For example, DPP-IV inhibitors have been shown to promote beta-cell survival and function, characterized as augmented GSIS, in islets of non-diabetic and T2DM human donors (113, 114), demonstrating that ligands of DPP-IV enzymatic activity that function in a similar capacity to alpha-cell-derived proglucagon ligands are both present and active in isolated islets. Here, DPP4 is linked to type 2 diabetes mellitus.