DPP4 and type 2 diabetes mellitus: Since DPP4 inhibition can protect incretin hormones from degradation, DPP4 inhibitors have been widely used in the treatment of type 2 diabetes (Baggio and Drucker, 2007), and studies have also found that DPP4 plays important roles in cell death regulation, immunity, metabolic regulation, tumorigenesis, and other processes (Duan et al., 2017; Enz et al., 2019).