ALDH2 deficiency inhibits Ox-LDL induced foam cell formation via suppressing CD36 expression

https://doi.org/10.1016/j.bbrc.2019.02.012Get rights and content

Highlights

  • Aldh2 deficiency reduces ox-LDL rather than ac-LDL induced macrophage derived foam cell formation.

  • CD36 contributes to the decreased foam cell formation in ox-LDL treated ALDH2 deficient macrophages.

  • ALDH2 deficiency increases the level of 4-HNE and downregulates the expression of PPARγ in ox-LDL treated macrophages.

  • ALDH2 deficiency induced more cell apoptosis via promoting phosphorylation of P38 MAPK and suppressing phosphorylation of AKT.

Abstract

Foam cell formation plays an important role in the initiation and progression of atherosclerosis. Aldehyde dehydrogenase 2 (ALDH2), a key enzyme for aldehyde metabolism, is associated with coronary artery disease and affects atherosclerotic plaque vulnerability. However, the role of ALDH2 in foam cell formation remains unclear. Using peritoneal macrophages from ALDH2-deficient and control mice, we found that ALDH2 deficiency suppressed foam cell formation induced by oxidized low-density lipoproteins (ox-LDL) but not acetylated low-density lipoproteins (ac-LDL) ex vivo. After incubation with ox-LDL, ALDH2-deficient macrophages expressed lower levels of CD36 but the expression of other lipid metabolism-related proteins including SRA, LOX-1, ABCA-1, ABCG-1 and ACAT-1 was not changed in ALDH2−/− macrophages. Using CD36 inhibitor, we confirmed that CD36 contributes to the effect of ALDH2 on foam cell formation. PPARγ was downregulated in ox-LDL treated ALDH2−/− macrophages. 4-HNE was increased by ALDH2 deficiency and high concentration of 4-HNE suppressed the expression of PPARγ. These data suggest that ALDH2 plays an important role in foam cell formation via 4-HNE/PPARγ/CD36 pathway.

Introduction

Atherosclerosis is the primary cause of cardiovascular diseases. It is characterized by the accumulation of lipids in the arterial wall [1]. In atherosclerosis, circulating monocytes adhere, roll on the endothelial cells, transmigrate into the subintima and become inflammatory macrophages [2]. These macrophages differentiate into foam cells at the onset of the disease following exposure to modified lipoproteins such as oxidized low-density lipoproteins (ox-LDL) and uptake these lipids through macrophage scavenger receptors [3]. Foam cell formation has been recognized as a critical step in the development of atherosclerosis [4].

Foam cell formation mainly depends on lipid influx and efflux. Numerous scavenger receptors including scavenger receptor A (SRA), CD36 and lectin-type oxidized low-density lipoprotein receptor 1 (LOX-1) are responsible for the uptake of modified lipids [5]. ATP-Binding cassette transporter A family member 1 (ABCA1), ATP-Binding cassette transporter G family member 1 (ABCG1) and other transporters facilitate the efflux of lipids in response to excessive lipid accumulation in the foam cells [6]. Moreover, free cholesterol undergoes re-esterification in the foam cells by Acyl-CoA cholesterol ester transferase (ACAT), which can influence cholesterol trafficking and lipid efflux [7].

ALDH2 is a key metabolic enzyme for reactive aldehydes such as 4-hydroxy-2-nonenal (4-HNE) and malondialdehyde (MDA) [8,9]. In the present study, we found that ALDH2 inhibition using lentivirus-ALDH2-RNAi increased the size of plaques. Based on the important role of foam cell formation in atherosclerosis, we hypothesized that ALDH2 plays a role in foam cell formation. To validate this hypothesis and examine the underlying signaling pathways, a series of in vivo and ex vivo experiments were designed and performed.

Section snippets

Reagents and antibodies

The lentivirus GFP and ALDH2-RNAi vector construct was acquired from Genechem (Shanghai, China). Sulfo-N-succinimidyl oleate (SSO, sc-208408) was from Santa Cruz Biotechnology (Dallas, USA). Anti-ALDH2 (ab196494) and anti-MOMA-2 (ab33451) for immunofluorescence experiments were purchased from Abcam (San Francisco, USA). Goat anti-rabbit IgG (DyLight 488) and goat anti-mouse IgG (DyLight 594) secondary antibodies were purchased from Abokin Inc. (Redlands, USA). Primary antibodies for western

ALDH2 deficiency reduces foam cell formation in ox-LDL treated mouse peritoneal macrophages

Oil red O staining revealed more atherosclerotic lesions in the sections of aortic roots in mice treated with Lv-ALDH2-RNAi versus the control mice (Supplemental Fig. 1). Two groups of mice had similar serum triglyceride and cholesterol levels (Supplemental Table). To determine the effect of ALDH2 on foam cell formation, we collected and cultured peritoneal macrophages from ALDH2−/− and ALDH2+/+ mice (Supplemental Fig. 2). Intracellular cholesterol levels were lower in ALDH2-deficient

Discussion

The present study shows that ALDH2 inhibition suppresses ox-LDL rather than ac-LDL induced macrophage-derived foam cell formation. CD36 plays a critical role in the effect of ALDH2 on foam cell formation and it might be regulated by 4-HNE/PPARγ pathway. Moreover, ALDH2 deficiency promotes macrophage apoptosis possibly by inhibiting AKT phosphorylation and promoting P38 MAPK phosphorylation.

Lipids play a central role in the pathogenesis of atherosclerotic plaque [11]. Elevated LDL levels

Conflicts of interest

None.

Acknowledgments

This study was supported by National Key R&D Program of China (2017YFC0908700, 2017YFC0908703), National Science Foundation of China (81570401, 81772036, 81571934, 81601717, 81873950), Taishan Young Scholar Program of Shandong Province(tsqn20161065), Key R&D Program of Shandong Province (2016GSF201235, 2016ZDJS07A14,2018GSF118003) and the Fundamental Research Funds of Shandong University (2014QLKY04, 2018JC011).

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