Tuberculosis(TB),theleadingcauseofdeathduetoaninfectiousdisease,isfacedbyanumberofchallenges, oneofwhichisourinabilitytopredictdiseaseoutcomeafterexposure.Thelimitedknowledgeonriskfactorsfor TB progression and the mechanisms by which these promote susceptibility limits the ability to develop new preventionandtreatmentapproaches.Recently,ourcollaboratorshaveidentifiedmoderate,subclinicalvitamin AdeficiencyasasubstantialriskfactorfordevelopingactiveTB,carryinga10-foldhigherriskwhenserumlevels oftheintermediatevitaminAmetabolite,retinol,arebelow200g/L.WhilevitaminAisknowntoplayacritical role in immunity from innate function to polarization of antigen specific T cells, the contribution of vitamin A to protectionfromactiveTBdiseasehasonlybeenminimallyexplored.ThesubstantialTBriskcarriedbydeficiency invitaminAhighlightstheneedtounderstandthemechanismsbywhichthismoleculecontributestoprotection, particularly in the context of malnutritionamong TB-affected communities.VitaminAfunctions through nuclear receptors that are ligand-activated transcription factors. Other nuclear receptors beyond vitamin A receptors havebeenshowntoregulateimmunefunctionandcontributetoresponsetoM.tuberculosisinfection,including PPARg?, a nuclear receptor with obligatory association with vitamin A receptors. Because we have shown that rosiglitazone,anactivatorofPPARg?,improvesoutcomeoftuberculosisinguineapigs,wehypothesizethatthat availabilityofvitaminAandPPARligandstogetherinfluencethetranscriptionaloutcomeofTBandconsequently, the ability to control infection. The goal of this research is to better understand the contribution of nuclear receptor-ligand interaction, and the impact of impaired vitamin A availability on immune response, control of bacterialgrowth,andTBdiseaseoutcome.ThesewillbeinvestigatedthroughAimsusingbonemarrow-derived macrophagecellmodelsandaguineapigmodelofvitaminAdeficiency,bothdevelopedinourlaboratory.We will first determine the contribution of ligand activation of nuclear receptor heterodimers to transcriptional and microbicidalresponsetoinfectionwithM.tuberculosisinbonemarrowmacrophagesthroughacombinationof validated knock-down techniques targeting vitamin A (RAR, RXR) and PPARg? receptors, alongside ligand agonists, all-trans retinoic acid (RAR), 9-cis retinoic acid (RXR), and thiazolidenones (PPARg?). This will be followedbytheuseofourrecentlydevelopedguineapigmodelofdietaryvitaminAdeficiencytodeterminethe impact of vitamin A and PPARg? signaling on TB immunity. Guinea pigs with sufficient, partially deficient, and completely deficient vitamin A will betreated withor without rosiglitazone, a specificPPARg?agonist, based on our previous assessment of this drug in guinea pigs and immune response and disease outcome measured. Upon completing these experiments, we will have determined the impact of vitamin A and nuclear receptor controloverresponsetoinfectionandconsequently,TBdiseaseoutcome.Theseresultswillguidedevelopment ofnewhost-directedtherapiestominimizeriskandimproveoutcomeofexposureinTB-endemicregions.
VitaminAdeficiencyisawidespreadprobleminlow-incomecountriesandrecentlyhasbeenidentifiedasa strongriskfactorfordevelopingclinicaltuberculosis.Thisresearchaimstobetterunderstandthemechanisms bywhichalackofvitaminAinfluencestheabilityofimmunecellstorespondtoinfection,andconsequently, theoutcomeoftuberculosisdisease.
