Mechanisms of free fatty acid receptor 4 signaling in the ischemic myocardium

Project Summary/Abstract Coronary heart disease (CHD) is a significant contributor to morbidity and mortality. The association between increased inflammation and CHD pathogenesis is now well-established. Inflammatory pathways underlie all the major contributors to CHD, including atherogenesis, plaque rupture, myocardial ischemia, reperfusion injury, leukocyte infiltration, and tissue fibrosis. However, an unmet need remains for additional candidate therapies to reduce CHD mortality. Free fatty acid receptor 4 (Ffar4) is a G-protein coupled receptor that is activated by long chain fatty acids, including the ?3-polyunsatured fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid. Ffar4 was characterized first as a nutrient sensor, centrally involved in regulation of glucose metabolism and lipogenesis. Ffar4 also has anti-inflammatory and anti-fibrotic effects: it is expressed on macrophages, and its stimulation results in decreased production of interleukin-1?, IL6, TNF?, and inhibition of the LPS-TLR4 path- way. Finally, Ffar4 is expressed on cardiac fibroblasts, and its stimulation results in decreased TGF-?1 signaling and collagen production. Although Ffar4 also is expressed in cardiac myocytes, its role in the heart remains unclear. Our prior studies indicated that EPA-mediated reduction of fibrosis and contractile dysfunction following induction of pressure overload by transverse aortic constriction may involve EPA signaling through Ffar4. How- ever, our preliminary data in mice with systemic Ffar4 deletion (Ffar4KO) subjected to transverse aortic con- striction resulted in exaggerated hypertrophy, greater systolic and diastolic dysfunction, but without exaggerated fibrosis. The latter suggests that the maladaptive response was driven by the absence of Ffar4 in cardiac myo- cytes. Despite these interesting findings, the role of cardiac myocyte Ffar4 in ischemia reperfusion injury is un- known. Because many of the inflammatory pathways orchestrating cardiac remodeling after pressure overload overlap with pathways after ischemia and reperfusion (I/R) injury, we therefore hypothesize, that in cardiac my- ocytes, Ffar4 prevents cell death and induces a salutary inflammatory response that prevents pathologic remod- eling induced by I/R injury. To test this, we will determine if cardiac myocyte Ffar4 expression is necessary to protect against I/R injury. We will generate mice with cardiac myocyte-specific deletion of Ffar4, subject them to I/R injury, and measure infarct size, cardiac function, and fibrosis. We will also define the Ffar4 signaling network in cardiac myocytes, and determine how this signaling network promotes a salutary immune response to cardiac injury by measuring the influence of Ffar4 on myocyte cell death, cytokine and chemokine production, and ox- ylipin production. In summary, Ffar4 has an established role in regulating inflammation outside the heart; this study will define its role in the heart. It will advance a novel paradigm that polyunsaturated fatty acids stimulate GPCRs and function as signaling molecules to maintain cardiac homeostasis. This study can establish the can- didacy of Ffar4 as a new drug target for attenuation of inflammation in CHD.