M2 macrophages exhibit higher sensitivity to oxLDL-induced lipotoxicity than other monocyte/macrophage subtypes

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2011

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Keith Morris , Ruffino , Ahluwalia Maninder , Webb , Webb Richard , Thomas , Isa

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In obesity, phenotypic switches occur in macrophage populations such that the predominantly M2-polarised anti-inflammatory state seen in lean individuals changes to a predominantly M1-polarised pro-inflammatory state in those who are obese. However, the mechanisms by which these phenotypic shifts occur have not yet been fully elucidated. Results The effects of oxLDL (1-40 μg/ml; 24 h) on several parameters relevant to the Unfolded Protein Response (UPR)-mediated lipotoxic effects of oxLDL (disruption of ER Ca 2+ handling; activation of the UPR transcription factor XBP-1; upregulation of the UPR target genes BiP and CHOP; apoptosis; cell viability) were investigated in human primary monocyte-derived macrophages, and also in monocyte-macrophages derived from the THP-1 monocytic cell line. A consistent pattern was observed: M2-polarised macrophages were more sensitive to the lipotoxic effects of oxLDL than either non-polarised macrophages or non-differentiated monocytic cells. Specifically, M2-polarised macrophages were the only cell type to undergo significantly increased apoptosis (Primary cells: 1.23 ± 0.01 basal; THP-1-derived: 1.97 ± 0.12 basal; P < 0.05 in both cases) and decreased cell viability (Primary cells: 0.79 ± 0.04 basal; THP-1-derived: 0.67 ± 0.02 basal; P < 0.05 in both cases) when exposed to oxLDL levels similar to those seen in overweight individuals (ie. 1 μg/ml). Conclusions We propose that the enhanced susceptibility of M2-polarised macrophages to lipotoxicity seen in the present in vitro study could, over time, contribute to the phenotypic shift seen in obese individuals in vivo . This is because a higher degree of oxLDL-induced lipotoxic cell death within M2 macrophages could contribute to a decrease in numbers of M2 cells, and thus a relative increase in proportion of non-M2 cells, within macrophage populations. Given the pro-inflammatory characteristics of a predominantly M1-polarised state, the data presented here may constitute a useful contribution to our understanding of the origin of the pro-inflammatory nature of obesity, and of the pathogenesis of obesity-associated inflammatory disorders such as Type 2 Diabetes and atherosclerosis.

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biomed

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01 janvier 2011

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UPR

Isa et al . Lipids in Health and Disease 2011, 10 :229 http://www.lipidworld.com/content/10/1/229

R E S E A R C H Open Access M2 macrophages exhibit higher sensitivity to oxLDL-induced lipotoxicity than other monocyte/macrophage subtypes Suleiman A Isa, José S Ruffino, Maninder Ahluwalia, Andrew W Thomas, Keith Morris and Richard Webb *

Abstract Background: In obesity, phenotypic switches occur in macrophage populations such that the predominantly M2-polarised anti-inflammatory state seen in lean individuals changes to a predominantly M1-polarised pro-inflammatory state in those who are obese. However, the mechanisms by which these phenotypic shifts occur have not yet been fully elucidated. Results: The effects of oxLDL (1-40 μ g/ml; 24 h) on several parameters relevant to the Unfolded Protein Response (UPR)-mediated lipotoxic effects of oxLDL (disruption of ER Ca 2+ handling; activation of the UPR transcription factor XBP-1; upregulation of the UPR target genes BiP and CHOP; apoptosis; cell viability) were investigated in human primary monocyte-derived macrophages, and also in monocyte-macrophages derived from the THP-1 monocytic cell line. A consistent pattern was observed: M2-polarised macrophages were more sensitive to the lipotoxic effects of oxLDL than either non-polarised macrophages or non-differentiated monocytic cells. Specifically, M2-polarised macrophages were the only cell type to undergo significantly increased apoptosis (Primary cells: 1.23 ± 0.01 basal; THP-1-derived: 1.97 ± 0.12 basal; P < 0.05 in both cases) and decreased cell viability (Primary cells: 0.79 ± 0.04 basal; THP-1-derived: 0.67 ± 0.02 basal; P < 0.05 in both cases) when exposed to oxLDL levels similar to those seen in overweight individuals (ie. 1 μ g/ml). Conclusions: We propose that the enhanced susceptibility of M2-polarised macrophages to lipotoxicity seen in the present in vitro study could, over time, contribute to the phenotypic shift seen in obese individuals in vivo . This is because a higher degree of oxLDL-induced lipotoxic cell death within M2 macrophages could contribute to a decrease in numbers of M2 cells, and thus a relative increase in proportion of non-M2 cells, within macrophage populations. Given the pro-inflammatory characteristics of a predominantly M1-polarised state, the data presented here may constitute a useful contribution to our understanding of the origin of the pro-inflammatory nature of obesity, and of the pathogenesis of obesity-associated inflammatory disorders such as Type 2 Diabetes and atherosclerosis. Keywords: alternative M2 monocyte/macrophage polarisation, UPR, oxLDL, lipotoxicity

Background lead to cell death, a phenomenon known as “ lipotoxicity ” Obesity and associated disorders such as Type-2 Diabetes [2]. (T2D) and atherosclerosis are associated with elevated Due to their wide tissue distribution, monocyte/macro-levels of many lipids (eg. increased circulating oxidized phages, which play vital roles in inflammation and the low-density lipoprotein (oxLDL) [1,2]), and with chronic development of obesity, T2D and atherosclerosis [3], are inflammation [3]. This can lead to intracellular lipid involved in lipid accumulation within many tissues [4]. For accumulation in non-adipocyte cells, which can in turn example, the intracellular accumulation of oxLDL within macrophages is mediated by scavenger receptors (such as * Correspondence: rwebb@uwic.ac.uk lCatDt3r6,isSRc-uArreanntdlypocsosnitbrlyovSeRr-siBaIl,[a5lt])horeucgohgtnhiezirnoglealotfertehde Cardiff School of Health Sciences, University of Wales Institute Cardiff, UWIC e Llandaf Campus, CARDIFF CF5 2YB, UK © 2011 Isa et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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