Radiation exposure accelerates the onset of age-related diseases such as diabetes, cardiovascular disease, and neoplasia and, thus, lends insight into in vivo mechanisms common to these disorders. Fibrosis and extracellular matrix (ECM) remodeling, which occur with aging and overnutrition and following irradiation, are risk factors for development of type 2 diabetes mellitus. We previously demonstrated an increased incidence of skeletal muscle insulin resistance and type 2 diabetes mellitus in monkeys that had been exposed to whole body irradiation 5-9 yr prior. We hypothesized that irradiation-induced fibrosis alters muscle architecture, predisposing irradiated animals to insulin resistance and overt diabetes. Rhesus macaques (Macaca mulatta, n = 7-8/group) grouped as nonirradiated age-matched controls (Non-Rad-CTL), irradiated nondiabetic monkeys (Rad-CTL), and irradiated monkeys that subsequently developed diabetes (Rad-DM) were compared. Prior radiation exposure resulted in persistent skeletal muscle ECM changes, including a relative overabundance of collagen IV and a trend toward increased transforming growth factor-β1. Preservation of microvascular markers differentiated the irradiated diabetic and nondiabetic groups. Microvascular density and plasma nitrate and heat shock protein 90 levels were lower in Rad-DM than Rad-CTL. These results are consistent with a protective effect of abundant microvasculature in maintaining glycemic control within radiation-induced fibrotic muscle.
Keywords: fibrosis; irradiation; microvasculature; monkey; muscle; type 2 diabetes.
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