4388364
MicroRNA-146a Promotes Oligodendrogenesis in Stroke
Stroke induces new myelinating oligodendrocytes that are involved in ischemic brain repair. Molecular mechanisms that regulate oligodendrogenesis have not been fully investigated. MicroRNAs (miRNAs) are small non-coding RNA molecules that post-transcriptionally regulate gene expression. MiR-146a has been reported to regulate immune response, but the role of miR-146a in oligodendrocyte progenitor cells (OPCs) remains unknown. Adult Wistar rats were subjected to the right middle cerebral artery occlusion (MCAo). In situ hybridization analysis with LNA probes against miR-146a revealed that stroke considerably increased miR-146a density in the corpus callosum and subventricular zone (SVZ) of the lateral ventricle of the ischemic hemisphere. In vitro, overexpression of miR-146a in neural progenitor cells (NPCs) significantly increased their differentiation into O4+ OPCs. Overexpression of miR-146a in primary OPCs increased their expression of myelin proteins, whereas attenuation of endogenous miR-146a suppressed generation of myelin proteins. MiR-146a also inversely regulated its target gene-IRAK1 expression in OPCs. Attenuation of IRAK1 in OPCs substantially increased myelin proteins and decreased OPC apoptosis. Collectively, our data suggest that miR-146a may mediate stroke-induced oligodendrogenesis.
3240280
Oligodendrocytes: biology and pathology
Oligodendrocytes are the myelinating cells of the central nervous system (CNS). They are the end product of a cell lineage which has to undergo a complex and precisely timed program of proliferation, migration, differentiation, and myelination to finally produce the insulating sheath of axons. Due to this complex differentiation program, and due to their unique metabolism/physiology, oligodendrocytes count among the most vulnerable cells of the CNS. In this review, we first describe the different steps eventually culminating in the formation of mature oligodendrocytes and myelin sheaths, as they were revealed by studies in rodents. We will then show differences and similarities of human oligodendrocyte development. Finally, we will lay out the different pathways leading to oligodendrocyte and myelin loss in human CNS diseases, and we will reveal the different principles leading to the restoration of myelin sheaths or to a failure to do so.
1312870
Biology of oligodendrocyte and myelin in the mammalian central nervous system.
Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.
86602746
MicroRNAs: small RNAs with a big role in gene regulation
Key PointsMicroRNAs (miRNAs) are a family of ∼21–25-nucleotide small RNAs that negatively regulate gene expression at the post-transcriptional level.The founding members of the miRNA family, lin-4 and let-7, were identified through genetic screens for defects in the temporal regulation of Caenorhabditis elegans larval development.Owing to genome-wide cloning efforts, hundreds of miRNAs have now been identified in almost all metazoans, including flies, plants and mammals.MiRNAs exhibit temporally and spatially regulated expression patterns during diverse developmental and physiological processes.Most of the miRNAs that have been characterized so far seem to regulate aspects of development, including larval developmental transitions and neuronal development in C. elegans, growth control and apoptosis in Drosophila melanogaster, haematopoietic differentiation in mammals, and leaf development, flower development and embryogenesis in Arabidopsis thaliana.The majority of the animal miRNAs that have been characterized so far affect protein synthesis from their target mRNAs. On the other hand, most of the plant miRNAs studied so far direct the cleavage of their targets.The degree of complementarity between a miRNA and its target, at least in part, determines the regulatory mechanism.In animals, primary transcripts of miRNAs are processed sequentially by two RNase-III enzymes, Drosha and Dicer, into a small, imperfect dsRNA duplex (miRNA:miRNA*) that contains both the mature miRNA strand and its complementary strand (miRNA*). Relative instability at the 5′ end of the mature miRNA leads to the asymmetric assembly of the mature miRNA into the effector complex, the RNA-induced silencing complex (RISC).Ago proteins are a key component of the RISC. Multiple Ago homologues in various metazoan genomes indicate the existence of multiple RISCs that carry out related but specific biological functions.Bioinformatic prediction of miRNA targets has provided an important tool to explore the functions of miRNAs. However, the overall success rate of such predictions remains to be determined by experimental validation.AbstractMicroRNAs are a family of small, non-coding RNAs that regulate gene expression in a sequence-specific manner. The two founding members of the microRNA family were originally identified in Caenorhabditis elegans as genes that were required for the timed regulation of developmental events. Since then, hundreds of microRNAs have been identified in almost all metazoan genomes, including worms, flies, plants and mammals. MicroRNAs have diverse expression patterns and might regulate various developmental and physiological processes. Their discovery adds a new dimension to our understanding of complex gene regulatory networks.
22872062
The neuronal microRNA system
A class of small, non-coding transcripts called microRNAs (miRNAs) that provide a crucial and pervasive layer of post-transcriptional gene regulation has recently emerged and become the focus of intense research. miRNAs are abundant in the nervous system, where they have key roles in development and are likely to be important mediators of plasticity. A highly conserved pathway of miRNA biogenesis is closely linked to the transport and translatability of mRNAs in neurons. Although there are nearly 500 known human miRNA sequences, each of only ∼21 nucleotides, which bind to multiple mRNA targets, the accurate prediction of miRNA targets seems to lie just beyond our grasp. Nevertheless, the identification of such targets promises to provide new insights into many facets of neuronal function.
34299726
MicroRNAs in neuronal function and dysfunction
MicroRNAs (miRNAs) are small noncoding RNA transcripts expressed throughout the brain that can regulate neuronal gene expression at the post-transcriptional level. Here, we provide an overview of the role for miRNAs in brain development and function, and review evidence suggesting that dysfunction in miRNA signaling contributes to neurodevelopment disorders such as Rett and fragile X syndromes, as well as complex behavioral disorders including schizophrenia, depression and drug addiction. A better understanding of how miRNAs influence the development of neuropsychiatric disorders may reveal fundamental insights into the causes of these devastating illnesses and offer novel targets for therapeutic development.
23805996
MicroRNAs Shape the Neuronal Landscape
The nervous system equips us with capability to adapt to many conditions and circumstances. We rely on an armamentarium of intricately formed neural circuits for many of our adaptive strategies. However, this capability also depends on a well-conserved toolkit of different molecular mechanisms that offer not only compensatory responses to a changing world, but also provide plasticity to achieve changes in cellular state that underlie a broad range of processes from early developmental transitions to life-long memory. Among the molecular tools that mediate changes in cellular state, our understanding of posttranscriptional regulation of gene expression is expanding rapidly. Part of the "epigenetic landscape" that shapes the deployment and robust regulation of gene networks during the construction and the remodeling of the brain is the microRNA system controlling both levels and translation of messenger RNA. Here we consider recent advances in the study of microRNA-mediated regulation of synaptic form and function.
26797651
Transient Focal Ischemia Induces Extensive Temporal Changes in Rat Cerebral MicroRNAome
MicroRNAs (miRNAs) are ∼22 nucleotides long, noncoding RNAs that control cellular function by either degrading mRNAs or arresting their translation. To understand their functional significance in ischemic pathophysiology, we profiled miRNAs in adult rat brain as a function of reperfusion time after transient middle cerebral artery occlusion. Of the 238 miRNAs evaluated, 8 showed increased and 12 showed decreased expression at least at 4 out of 5 reperfusion time points studied between 3 h and 3 days compared with sham. Of those, 17 showed > 5 fold change. Bioinformatics analysis indicated a correlation between miRNAs altered to several mRNAs known to mediate inflammation, transcription, neuroprotection, receptors function, and ionic homeostasis. Antagomir-mediated prevention of mir-145 expression led to an increased protein expression of its downstream target superoxide dismutase-2 in the postischemic brain. In silico analysis showed sequence complementarity of eight miRNAs induced after focal ischemia to 877 promoters indicating the possibility of noncoding RNA-induced activation of gene expression. The mRNA expression of the RNases Drosha and Dicer, cofactor Pasha, and the pre-miRNA transporter exportin-5, which modulate miRNA biogenesis, were not altered after transient middle cerebral artery occlusion. Thus, the present studies indicate a critical role of miRNAs in controlling mRNA transcription and translation in the postischemic brain.
81415718
MicroRNA Expression in the Blood and Brain of Rats Subjected to Transient Focal Ischemia by Middle Cerebral Artery Occlusion
Background and Purpose— Several hundred small RNAs called microRNAs (miRNAs) have been identified and characterized from various organisms, including humans. In humans, some of these miRNAs have been found to regulate (patho)physiologic conditions such as tumor progression/regression, cholesterol and glucose homeostasis, etc. In this report, we present data on the miRNAs expressed under ischemic conditions in both the brain and blood of rats subjected to middle cerebral artery occlusion (MCAo). Methods— Sprague-Dawley rats subjected to MCAo were reperfused for either 24 or 48 hours, and both blood and brain samples were harvested. miRNA expression profiling and oligonucleotide microarray were carried out, and the data were validated by quantitative real-time polymerase chain reaction and correlated with published data on protein and gene expression in MCAo rats. Results— We report here for the first time the involvement of miRNA regulation in brain pathogenesis associated with MCAo. Comparison with the co...
38211279
Brain and Blood microRNA Expression Profiling of Ischemic Stroke, Intracerebral Hemorrhage, and Kainate Seizures
MicroRNAs (miRNAs) regulate gene expression and have a critical role in many biologic and pathologic processes. We hypothesized that miRNA expression profiles in injured brain (hippocampus) would show common as well as unique profiles when compared with those of blood. Adult, untouched, control rats were compared with rats with sham surgeries, ischemic strokes, brain hemorrhage (lysed blood, fresh blood, or thrombin), and kainate-induced seizures. Brain and whole-blood miRNA expression profiles were assessed 24 h later using TaqMan rodent miRNA arrays. MicroRNA response profiles were different for each condition. Many miRNAs changed more than 1.5-fold in brain and blood after each experimental manipulation, and several miRNAs were upregulated or downregulated in both brain and blood after a given injury. A few miRNAs (e.g., miR-298, miR-155, and miR-362-3p) were upregulated or downregulated more than twofold in both brain and blood after several different injuries. The results show the possible use of blood miRNAs as biomarkers for brain injury; that selected blood miRNAs may correlate with miRNA changes in the brain; and that many of the mRNAs, previously shown to be regulated in brain and blood after brain injury, are likely accounted for by changes in miRNA expression.
15345137
Expression Profile of MicroRNAs in Young Stroke Patients
Background The methods currently available for diagnosis and prognosis of cerebral ischaemia still require further improvements. Micro-RNAs (small non-coding RNAs) have been recently reported as useful biomarkers in diseases such as cancer and diabetes. We therefore carried out microRNA (miRNA) profiling from peripheral blood to detect and identify characteristic patterns in ischaemic stroke. Methods/Principal Findings The ischaemic stroke patients aged between 18–49 years, characterized based on World Health Organization clinical criteria were further classified according to TOAST classification, a) Large-vessel atherosclerosis [n = 8] b) Small-vessel disease [n = 3] c) Cardioembolism [n = 5] d) Undetermined cause [n = 3]. The patients' functional status at the time of blood sampling (at the outpatient clinics) was evaluated with the modified Rankin Scale (mRS). Blood samples from normal (n = 5) individuals were used as controls. Total RNA extracted from whole blood was subjected to miroRNA profiling and real-time PCR analysis. miRNAs that are implicated in the endothelial/vascular function, erythropoiesis, angiogenesis and neural function showed differential expression profile as compared to the normal control. Interestingly, miRNAs that are involved in hypoxic conditions have also been found in our miRNA profiles. Conclusion We demonstrate that the peripheral blood miRNAs and their profiles can be developed as biomarkers in diagnosis and prognosis of cerebral ischaemic stroke. The dysregulated miRNAs have been detectable even after several months from the onset of stroke in what is usually regarded as neurologically stable patients.
14878847
MicroRNA Profiling in Subventricular Zone after Stroke: MiR-124a Regulates Proliferation of Neural Progenitor Cells through Notch Signaling Pathway
Background The Notch signaling pathway regulates adult neurogenesis under physiological and pathophysiological conditions. MicroRNAs are small non-coding RNA molecules that regulate gene expression. The present study investigated the effect of miR-124a on the Notch signaling pathway in stroke-induced neurogenesis. Methodology and Principal Findings We found that adult rats subjected to focal cerebral ischemia exhibited substantial reduction of miR-124a expression, a neuron specific miRNA, in the neural progenitor cells of the subventricular zone (SVZ) of the lateral ventricle, which was inversely associated with activation of Notch signals. In vitro, transfection of neural progenitor cells harvested from the SVZ of adult rat with miR-124a repressed Jagged-1 (JAG1), a ligand of Notch, in a luciferase construct containing the JAG1 target site. Introduction of miR-124a in neural progenitor cells significantly reduced JAG1 transcript and protein levels, leading to inactivation of Notch signals. Transfection of neural progenitor cells with miR-124a significantly reduced progenitor cell proliferation and promoted neuronal differentiation measured by an increase in the number of Doublecortin positive cells, a marker of neuroblasts. Furthermore, introduction of miR-124a significantly increased p27Kip1 mRNA and protein levels, a downstream target gene of the Notch signaling pathway. Conclusions Collectively, our study demonstrated that in vivo, stroke alters miRNA expression in SVZ neural progenitor cells and that in vitro, miR-124a mediates stroke-induced neurogenesis by targeting the JAG-Notch signaling pathway.
6344170
Fine-Tuning Oligodendrocyte Development by microRNAs
Myelination of axons by oligodendrocytes in the central nervous system is essential for normal neuronal functions. The failure of remyelination due to injury or pathological insults results in devastating demyelinating diseases. Oligodendrocytes originate in restricted regions of the embryonic ventral neural tube. After migration to populate all areas of the brain and spinal cord, oligodendrocyte precursors undergo a temporally well-defined series of molecular and structural changes, ultimately culminating in the cessation of proliferation, and the elaboration of a highly complex myelin sheath. The emergence of microRNAs (miRNAs) as potent regulators of gene expression at the posttranscriptional level has broad implications in all facets of cell biology. Recent studies have demonstrated a critical role of miRNAs in oligodendrocyte development, including cell proliferation, differentiation, and myelin formation. In this review, we will highlight and discuss the recent understanding of functional links of miRNAs to regulatory networks for central myelination, as well as perspectives on the role of miRNAs in demyelinating diseases.
12404037
MicroRNAs in Oligodendrocyte and Schwann Cell Differentiation
MicroRNAs (miRNAs) are a class of small (approx. 22 nt) noncoding RNAs that are capable of post-transcriptionally silencing mRNAs that contain sequences complementary to the miRNAs’ 7- to 8-bp ‘seed’ sequence. As single miRNAs are often predicted to target up to hundreds of individual transcripts, miRNAs are able to broadly affect the overall protein expression state of the cell. This can translate into global effects on cellular health and differentiation state. Recently, several reports have identified crucial roles for miRNAs in controlling the production, differentiation, and health of myelinating cells of the mammalian nervous system. In this review, we will discuss how individual miRNAs regulate these various processes, and also how miRNA production in general is required for several stages of myelin generation and maintenance.
6904322
Regulation of Oligodendrocyte Differentiation and Myelination
Despite the importance of myelin for the rapid conduction of action potentials, the molecular bases of oligodendrocyte differentiation and central nervous system (CNS) myelination are still incompletely understood. Recent results have greatly advanced this understanding, identifying new transcriptional regulators of myelin gene expression, elucidating vital roles for microRNAs in controlling myelination, and clarifying the extracellular signaling mechanisms that orchestrate the development of myelin. Studies have also demonstrated an unexpected level of plasticity of myelin in the adult CNS. These recent advances provide new insight into how remyelination may be stimulated in demyelinating disorders such as multiple sclerosis.
1569347
Control of oligodendroglial cell number by the miR-17-92 cluster
The generation of myelinating cells in the central nervous system requires the initiation of specific gene expression programs in oligodendrocytes. We reasoned that microRNAs (miRNAs) could play an important role in this process by regulating crucial developmental genes. Microarray profiling of cultured oligodendrocytes identified the miR-17-92 miRNA cluster as highly enriched in oligodendrocytes. We specifically deleted the miR-17-92 cluster in oligodendrocytes using 2′,3′-cyclic nucleotide 3′ phosphodiesterase (Cnp)-Cre mice. Absence of miR-17-92 leads to a reduction in oligodendrocyte number in vivo and we find that the expression of these miRNAs in primary cultures of oligodendrocyte precursor cells promotes cell proliferation by influencing Akt signaling. Together, these results suggest that the miRNA pathway is essential in determining oligodendroglial cell number and that the miR-17-92 cluster is crucial in this process.
18363421
Micromanaging Oligodendrocyte Differentiation by Noncoding RNA: Toward a Better Understanding of the Lineage Commitment Process
Differentiation is one of the most complex and paradoxical cellular processes that multicellular organisms undergo ([Chen and Daley, 2008][1]). Although each cell in a multicellular organism contains the same genome, genetic information is processed differently once cells terminally differentiate.
16152688
Dicer1 and miR-219 Are Required for Normal Oligodendrocyte Differentiation and Myelination
To investigate the role of microRNAs in regulating oligodendrocyte (OL) differentiation and myelination, we utilized transgenic mice in which microRNA processing was disrupted in OL precursor cells (OPCs) and OLs by targeted deletion of Dicer1. We found that inhibition of OPC-OL miRNA processing disrupts normal CNS myelination and that OPCs lacking mature miRNAs fail to differentiate normally in vitro. We identified three miRNAs (miR-219, miR-138, and miR-338) that are induced 10-100x during OL differentiation; the most strongly induced of these, miR-219, is necessary and sufficient to promote OL differentiation, and partially rescues OL differentiation defects caused by total miRNA loss. miR-219 directly represses the expression of PDGFRalpha, Sox6, FoxJ3, and ZFP238 proteins, all of which normally help to promote OPC proliferation. Together, these findings show that miR-219 plays a critical role in coupling differentiation to proliferation arrest in the OL lineage, enabling the rapid transition from proliferating OPCs to myelinating OLs.
16048042
Oligodendrocytes and the “Micro Brake” of Progenitor Cell Proliferation
A large fraction of mammalian genes is regulated posttranscriptionally by microRNAs. In the developing nervous system, a small subset of these short RNA molecules is important to orchestrate the rapid switch from OPCs to myelin-forming oligodendrocytes. But putting the miRNA brake on oligodendrocyte gene expression is required throughout life.
16359051
MicroRNA-Mediated Control of Oligodendrocyte Differentiation
MicroRNAs (miRNAs) regulate various biological processes, but evidence for miRNAs that control the differentiation program of specific neural cell types has been elusive. To determine the role of miRNAs in the formation of myelinating oligodendrocytes, we selectively deleted a miRNA-processing enzyme, Dicer1, in oligodendrocyte lineage cells. Mice lacking Dicer1 display severe myelinating deficits despite an expansion of the oligodendrocyte progenitor pool. To search for miRNAs responsible for the induction of oligodendrocyte maturation, we identified miR-219 and miR-338 as oligodendrocyte-specific miRNAs in spinal cord. Overexpression of these miRNAs is sufficient to promote oligodendrocyte differentiation. Additionally, blockage of these miRNA activities in oligodendrocyte precursor culture and knockdown of miR-219 in zebrafish inhibit oligodendrocyte maturation. miR-219 and miR-338 function in part by directly repressing negative regulators of oligodendrocyte differentiation, including transcription factors Sox6 and Hes5. These findings illustrate that miRNAs are important regulators of oligodendrocyte differentiation, providing new targets for myelin repair.
5272809
MicroRNA‐146a and Human Disease
MicroRNAs (MiRNAs) belong to a class of small non‐coding regulatory RNAs that act through repression of protein expression at post‐transcriptional level and emerge to play important roles in many physiological and pathophysiological processes. MiR‐146a is a miRNA supposed to regulate innate immune, inflammatory response and antiviral pathway negatively. In this review, we focus on the recent progress in functional role of miR‐146a in innate immune, inflammatory response, virus infection and human diseases. Together, these findings indicate that manipulation of miR‐146a expression may represent a potential new therapy for several human diseases. Potential use of miR‐146a as a biomarker for disease diagnosis, prevention and treatment is also discussed.
5953969
Combination Therapy With VELCADE and Tissue Plasminogen Activator Is Neuroprotective in Aged Rats After Stroke and Targets MicroRNA-146a and the Toll-Like Receptor Signaling Pathway
Objective—Activation of the toll-like receptor (TLR) signaling pathway exacerbates ischemic brain damage. The present study tested the hypothesis that combination treatment with VELCADE and tissue plasminogen activator (tPA) modulates the TLR signaling pathway on cerebral vasculature, which leads to neuroprotection in aged rats after stroke. Methods and Results—Focal cerebral ischemia acutely increased TLR2, TLR4, and interleukin-1 receptor–activated kinases 1 immunoreactivity on fibrin/fibrinogen-positive vessels in aged rats. Monotherapy of tPA further amplified these signals. However, VELCADE in combination with tPA-blocked stroke- and tPA-potentiated vascular TLR signals, leading to robust reduction of infarct volume compared with respective monotherapies. Quantitative reverse transcription polymerase chain reaction analysis of cerebral endothelial cells isolated by laser capture microdissection revealed that the combination treatment increased miR-l46a levels, which was inversely associated with the reduction of vascular interleukin-1 receptor–activated kinases 1 immunoreactivity. In vitro, fibrin upregulated interleukin-1 receptor–activated kinases 1 and TLR4 expression and downregulated miR-146a on primary human cerebral endothelial cells. VELCADE elevated miR-146 levels and abolished fibrin-increased interleukin-1 receptor activated kinases 1 proteins. Conclusion—Stroke acutely activates the TLR signaling pathway on cerebral vasculature. Upregulation of miR-146a and inactivation of ischemia and tPA-potentiated TLR signaling pathway by VELCADE may play an important role in the neuroprotective effect of the combination therapy of VELCADE and tPA for acute stroke.
5309709
Association of the miR-146a, miR-149, miR-196a2, and miR-499 Polymorphisms With Ischemic Stroke and Silent Brain Infarction Risk
Objective—MicroRNAs play a role in atherosclerosis-related diseases, such as cerebrovascular or cardiovascular disease. However, the effect of miR-146a, miR-149, miR-196a2, and miR-499 polymorphisms on stroke and silent brain infarction (SBI) susceptibility has not been reported. Methods and Results—Using polymerase chain reaction-amplified DNA, microRNA polymorphisms were analyzed in 678 patients with ischemic stroke, 373 patients with SBI, and 553 control subjects. The miR-146aC>G polymorphism and miR-146aG/-149T/-196a2C/-499G allele combination was significantly associated with ischemic stroke prevalence. For SBI prevalence, there were no statistically significant genetic markers. However, some allele combinations were associated with increased SBI incidence (C-T-C-G and G-T-T-A of miR-146a/-149/-196a2/-499). In subgroup analyses, miR-146aC>G increased stroke risk in female, normotensive, and nondiabetic groups. There were significant combined effects between microRNA polymorphisms and homocysteine/folate levels on ischemic stroke and SBI prevalence. Conclusion—The miR-146aG allele and miR-146aG/-149T/-196a2C/-499G allele combination were associated with ischemic stroke pathogenesis. The combined effects between microRNA polymorphisms and homocysteine/folate levels may contribute to stroke and SBI prevalence.
40773467
Focal cerebral ischemia in the mouse: description of a model and effects of permanent and temporary occlusion.
Our study is to demonstrate the advantages and disadvantages of middle cerebral artery occlusion (MCAO) model in the mouse. CD-1 mice had permanent MCAO for 24 h, or temporary occlusion for either 1 h followed by 23 h of reperfusion or 2 h of occlusion with 22 h of reperfusion. The infarct volume and blood-brain barrier disruption were smaller in the 1-h/23-h temporary occlusion than in either the 24-h permanent occlusion group or the 2-h/22-h temporary occlusion group (p<0.05). Our study demonstrates that blood flow, infarct volume, and blood-brain barrier disruption remain important markers of focal cerebral ischemia.
17905159
Generation of neurons and astrocytes from isolated cells of the adult mammalian central nervous system.
Neurogenesis in the mammalian central nervous system is believed to end in the period just after birth; in the mouse striatum no new neurons are produced after the first few days after birth. In this study, cells isolated from the striatum of the adult mouse brain were induced to proliferate in vitro by epidermal growth factor. The proliferating cells initially expressed nestin, an intermediate filament found in neuroepithelial stem cells, and subsequently developed the morphology and antigenic properties of neurons and astrocytes. Newly generated cells with neuronal morphology were immunoreactive for gamma-aminobutyric acid and substance P, two neurotransmitters of the adult striatum in vivo. Thus, cells of the adult mouse striatum have the capacity to divide and differentiate into neurons and astrocytes.
42965253
Neural stem cells in the adult mammalian forebrain: A relatively quiescent subpopulation of subependymal cells
Dissection of the subependyma from the lateral ventricle of the adult mouse forebrain is necessary and sufficient for the in vitro formation of clonally derived spheres of cells that exhibit stem cell properties such as self-maintenance and the generation of a large number of progeny comprising the major cell types found in the central nervous system. Killing the constitutively proliferating cells of the subependyma in vivo has no effect on the number of stem cells isolated in vitro and induces a complete repopulation of the subependyma in vivo by relatively quiescent stem cells found within the subependyma. Depleting the relatively quiescent cell population within the subependyma in vivo results in a corresponding decrease in spheres formed in vitro and in the final number of constitutively proliferating cells in vivo, suggesting that a relatively quiescent subependymal cell is the in vivo source of neural stem cells.
33887887
Angiopoietin 2 Mediates the Differentiation and Migration of Neural Progenitor Cells in the Subventricular Zone after Stroke*
Ischemic stroke stimulates neurogenesis in the adult rodent brain. The molecules underlying stroke-induced neurogenesis have not been fully investigated. Using real-time reverse transcription-PCR, we found that stroke substantially up-regulated angiopoietin 2 (ANG2), a proangiogenic gene, expression in subventricular zone neural progenitor cells. Incubation of neural progenitor cells with recombinant human ANG2 significantly increased the number of β-III tubulin-positive cells, a marker of immature neurons, but did not alter the number of glial fibrillary acidic protein (GFAP)-positive cells, a marker of astrocytes, suggesting that ANG2 promotes neuronal differentiation. Blockage of the ANG2 receptor, Tie2, with small interference RNA (siRNA)-Tie2 attenuated recombinant human ANG2 (rhANG2)-increased β-III tubulin mRNA levels compared with levels in the progenitor cells transfected with control siRNA. Chromatin immunoprecipitation analysis revealed that CCAAT/enhancer-binding protein (C/EBPβ) up-regulated by rhANG2 bound to β-III tubulin, which is consistent with published data that there are several C/EBPβ binding sites in the promoter of β-III tubulin gene. In addition, rhANG2 enhanced migration of neural progenitor cells measured by single neurosphere assay. Blockage of Tie2 with siRNA-Tie2 and a Tie2-neutralizing antibody did not suppress ANG2-enhanced migration. However, inhibition of matrix metalloproteinases with GM6001 blocked ANG2-enhanced migration. Collectively, our data suggest that interaction of ANG2, a proangiogenic factor, with its receptor Tie2 promotes neural progenitor cell differentiation into neuronal lineage cells, whereas ANG2 regulates neural progenitor cell migration through matrix metalloproteinases, which do not require its receptor Tie2.
17833809
Apoptosis-associated microRNAs are modulated in mouse, rat and human neural differentiation
BackgroundMicroRNAs (miRs or miRNAs) regulate several biological processes in the cell. However, evidence for miRNAs that control the differentiation program of specific neural cell types has been elusive. Recently, we have shown that apoptosis-associated factors, such as p53 and caspases participate in the differentiation process of mouse neural stem (NS) cells. To identify apoptosis-associated miRNAs that might play a role in neuronal development, we performed global miRNA expression profiling experiments in NS cells. Next, we characterized the expression of proapoptotic miRNAs, including miR-16, let-7a and miR-34a in distinct models of neural differentiation, including mouse embryonic stem cells, PC12 and NT2N cells. In addition, the expression of antiapoptotic miR-19a and 20a was also evaluated.ResultsThe expression of miR-16, let-7a and miR-34a was consistently upregulated in neural differentiation models. In contrast, expression of miR-19a and miR-20a was downregulated in mouse NS cell differentiation. Importantly, differential expression of specific apoptosis-related miRNAs was not associated with increased cell death. Overexpression of miR-34a increased the proportion of postmitotic neurons of mouse NS cells.ConclusionsIn conclusion, the identification of miR-16, let-7a and miR-34a, whose expression patterns are conserved in mouse, rat and human neural differentiation, implicates these specific miRNAs in mammalian neuronal development. The results provide new insights into the regulation of neuronal differentiation by apoptosis-associated miRNAs.
24863991
Activated Neural Stem Cells Contribute to Stroke-Induced Neurogenesis and Neuroblast Migration toward the Infarct Boundary in Adult Rats
Stroke increases neurogenesis. The authors investigated whether neural stem cells or progenitor cells in the adult subventricular zone (SVZ) of rats contribute to stroke-induced increase in neurogenesis. After induction of stroke in rats, the numbers of cells immunoreactive to doublecortin, a marker for immature neurons, increased in the ipsilateral SVZ and striatum. Infusion of an antimitotic agent (cytosine-β-D-arabiofuranoside, Ara-C) onto the ipsilateral cortex eliminated more than 98% of actively proliferating cells in the SVZ and doublecortin-positive cells in the ipsilateral striatum. However, doublecortin-positive cells rapidly replenished after antimitotic agent depletion of actively proliferating cells. Depleting the numbers of actively proliferating cells in vivo had no effect on the numbers of neurospheres formed in vitro, yet the numbers of neurospheres derived from stroke rats significantly (P < 0.05) increased. Neurospheres derived from stroke rats self-renewed and differentiated into neurons and glia. In addition, doublecortin-positive cells generated in the SVZ migrated in a chainlike structure toward ischemic striatum. These findings indicate that in the adult stroke brain, increases in recruitment of neural stem cells contribute to stroke-induced neurogenesis, and that newly generated neurons migrate from the SVZ to the ischemic striatum.
23708604
Proliferation and differentiation of progenitor cells in the cortex and the subventricular zone in the adult rat after focal cerebral ischemia
Progenitor cells in the subventricular zone of the lateral ventricle and in the dentate gyrus of the hippocampus can proliferate throughout the life of the animal. To examine the proliferation and fate of progenitor cells in the subventricular zone and dentate gyrus after focal cerebral ischemia, we measured the temporal and spatial profiles of proliferation of cells and the phenotypic fate of proliferating cells in ischemic brain in a model of embolic middle cerebral artery occlusion in the adult rat. Proliferating cells were labeled by injection of bromodeoxyuridine (BrdU) in a pulse or a cumulative protocol. To determine the temporal profile of proliferating cells, ischemic rats were injected with BrdU every 4 h for 12 h on the day preceding death. Rats were killed 2-14 days after ischemia. We observed significant increases in numbers of proliferating cells in the ipsilateral cortex and subventricular zone 2-14 days with a peak at 7 days after ischemia compared with the control group. To maximize labeling of proliferating cells, a single daily injection of BrdU was administered over a 14-day period starting the day after ischemia. Rats were killed either 2 h or 28 days after the last injection of BrdU. A significant increase in numbers of BrdU immunoreactive cells in the subventricular zone was coincident with a significant increase in numbers of BrdU immunoreactive cells in the olfactory bulb 14 days after ischemia and numbers of BrdU immunoreactive cells did not significantly increase in the dentate gyrus. However, 28 days after the last labeling, the number of BrdU labeled cells decreased by 90% compared with number at 14 days. Clusters of BrdU labeled cells were present in the cortex distal to the infarction. Numerous cells immunostained for the polysialylated form of the neuronal cell adhesion molecule were detected in the ipsilateral subventricular zone. Only 6% of BrdU labeled cells exhibited glial fibrillary acidic protein immunoreactivity in the cortex and subcortex and no BrdU labeled cells expressed neuronal protein markers (neural nuclear protein and microtubule associated protein-2). From these data we suggest that focal cerebral ischemia induces transient and regional specific increases in cell proliferation in the ipsilateral hemisphere and that proliferating progenitor cells may exist in the adult cortex.
2258569
Isolation and culture of rat and mouse oligodendrocyte precursor cells
The ability to isolate oligodendroglial precursor cells (OPCs) provides a powerful means to characterize their differentiation, properties and potential for myelin repair. Although much knowledge is available for isolation of OPCs from the rat central nervous system, preparation and maintenance of mouse OPCs has been until recently a challenge owing to difficulties in obtaining a sufficient quantity of purified OPCs. Here, we describe protocols to prepare highly enriched rat OPCs and nearly homogenous mouse OPCs. The mouse method generates predominantly OPCs from cortical neural progenitor cells as clonal aggregates called “oligospheres” by taking advantage of molecular genetic tools. Isolated OPCs can be further differentiated into oligodendrocytes. Collectively, we describe simple and efficient methods for the preparation and in vitro maintenance of enriched OPCs from rats and mice. Isolation and culture of a large, homogenous population of rodent OPCs should significantly facilitate studies on OPC lineage progression and their utility in myelin repair after injury.
6844186
Regulation of serum response factor by miRNA‐200 and miRNA‐9 modulates oligodendrocyte progenitor cell differentiation
Serum response factor (SRF) is a transcription factor that transactivates actin‐associated genes and has been implicated in oligodendrocyte (OL) differentiation. To date, it has not been investigated in cerebral ischemia. We investigated the dynamics of SRF expression after stroke in vivo and the role of SRF in OL differentiation in vitro. Using immunohistochemistry, we found that SRF was upregulated in OLs and OL precursor cells (OPCs) after stroke. Moreover, upregulation of SRF was concurrent with downregulation of the micro‐RNAs (miRNAs) miR‐9 and the miR‐200 family in the ischemic white matter region, the corpus callosum. Inhibition of SRF activation by CCG‐1423, a specific inhibitor of SRF function, blocked OPCs from differentiating into OLs. Overexpression of miR‐9 and miR‐200 in cultured OPCs suppressed SRF expression and inhibited OPC differentiation. Moreover, co‐expression of miR‐9 and miR‐200 attenuated activity of a luciferase reporter assay containing the Srf 3′ untranslated region. Collectively, this study is the first to show that stroke upregulates SRF expression in OPCs and OLs, and that SRF levels are mediated by miRNAs and regulate OPC differentiation. © 2012 Wiley Periodicals, Inc.
28013609
MicroRNA-17-92 Cluster Mediates the Proliferation and Survival of Neural Progenitor Cells after Stroke*
Background: The role of miRNAs in mediating stroke-induced neurogenesis remains largely unknown. Results: The miR17-92 cluster regulated ischemia-induced neural progenitor cell proliferation, and activation of the Shh pathway up-regulated miR17-92 cluster expression. Conclusion: The miR17-92 cluster plays an important role in mediating adult neural progenitor cell proliferation. Significance: The present study provides molecular mechanisms underlying miR17-92 cluster in mediating stroke-induced neurogenesis. The role of microRNAs (miRNAs) in mediating adult neurogenesis after stroke has not been extensively studied. The present study investigated the function of the miR17-92 cluster in adult neural progenitor cells after experimental stroke. We found that stroke substantially up-regulated miR17-92 cluster expression in neural progenitor cells of the adult mouse. Overexpression of the miR17-92 cluster either in cultured ischemic neural progenitor cells or in the subventricular zone (SVZ) of ischemic animals significantly increased cell proliferation, whereas inhibition of individual members of the miR17-92 cluster, miR-18a and miR-19a, suppressed cell proliferation and increased cell death. The miR17-92 cluster mediated PTEN (phosphatase and tensin homolog) expression, which is a predicted target of the miR17-92 cluster. Addition of Sonic hedgehog (Shh) protein up-regulated miR17-92 expression and elevated c-Myc protein in ischemic neural progenitor cells, whereas blockade of the Shh signaling pathway down-regulated miR17-92 cluster expression and reduced c-Myc levels. Overexpression of c-Myc up-regulated miR17-92 cluster expression. Intraventricular infusion of Shh and a Shh receptor inhibitor, cyclopamine, to ischemic animals further elevated and suppressed, respectively, miR17-92 cluster expression in the SVZ. These data indicate that the miR17-92 cluster plays an important role in mediating neural progenitor cell function and that the Shh signaling pathway is involved in up-regulating miR17-92 cluster expression.
195690256
miRNA in situ hybridization in formaldehyde and EDC–fixed tissues
MicroRNAs are small regulatory RNAs with many biological functions and disease associations. We showed that in situ hybridization (ISH) using conventional formaldehyde fixation results in substantial microRNA loss from mouse tissue sections, which can be prevented by fixation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide that irreversibly immobilizes the microRNA at its 5′ phosphate. We determined optimal hybridization parameters for 130 locked nucleic acid probes by recording nucleic acid melting temperature during ISH.
28151554
Clonal heterogeneity in the early embryonic rodent cortical germinal zone and the separation of subventricular from ventricular zone lineages
The cell cycle kinetics of individual clones of cells in the embryonic cortex were studied to determine the amount of heterogeneity among cortical progenitors. This kinetic heterogeneity may be the first sign of heterogeneous differentiation in the proliferating cortical germinal zone. Retroviral lineage tracing of clonal progeny in the embryonic day 16 (E16) rat cortex (48 hr after the retroviral infection and [3H]thymidine labeling of proliferating cells) permitted a description of the formation of the preplate in the medial cortex and the formation of the subventricular zone (SVZ) in the lateral cortex. Forty percent of the retrovirally tagged clones were double‐labeled with a pulse of [3H]thymidine, corresponding to the 40% of ventricular zone cells in S‐phase at the time of [3H]thymidine injection. Most of clones had cell numbers with powers of 2 (2, 4, and 8 cells), suggesting synchronous modes of division. Nevertheless, 15% of the retrovirally tagged clones that were double‐labeled with [3H]thymidine at the time of [3H]thymidine injection showed asynchronous mode of division. Clonally related cells in the ventricular zone showed considerable variability in cell cycle times: 56% of the clones (8‐cell clones) were composed of faster cycling cells with cell cycle times of 12 hr, and 25% of the clones (4‐cell clones) represented slower cycling cells with cell cycle times of 16 hr. The clones migrating outside the ventricular zone differed in size and spatial distribution in the lateral versus medial cortex. In the lateral cortex, half the migrating clones were large proliferating 8‐cell clones with all their members contained within the forming SVZ. In the medial cortex, the majority of the migrating clones were 2‐cell and 4‐cell clones. Given that the medial cortex matures later than the lateral neocortex and that no SVZ has formed in the rat medial cortex by E16, we suggest that the majority of cells that leave the medial cortical VZ by E16 are cells destined to form the neuronal populations of the preplate. The early embryonic cortical ventricular zone includes a mosaic of specialized progenitor cells. Dev. Dyn. 1997;210:328–343. © 1997 Wiley‐Liss, Inc.
12056148
NF-κB-dependent induction of microRNA miR-146, an inhibitor targeted to signaling proteins of innate immune responses
Activation of mammalian innate and acquired immune responses must be tightly regulated by elaborate mechanisms to control their onset and termination. MicroRNAs have been implicated as negative regulators controlling diverse biological processes at the level of posttranscriptional repression. Expression profiling of 200 microRNAs in human monocytes revealed that several of them (miR-146a/b, miR-132, and miR-155) are endotoxin-responsive genes. Analysis of miR-146a and miR-146b gene expression unveiled a pattern of induction in response to a variety of microbial components and proinflammatory cytokines. By means of promoter analysis, miR-146a was found to be a NF-κB-dependent gene. Importantly, miR-146a/b were predicted to base-pair with sequences in the 3′ UTRs of the TNF receptor-associated factor 6 and IL-1 receptor-associated kinase 1 genes, and we found that these UTRs inhibit expression of a linked reporter gene. These genes encode two key adapter molecules downstream of Toll-like and cytokine receptors. Thus, we propose a role for miR-146 in control of Toll-like receptor and cytokine signaling through a negative feedback regulation loop involving down-regulation of IL-1 receptor-associated kinase 1 and TNF receptor-associated factor 6 protein levels.
34231280
Erratum: MicroRNA-146a directs the symmetric division of Snail-dominant colorectal cancer stem cells
In the version of this News and Views article originally published, the author affiliations were incorrect. The correct affiliations are as follows: Peter Friedl, Katarina Wolf and Mirjam M. Zegers are in the Department of Cell Biology, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands. Peter Friedl is at the David H. Koch Center for Applied Research of Genitourinary Cancers, Department of Genitourinary Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, 77030, USA. This has been corrected in all online versions of this News and Views article.
205902156
Cyclic stretch induced miR-146a upregulation delays C2C12 myogenic differentiation through inhibition of Numb.
Proliferation and differentiation of muscle stem cells must be tightly regulated by intrinsic and extrinsic signals for effective regeneration and adaptive response. MicroRNAs have been implicated as potent regulators in diverse biological processes at the level of posttranscriptional repression. In this study, we found that miR-146a was significantly upregulated upon a 48-h cyclic stretch of 5% elongation/10cycles/min. Importantly, miR-146 was predicted to base-pair with sequences in the 3' UTR of Numb, which promotes satellite cell differentiation towards muscle cells by inhibiting Notch signaling. Through reporter assay and exogenous expression experiment, we confirmed Numb was inhibited by miR-146a. Inhibition of miR-146a by antago-miR-146a rescued the expression of Numb and facilitated the differentiation of C2C12 at a cost of compromised proliferation. Thus, for the first time, we propose a role of miR-146a in skewing the balance of muscle differentiation and proliferation through inhibiting the expression of Numb.
40291032
Chromatin remodeling and histone modification in the conversion of oligodendrocyte precursors to neural stem cells.
We showed previously that purified rat oligodendrocyte precursor cells (OPCs) can be induced by extracellular signals to convert to multipotent neural stem-like cells (NSLCs), which can then generate both neurons and glial cells. Because the conversion of precursor cells to stem-like cells is of both intellectual and practical interest, it is important to understand its molecular basis. We show here that the conversion of OPCs to NSLCs depends on the reactivation of the sox2 gene, which in turn depends on the recruitment of the tumor suppressor protein Brca1 and the chromatin-remodeling protein Brahma (Brm) to an enhancer in the sox2 promoter. Moreover, we show that the conversion is associated with the modification of Lys 4 and Lys 9 of histone H3 at the same enhancer. Our findings suggest that the conversion of OPCs to NSLCs depends on progressive chromatin remodeling, mediated in part by Brca1 and Brm.
6152125
Pathophysiology of the brain extracellular matrix: a new target for remyelination
The extracellular matrix (ECM) occupies a notable proportion of the CNS and contributes to its normal physiology. Alterations to the ECM occur after neural injury (for example, in multiple sclerosis, spinal cord injury or Alzheimer's disease) and can have drastic consequences. Of note, injury-induced changes in chondroitin sulphate proteoglycans (CSPGs) — a family of ECM proteoglycans — can lead to the inhibition of myelin repair. Here, we highlight the pathophysiological roles of the brain's ECM, particularly those of CSPGs, after neural insults and discuss how the ECM can be targeted to promote remyelination.
22930185
Oligodendrocyte-Specific FADD Deletion Protects Mice from Autoimmune-Mediated Demyelination
Apoptosis of oligodendrocytes (ODCs), the myelin-producing glial cells in the CNS, plays a central role in demyelinating diseases such as multiple sclerosis and experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. To investigate the mechanism behind ODC apoptosis in EAE, we made use of conditional knockout mice lacking the adaptor protein FADD specifically in ODCs (FADDODC-KO). FADD mediates apoptosis by coupling death receptors with downstream caspase activation. In line with this, ODCs from FADDODC-KO mice were completely resistant to death receptor-induced apoptosis in vitro. In the EAE model, FADDODC-KO mice followed an ameliorated clinical disease course in comparison with control littermates. Lymphocyte and macrophage infiltration into the spinal cord parenchyma was significantly reduced, as was the extent of demyelination and proinflammatory gene expression. Collectively, our data show that FADD is critical for ODC apoptosis and the development of autoimmune demyelinating disease.
10825453
Notch Receptor Activation Inhibits Oligodendrocyte Differentiation
In this study, we show that oligodendrocyte differentiation is powerfully inhibited by activation of the Notch pathway. Oligodendrocytes and their precursors in the developing rat optic nerve express Notch1 receptors and, at the same time, retinal ganglion cells express Jagged1, a ligand of the Notch1 receptor, along their axons. Jagged1 expression is developmentally regulated, decreasing with a time course that parallels myelination in the optic nerve. These results suggest that the timing of oligodendrocyte differentiation and myelination is controlled by the Notch pathway and raise the question of whether localization of myelination is controlled by this pathway.
15072290
ProNGF Induces p75-Mediated Death of Oligodendrocytes following Spinal Cord Injury
The neurotrophin receptor p75 is induced by various injuries to the nervous system, but its role after injury has remained unclear. Here, we report that p75 is required for the death of oligodendrocytes following spinal cord injury, and its action is mediated mainly by proNGF. Oligodendrocytes undergoing apoptosis expressed p75, and the absence of p75 resulted in a decrease in the number of apoptotic oligodendrocytes and increased survival of oligodendrocytes. ProNGF is likely responsible for activating p75 in vivo, since the proNGF from the injured spinal cord induced apoptosis among p75(+/+), but not among p75(-/-), oligodendrocytes in culture, and its action was blocked by proNGF-specific antibody. Together, these data suggest that the role of proNGF is to eliminate damaged cells by activating the apoptotic machinery of p75 after injury.
14479427
Toll-Like Receptor 3 Is a Negative Regulator of Embryonic Neural Progenitor Cell Proliferation
Toll-like receptors (TLRs) play important roles in innate immunity. Several TLR family members have recently been shown to be expressed by neurons and glial cells in the adult brain, and may mediate responses of these cells to injury and infection. To address the possibility that TLRs play a functional role in development of the nervous system, we analyzed the expression of TLRs during different stages of mouse brain development and assessed the role of TLRs in cell proliferation. TLR3 protein is present in brain cells in early embryonic stages of development, and in cultured neural stem/progenitor cells (NPC). NPC from TLR3-deficient embryos formed greater numbers of neurospheres compared with neurospheres from wild-type embryos. Numbers of proliferating cells, as assessed by phospho histone H3 and proliferating cell nuclear antigen labeling, were also increased in the developing cortex of TLR3-deficient mice compared with wild-type mice in vivo. Treatment of cultured embryonic cortical neurospheres with a TLR3 ligand (polyIC) significantly reduced proliferating (BrdU-labeled) cells and neurosphere formation in wild type but not TLR3−/−-derived NPCs. Our findings reveal a novel role for TLR3 in the negative regulation of NPC proliferation in the developing brain.
18992949
The Toll-Like Receptor TLR4 Is Necessary for Lipopolysaccharide-Induced Oligodendrocyte Injury in the CNS
The immediate or innate immune response is the first line of defense against diverse microbial pathogens and requires the expression of recently discovered toll-like receptors (TLRs). TLR4 serves as a specific receptor for lipopolysaccharide (LPS) and is localized on the surface of a subset of mammalian cells. Although innate immunity is a necessary host defense against microbial pathogens, the consequences of its activation in the CNS can be deleterious, as we show here in a developing neural model. We examined the major non-neuronal cell types in the CNS for expression of TLR4 and found that microglia expressed high levels, whereas astrocytes and oligodendrocytes expressed none. Consistent with TLR4 expression solely in microglia, we show that microglia are the only CNS glial cells that bind fluorescently tagged lipopolysaccharide. Lipopolysaccharide led to extensive oligodendrocyte death in culture only under conditions in which microglia were present. To determine whether TLR4 is necessary for lipopolysaccharide-induced oligodendrocyte death in mixed glial cultures, we studied cultures generated from mice bearing a loss-of-function mutation in the tlr4 gene. Lipopolysaccharide failed to induce oligodendrocyte death in such cultures, in contrast to the death induced in cultures from wild-type mice. Finally, stereotactic intracerebral injection of lipopolysaccharide into the developing pericallosal white matter of immature rodents resulted in loss of oligodendrocytes and hypomyelination and periventricular cysts. Our data provide a general mechanistic link between (1) lipopolysaccharide and similar microbial molecular motifs and (2) injury to oligodendrocytes and myelin as occurs in periventricular leukomalacia and multiple sclerosis.
23154014
Oligodendrogliogenic and neurogenic adult subependymal zone neural stem cells constitute distinct lineages and exhibit differential responsiveness to Wnt signalling
The adult mouse subependymal zone (SEZ) harbours adult neural stem cells (aNSCs) that give rise to neuronal and oligodendroglial progeny. However it is not known whether the same aNSC can give rise to neuronal and oligodendroglial progeny or whether these distinct progenies constitute entirely separate lineages. Continuous live imaging and single-cell tracking of aNSCs and their progeny isolated from the mouse SEZ revealed that aNSCs exclusively generate oligodendroglia or neurons, but never both within a single lineage. Moreover, activation of canonical Wnt signalling selectively stimulated proliferation within the oligodendrogliogenic lineage, resulting in a massive increase in oligodendrogliogenesis without changing lineage choice or proliferation within neurogenic clones. In vivo activation or inhibition of canonical Wnt signalling respectively increased or decreased the number of Olig2 and PDGFR- α positive cells, suggesting that this pathway contributes to the fine tuning of oligodendrogliogenesis in the adult SEZ.
8077109
Origin of Oligodendrocytes in the Subventricular Zone of the Adult Brain
Glial fibrillary acidic protein (GFAP)-positive astrocytes (type B cells) in the subventricular zone (SVZ) generate large numbers of new neurons in the adult brain. SVZ stem cells can also generate oligodendrocytes in vitro, but it is not known whether these adult primary progenitors generate oligodendrocytes in vivo. Myelin repair and oligodendrocyte formation in the adult brain is instead associated with glial-restricted progenitors cells, known as oligodendrocyte progenitor cells (OPCs). Here we show that type B cells also generate a small number of nonmyelinating NG2-positive OPCs and mature myelinating oligodendrocytes. Some type B cells and a small subpopulation of actively dividing type C (transit-amplifying) cells expressed oligodendrocyte lineage transcription factor 2 (Olig2), suggesting that oligodendrocyte differentiation in the SVZ begins early in the lineage. Olig2-positive, polysialylated neural cell adhesion molecule-positive, PDGF receptor α-positive, and β-tubulin-negative cells originating in the SVZ migrated into corpus callosum, striatum, and fimbria fornix to differentiate into the NG2-positive nonmyelinating and mature myelinating oligodendrocytes. Furthermore, primary clonal cultures of type B cells gave rise to oligodendrocytes alone or oligodendrocytes and neurons. Importantly, the number of oligodendrocytes derived from type B cells in vivo increased fourfold after a demyelinating lesion in corpus callosum, indicating that SVZ astrocytes participate in myelin repair in the adult brain. Our work identifies SVZ type B cells as progenitors of oligodendrocytes in normal and injured adult brain.
918781
Mechanisms of oligodendrocyte regeneration from ventricular-subventricular zone-derived progenitor cells in white matter diseases
White matter dysfunction is an important part of many CNS disorders including multiple sclerosis (MS) and vascular dementia. Within injured areas, myelin loss and oligodendrocyte death may trigger endogenous attempts at regeneration. However, during disease progression, remyelination failure may eventually occur due to impaired survival/proliferation, migration/recruitment, and differentiation of oligodendrocyte precursor cells (OPCs). The ventricular-subventricular zone (V-SVZ) and the subgranular zone (SGZ) are the main sources of neural stem/progenitor cells (NSPCs), which can give rise to neurons as well as OPCs. Under normal conditions in the adult brain, the V-SVZ progenitors generate a large number of neurons with a small number of oligodendrocyte lineage cells. However, after demyelination, the fate of V-SVZ-derived progenitor cells shifts from neurons to OPCs, and these newly generated OPCs migrate to the demyelinating lesions to ease white matter damage. In this mini-review, we will summarize the recent studies on extrinsic (e.g., vasculature, extracellular matrix (ECM), cerebrospinal fluid (CSF)) and intrinsic (e.g., transcription factors, epigenetic modifiers) factors, which mediate oligodendrocyte generation from the V-SVZ progenitor cells. A deeper understanding of the mechanisms that regulate the fate of V-SVZ progenitor cells may lead to new therapeutic approaches for ameliorating white matter dysfunction and damage in CNS disorders.
35413156
Thymosin β4 Up-regulation of MicroRNA-146a Promotes Oligodendrocyte Differentiation and Suppression of the Toll-like Proinflammatory Pathway*
Background: Thymosin β4 (Tβ4) promotes differentiation of oligoprogenitor cells (OPCs) to oligodendrocytes in animal models of neurological injury. Results: Tβ4 increased expression of microRNA-146a and suppressed expression of TLR (Toll-like) proinflammatory cytokines. Conclusion: Tβ4 suppresses the TLR proinflammatory pathway by up-regulating miR-146a to promote OPC differentiation. Signficance: Learning how Tβ4 promotes oligodendrogenesis supports its development for clinical studies. Thymosin β4 (Tβ4), a G-actin-sequestering peptide, improves neurological outcome in rat models of neurological injury. Tissue inflammation results from neurological injury, and regulation of the inflammatory response is vital for neurological recovery. The innate immune response system, which includes the Toll-like receptor (TLR) proinflammatory signaling pathway, regulates tissue injury. We hypothesized that Tβ4 regulates the TLR proinflammatory signaling pathway. Because oligodendrogenesis plays an important role in neurological recovery, we employed an in vitro primary rat embryonic cell model of oligodendrocyte progenitor cells (OPCs) and a mouse N20.1 OPC cell line to measure the effects of Tβ4 on the TLR pathway. Cells were grown in the presence of Tβ4, ranging from 25 to 100 ng/ml (RegeneRx Biopharmaceuticals Inc., Rockville, MD), for 4 days. Quantitative real-time PCR data demonstrated that Tβ4 treatment increased expression of microRNA-146a (miR-146a), a negative regulator the TLR signaling pathway, in these two cell models. Western blot analysis showed that Tβ4 treatment suppressed expression of IL-1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6), two proinflammatory cytokines of the TLR signaling pathway. Transfection of miR-146a into both primary rat embryonic OPCs and mouse N20.1 OPCs treated with Tβ4 demonstrated an amplification of myelin basic protein (MBP) expression and differentiation of OPC into mature MBP-expressing oligodendrocytes. Transfection of anti-miR-146a nucleotides reversed the inhibitory effect of Tβ4 on IRAK1 and TRAF6 and decreased expression of MBP. These data suggest that Tβ4 suppresses the TLR proinflammatory pathway by up-regulating miR-146a.
43429841
Role of toll-like receptor 2 in ischemic demyelination and oligodendrocyte death
White matter is frequently involved in ischemic stroke, and progressive ischemic white matter injuries are associated with various neurologic dysfunctions in the elderly population. Demyelination and oligodendrocyte (OL) loss are prominent features of ischemic white matter injury. Endothelin-1 injection into the internal capsule resulted in a localized demyelinating lesion in mice, where loss of OL lineage cells and inflammatory cell infiltration were observed accompanied by upregulation of toll-like receptor 2 (TLR2). Intriguingly, the extent of demyelinating pathology was markedly larger in TLR2 deficient mice than that of wild-type (WT) mice. TLR2 deficient mice showed enhanced OL death and decreased phosphorylation of ERK1/2 compared with WT animals. Cultured OLs from TLR2 deficient mice were more vulnerable to oxygen-glucose deprivation than WT OLs. Applying TLR2 agonists Pam3CSK4 or Zymosan after oxygen-glucose deprivation substantially rescued WT OL death with augmentation of ERK1/2 phosphorylation. Treatment with Pam3CSK4 also reduced the extent of endothelin-1 induced ischemic demyelination in vivo. Our data indicate TLR2 may provide endogenous protective effects on ischemic demyelination and OL degeneration.
37361597
IRAK1: a critical signaling mediator of innate immunity.
The innate immune system is equipped with sensitive and efficient machineries to provide an immediate, first line defense against infections. Toll-like receptors (TLRs) detect pathogens and the IL-1 receptor (IL-1R) family enables cells to quickly respond to inflammatory cytokines by mounting an efficient protective response. Interleukin-1 receptor activated kinases (IRAKs) are key mediators in the signaling pathways of TLRs/IL-1Rs. By means of their kinase and adaptor functions, IRAKs initiate a cascade of signaling events eventually leading to induction of inflammatory target gene expression. Due to this pivotal role, IRAK function is also highly regulated via multiple mechanisms. In this review, we focus on IRAK1, the earliest known and yet the most interesting member of this family. An overview on its structure, function and biology is given, with emphasis on the different novel mechanisms that regulate IRAK1 function. We also highlight several unresolved questions in this field and evaluate the potential of IRAK1 as a target for therapeutic intervention.
205784061
Unexpected regulatory roles of TLR4 and TLR9 in experimental autoimmune encephalomyelitis
Innate immune mechanisms essential for priming encephalitogenic T cells in autoimmune neuroinflammation are poorly understood. Experimental autoimmune encephalomyelitis (EAE) is a IL‐17‐producing Th (Th17) cell‐mediated autoimmune disease and an animal model of multiple sclerosis. To investigate how upstream TLR signals influence autoimmune T cell responses, we studied the role of individual TLR and MyD88, the common TLR adaptor molecule, in the initiation of innate and adaptive immune responses in EAE. Wild type (WT) C57BL/6, TLR‐deficient and MyD88‐deficient mice were immunized with myelin oligodendrocyte glycoprotein (MOG) in CFA. MyD88–/– mice were completely EAE resistant. Purified splenic myeloid DC (mDC) from MyD88–/– mice expressed much less IL‐6 and IL‐23, and serum and T cell IL‐17 were absent. TLR4–/– and TLR9–/– mice surprisingly exhibited more severe EAE symptoms than WT mice. IL‐6 and IL‐23 expression by mDC and Th17 responses were higher in TLR4–/– mice, suggesting a regulatory role of TLR4 in priming Th17 cells. IL‐6 expression by splenocytes was higher in TLR9–/– mice. Our data suggest that MyD88 mediates the induction of mDC IL‐6 and IL‐23 responses after MOG immunization, which in turn drives IL‐17‐producing encephalitogenic Th17 cell activation. Importantly, we demonstrate that TLR4 and TLR9 regulate disease severity in MOG‐induced EAE.
37473861
The role of Toll-like receptors in multiple sclerosis and possible targeting for therapeutic purposes
Abstract The interaction between the immune and nervous systems suggests invaluable mechanisms for several pathological conditions, especially neurodegenerative disorders. Multiple sclerosis (MS) is a potentially disabling chronic autoimmune disease, characterized by chronic inflammation and neurodegenerative pathology of the central nervous system. Toll-like receptors (TLRs) are an important family of receptors involved in host defense and in recognition of invading pathogens. The role of TLRs in the pathogenesis of autoimmune disorders such as MS is only starting to be uncovered. Recent studies suggest an ameliorative role of TLR3 and a detrimental role of other TLRs in the onset and progression of MS and experimental autoimmune encephalomyelitis, a murine model of MS. Thus, modulating TLRs can represent an innovative immunotherapeutic approach in MS therapy. This article outlines the role of these TLRs in MS, also discussing TLR-targeted agonist or antagonists that could be used in the different stages of the disease.