MAPK1 and Obesity: Moreover, the phosphorylation levels of extracellular regulated protein kinases (ERK) involved in the GPR54 signaling pathway were significantly reduced in the adipose tissues of castrated or ovariectomized GPR54 KO mice; this result suggested that kisspeptin promotes lipid synthesis and obesity development by activating GPR54 and then the MAP kinase pathway, as ERK phosphorylation level may be a landmark of adipocyte proliferation [66] (Figure 3).