INS and type 2 diabetes mellitus: In ob/ob and db/db T2DM mice, insulin signaling impairment and α-Syn aggregation occurred in both pancreas and midbrain, and T2DM mice were more susceptible to neurotoxicity induced by acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) admini-stration [44].