MECHANISM OF GPR120 SIGNALING TO ANTII-NFLAMMATORY/INSULIN SENSITIZING PATHWAYS

University Of California, San Diego, La Jolla CA

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Abstract

The project focuses on the concept that chronic activation of infiammatory pathways and that the macro- phage/adipocyte nexus provides a l<ey mechanism underlying the common disease states of decreased insulin sensitivity. Our recent studies have demonstrated that GPR120 is the omega 3 fatty acid receptor/ sensor in macrophages and adipocytes and that stimulation of this receptor produces robust anti-inflam- matory, insulin sensitizing effects. We will pursue these observations to further define the mechanisms of the anti-inflammatory effects of GPR120 signaling. We found that treatment of macrophages with omega 3 fatty acids caused a marked GPR120-dependent decrease in macrophage migration towards chemotactic signals. We now hypothesize that this is due to GPR120-induced heterologous desensitization of other GPCR chemokine receptors such as CCR2. We will test this idea by measuring CCR2 signaling with and without omega 3 fatty acid treatment. We hypo-thesize that the desensitization is due to a DHA-mediated loss of function phosphorylation of CCR2, and we plan to map this phosphorylation site, mutate it to alanine and study it's functional significance. We've also found that the ability of p arrestin-2 to physically associate with GPR120 is a key mechanism in the anti-inflammatory pathway. Based on our preliminary data, we hypothesize that GRK5 is the kinase which phosphorylates GPR120 to create the p arrestin-2 docking site under the influence of omega 3 fatty acid treatment. We will rigorously test this idea by conducting in vivo phenotyping studies in GRK knockout mice. We will also conduct similar phenotyping studies in p arrestin-2 knockout mice and predict that both the GRK5 KOs and the p arrestin-2 KOs will generally phenocopy the results observed with the GPR120 KOs. Taken together, the experiments proposed in this application should elucidate detailed mechanisms underlying the interlocking nature of proinflammatory and anti- inflammatory pathways as they modulate pathophysiologic states. In addition, since GPR120 is a druggable GPCR, these studies chould provide impetus to the identification of new small molecule agonists for this receptor, which could ultimately prove to be effective anti-inflammatory/insulin sensitizing agents. RELEVANCE (See instructions): Insulin resistance is a key feature in Type 2 diabetes mellitus, and macrophage mediated chronic tissue inflammation is an Important etiologic component in this insulin resistant state. This project should elucidate novel actions of anti-inflammatory signaling, and reveal the specific mechanisms underlying the anti-inflam- matory and insulin sensitizing effects of GPR120/omega 3 fatty acids. An improved basic understanding of these cellular events has the potential to lead to new therapeutic opportunities.