Sex hormone-binding globulin controls sex-specific lipolytic activity in human abdominal subcutaneous adipocytes

Abstract

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 isoprenaline 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.

Keywords: Adipocyte; Lipolysis; Sex-hormone binding globulin.

Graphical abstract

Figure 1

Associations between ex vivo adipocyte lipolysis and serum sex hormone-binding globulin (SHBG) in men and women. a) Serum SHBG and basal lipolysis in women (N = 67). b) Serum SHBG and basal lipolysis in men (N = 23). c) Serum SHBG and isoprenaline stimulated lipolysis in women (N = 67). d) Serum SHBG and isoprenaline stimulated lipolysis in men (N = 23). e) Serum SHBG and HOMA-insulin resistance index (HOMA-IR) in women (N = 67). f) Serum SHBG and HOMA-IR in men (N = 23).

Figure 2

Effects of sex hormone-binding globulin (SHBG) on lipid metabolism in cultured primary adipocytes. a) Basal and nor-epinephrine (NE) stimulated lipolysis in cultured primary subcutaneous white adipocytes stimulated with SHBG or control (short-term = 2 h, long-term = 3 days). ∗ Significantly different from control + NE, p < 0.05. (N = 5). b) Oxygen consumption rate (OCR) in cultured primary subcutaneous white adipocytes stimulated with short-term SHBG. ∗ Significantly different from control + NE, p < 0.05. Oligomycin (Oligo), Carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), AntimycinA/Rotenone (A/R). c) OCR in cultured primary brown adipocytes stimulated with short-term SHBG. ∗ Significantly different from control + NE, p < 0.05. d) Primary component analysis (PCA) plot of cultured primary subcutaneous white adipocytes stimulated with long-term SHBG vs. control. e) Heat-map of selected up and down regulated genes related to lipid metabolism in differentiated adipocytes stimulated with long-term SHBG versus control. f) Gene set enrichment analysis of up- and down regulated pathways based on bulk sequencing of differentiated adipocytes stimulated with long-term SHBG versus control. g) Most significantly upregulated genes related to lipid metabolic processes, in response to SHBG stimulation. h) NE-stimulated lipolysis in cultured primary subcutaneous white adipocytes stimulated with long-term SHBG or control in combination with different doses of testosterone (N = 3). ∗ Significantly different from control + NE (0 nM SHBG, 0 nM T), p < 0.05. i) NE-stimulated lipolysis in cultured primary subcutaneous white adipocytes stimulated with long-term SHBG or control in combination with different doses of estradiol (N = 3). ∗ Significantly different from control + NE (0 nM SHBG, 0 nM E2), p < 0.05. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Figure 3

Sex hormone-binding globulin (SHBG) internalization in cultured primary adipocytes and endogenous SHBG expression in human adipocytes. a) SHBG protein content in cultured primary subcutaneous white adipocytes stimulated with short-term SHBG vs. controls. b) 3D-model of SHBG content in differentiated cultured adipocytes stimulated with short-term SHBG. c) Inhibition of SHBG Endocytosis in Human Adipocytes by 2-Deoxy-d-Glucose and untreated controls (scale bar = 50 μM) d) 3D representation of SHBG endocytosis in human adipocytes: inhibition by 2-Deoxy-d-Glucose compared to controls (scale bar = 50 μM) e) Endogenous SHBG expression in human adipocyte subtypes assessed through spatial transcriptomics. f) Endogenous SHBG expression specific for the adipocyte subpopulation of cellular subtypes assessed through single nuclei RNA sequencing (snRNAseq). g) Endogenous SHBG expression in adipose subpopulation from differing adipose depots (sub cutaneous (sc), perivascular (pvat), and omental (om)) based on snRNAseq.

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