Biology subjects

Walker, R. E.

Publications and source records attributed to Walker, R. E..

2 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↗

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↗