Objectives: A clinical feature of insulin resistance is the development of fatty liver (hepatic steatosis). Testosterone deficiency is common in men with type-2 diabetes and is associated with insulin resistance. The testicular feminised mouse (Tfm) exhibits a non-functional androgen receptor (AR) and low circulating testosterone. We have previously shown that a high-cholesterol diet promotes hepatic steatosis in Tfm mice, and testosterone replacement therapy (TRT) attenuates these changes. The exact mechanism of this effect is unclear. This study investigates whether the known protective effect of testosterone in the Tfm mouse model is associated with an effect on the expression of key enzymes involved with fatty acid metabolism.
Methods: Tfm mice were fed a high-cholesterol diet ad libitum for 28 weeks and received either physiological TRT (intramuscular mixed testosterone esters) or placebo (saline) and were compared to wild-type littermates. Liver tissue was collected and relative concentrations of mRNA and protein were analysed by qPCR and western blotting for expression of Fatty Acid Synthase (FAS) and Acetyl-CoA Carboxylase (ACC).
Results: There was a significant increase in the relative expression of FAS (Relative fold change in mRNA Mean ± SD 11.4±4.9 P=0.049) and ACC (2.5±0.6 P=0.041) in the Tfm mouse compared with their XY littermates. Following TRT, mRNA expression was significantly decreased for FAS (3±0.8 P=0.018) and showed a non-significant decrease in ACC (1.3±0.3 P=0.42). Western blot analysis confirmed an increase in FAS (Relative Density Difference, mean±S.D., 2.42±1.27 P=0.002) and ACC (3.48±0.94 P<0.001) protein expression in Tfm mice compared with XY littermates. Following TRT, protein expression of these enzymes decreased to wild-type levels.
Discussion: TRT significantly suppressed the increased FAS and ACC expression in the liver of Tfm mice compared to wild-type. Therefore, testosterone has favourable actions on fatty acid metabolism in liver which is, in part, independent of the AR.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.