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Background: Non-resolving activation of immune responses is central to the pathogenesis ofheart failure (HF). Free fatty acid receptor 4 (Ffar4) is a G-protein coupled receptor (GPR) for medium- and long-chain fatty acids (FA) that regulates metabolism and attenuates inflammation in diabetes and obesity. Here, we tested the hypothesis that Ffar4 functions as a cardioprotective nutrient sensor that resolves inflammation to maintain cardiac homeostasis.
Methods: Mice with systemic deletion of Ffar4 (Ffar4KO) were subjected to pressure overloadby transverse aortic constriction (TAC). Transcriptome analysis of cardiac myocytes was performed three days post-TAC. Additionally, Ffar4-mediated effects on inflammatory oxylipin production in cardiac myocytes and oxylipin composition in plasma lipoproteins were evaluated.
Results: In Ffar4KO mice, TAC induced more severe remodeling, identifying an entirely novelcardioprotective role for Ffar4 in the heart. Transcriptome analysis 3-days post-TAC indicated a failure to induce cell death and inflammatory genes in Ffar4KO cardiac myocytes, as well as a specific failure to induce cytoplasmic phospholipase A2a (cPLA2a) signaling genes. In cardiac myocytes, Ffar4 signaling through cPLA2a-cytochrome p450 w/w-1 hydroxylase induced production of the EPA-derived anti-inflammatory oxylipin 18-hydroxyeicosapentaenoic acid (18-HEPE). Systemically, loss of Ffar4 altered oxylipin content in circulating plasma lipoproteins consistent with a loss of anti-inflammatory oxylipins at baseline, and inability to produce both pro-inflammatory and pro-resolving oxylipins following TAC. Finally, we confirmed that Ffar4 is expressed in human heart and down-regulated in HF.
Conclusions: Our results identify a novel function for Ffar4 in the heart as a FA nutrient sensorthat resolves inflammation to maintain cardiac homeostasis.Keywords: Free fatty acid receptor 4 (Ffar4), GPR120, heart failure, cytoplasmic phospholipase A2a (cPLA2a), 18-hydroxyeicosapentaenoic acid (18-HEPE)