DPP4 and type 2 diabetes mellitus: The link between regulatory T (Treg) function and microglia polarization is well established in the brain (55), dipeptidyl peptidase-4 (DPP4)-mediated impairment of Tregs function polarize microglia toward a pro-inflammatory phenotype and subsequently lead to neuroinflammation and cognitive dysfunction in T2DM patients (54).