Investigating the Potential of Long-Chain Polyunsaturated Fatty Acids and Exercise on Mitigating Skeletal Muscle Inflammation in Obesity
Chronic low-grade inflammation causally links obesity to the development of insulin resistance and type 2 diabetes, a disease that affects 462 million individuals world-wide. This thesis utilized both in vivo, ex vivo and in vitro methodologies to study whether n-6 and n-3 polyunsaturated fatty acids (PUFA) and exercise can mitigate obesity-induced skeletal muscle dysfunction with a particular focus on macrophage-myocyte crosstalk. Using an in vitro model designed to recapitulate the inflammatory microenvironment characteristic of obese macrophage-myocyte crosstalk, we showed that both the n-6 PUFA, arachidonic acid, and the n-3 PUFA, docosahexaenoic acid, reduced macrophage production of inflammatory cytokines which in turn promoted improved myocyte metabolic function. In an in vivo high fat diet-induced obese rodent model, we showed that dietary n-3 PUFA blunted skeletal muscle CD4+ and CD8+ T cell accumulation at 12 weeks. Subsequently, using an in vitro co-culture model with splenic-derived CD11b+ macrophages and L6 myocytes to recapitulate obese skeletal muscle stimulated with or without lipopolysaccharide, we showed that short-term (2 week) n-6 and n-3 PUFA reduced and long-term (12 week) n-6 PUFA promoted, inflammatory macrophage-myocyte crosstalk. Finally, we sought to understand how n-3 PUFA and/or moderate exercise (treadmill training 5 days/week for 3 weeks) mitigate the effects of simultaneously consuming a high fat diet on skeletal muscle inflammation. Using an ex vivo model, we demonstrated that n-3 PUFA improved, while exercise reduced, AT-myocyte inflammatory crosstalk suggesting that a high fat diet may inhibit the effects of exercise on skeletal muscle and AT inflammation to worsen insulin resistance. Overall, these studies were the first to investigate the effects of n-6 and n-3 PUFA on obesity-induced skeletal muscle immune cell infiltration and subsequent inflammatory macrophage-myocyte crosstalk. This thesis provides support for n-3 PUFA and short-term n-6 PUFA consumption as dietary strategies to mitigate obesity-associated skeletal muscle inflammation by reducing both immune cell infiltration and subsequent inflammatory macrophage-myocyte crosstalk thereby improving skeletal muscle function.