Deficiency of LMP10 Attenuates Diet-Induced Atherosclerosis by Inhibiting Macrophage Polarization and Inflammation in Apolipoprotein E Deficient Mice.

Jiawei Liao,Hui-Hua Li,Qiu-Yue Lin,Xiangbo An,Shuang Liu,Yun-Long Xia,Jie Bai,Yunpeng Xie,Xiaolei Yang

doi:10.3389/fcell.2020.592048

Abstract

Macrophage polarization and inflammation are key factors for the onset and progression of atherosclerosis. The immunoproteasome complex consists of three inducible catalytic subunits (LMP2, LMP10, and LMP7) that play a critical role in the regulation of these risk factors. We recently demonstrated that the LMP7 subunit promotes diet-induced atherosclerosis via inhibition of MERTK-mediated efferocytosis. Here, we explored the role of another subunit of LMP10 in the disease process, using ApoE knockout (ko) mice fed on an atherogenic diet (ATD) containing 0.5% cholesterol and 20% fat for 8 weeks as an in vivo atherosclerosis model. We observed that ATD significantly upregulated LMP10 expression in aortic lesions, which were primarily co-localized with plaque macrophages. Conversely, deletion of LMP10 markedly attenuated atherosclerotic lesion area, CD68+ macrophage accumulation, and necrotic core expansion in the plaques, but did not change plasma metabolic parameters, lesional SM22α+ smooth muscle cells, or collagen content. Myeloid-specific deletion of LMP10 by bone marrow transplantation resulted in similar phenotypes. Furthermore, deletion of LMP10 remarkably reduced aortic macrophage infiltration and increased M2/M1 ratio, accompanied by decreased expression of pro-inflammatory M1 cytokines (MCP-1, IL-1, and IL-6) and increased expression of anti-inflammatory M2 cytokines (IL-4 and IL-10). In addition, we confirmed in cultured macrophages that LMP10 deletion blunted macrophage polarization and inflammation during ox-LDL-induced foam cell formation in vitro, which was associated with decreased IκBα degradation and NF-κB activation. Our results show that the immunoproteasome subunit LMP10 promoted diet-induced atherosclerosis in ApoE ko mice possibly through regulation of NF-κB-mediated macrophage polarization and inflammation. Targeting LMP10 may represent a new therapeutic approach for atherosclerosis.

Highlights

Atherosclerosis is a chronic immune-inflammatory response within the artery, with lipid accumulation and oxidation in the intima being hallmarks of the disease (Ross, 1999)
To investigate the role of the immunoproteasome subunit LMP10 in the development of atherosclerosis, we first examined the expression of LMP10 in the aorta of apolipoprotein E (ApoE) ko mice after 8 weeks of atherogenic diet (ATD) feeding
Immunoblotting analysis showed that protein expression of LMP10 was significantly upregulated in the aorta of mice fed on an ATD, as compared to mice without ATD feeding (Figure 1A)

Summary

Introduction

Atherosclerosis is a chronic immune-inflammatory response within the artery, with lipid accumulation and oxidation in the intima being hallmarks of the disease (Ross, 1999). Once oxidized lipids accumulate in the intima, they attract circulating monocytes to enter the sub-endothelial space and differentiate into macrophages to scavenge these oxidized lipids (Moore et al, 2013) These lipid-laden macrophages ( known as foam cells) secrete inflammatory cytokines, including chemokines and adhesion molecules, as well as pro- and anti-inflammatory cytokines, to recruit more monocytes, initiating inflammatory responses (Moore et al, 2013). Upon pro-inflammatory stimulation, these three subunits can be replaced by their inducible forms, namely β1i (PSMB9 and LMP2), β2i (PSMB10, LMP10, and Mecl-1), and β5i (PSMB8 and LMP7), to fill in a specialized type of proteasome called the immunoproteasome (Angeles et al, 2012; Basler et al, 2013). Proteasome inhibition decreases early atherosclerosis (Feng et al, 2010; Wilck et al, 2012) but might promote advanced plaque instability (Van Herck et al, 2010; Wilck et al, 2017)

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