Project Summary Transgender individuals experience persistent psychological distress caused by an incongruency between one’s assigned sex at birth and one’s internal sense of self. For transgender males (i.e., assigned female at birth and identifying as male), medical treatment can involve administration of lifelong exogenous testosterone (T) and/or gender affirming surgery (GAS). It is estimated that over one million individuals in the United States currently identify as transgender, and demand for GAS has increased over the past two decades. As more of these procedures are performed, a handful of reports have recently started trickling in claiming that there are worse healing outcomes among transgender male patients, but the breakdown of transgender males who were on T versus not on T at the time of surgery was not elucidated by these reports. Co-Sponsor Dr. Devin O’Brien-Coon is a plastic surgeon who performs GAS and observed this same phenomenon and hypothesized that presence of T perioperatively may be playing a role in mediating wound healing in this patient population. To validate these observations, the Coon lab conducted an assessment on 148 transgender male patients (XX-chromosome individuals, some on T and some not on T) showing statistically significant differences in grading of wounds and scars between both groups. Meanwhile, no disparity is observed between transgender females (who take estrogen and suppress T) and cisgender females. We hypothesize that T may modulate wound healing in a more complex manner than the scientific community had understood up until this point by shifting cell phenotypes and operating under novel pathways, with sex chromosome- and sex hormone receptor-dependent effects, and by preferentially affecting immune cells. We will test these hypotheses using various assays including planimetry, histology, immunofluorescence, flow cytometry, single cell RNA sequencing, transgenic mouse models, and chemical and genetic depletion. By performing these experiments, we will obtain wound healing metrics such as comparing collagen deposition, granulation tissue, wound area remaining, localization of cell phenotype markers, identifying causal pathways, gene expression, involvement of the Y chromosome and Sry testes-determining gene, and immune cell quantification and visualization. Successful completion of these aims will give us a new understanding of the biological mechanisms responsible for this observed impaired wound healing in transgender men, who undergo lifelong T therapy, and has the potential to significantly rewrite perioperative guidelines for gender affirming surgery. By filling this knowledge gap, this research may ultimately offer improved wound healing and personalized medicine therapies to not only transgender patients but all patients.