Mechanism of autophagy activation in exercise-induced anti-diabetic benefits

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Modified Project Summary / Abstract Section This is a renewal application for R01 DK113170 to investigate the role and mechanism of autophagy activation in the regulation of exercise-induced metabolic benefits against type 2 diabetes (T2D). T2D is a sedentarism-associated disease affecting glucose metabolism and a risk factor for other disorders. Physical exercise has been widely recognized to exert beneficial effects against T2D. However, the mechanisms by which exercise elicits systemic metabolic benefits are unclear, which limits the development of therapeutic interventions. Autophagy is an essential intracellular degradation pathway, in which damaged or unnecessary cargos are transported to and broken down in lysosomes. It occurs at a low basal level under normal conditions, and can be induced by stressors such as fasting. We found that exercise is a potent inducer of autophagy, not only in contracting muscle tissues but also systemically in non-contractile tissues such as the liver. The mechanism and metabolic importance of autophagy activation by exercise in non-contractile tissues have never been addressed. Our preliminary data reveal that systemic autophagy activation may be mediated by exercise-induced circulating factors. By proteomic studies we discovered that fibronectin (Fn1), generally considered as an extracellular matrix protein under normal (resting) conditions, is significantly increased in the circulation after acute exercise. Importantly, muscle-specific depletion of fibronectin (FN1[delta]muscle mice) abolishes exercise-induced circulating fibronectin levels, autophagy activation in the liver, and systemic insulin sensitization, suggesting that muscle-secreted fibronectin is an essential regulator of exercise-induced systemic autophagy and metabolic benefits. In addition, knockdown of the fibronectin receptor, α5β1 integrin, abolishes the ability of exercised mouse serum in activating autophagy in cultured cells, further supporting the key role of the fibronectin-α5β1 integrin pathway in exercise-induced autophagy. Based on these data, we propose our overall hypothesis that autophagy activation in non-contractile tissues drives exercise-induced metabolic benefits against T2D, through a fibronectin-α5β1 integrin-IKK-JNK1 pathway. Using a combination of genetic, metabolic, biochemical, and cell biology approaches, we propose two aims: Aim 1 is to determine whether exercise activates autophagy systemically in non-contractile tissues via the fibronectin-α5β1 integrin-IKK-JNK1 pathway; and Aim 2 is to determine whether autophagy activation by the fibronectin-α5β1 integrin-JNK pathway in non-contractile tissues mediates exercise-induced metabolic benefits against T2D. Overall, our studies will establish the physiological importance of exercise-activated autophagy in non-contractile tissues in the prevention of T2D, and will demonstrate the previously uncharacterized function and mechanism of the fibronectin-integrin signaling pathway in regulating muscle-liver communication and whole-body metabolism.