Endocrine Abstracts

Introduction: Testosterone deficiency is associated with an increased risk of type-2 diabetes (T2D) in men. Physiological testosterone replacement (TRT) improves insulin resistance and glycaemic control in hypogonadal men with T2D. The mechanisms underlying these actions remain unknown, but may be due in part to an effect on the liver as a major metabolic organ involved in glucose regulation. We have previously shown in testicular feminised mice, which have low testosterone levels and a non-functional androgen receptor, that hepatic expression of glucose regulatory targets (Hexokinase 4, HK4; Phosphofructokinase, PFK; Mitogen-activated protein kinase kinase, MAP2K) were significantly reduced and that TRT increased HK4 expression. Here we investigate the effects of testosterone on glucose uptake and metabolism in human liver cells.

Methods: Glucose uptake was assessed using 2-NBDG, a fluorescent glucose analogue, in HepG2 cells treated with either testosterone (1–100 nM) or vehicle control for 24 h. Cells were analysed for mRNA and protein expression of targets of glucose regulation; HK4, PFK and liver X receptor (LXR), by qPCR and western blotting following 24 h treatment with testosterone or control.

Results: Glucose uptake was increased in testosterone treated cells at 10 nM (122±5.5% of control, P<0.05) and 100 nM (121±6.4%, P<0.05) concentrations compared to vehicle control. HK4 protein expression was increased in 10nM testosterone treated cells vs vehicle control (0.56±0.04 vs 0.24±0.11 arbitrary densitometry units (ADU). P=0.08), and significantly at 100 nM concentrations (0.68±0.25 vs 0.24±0.11 ADU. P<0.05). No difference was observed between treated and untreated cells for PFK and LXR protein expression and mRNA expression for all targets.

Conclusion: Testosterone increases glucose uptake in HepG2 cells as a mechanism to potentially improve hepatic glucose control and T2D in men. This action may be via increased hepatic glycolysis through the upregulation of HK4 expression, a key regulatory enzyme in glycolysis.