GPR119 and obesity due to melanocortin 4 receptor deficiency: Recently, GPR119 has become a research hotspot: it plays an important role in maintenance of glycemic control (Li et al., 2020); it has been considered as a novel therapeutic target of treating dyslipidemia and NASH (Bahirat et al., 2019); and it has emerged as a drug target for T2DM and obesity (Yang et al., 2018).