Virilizing doses of testosterone decrease circulating insulin levels and differentially regulate insulin signaling in liver and adipose tissue of females

Transgender men undergoing hormone therapy are at risk for insulin resistance. However, how virilizing testosterone therapy affects serum insulin and peripheral insulin sensitivity in transgender men is unknown. This study assessed the effect of acute, virilizing testosterone on serum insulin concentrations and insulin signaling in liver, skeletal muscle, and white adipose tissue (WAT) of female pigs as a translational model for transgender men. Females received three doses of intramuscular testosterone cypionate (TEST females; 50mg/day/pig) or corn oil (control) spaced 6 days apart starting on the day of estrus (D0). Fasting blood was collected on D0, D3, D5, D11, and D13, and females were euthanized on D13. On D13, TEST females had virilizing concentrations of serum testosterone with normal concentrations of serum estradiol. Virilizing serum testosterone concentrations (D13) were associated with decreased serum insulin and C-peptide concentrations. Blood glucose and serum glycerol concentrations were not altered by testosterone. Virilizing concentrations of testosterone downregulated AR and ESR1 in subcutaneous (sc) WAT and upregulated transcript levels of insulin-signaling pathway components in WAT and liver. At the protein level, virilizing testosterone concentrations were associated with increased PI3K 110α in liver and increased insulin receptor (INSR) and phospho(Ser256)-FOXO1 in visceral (v) WAT but decreased phospho(Ser473)-AKT in vWAT and scWAT. These results suggest that acute exposure to virilizing concentrations of testosterone suppresses circulating insulin levels and results in increased abundance of proteins in the insulin-signaling pathway in liver and altered phosphorylation of key proteins in control of insulin sensitivity in WAT.