Sex Hormone Binding Globulin Controls Sex-Specific Lipolytic Activity in Human Abdominal Subcutaneous Adipocytes

Regulation of lipid metabolism is fundamental for metabolic health, and adipose tissue is a central component in this process. Adipose tissue differs considerably between women and men in terms of a higher subcutaneous capacity for storage, which is linked to metabolic health, in women. Sex hormone-binding globulin (SHBG) contributes to the regulation of circulating sex hormone bioavailability and has been shown to predict risk of metabolic dysfunction. Here, we investigate the sex-specific relationship of SHBG with metabolic status and adipocyte-dependent lipolysis. We measured serum concentrations of sex hormones, SHBG, fasting glucose, and insulin in a cohort of 63 women and 27 men from which adipose biopsies were collected and mature adipocytes isolated. In women, high serum SHBG concentrations were strongly associated with low in vivo Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), and lower unstimulated ex vivo lipolysis but higher isopropanol stimulated ex vivo lipolysis. In contrast, no effect of SHBG on the above-mentioned parameters were observed in men. In vitro cultured human adipocytes also increased lipolytic activity in response to SHBG, but only in the absence of testosterone, suggesting that testosterone inhibits the catecholamine-induced lipolysis of SHBG in adipose tissue. In conclusion, we identify SHBG as a novel sex-specific regulator of adipocyte lipolysis and lipid metabolism. At the same time, our data emphasize sex-dependent effects of SHBG on adipocyte lipid metabolism, and we propose testosterone binding to SHBG as a driving factor mediating these sex differences.