The hepatokine FGF21 stopped lipogenesis and reduced testosterone production in mLTC-1 Leydig Cell Line

Beyond their link to metabolic issues like type 2 diabetes, factors like lifestyle, environment, and excess weight may also influence fertility. Fibroblast growth factor 21 (FGF21), a liver-derived hormone linked to energy balance, has recently emerged as a potential player in female mammalian reproduction. In male, only two studies have described potential effects of FGF21 on fertility. A recent study has described a negative correlation observed in obese patients presenting a low testosterone level associated with elevated FGF21 plasma levels. To investigate the role of FGF21 in steroidogenesis, we have studied the involvement of FGF21 in lipid and steroid activity by Leydig cells. Leydig cell model expressed all FGF21 receptors and β-Klotho cofactor as determined by RT-qPCR and by western-blot. Cultured mLTC-1 Leydig cell line exposed to increasing FGF21 concentration induced phosphorylation (Ser 473) of Akt and modified the CREB factor activity, suggesting the functionality of the FGF21 pathway. FGF21 consequences on mLTC-1 Leydig cells are inhibition of the lipid synthesis, leading to a reduction in the content of lipid droplets. The drop in lipid synthesis is associated with a reduction in the amount of lipids (mainly PUFA, cholesterol esterified, and triglycerides) as measured by lipidomic approach. The main consequence is to reduce the quantity of cholesterol, the steroid precursor, in mLTC-1 Leydig cells and is associated with a low production in testosterone. The decrease in androgens was also associated with a reduction in the steroid enzyme genes expression, which are under the control of CREB activity, and present a lower activity due to low cAMP intracellular levels. In vivo, steroid production was lowering after FGF21 administration in adult male mice associated to a decrease in progressive motility and velocity of sperm. In addition, these experimental data are reinforced by a data mining analysis focused on "gonad" terms in 1,319,905 article references showing the link already described between FGF21 with the fatty acids pathways, cholesterol storage, and steroid production. In conclusion, we demonstrated that Leydig cells in the testes present a functional FGF21 pathway, which regulates lipid metabolism and steroid function. In mLTC-1 Leydig cells, FGF21 reduced cholesterol, PUFA content, and testosterone production. Finally, this work highlighted that the hepatokine FGF21 could have a negative impact on androgen synthesis and testicular activity.