Melatonin Ameliorates Atherosclerotic Plaque Vulnerability by Regulating PPARδ-Associated Smooth Muscle Cell Phenotypic Switching.

Vulnerable atherosclerotic plaque rupture, the leading cause of fatal atherothrombotic events, is associated with an increased risk of mortality worldwide. Peroxisome proliferator-activated receptor delta (PPARδ) has been shown to modulate vascular smooth muscle cell (SMC) phenotypic switching, and, hence, atherosclerotic plaque stability. Melatonin reportedly plays a beneficial role in cardiovascular diseases; however, the mechanisms underlying improvements in atherosclerotic plaque vulnerability remain unknown. In this study, we assessed the role of melatonin in regulating SMC phenotypic switching and its consequential contribution to the amelioration of atherosclerotic plaque vulnerability and explored the mechanisms underlying this process. We analyzed features of atherosclerotic plaque vulnerability and markers of SMC phenotypic transition in high-cholesterol diet (HCD)-fed apolipoprotein E knockout (ApoE-/-) mice and human aortic SMCs (HASMCs). Melatonin reduced atherosclerotic plaque size and necrotic core area while enhancing collagen content, fibrous cap thickness, and smooth muscle alpha-actin positive cell coverage on the plaque cap, which are all known phenotypic characteristics of vulnerable plaques. In atherosclerotic lesions, melatonin significantly decreased the synthetic SMC phenotype and KLF4 expression and increased the expression of PPARδ, but not PPARα and PPARγ, in HCD-fed ApoE-/- mice. These results were subsequently confirmed in the melatonin-treated HASMCs. Further analysis using PPARδ silencing and immunoprecipitation assays revealed that PPARδ plays a role in the melatonin-induced SMC phenotype switching from synthetic to contractile. Collectively, we provided the first evidence that melatonin mediates its protective effect against plaque destabilization by enhancing PPARδ-mediated SMC phenotypic switching, thereby indicating the potential of melatonin in treating atherosclerosis.

Chen SJ ，Chien HC ，Tsai SH ，Jheng YS ，Chen Y ，Hsieh PS ，Tsui PF ，Chien S ，Tsai MC ... -  《-》

Peroxisome proliferator-activated receptor δ improves the features of atherosclerotic plaque vulnerability by regulating smooth muscle cell phenotypic switching.

Vascular smooth muscle cells (SMCs) undergo phenotypic switching during sustained inflammation, contributing to an unfavourable atherosclerotic plaque phenotype. PPARδ plays an important role in regulating SMC functions; however, its role in atherosclerotic plaque vulnerability remains unclear. Here, we explored the pathological roles of PPARδ in atherosclerotic plaque vulnerability in severe atherosclerosis and elucidated the underlying mechanisms. Plasma levels of PPARδ were measured in patients with acute coronary syndrome (ACS) and stable angina (SA). SMC contractile and synthetic phenotypic markers, endoplasmic reticulum (ER) stress, and features of atherosclerotic plaque vulnerability were analysed for the brachiocephalic artery of apolipoprotein E-knockout (ApoE-/- ) mice, fed a high-cholesterol diet (HCD) and treated with or without the PPARδ agonist GW501516. In vitro, the role of PPARδ was elucidated using human aortic SMCs (HASMCs). Patients with ACS had significantly lower plasma PPARδ levels than those with SA. GW501516 reduced atherosclerotic plaque vulnerability, a synthetic SMC phenotype, ER stress markers, and NLRP3 inflammasome expression in HCD-fed ApoE-/- mice. ER stress suppressed PPARδ expression in HASMCs. PPARδ activation inhibited ER stress-induced synthetic phenotype development, ER stress-NLRP3 inflammasome axis activation and matrix metalloproteinase 2 (MMP2) expression in HASMCs. PPARδ inhibited NFκB signalling and alleviated ER stress-induced SMC phenotypic switching. Low plasma PPARδ levels may be associated with atherosclerotic plaque vulnerability. Our findings provide new insights into the mechanisms underlying the protective effect of PPARδ on SMC phenotypic switching and improvement the features of atherosclerotic plaque vulnerability.

Lien CF ，Lin CS ，Shyue SK ，Hsieh PS ，Chen SJ ，Lin YT ，Chien S ，Tsai MC ... -  《-》

AMP-Activated Protein Kinase Alpha 2 Deletion Induces VSMC Phenotypic Switching and Reduces Features of Atherosclerotic Plaque Stability.

AMP-activated protein kinase (AMPK) has been reported to play a protective role in atherosclerosis. However, whether AMPKα2 controls atherosclerotic plaque stability remains unknown. The aim of this study was to evaluate the impact of AMPKα2 deletion on atherosclerotic plaque stability in advanced atherosclerosis at the brachiocephalic arteries and to elucidate the underlying mechanisms. Features of atherosclerotic plaque stability and the markers for contractile or synthetic vascular smooth muscle cell (VSMC) phenotypes were monitored in the brachiocephalic arteries from Apoe(-/-)AMPKα2(-/-) mice or VSMC-specific AMPKα2(-/-) mice in an Apoe(-/-) background (Apoe(-/-)AMPKα2(sm-/-)) fed Western diet for 10 weeks. We identified that Apoe(-/-)AMPKα2(-/-) mice and Apoe(-/-)AMPKα2(sm-/-) mice exhibited similar unstable plaque features, aggravated VSMC phenotypic switching, and significant upregulation of Kruppel-like factor 4 (KLF4) in the plaques located in the brachiocephalic arteries compared with those found in Apoe(-/-) and Apoe(-/-)AMPKα2(sm+/+) control mice. Pravastatin, an AMPK activator, suppressed VSMC phenotypic switching and alleviated features of atherosclerotic plaque instability in Apoe(-/-)AMPKα2(sm+/+) mice, but not in Apoe(-/-)AMPKα2(sm-/-) mice. VSMC isolated from AMPKα2(-/-) mice displayed a significant reduction of contractile proteins(smooth muscle actin-α, calponin, and SM-MHC [smooth muscle-mysion heavy chain]) in parallel with increased detection of synthetic proteins (vimentin and osteopontin) and KLF4, as observed in vivo. KLF4-specific siRNA abolished AMPKα2 deletion-induced VSMC phenotypic switching. Furthermore, pharmacological or genetic inhibition of nuclear factor-κB significantly decreased KLF4 upregulation in VSMC from AMPKα2(-/-) mice. Finally, we found that AMPKα2 deletion markedly promoted the binding of nuclear factor-κBp65 to KLF4 promoter. This study demonstrated that AMPKα2 deletion induces VSMC phenotypic switching and promotes features of atherosclerotic plaque instability in nuclear factor-κB-KLF4-dependent manner.

Ding Y ，Zhang M ，Zhang W ，Lu Q ，Cai Z ，Song P ，Okon IS ，Xiao L ，Zou MH ... -  《-》

Protein deglycase DJ-1 deficiency induces phenotypic switching in vascular smooth muscle cells and exacerbates atherosclerotic plaque instability.

Protein deglycase DJ-1 (DJ-1) is a multifunctional protein involved in various biological processes. However, it is unclear whether DJ-1 influences atherosclerosis development and plaque stability. Accordingly, we evaluated the influence of DJ-1 deletion on the progression of atherosclerosis and elucidate the underlying mechanisms. We examine the expression of DJ-1 in atherosclerotic plaques of human and mouse models which showed that DJ-1 expression was significantly decreased in human plaques compared with that in healthy vessels. Consistent with this, the DJ-1 levels were persistently reduced in atherosclerotic lesions of ApoE-/- mice with the increasing time fed by western diet. Furthermore, exposure of vascular smooth muscle cells (VSMCs) to oxidized low-density lipoprotein down-regulated DJ-1 in vitro. The canonical markers of plaque stability and VSMC phenotypes were evaluated in vivo and in vitro. DJ-1 deficiency in Apoe-/- mice promoted the progression of atherosclerosis and exaggerated plaque instability. Moreover, isolated VSMCs from Apoe-/- DJ-1-/- mice showed lower expression of contractile markers (α-smooth muscle actin and calponin) and higher expression of synthetic indicators (osteopontin, vimentin and tropoelastin) and Kruppel-like factor 4 (KLF4) by comparison with Apoe-/- DJ-1+/+ mice. Furthermore, genetic inhibition of KLF4 counteracted the adverse effects of DJ-1 deletion. Therefore, our results showed that DJ-1 deletion caused phenotype switching of VSMCs and exacerbated atherosclerotic plaque instability in a KLF4-dependent manner.

Wang ZY ，Cheng J ，Liu B ，Xie F ，Li CL ，Qiao W ，Lu QH ，Wang Y ，Zhang MX ... -  《-》

Cholesterol-Induced Phenotypic Modulation of Smooth Muscle Cells to Macrophage/Fibroblast-like Cells Is Driven by an Unfolded Protein Response.

Chattopadhyay A ，Kwartler CS ，Kaw K ，Li Y ，Kaw A ，Chen J ，LeMaire SA ，Shen YH ，Milewicz DM ... -  《-》