Oestrogen supplementation in male rats may have accentuated the 72 h post-downhill running increase in Pax7 detected myogenic satellite cell number in both soleus and white vastus muscles relative to unsupplemented rats. The mechanisms and physiological consequences of this effect are yet to be determined.

Patients with obesity and metabolic syndrome, as well as individuals with pre-type 2 diabetes, exhibit hyperinsulinemia prior to development of hyperglycemia due to underlying skeletal muscle insulin resistance. To mimic the effect of chronic hyperstimulation of the insulin receptor (IR), we overexpressed the IR specifically in skeletal muscle (IRMOE). This led to skeletal muscle post-receptor desensitization, with increased IR and IRS-1(Tyr) phosphorylation but decreased phosphorylation of Akt Ser473 and Thr308. To identify the regulators involved in this post-receptor insulin resistance, we performed RNA sequencing of IRMOE muscle. Among the most upregulated genes was Lrtm1, a poorly characterized leucine rich repeat transmembrane molecule while highly expressed in the heart and skeletal muscle. Overexpression of Lrtm1 in C2C12 myoblasts led to increased phosphorylation of early insulin signaling molecules (the insulin receptor, IRS-1, and Shc), but reduced phosphorylation of the downstream molecules Akt (at both Ser473 and Thr308) and Erk Thr202/204 following insulin stimulation. Mice with knockout of Lrtm1 (Lrtm1KO) showed significant increases in percent lean mass and decreases in percent fat mass, as well as a slight reduction in overall body weight. In addition, Lrtm1KO mice were more active than controls in both metabolic cages and an open field behavioral tests. Lrtm1KO mice also exhibited improved glucose tolerance and insulin sensitivity, especially in males, even on normal chow diet. Most importantly, Lrtm1KO mice were protected from high fat diet induced obesity and metabolic syndrome, with the knockouts showing 18% less body weight gain, 30% lower fat mass, significantly improved glucose tolerance and improved insulin sensitivity. Thus, Lrtm1 is a novel regulator of post-receptor insulin signaling and glucose metabolism that may provide a new target for therapy insulin resistant prediabetes and type 2 diabetes. Disclosure G. Wang: Employee; Agilent. Y. Yu: None. W. Chen: None. W. Cai: None. X. Liu: None. C. Kahn: None.