Transgender and gender diverse (TGD) individuals have rates of cardiovascular (CV) disease exceeding those expected by traditional CV risk factors. A recent AHA scientific statement highlighted the CV health disparities faced by this minoritized population, urging further study to address the reasons behind this. Gender affirming testosterone (hormonal) treatment (GAHT) is the cornerstone of masculinizing treatment for transmasculine young adults and adolescents (TMYA). GAHT results in testosterone levels equivalent to cisgender men (CM) and suppressed estradiol (E2). Knowledge of GAHT's cardiometabolic effects relies on small, low-quality, or poorly controlled cross-sectional studies that lack consideration for the impact of chronic stress on cardiometabolic risk in TMYA. To date, studies have not explored mechanisms by which GAHT affects vascular physiology in TMYA. The paucity of data in this area has been leveraged in successful legislative efforts to restrict GAHT in minors. There is an urgent need for higher-quality data. The higher physiologic circulating E2 in cisgender women (CW) causes a long-term increase in the vascular expression of the E2 receptor's (ER) alpha and beta isoforms. These stimulate acute and chronic endothelial nitric oxide (NO) production, critical for a healthy vascular endothelium. Reduced NO bioavailability increases CV event susceptibility; CW's unique capacity to augment endothelial NO through higher E2 levels and vascular ER signaling significantly contributes to their reduced lifetime CV risk relative to CM. GAHT's impact on E2 receptor expression and activity and NO bioavailability in TMYA are unknown. This proposal aims to better define the vascular and cardiometabolic effects of modern GAHT in TMYA. Based on pilot data, we hypothesize that GAHT in TMYA impacts cardiometabolic physiology by shifting endothelial responsiveness to E2 and E2 receptor expression in a CM-like pattern, suggesting a CV risk profile switch similar to, but not worse than, CM. Aim 1 will determine the impact of near-term GAHT on vascular endothelial and cardiometabolic health in TMYA: changes in in vivo endothelium-dependent vasodilation, peripheral arterial tonometry, vascular stiffness, cardiometabolic biomarkers, and heart rate variability will be assessed over 12-months from GAHT initiation, with changes correlated to psychosocial stress and resiliency measures and compared to age-matched cisgender controls. Aim 2 will determine GAHT's impact on sex-hormone receptor expression, endothelium- dependent vasodilation, and E2-stimulated NO production in resistance arterioles from TMYA: the impact of GAHT initiation in TMYA, and mechanism thereof, on ex vivo E2-dependent and non-E2-dependent endothelium- dependent vasodilation and NO will be assessed, using human resistance arterioles. Changes to genetic transcription of resistance arterioles in TMYA on GAHT will also be explored, relative to cisgender controls. Affirmative findings will provide information on the molecular and phenotypical vascular and cardiometabolic effects of GAHT, allowing for more informed discussion of CV disparities in TGD.

Men of trans experience have rates of cardiovascular (CV) disease exceeding those expected by traditional CV risk factors, and our knowledge of cardiometabolic effects of gender affirming testosterone (hormonal) treatment (GAHT) is limited. This application will determine the cardiometabolic effects of GAHT initiation in transmale young adults and adolescents and determine its impact on vascular estrogen receptor expression and activity.