Abstract-Atherosclerosis is a vascular disease characterized by lipid deposition and inflammation within the arterial wall.Oxidized phospholipids (oxPLs), such as 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (oxPAPC) and its constituents 1-palmytoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaroyl-snglycero-3-phosphocholine (PGPC) are concentrated within atherosclerotic lesions and are known to be potent proinflammatory mediators. Phenotypic switching of smooth muscle cells (SMCs) plays a critical role in the development, progression, and end-stage clinical consequences of atherosclerosis, yet little is known regarding the effects of specific oxPLs on SMC phenotype. The present studies were focused on determining whether oxPLs regulate expression of SMC differentiation marker genes and the molecular mechanisms involved. Results showed that POVPC and PGPC induced profound suppression of smooth muscle (SM) ␣-actin and SM myosin heavy chain expression while simultaneously increasing expression of MCP-1, MCP-3, and cytolysin. OxPLs also induced nuclear translocation of Krüppel-like transcription factor 4 (KLF4), a known repressor of SMC marker genes. siRNA targeting of KLF4 nearly blocked POVPC-induced suppression of SMC marker genes, and myocardin. POVPC-induced repression of SMC marker genes was also significantly attenuated in KLF4 knockout SMCs. Taken together, these results suggest a novel role for oxPLs in phenotypic modulation of SMCs and indicate that these effects are dependent on the transcription factor, KLF4. These results may have important novel implications for the mechanisms by which oxPLs contribute to the pathogenesis of atherosclerosis. Key Words: atherosclerosis Ⅲ smooth muscle cell phenotypic switching Ⅲ oxidized phospholipids V ascular smooth muscle cells (SMCs) are a predominant cell type in atherosclerotic plaques and are crucial in the development of vascular disease. 1 Unlike either terminallydifferentiated skeletal or cardiac muscle cells, SMCs within adult animals retain remarkable plasticity and can undergo profound and reversible changes in phenotype in response to changes in local environmental cues. 1 During early atherogenesis, SMCs undergo phenotypic switching which is characterized by decreased expression of SMC differentiation marker proteins, a high rate of cellular proliferation, and increased synthesis of extracellular matrix proteins. 1 In contrast, in late disease stage, SMCs within the fibrous cap of vulnerable atherosclerotic plaques exhibit reduced rates of proliferation and matrix production. These cells also undergo apoptosis and activation of matrix metalloproteinases, which may contribute to plaque rupture, thrombosis, and myocardial infarction. 2 Despite the importance of SMC phenotypic switching in the pathogenesis of atherosclerosis, virtually nothing is known regarding specific factors and mechanisms that control this process.Oxidized lipids, particularly oxidized phospholipids (oxPLs), accumulate in atherosclerotic les...
Stable atherosclerotic plaques are characterized by a thick extracellular matrix (ECM)-rich fibrous cap populated by protective ACTA2 + myofibroblast (MF)-like cells, assumed to be almost exclusively derived from smooth muscle cells (SMC). Herein, we show that in murine and human lesions, 20 to 40% of ACTA2 + fibrous caps cells, respectively, are derived from non-SMC sources, including endothelial cells (EC) or macrophages that have undergone Endothelial-to-Mesenchymal (EndoMT) or Macrophage-to-Mesenchymal (MMT) transitions. In addition, we show that SMC-specific knockout of the platelet derived growth factor receptor beta (PDGFRB) in Apoe −/− mice fed a Western diet (WD) for 18 weeks resulted in brachiocephalic artery (BCA) lesions nearly devoid of SMC but with no changes in lesion size, remodeling, or indices of stability including percent of ACTA2 + fibrous cap cells. However, prolonged WD feeding of SMC-PDGFRB knockout mice resulted in reduced indices of stability, indicating that EndoMT and MMT-derived MFs cannot compensate indefinitely for loss of SMC-derived MFs. Using single cell and bulk RNA-seq analyses of the BCA region and in vitro models, we provide evidence that SMC to MF transitions (SMC-MFT) are induced by PDGF and TFGβ and dependent on aerobic glycolysis, while EndoMT is induced by IL1β and TGFβ. Together, we provide evidence that the ACTA2 + fibrous cap originates from a tapestry of cell types, which transition to an MF state through distinct signaling pathways that are either dependent on or associated with extensive metabolic reprogramming.
Differentiated vascular smooth muscle cells (SMCs) exhibit a work phenotype characterized by expression of several well documented contractile apparatus-associated proteins. However, SMCs retain the ability to de-differentiate into a proliferative phenotype, which is involved in the progression of vascular diseases such as atherosclerosis and restenosis. Understanding the mechanisms involved in maintaining SMC differentiation is critical for preventing proliferation associated with vascular disease. In this study, the molecular mechanisms through which transforming growth factor-1 (TGF-1) induces differentiation of SMCs were examined. TGF-1 stimulated actin re-organization, inhibited cell proliferation, and up-regulated SMC marker gene expression in PAC-1 SMCs. These effects were blocked by pretreatment of cells with either HA1077 or Y-27632, which inhibit the kinases downstream of RhoA. Moreover, TGF-1 activated RhoA and its downstream target PKN. Overexpression of active PKN alone was sufficient to increase the transcriptional activity of the promoters that control expression of smooth muscle (SM) ␣-actin, SM-myosin heavy chain, and SM22␣. In addition, PKN increased the activities of serum-response factor (SRF), GATA, and MEF2-dependent enhancer-reporters. RNA interference-mediated inhibition of PKN abolished TGF-1-induced activation of SMC marker gene promoters. Finally, examination of MAPK signaling demonstrated that TGF-1 increased the activity of p38 MAPK, which was required for activation of the SMC marker gene promoters. Co-expression of dominant negative p38 MAPK was sufficient to block PKN-mediated activation of the SMC marker gene promoters as well as the serumresponse factor, GATA, and MEF2 enhancers. Taken together, these results identify components of an important intracellular signaling pathway through which TGF-1 activates PKN to promote differentiation of SMCs.
There is clear evidence that the phenotypic modulation of smooth muscle cells (SMCs) contributes to the pathophysiology of vascular disease. Phenotypic modulation refers to the unique ability of SMCs to alter their phenotype in response to extracellular stimuli and is hallmarked by the loss of SMC marker gene expression. The transcription factor Krüppel-like factor 4 (KLF4) is a known powerful negative regulator of SMC marker gene expression that works, in part, by decreasing the expression of the serum response factor (SRF) myocardin. KLF4 is not expressed in healthy adult SMCs but is increased in SMCs in response to vascular injury in vivo or PDGF-BB treatment in vitro. The aim of the present study was to determine the molecular mechanisms that regulate the expression of KLF4 in phenotypically modulated SMCs. The results demonstrated that the transcription factor stimulating protein-1 (Sp1) regulated the expression of KLF4 in SMCs. The KLF4 promoter contains three consensus Sp1 binding sites. Using a series of truncated KLF4 promoters, we showed that only fragments containing these Sp1 sites could be activated by PDGF-BB. In addition, overexpression of Sp1 alone was sufficient to increase the activity of the KLF4 promoter. Moreover, inhibiting Sp1 expression with small-interfering RNA attenuated the effects of PDGF-BB on KLF4 expression. Mutation of the three Sp1 sites within the KLF4 promoter abolished both baseline and PDGF-BB-induced activity. Finally, the results demonstrated enhanced Sp1 binding to the KLF4 promoter in SMCs treated with PDGF-BB in vitro and following vascular injury in vivo. Taken together, the results suggest a novel role for Sp1 in increasing the expression of KLF4 in phenotypically modulated SMCs.
GK. PDGF-DD, a novel mediator of smooth muscle cell phenotypic modulation, is upregulated in endothelial cells exposed to atherosclerosis-prone flow patterns. Am J Physiol Heart Circ Physiol 296: H442-H452, 2009. First published November 21, 2008 doi:10.1152/ajpheart.00165.2008.-Platelet-derived growth factor (PDGF)-BB is a well-known smooth muscle (SM) cell (SMC) phenotypic modulator that signals by binding to PDGF ␣␣-, ␣-, and -membrane receptors. PDGF-DD is a recently identified PDGF family member, and its role in SMC phenotypic modulation is unknown. Here we demonstrate that PDGF-DD inhibited expression of multiple SMC genes, including SM ␣-actin and SM myosin heavy chain, and upregulated expression of the potent SMC differentiation repressor gene Kruppel-like factor-4 at the mRNA and protein levels. On the basis of the results of promoter-reporter assays, changes in SMC gene expression were mediated, at least in part, at the level of transcription. Attenuation of the SMC phenotypic modulatory activity of PDGF-DD by pharmacological inhibitors of ERK phosphorylation and by a small interfering RNA to Kruppel-like factor-4 highlight the role of these two pathways in this process. PDGF-DD failed to repress SM ␣-actin and SM myosin heavy chain in mouse SMCs lacking a functional PDGF -receptor. Importantly, PDGF-DD expression was increased in neointimal lesions in the aortic arch region of apolipoprotein C-deficient (ApoE Ϫ/Ϫ ) mice. Furthermore, human endothelial cells exposed to an atherosclerosis-prone flow pattern, as in vascular regions susceptible to the development of atherosclerosis, exhibited a significant increase in PDGF-DD expression. These findings demonstrate a novel activity for PDGF-DD in SMC biology and highlight the potential contribution of this molecule to SMC phenotypic modulation in the setting of disturbed blood flow. shear stress; disturbed blood flow; smooth muscle myosin heavy chain; smooth muscle ␣-actin ATHEROSCLEROSIS IS A COMPLEX disease characterized by the accumulation of lipid and cholesterol deposits within the walls of blood vessels, as well as intimal proliferation and extracellular matrix deposition by phenotypically modulated smooth muscle (SM) cells (SMCs) (1). SMCs within human atherosclerotic lesions and experimental atherosclerosis exhibit a distinct morphological change compared with medial SMCs within the normal vessel wall (32). Along with this morphological change, phenotypically modulated SMCs exhibit decreased expression of a variety of contractile genes, including SM ␣-actin, SM myosin heavy chain (MHC), SM22␣, smoothelin, and h1-calponin (32). Advanced atherosclerotic lesions are characterized by a large lipid and necrotic core covered by a fibrous cap, and the thickness and mechanical properties of these lesions are key determinants of the probability of plaque rupture (3, 12, 13), thrombosis, and subsequent acute myocardial infarction or stroke, the leading causes of death in developed countries (3,12,13). Although the precise factors and mechanisms that con...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.