Biology subjects

Shearer, G. C.

Publications and source records attributed to Shearer, G. C..

4 recordsLinked to original sources

bioRxiv2024

ABCA1 and apoA-I dependent 12-hydroxyeicosatetraenoic acid efflux regulates macrophage inflammatory signaling

Aberrant high-density lipoprotein (HDL) function is implicated in inflammation-associated pathologies. While HDL ABCA1-mediated reverse cholesterol and phospholipid transport are well described, the movement of pro-/anti-inflammatory lipids has not been explored. HDL phospholipids are the largest reservoir of circulating arachidonic acid-derived oxylipins. Endotoxin-stimulation activates inflammatory cells leading to hydroxyeicosatetraenoic acid (HETE) production, oxylipins which are involved in inflammatory response coordination. Active signaling in the non-esterified (NE) pool is terminated by sequestration of HETEs as esterified (Es) forms and degradation. We speculate that an ABCA1-apoA-I-dependent efflux of HETEs from stimulated cells could regulate intracellular HETE availability. Here we test this hypothesis both in vitro and in vivo. In endotoxin-stimulated RAW-264.7 macrophages preloaded with d8-arachidonic acid we use compartmental tracer modeling to characterize the formation of HETEs, and their efflux into HDL. We found that in response to endotoxin: I) Cellular NE 12-HETE is positively associated with MCP-1 secretion (p<0.001); II) HETE transfer from NE to Es pools is ABCA1-depedent (p<0.001); III) Cellular Es HETEs are transported into media when both apoA-I and ABCA1 are present (p<0.001); IV) The stimulated efflux of HETEs >> arachidonate (p<0.001). Finally, in endotoxin challenged humans (n=17), we demonstrate that intravenous lipopolysaccharide (0.6 ng/kg body weight) resulted in accumulation of 12-HETE in HDL over a 168-hour follow-up. Therefore, HDL can suppress inflammatory responses in macrophages by regulating intracellular HETE content in an apoA-I/ABCA1 dependent manner. The described mechanism may apply to other oxylipins and explain anti-inflammatory properties of HDL. This newly defined HDL property opens new doors for the study of lipoprotein interactions in metabolic diseases.

molecular biology↗

bioRxiv2024

Free fatty acid receptor 4 in cardiac myocytes ameliorates ischemic cardiomyopathy

AimsFree fatty acid receptor 4 (Ffar4) is a receptor for long-chain fatty acids that attenuates heart failure driven by increased afterload. Recent findings suggest that Ffar4 prevents ischemic injury in brain, liver, and kidney, and therefore, we hypothesized that Ffar4 would also attenuate cardiac ischemic injury. Methods and ResultsUsing a mouse model of ischemia-reperfusion (I/R), we found that mice with systemic deletion of Ffar4 (Ffar4KO) demonstrated impaired recovery of left ventricular systolic function post-I/R with no effect on initial infarct size. To identify potential mechanistic explanations for the cardioprotective effects of Ffar4, we performed bulk RNAseq to compare the transcriptomes from wild-type (WT) and Ffar4KO infarcted myocardium 3-days post-I/R. In the Ffar4KO infarcted myocardium, gene ontology (GO) analyses revealed augmentation of glycosaminoglycan synthesis, neutrophil activation, cadherin binding, extracellular matrix, rho signaling, and oxylipin synthesis, but impaired glycolytic and fatty acid metabolism, cardiac repolarization, and phosphodiesterase activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated impaired AMPK signaling and augmented cellular senescence in the Ffar4KO infarcted myocardium. Interestingly, phosphodiesterase 6c (PDE6c), which degrades cGMP, was the most upregulated gene in the Ffar4KO heart. Further, the soluble guanylyl cyclase stimulator, vericiguat, failed to increase cGMP in Ffar4KO cardiac myocytes, suggesting increased phosphodiesterase activity. Finally, cardiac myocyte-specific overexpression of Ffar4 prevented systolic dysfunction post-I/R, defining a cardioprotective role of Ffa4 in cardiac myocytes. ConclusionsOur results demonstrate that Ffar4 in cardiac myocytes attenuates systolic dysfunction post-I/R, potentially by attenuating oxidative stress, preserving mitochondrial function, and modulation of cGMP signaling.

physiology↗

bioRxiv2022

Free fatty acid receptor 4 (FFAR4) regulates cardiac oxylipin balance to promote inflammation resolution in a model of heart failure preserved ejection fraction secondary to metabolic syndrome

Free fatty acid receptor 4 (Ffar4) is a G-protein coupled receptor for long-chain fatty acids that improves metabolism and attenuates inflammation. Heart failure preserved ejection fraction (HFpEF) is a complex clinical syndrome, but a predominant subset of patients has meta-bolic syndrome (MetS). Mechanistically, systemic, non-resolving inflammation associated with MetS might promote HFpEF. Interestingly, we recently demonstrated that Ffar4 is cardioprotective in pressure overload. The beneficial effects of Ffar4 on metabolism/inflammation, the high incidence of MetS in HFpEF patients, and the cardioprotective effects of Ffar4 led us to hypothesize that loss of Ffar4 would worsen remodeling in HFpEF secondary to MetS (HFpEF-MetS). To test this, mice with systemic deletion of Ffar4 (Ffar4KO) were fed a high-fat/high-sucrose diet with L-NAME in their water (HFpEF-MetS diet) to induce HFpEF-MetS. In male Ffar4KO mice, the HFpEF-MetS diet induced similar metabolic deficits, but worsened diastolic function and microvascular rarefaction compared to wild-type mice. Conversely, in female Ffar4KO mice, the diet produced greater obesity but no worsening of HFpEF. Loss of Ffar4 in males altered the balance of inflammatory oxylipins in the heart, decreasing the eicosapentaenoic acid derived, pro-resolving oxylipin 18-hydroxyeicosapentaenoic acid (18-HEPE), while increasing the arachadonic acid derived, proinflammatory oxylipin 12-hydroxyeicosatetraenoic acid (12-HETE). This increased 12-HETE/18-HEPE ratio, reflecting a more proinflammatory state, was associated with increased macrophage numbers, which in turn correlated with worsened ventricular remodeling in male Ffar4KO hearts. In summary, our data suggest that Ffar4 controls the pro/anti-inflammatory oxylipin balance in the heart to modulate macrophage function and attenuate HFpEF remodeling.

physiology↗

bioRxiv2019

Free fatty acid receptor 4 is a nutrient sensor that resolves inflammation to maintain cardiac homeostasis

BackgroundNon-{-}resolving activation of immune responses is central to the pathogenesis of heart 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.\n\nMethodsMice with systemic deletion of Ffar4 (Ffar4KO) were subjected to pressure overload by 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.\n\nResultsIn Ffar4KO mice, TAC induced more severe remodeling, identifying an entirely novel cardioprotective 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 A2 (cPLA2) signaling genes. In cardiac myocytes, Ffar4 signaling through cPLA2-cytochrome p450 {omega}/{omega}-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.\n\nConclusionsOur results identify a novel function for Ffar4 in the heart as a FA nutrient sensor that resolves inflammation to maintain cardiac homeostasis.

physiology↗