PROJECT SUMMARY/ABSTRACT Post-traumatic stress disorder (PTSD) is a chronic, debilitating, mental disorder that occurs in susceptible individuals after traumatic stress exposure, with a prevalence of ~8%. While pathway driven approaches and molecular profiling have implicated multiple biological systems in PTSD, there are no established biomarkers or effective treatments due to the incomplete understanding of the disorder’s complex mechanisms. This partial understanding is significantly restricted by our reliance on studying PTSD with human blood and post mortem brain samples, due to limited access to living human PTSD neural tissue. Without a significant breakthrough, PTSD will continue to be a severe public health and socio-economic burden. The hypothalamic-pituitary-adrenal (HPA) axis has been much studied in PTSD since it is the central coordinator of the neuroendocrine response to traumatic stress. HPA-axis imbalance in PTSD involves low glucocorticoid (GC) signaling due to low circulating GC levels, and epigenetic dysregulation of certain GC related genes has been shown to be pathogenic for PTSD. Various studies have utilized the synthetic GC, dexamethasone (DEX), to model the epigenetic and transcriptional effects of PTSD associated stress with in vitro and in vivo models. Yet, the mechanisms for how GC dysregulation develops into PTSD are not fully uncovered, and accurate GC-based biomarkers and treatments are lacking. Elucidating the pathogenesis of PTSD has been challenging, but other psychiatric disorders’ molecular etiologies have been successfully illuminated with induced pluripotent stem cell (iPSC) modeling, possibly due to the approaches’ capacity to interrogate diseases while controlling for genetics and external stimuli. To date, human neurons containing PTSD pathology (genetics, epigenetics, and transcriptomics) have never been interrogated in vitro. A recent advancement beyond iPSC modeling, transdifferentiation of human blood lymphocytes into neurons via direct reprogramming, opens the door for PTSD to be studied holistically. As an acquired disease, evidence is growing about the role epigenetic marks acquired from life stress plays in PTSD pathogenesis, and there is currently no in vitro modality for capturing human PTSD epigenetics in neural tissue, as typical induced pluripotent stem cell reprogramming resets the epigenetic landscape. Excitingly, evidence suggests directly reprogrammed neurons (iNs) can maintain their original cell’s epigenetic signatures. The objective for this award is to begin to model the genetics and epigenetics of PTSD in human lymphocytes differentiated to iNs in basal and GC-exposed conditions and determine molecular differences across groups. We postulate that identifying methylation and gene expression changes due to GC activity that are shared across lymphocytes and iNs in PTSD individuals will allow for better discrimination and detection of the key pathways driving PTSD pathogenesis.