INS and type 2 diabetes mellitus: Despite the strong evidence of miR-21 expression levels alteration in T2D mouse models and of its involvement in the regulation of insulin signaling, no direct confirmation of altered miR-21 expression in human T2D insulin target tissues has been provided yet; although, altered circulating miR-21 levels have been reported in plasma/serum of T2D patients and of obese subjects [114,115].