FGF21 and diabetes mellitus: Deletion of Fgf-21 gene significantly enhances diabetes-induced testicular apoptosis along with the activation of mitochondrial-dependent apoptosis pathways, endoplasmic reticulum stress-dependent pathways, and oxidative damage but did not change the expression of cleaved caspase-3 and caspase-8, which was significantly prevented by the supplementation of exogenous FGF-21.