RBP4 and type 2 diabetes mellitus: Thus, asprosin contributed to beta cell apoptosis by the inhibition of protective autophagy in beta cells through the AMPK-mammalian target of rapamycin (mTOR) pathway in in vitro models (33), whereas RBP4 has been shown to be stimulated by retinoic acid 6 (STRA6), which provoked pancreatic beta cell failure and T2D progression in rodent models (34).