INS and type 2 diabetes mellitus: As leptin is linked to glucose uptake and energy utilization in cells, it is not surprising that leptin signaling desensitizes in T2DM, just as insulin signaling does (Kautzky-Willer et al., 2001; Carey et al., 2003; Cummings, 2013; Sharma and Hölscher, 2014).