Figure 1. Summary of molecular pathways involved in β cell regeneration. Exendin-4 agonizes GLP-1R signaling, followed by the activation of NFAT and the entry of cell cycling. P38 MAPK signals activate BMI1 and inhibit p16Ink4a. PDGFRa transduces proliferative signals to EZH2, thereby attenuating p16Ink4a activity while enhancing p19Arf activation. PTTG partially promotes β cell proliferation via p21 inhibition.