FFAR4 and obesity due to melanocortin 4 receptor deficiency: Ensures sperm membrane integrity and sperm motility (Mourvaki et al., 2010); activates GPR120/ERK signaling pathway in Leydig cells and upregulates 3β-HSDH and StAR to promote testosterone (Xu et al., 2020); confers host resistance to HFD-induced obesity and inflammation (Miyamoto et al., 2019).