Endocrine Abstracts

Extracellular proteolytic cleavage of insulin receptor (IR) and the generation of soluble insulin receptor (sIR) is a response of the liver and fat associated with physiological conditions and metabolic alterations mainly related to hyperinsulinemia. However, cleavage of this receptor has not been analyzed in skeletal muscle, a central tissue in insulin-mediated glucose homeostasis. This study aimed to analyze the insulin receptor subunits in the gastrocnemius and soleus muscles in a model of male young Wistar rats of metabolic syndrome induced by sucrose 20% in drinking water for 8 weeks. Using quantitative western blot analysis, we found the presence of at least 7 protein bands when using an antibody against the alpha subunit under reducing and non-reducing conditions. The band with the highest molecular weight in non-reducing conditions, which appears close to 315 kDa, possibly corresponds to the intact insulin receptor, whose abundance is not altered in our model. A greater abundance of the 157 kDa and 60 kDa fragments in non-reducing conditions and 25 kDa in reducing conditions was found in the treated animals compared to the control group. An additional 48 kDa fragment was found in the soleus muscle under non-reducing conditions, whose presence could be related to the metabolic differences between both muscles. A subsequent in silico analysis suggested that the fragments obtained through western blot may correspond to fragments resulting from proteolysis mediated by membrane proteases families (ADAM, MMP, calpains) that have been implicated in the past in the generation of IR soluble ectodomain. These findings suggest the shedding of IR from skeletal muscle in a hyperinsulinemic state characteristic of our metabolic syndrome model.