Muscle Specific Insulin Receptor Overexpression Protects Mice from Diet-Induced Glucose Intolerance but Leads to Post-Receptor Insulin Resistance

Skeletal muscle insulin resistance is a prominent early feature in the pathogenesis of type 2 diabetes (T2D). In attempt to overcome this defect, we generated mice overexpressing insulin receptors (IR) specifically in skeletal muscle (IRMOE). On normal chow, IRMOE mice have similar body weight as controls, but an increase in lean mass and glycolytic muscle fibers and reduced fat mass. IRMOE mice also show higher basal phosphorylation of IR, IRS-1 and Akt in muscle and improved glucose tolerance compared to controls. When challenged with high fat diet (HFD), IRMOE mice are protected from diet-induced obesity. This is associated with reduced inflammation in fat and liver, improved glucose tolerance and improved systemic insulin sensitivity. Surprisingly, however, in both chow and HFD-fed mice, insulin stimulated Akt phosphorylation is significantly reduced in muscle of IRMOE mice, indicating post-receptor insulin resistance. RNA sequencing reveals downregulation of several post-receptor signaling proteins that contribute to this resistance. Thus, enhancing early insulin signaling in muscle by overexpression of the insulin receptor protects mice from diet-induced obesity and its effects on glucose metabolism. However, chronic overstimulation of this pathway leads to post-receptor desensitization, indicating the critical balance between normal signaling and hyperstimulation of the insulin signaling pathway. Male mice were used for studies unless indicated. Mice transgenic for loxP-stop-loxP insulin receptor (LSL-IR) were generated through pronuclear injection of a linearized cassette carrying mouse IR isoform A cDNA driven by CAG promoter and interrupted by a floxed beta-gal cDNA and a stop codon. IRMOE mice were then generated by crossing the LSL-IR mice with mice carrying a Cre transgene driven by the human skeletal muscle actin (HSA) promoter. Muscle RNA of Control or IRMOE mice was extracted by homogenizing tissues in TRIzol, treating with chloroform, and precipitating in 70% ethanol. cDNA was made using High Capacity cDNA Reverse Transcription Kit (Applied Biosystems, catalog 4368813). RNA-seq libraries were made and sequencing was performed on an Illumina NextSeq 500.