Reproductive Impact of Testosterone Therapy in a Transgender Mouse Model

Abstract

Long-term gender-affirming testosterone (T) therapy may negatively impact reproductive capacity for transgender men transitioning from female to male. Given clinical guidelines assuming fertility loss and anecdotal evidence to the contrary, clinicians have minimal data with which to counsel transmasculine individuals interested in harvesting oocytes or carrying a pregnancy after starting T therapy. The impact of T on reproductive potential, the reversibility of this impact, and the ovarian dynamics of taking and pausing T have not been well established. The objective of my dissertation was to establish a mouse model of postpubertal gender-affirming T therapy and to utilize this model to evaluate the reversibility of T-induced changes if T is paused for reproductive purposes. In order to establish our model, we treated postpubertal female mice with 6 weeks of T injections. The T-treated mice demonstrated acyclicity, elevated T, a reduction in serum luteinizing hormone levels, and ovarian perturbations including a lack of corpora lutea and an increased number of atretic late antral follicles. These findings are similar to changes seen with transmasculine individuals on T and support the use of mouse models of gender-affirming T therapy for reproductive inquiry. We then investigated the reversibility of T-induced persistent diestrus in a model that allows for well-defined T cessation timing. We found that after 6 weeks of T therapy using subcutaneously implanted commercial pellets, mice promptly resumed cycling within a week of pellet removal, closely correlated with T levels returning to control levels. Four cycles after T cessation, ovarian histological analyses from T-treated mice were comparable to controls, including the formation of corpora lutea, in support of the return of regular cyclic ovulatory function following T cessation. Intriguingly, we found that a longer exposure to elevated T after a prolonged washout following 6 weeks of T injections resulted in an aberrant ovarian stromal phenotype and reduced number of corpora lutea four estrous cycles after T cessation. Immunohistochemical staining for macrophage-associated markers CD68 and CD11b suggests changes in ovarian stromal macrophages after resumption of cyclicity following the washout of T. Ovarian transcriptomic comparisons also support this upregulation of immune response pathways in mice after T cessation as compared to age-matched controls and mice at 6 weeks on T. Limitations of the study design prevent us from attributing these differences to the additional duration of T therapy during the washout or to changes that might be arising during the resumption of cyclicity. We postulate that this stromal macrophage response may be a temporally limited state, as related studies have described histologically similar findings, which they reported to resolve after a period of time or with superovulation. Collectively, this dissertation characterizes a mouse model on T and interrogates changes that occur if T is paused for reproductive purposes, laying the groundwork for further functional assessments to provide insights into reproductive options after prolonged T therapy.