesis caused by a reduction in nad + levels . furthermore , systemic nmn administration was able to substantially augment hippocampal nad + levels and increase the nspc pool . thus , nmn administration could be an efficient intervention to enhance the nspc pool and promote remyelination by activating endogenous nspcs during the aging process and / or in neurodegenerative diseases that cause demyelination . the results provide evidence of the therapeutic potential of nampt - mediated nspc self - renewal , proliferation , and differentiation into oligodendrocytes . this example illustrates an increase in bone density in aged individuals by nmn administration . the inventors measured the bone mineral density ( bmd ) of control and nmn - treated mice at the 12 - month time point of a 12 month long nmn administration experiment ( fig2 a - b ) by dual - energy x - ray absorptiometry ( dxa ). at this time point , mice were 17 - 18 month old . the inventors found that nmn - treated mice showed increases in the bmd in a dose - dependent manner , and the difference between control and 300 mg / kg groups is statistically significant ( p = 0 . 037 , anova , tukey hsd post hoc test ). mice from 100 and 300 mg / kg groups showed 2 . 8 % and 5 . 9 % increases in the bmd , respectively . although age - associated bmd loss is extensively varied among mouse strains ( http :// phenome . jax . org ), the extent of these observed bmd increases is significant , indicating that nmn is able to enhance the bmd in aged individuals . these data indicate that nmn administration can be used to treat age - associated osteoporosis in humans . this example illustrates characterization of loss of nampt - mediated nad biosynthesis on pr neuron survival . the inventors examined the effect of selectively disrupting nad biosynthesis within pr . the inventors utilized the cre - lox strategy to generate mice that had nampt conditionally deleted from either rods ( nampt rod - cko ) or cones ( nampt cone - cko ). the nampt fl / fl mice as well as the rhodopsin - cre and cone opsin - cre mice have been previously characterized . both rod and cone cko mice are generated with normal mendelian frequencies and are born normal with no observable systemic abnormalities ( data not shown ). all structural and functional analyses performed in cko mice are analyzed in comparison to littermate controls . rods constitute a majority of the pr neurons ( 97 % of all photoreceptors ). retinas from nampt rod - cko mice showed a significant reduction of nampt within rods by pcr , immunohistochemistry and immunoblotting ( fig2 a - b ). biomicroscopic examination of nampt rod - cko mice demonstrated a degenerative phenotype characterized by massive atrophy of the neurosensory retina , vascular attenuation with pigment mottling and atrophy of the underlying retinal pigment epithelium . neurosensory retinal degeneration was associated with secondary atrophy and pallor of the optic nerve ( fig2 c ). this example illustrates electroretinography ( erg ) performed to measure pr neuron and retinal function . nampt rod - cko mice demonstrated a dramatic reduction in scotopic ( rod - associated ) and photopic ( cone - associated ) responses compared to littermate control animals ( fig2 d - h ) photopic visual acuity measurements confirmed vision loss in rod - cko mice ( fig2 g ). histopathologic examination of eyes from nampt rod - cko mice was characterized by retinal degeneration with progressive loss of the outer nuclear layer over time with significant reduction of retinal thickness and subsequent extension of the neurodegeneration to multiple retinal layers ( fig2 h ). normalized nad measurements obtained from nampt rod - cko whole retinas showed a significant reduction in nad which is especially important given that nampt function is selectively eliminated only from rod pr neurons with other retinal cells being normal ( fig2 i ). these results suggest that , without being limited to theory , if enzymatic activity of nampt in nad biosynthesis in rod pr neurons is necessary for cell survival , intracellular conversion of nam to nmn by nampt can play a role . the present inventors determined that exogenous supplementation with nmn is able to rescue pr neurons from cell death in cko mice . intraperitoneal ( i . p .) delivery was chosen to obtain early and sustained levels of nmn . in these experiments , nampt rod - cko mice were given nmn ( 150 mg / kg ) or pbs i . p . daily starting at day p5 . erg at 4 weeks in cko mice treated with nmn showed significant rescue of photopic and scotopic function compared to pbs treatment ( fig2 j - l ). there was no effect of nmn on littermate control animals . in these experiments , nampt cone - cko mice ( without nmn treatment ) demonstrated similar but milder changes on biomicroscopy consistent with neuroretinal degeneration as seen in the rod - cko mice ( fig3 a ). erg demonstrated significant and progressive decline in cone function as evidenced by reduced photopic responses over time with secondary reduction in scotopic responses ( fig3 b - d ). these quantifiable structural and functional changes were associated with decrease in visual acuity in cone - cko mice ( fig3 e ). histopathologic analyses confirmed outer nuclear layer degeneration with subsequent multilayer retinal degeneration and cell death in cone - cko mice similar to the changes seen above for rod - cko mice . as with nampt rod - cko mice , delivery of nmn i . p . to nampt cone - cko mice was also able to improve erg function compared to pbs treated cone - cko mice ( fig3 f - h ). nmn treatment had no effect on littermate controls ( fig3 a - b ). these data suggest that , without being limited by theory , nampt - mediated nad biosynthesis is necessary for the survival and function of both rod and cone pr neurons . furthermore , providing nmn treatment is able to rescue pr neurons and vision . the inventors used a 661w cone pr cell line and treated the cells with the specific pharmacological nampt inhibitor fk866 ( 200 nm ). fk866 treatment of cone cells in vitro causes decrease in intracellular nad levels and significant cell death after the 4 hours of treatment ( fig3 i , 31j ). cell death progresses dramatically over the next 20 hours . nmn ( 100 μm ) was able to completely rescue cells from death associated with fk866 treatment and restore nad to normal levels ( fig3 i , 31k ). these in vitro results confirm that nmn administration can promote pr neuron survival . this example illustrates that nad - regulated pr survival is independent of individual sirtuins . the inventors examined the effect of deletion of several sirtuins on pr survival . sirt 1 pr cko mice and sirt 2 - 5 −/− mice had normal retinal and pr neuron structure and function when examined by fundus biomicroscopy and erg ( fig3 a - j and fig . s2 ). sirt6 −/− mice have a profound neurodegenerative phenotype and die around 3 - 4 weeks of age . as such , we examined sirt6 rod and cone conditional knockout mice that also had normal retinal structure and function ( fig3 a - n , and fig3 a - f ). without being limited by theory , these findings demonstrate that individual sirtuins are not causative of nampt - mediated pr degeneration . this example illustrates that photoreceptor loss and blindness is associated with mitochondrial dysfunction . electron microscopic examination demonstrated dysmorphic changes in the retinal inner segments along with disruption of the outer segments in rod cko mice but showed normal cellular organization and sub - cellular structures in littermate controls at 4 weeks of age ( fig3 a - c , 32 d ). by 4 weeks of age , the mitochondrial numbers in cko retinas were significantly reduced , the mitochondria were rounded and constricted with loss of cristae as opposed to the normally elongated mitochondria with healthy cristae seen in age - matched littermate control mice ( fig3 a - d ). there was an abundance of degenerative vacuoles with ingested organelles including mitochondria in rod - cko mice with no such structures identified in littermate wild type controls . at 3 weeks of age , subtle changes in inner segments could be identified in rod - cko mice although they were not as dramatic as those seen by 4 weeks ( fig3 ). these results suggest that , without being limited by theory , nad deficiency might impair mitochondrial structure and function . the inventors treated 661w cone cells with nampt inhibitor fk866 ( 200 nm ). in the oxygen consumption rate measurement assay , multiple aspects of mitochondrial function were analyzed . as shown in fig3 e , maximal respiration was significantly reduced in 661w cone cells after inhibition of nampt function ( fig3 e ). nmn treatment was able to completely reverse the effects of fk866 on cone cell photoreceptor mitochondrial function confirming the role of nad in nampt - mediated effects on pr neurons ( fig3 e ). a non - biased metabolomic analysis using mass spectrophotometry ( gc - ms and lc - ms ) was performed on retinas isolated from nampt rod cko mice and compared to littermate control retinas . significant differences were identified in mitochondrial metabolites involved in the tca cycle . ben abdallah , n . m ., et al . neurobiol . aging 31 , 151 - 161 , 2010 . collins , p . b ., et al ., j . biol . chem . 247 , 778 - 783 , 1972 . cooper - kuhn , c . m ., et al ., mol . cellular neurosci . 21 , 312 - 323 , 2002 . doucette , j . r ., et al ., cell . molec . neurobiol . 30 , 607 - 629 , 2010 . gao , q ., et al ., int . j . dev . neurosci . 25 , 349 - 357 , 2007 . hack , m . a ., et al ., molec . cell . neurosci . 25 , 664 - 678 , 2004 . higuchi , t , and stella , v ., pro - drugs as novel drug delivery systems , a . c . s . symposium series 14 , 1975 . hisahara , s ., et al ., proc . nat &# 39 ; l . acad . sci . usa 105 , 15599 - 15604 , 2008 . jadasz , j . j ., et al ., cell tissue res . 349 , 331 - 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428 , 2012 . stoll , e . a ., et al ., j . biol . chem . 286 , 38592 - 38601 , 2011 . van leeuwen , i . m ., et al ., molec . cancer ther . 12 , 471 - 480 , 2013 . von bohlen und halbach o ., cell tissue res . 345 , 1 - 19 , 2011 . zhang , w ., et al ., j . cereb . blood flow metab . 30 , 1962 - 1971 , 2010 . zhang , y ., et al ., biochem . biophys . res . comm . 404 , 610 - 614 , 2011 . all publications cited in this application are herein incorporated by reference in their entirety as if each individual publication , patent , patent application or other reference were specifically and individually indicated to be incorporated by reference . applicant reserves the right to challenge the accuracy and pertinency of the cited references .
disclosed are methods and compositions related to methods of treating , ameliorating , mitigating , slowing , arresting , preventing or reversing various diseases and conditions , including age - related obesity , age - related increases in blood lipid levels , age - related decreases in insulin sensitivity , age - related decreases in memory function , and age - related changes in eye function such as macular degeneration . the methods comprise administering nicotinamide mononucleotide to a subject . in some embodiments , the administration can be oral administration . also disclosed are pharmaceutical compositions comprising nmn .