ProjectSummary Background: Pulmonary hypertension (PH) is a deadly disease of the lung vasculature with a complex pathophysiology that remains largely undefined. My mentor?s laboratory established the microRNA-130/301 familyasamediatorofPHdevelopmentanddefinedaseparatemechanismbywhichiron-sulfur(Fe-S)cluster deficiencypromotesPH.Fe-Sclustersarebioinorganiccofactorsessentialtomitochondrialandcellularfunction. Frataxin(FXN)isamitochondrialproteincrucialtoFe-Sbiogenesis.LossofFXNduetoatrinucleotiderepeat mutationcausesFriedreich?sataxia(FRDA),adiseasecharacterizedbyneurologicdysfunctionandhypertrophic cardiomyopathy. Hypertrophic cardiomyopathy is often accompanied by PH, thought to be the result of left ventricularstiffeningratherthandirectdysfunctionofthepulmonaryvessels.However,Ihavefoundthathypoxia, a key trigger of PH, down-regulated FXN expression in pulmonary arterial endothelial cells. FXN was also decreased in the pulmonary vasculature of mice and humans with PH. Consequently, such FXN deficiency alteredendothelialmitochondrial,vasomotor,apoptoticindices,thusleadingtopreliminarydataregardingthe alterationofPHinvivo.Takentogether,theremaybeadirectroleforFXNinPH.Hypothesis:FXNdeficiency, inducedbyhypoxiaorgeneticmutation,disruptsendothelialmetabolismandfunctiontopromotePH. SpecificAims:1)Determinewhetherhypoxicdown-regulationofFXNiscontrolledbymiR-130b.Ihave foundthattheFXNtranscriptcontainsapossiblebindingsiteforthePH-relevantmiR-130b.Bygain-andloss- of-functionmethodsinpulmonaryarterialendothelialcells,Iwilldeterminewhetherhypoxia-inducedmiR-130b decreasesFXNexpression,thusdefiningacausativerelationshipamongmiR-130b,FXN,andFe-Sbiogenesis. 2)DeterminewhetherFXNlossattenuatesmitochondrialrespirationandendothelialfunction.Inprimary endothelialcellsandinduciblepluripotentstemcell-derivedendothelialcells(iPSC-ECs)fromFRDApatients,I willtestthehypothesisthatFXNdeficiencyinducesFe-Scluster-dependentmitochondrialdysfunction,resulting inendothelialphenotypicchanges(e.g.,apoptosis,proliferation).Ifsuccessful,findingscouldestablishakeylink betweenhypoxia-orgenetically-drivenFXNlossandendothelialdysfunctionconsistentwithPH. 3)EstablishwhetherFXNlossandresultingmitochondrialdysfunctionpredisposestoPHinvivo.Ina tamoxifen-dependentendothelialcellFXNknockoutmousemodel,IwilltestthehypothesisthatFXNdeficiency inthepulmonaryendotheliumpromotesmolecular,histologic,andhemodynamicchangesconsistentwithPH.If successful,theseresultswillvalidateanintegralanddirectroleforFXNinthedevelopmentofPH. Significance:Thisprojectisideallystructuredtotrainmeasaphysician-scientistandbridgethegapbetween basicscienceandclinicalmedicine.IaimtocontributetothecurrentlydeficientunderstandingofFe-Sassembly proteinsinendothelialfunction.IcouldalsoidentifyFXNasakeypathogenicfactorinPH,offeringthepotential ofdiagnosingFRDApatientsatriskforPHanddefiningFXNasanewdrugtargettobenefitallPHpatients.