Obesity-Induced Inflammation and Insulin Resistance by the p62/PKCzeta Signaling

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DESCRIPTION (provided by applicant): Obesity is a rapidly growing public health problem. However, the underlying mechanisms that lead to excess body fat and that link obesity to its associated pathologies remain poorly understood. Recent work has revealed a role for inflammation in the pathogenesis of chronic metabolic diseases including obesity, type 2 diabetes and cardiovascular disease. In this regard, there is a significant interest in the role that macrophages play in these inflammatory processes. It is known that increased adiposity promotes macrophage infiltration into adipose tissue, maintaining local inflammation and causing insulin resistance. Recent results suggest that macrophages undergo a polarization switch from pro-inflammatory (M1 phenotype) to anti-inflammatory (M2 phenotype) in response to adipocyte-secreted cytokines such as IL-4 and IL-13 and the balance between M1 and M2 determines the final inflammatory outcome and its impact on insulin resistance. However, key questions concerning the different signaling pathways responsible for these inflammatory networks and their relative importance in vivo remain unanswered. Therefore, investigation of the inflammatory pathways activated during obesity could be a promising approach to identifying novel therapeutic targets for diabetes. This grant application focuses on the p62/PKC6 signaling complex, which is formed by the scaffold protein p62 and its PB1-interacting kinase PKC6, and their potential role in obesity-induced inflammation and insulin resistance. It is based on previous results demonstrating that the genetic inactivation of p62 leads to late-onset obesity and insulin resistance, and to an associated systemic hyperinflammatory state. Moreover, the preliminary data show that PKC6-/- mice also develop late-onset obesity suggesting a critical role of the p62/PKC6 complex in the control of adiposity and obesity. Importantly, high-fat diet-fed PKC6-/- mice displayed higher insulin resistance, increased macrophage infiltration in adipose tissue, and an enhanced M1 inflammatory response as compared to equally fed WT mice, despite equal body fat content. These observations led to the hypothesis that PKC6 is a regulator of the macrophage M2 polarization switch. The overall objective of this proposal is to rigorously test the hypothesis that the p62/PKC6 complex is a critical negative regulator of inflammation during obesity and to determine its mechanism of action at the organismal and cellular levels. Therefore, this project is designed to 1) determine the role of p62 and PKC6 in M2 polarization of macrophages, and 2) to determine the in vivo role of PKC6 and p62 in macrophages in obesity and obesity-associated inflammation. This work will increase understanding of the mechanisms involved in the regulation of obesity-induce inflammation and insulin resistance, and, in the long term, will lay the groundwork for the development of novel, more specific therapies for insulin resistance and type 2 diabetes. PUBLIC HEALTH RELEVANCE: Chronic inflammation is causally linked to obesity, insulin resistance and type 2 diabetes. Increased adiposity promotes macrophage infiltration into adipose tissue creating a vicious cycle that perpetuates inflammation and causes insulin resistance. This project will determine how a cell signaling complex assembled by p62/Sqstm1 and PKC6 regulates obesity-associated inflammation and insulin resistance in vivo, laying the groundwork for the development of novel, more specific therapies for obesity.