Smooth Muscle Foam Cell Formation Research Articles

Scutellarin inhibits oleic acid induced vascular smooth muscle foam cell formation via activating autophagy and inhibiting NLRP3 inflammasome activation.

Abnormalities in vascular smooth muscle cells (VSMCs) are pivotal in the pathogenesis of cardiovascular pathologies such as atherosclerosis and hypertension. Scutellarin (Scu), a flavonoid derived from marigold flowers, exhibits a spectrum of biological activities including anti-inflammatory, antioxidant, antitumor, immunomodulatory and antimicrobial effects. Notably, Scu has demonstrated the capacity to mitigate vascular endothelial damage and prevent atherosclerosis via its antioxidative properties. Nevertheless, the influence of Scu on the formation of VSMC-derived foam cells remains underexplored. In this study, Scu was evidenced to efficaciously attenuate oleic acid (OA)-induced lipid accumulation and the upregulation of adipose differentiation-associated protein Plin2 in a dose- and time-responsive manner. We elucidated that Scu effectively diminishes OA-provoked VSMC foam cell formation. Further, it was established that Scu pretreatment augments the protein expression of LC3B-II and the mRNA levels of Map1lc3b and Becn1, concurrently diminishing the protein levels of the NLRP3 inflammasome compared to the OA group. Activation of autophagy through rapamycin attenuated NLRP3 inflammasome protein expression, intracellular lipid droplet content and Plin2 mRNA levels. Scu also counteracted the OA-induced decrement of LC3B-II levels in the presence of bafilomycin-a1, facilitating the genesis of autophagosomes and autolysosomes. Complementarily, in vivo experiments revealed that Scu administration substantially reduced arterial wall thickness, vessel wall cross-sectional area, wall-to-lumen ratio and serum total cholesterol levels in comparison to the high-fat diet model group. Collectively, our findings suggest that Scu attenuates OA-induced VSMC foam cell formation through the induction of autophagy and the suppression of NLRP3 inflammasome activation.

MRTFA overexpression promotes conversion of human coronary artery smooth muscle cells into lipid-laden foam cells

ObjectiveSmooth muscle cells contribute significantly to lipid-laden foam cells in atherosclerotic plaques. However, the underlying mechanisms transforming smooth muscle cells into foam cells are poorly understood. The purpose of this study was to gain insight into the molecular mechanisms regulating smooth muscle foam cell formation. Approach and resultsUsing human coronary artery smooth muscle cells we found that the transcriptional co-activator MRTFA promotes lipid accumulation via several mechanisms, including direct transcriptional control of LDL receptor, enhanced fluid-phase pinocytosis and reduced lipid efflux. Inhibition of MRTF activity with CCG1423 and CCG203971 significantly reduced lipid accumulation. Furthermore, we demonstrate enhanced MRTFA expression in vascular remodeling of human vessels. ConclusionsThis study demonstrates a novel role for MRTFA as an important regulator of lipid homeostasis in vascular smooth muscle cells. Thus, MRTFA could potentially be a new therapeutic target for inhibition of vascular lipid accumulation.

Elevated Neuropeptide Y in Endothelial Dysfunction Promotes Macrophage Infiltration and Smooth Muscle Foam Cell Formation.

Endothelial dysfunction has been linked to vascular inflammation and foam cell formation but the underlying mechanisms still remain unclear. We sought to define the factors inducing inflammation and smooth muscle foam cell formation under endothelial dysfunction using endothelial nitric oxide synthase (eNOS)-deficient mice. Vascular smooth muscle cells (VSMCs) from eNOS-deficient mice displayed increased expression of macrophage-related genes and elevated lipid uptake. Neuropeptide Y (NPY) was upregulated in the aorta from the eNOS-deficient mice and promoted macrophage chemotaxis toward VSMCs while enhancing the activity of matrix metalloproteinase-3. Notably, NPY induced lipid uptake in VSMCs, facilitating smooth muscle foam cell formation, in association with enhanced expression of genes related to modified low-density lipoprotein uptake and macrophages. NPY was augmented by inflammatory pentraxin 3 (PTX3) in VSMCs. PTX3 enhanced macrophage migratory capacity through the NPY/neuropeptide Y receptor axis and this effect was attenuated by pharmacological inhibition with a receptor-specific antagonist. These observations suggest that endothelial dysfunction leads to the elevation of NPY that amplifies vascular inflammation by increasing inflammatory cell chemotaxis and triggers smooth muscle foam cell formation.

Global Knockout of LDLRAP1 Regulates Atherosclerosis, Insulin Resistance, and VSMC Foam Cell Formation

IntroductionAtherosclerotic vascular syndromes account for 50% of all mortality in the United States, and are a considerable medical and socioeconomic problem contributing to mortality of many conditions including myocardial infarction, stroke, renal failure, and peripheral vascular disease. Recent studies have implicated that as many as 70% of all cells in atherosclerotic lesions are vascular smooth muscle cell (VSMC)‐derived. VSMC express lipid receptors and can uptake oxidized‐LDL to form foam cells, affecting the size and lipid content of atherosclerotic plaques. Low‐Density Lipoprotein Receptor Adaptor Protein 1 (LDLRAP1) is a cytosolic adaptor protein which interacts with the cytoplasmic tail of the LDL receptor, internalizing the receptor when it engages with LDL. Mutations in this gene lead to LDL receptor malfunction and cause Autosomal Recessive Hypercholesterolemia (ARH) in humans. The hypercholesterolemia is assumed to be a result of impaired LDL internalization by hepatocytes. Surprisingly, no investigation into a function for LDLRAP1 in lipid internalization in VSMC, or ramifications on atherogenesis in mice lacking LDLRAP1 has been reported. The purpose of this study was to test the hypothesis that while hepatic expression of LDLRAP1 is beneficial, LDLRAP1 expression in VSMC leads to VSMC foam cell formation and increased atherosclerosis.ResultssiRNA knockdown of LDLRAP1 in human primary VSMC leads to significantly reduced lipid uptake quantified by flow cytometry (p<0.01). Foam cell formation was quantitated in LDLRAP1−/− VSMC – similar to human VSMC, VSMC excised and cultured from aortas of LDLRAP1−/− mice had reduced lipid uptake compared with wild‐type controls (p<0.01). VSMC proliferation is also a key step in atherosclerotic plaque formation, and LDLRAP1−/− VSMC proliferated more slowly than wild‐type controls over a 7‐day period (p<0.05). LDLRAP1−/− mice fed a high‐fat western diet (HFD) for 15 weeks had increased plaque burden compared with wild‐type controls (p<0.01). Unexpectedly, LDLRAP1−/− mice gained significantly more weight on HFD compared with wild‐type control mice (25.72 ± 1.07 vs. 10.95 ± 0.7 grams). Obesity is associated with insulin resistance, and insulin tolerance tests indicated that LDLRAP1−/− mice are insulin resistant.Summary and conclusionsThese data are the first to suggest that lack of LDLRAP1 directly leads to atherosclerosis in mice. LDLRAP1 may play an important role in VSMC foam cell formation, and an unexpected role in metabolism. These data are a first step and imply that knocking out LDLRAP1 specifically in vascular smooth muscle cells may provide a novel approach to reduce vascular smooth muscle foam cell formation and subsequently atherogenesis without inducing the hypercholesterolemia associated with a global knockout.Support or Funding InformationNIH‐NHLBIThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pathways of smooth muscle foam cell formation in atherosclerosis.

Smooth muscle cells (SMCs) are the major cell type in human atherosclerosis-prone arteries and take up excess lipids, thereby contributing to luminal occlusion. Here we provide a focused review on pathways by which smooth muscle cells (SMCs) can become foam cells in atherosclerosis. A synthesis of recent and older investigations provides key mechanistic insights into SMC foam cell formation. LDL and other apoB-containing lipoproteins are modified by a diverse array of oxidative, enzymatic, and nonenzymatic processes present in the arterial intima. These modifications of LDL all promote the aggregation of LDL (agLDL), a key finding from analysis of arterial lesion particles. Scavenger receptor and phagocytic capacity of SMCs can vary greatly, perhaps related to differences in SMC phenotype or in-vitro cell culture environments, and can be increased with exposure to cytokines, growth factors, and cholesterol. Macrophages promote the formation of SMC foam cells in direct or indirect co-culture models. SMCs contribute significantly to the foam cell population in atherosclerosis. Further investigation and identification of key mechanisms of SMC foam cell formation will help drive new therapeutics to reduce cardiovascular disease.

Oleic acid induces smooth muscle foam cell formation and enhances atherosclerotic lesion development via CD36

BackgroundElevated plasma free fatty acid (FFA) levels have been linked to the development of atherosclerosis. However, how FFA causes atherosclerosis has not been determined. Because fatty acid translocase (FAT/CD36) is responsible for the uptake of FFA, we hypothesized that the atherogenic effects of FFA may be mediated via CD36.ResultsWe tested this hypothesis using cultured rat aortic smooth muscle cells (SMCs) treated with oleic acid (OA). We found that OA induces lipid accumulation in SMCs in a dose dependent manner. Rat aortic SMCs treated for 48 hours with OA (250 μmol/L) became foam cells based on morphological (Oil Red O staining) and biochemical (5 times increase in cellular triglyceride) criteria. Moreover, specific inhibition of CD36 by sulfo-N-succinimidyl oleate significantly attenuated OA induced lipid accumulation and foam cell formation. To confirm these results in vivo, we used ApoE-deficient mice fed with normal chow (NC), OA diet, NC plus lipolysis inhibitor acipimox or OA plus acipimox. OA-fed mice showed increased plasma FFA levels and enhanced atherosclerotic lesions in the aortic sinus compared to the NC group (both p < 0.01). This effect was partially reversed by acipimox (lesion area: OA: 3.09 ± 0.10 ×105 μm2 vs. OA plus acipimox: 2.60 ± 0.10 ×105 μm2, p < 0.05; FFA: OA: 0.91 ± 0.03 mmol/L vs. OA plus acipimox: 0.78 ± 0.03 mmol/L, p < 0.05).ConclusionsThese findings suggest that OA induces smooth muscle foam cell formation and enhances atherosclerotic lesions in part though CD36. Furthermore, these findings provide a novel model for the investigation of atherosclerosis.

Biological Characteristics of Foam Cell Formation in Smooth Muscle Cells Derived from Bone Marrow Stem Cells

Bone marrow mesenchymal stem cells (BMSC) can differentiate into diverse cell types, including adipogenic, osteogenic, chondrogenic and myogenic lineages. There are lots of BMSC accumulated in atherosclerosis vessels and differentiate into VSMC. However, it is unclear whether VSMC originated from BMSC (BMSC-SMC) could remodel the vessel in new tunica intima or promote the pathogenesis of atherosclerosis. In this study, BMSC were differentiated into VSMC in response to the transforming growth factor β (TGF-β) and shown to express a number of VSMC markers, such as α-smooth muscle actin (α-SMA) and smooth muscle myosin heavy chain1 (SM-MHC1). BMSC-SMC became foam cells after treatment with 80 mg/L ox-LDL for 72 hours. Ox-LDL could upregulate scavenger receptor class A (SR-A) but downregulate the ATP-binding cassette transporter A1 (ABCA1) and caveolin-1 protein expression, suggesting that modulating relative protein activity contributes to smooth muscle foam cell formation in BMSC-SMC. Furthermore, we found that BMSC-SMC have some biological characteristics that are similar to VSMC, such as the ability of proliferation and secretion of extracellular matrix, but, at the same time, retain some biological characteristics of BMSC, such as a high level of migration. These results suggest that BMSC-SMC could be induced to foam cells and be involved in the development of atherosclerosis.

ATP-Binding Cassette Transporter A1 Expression and Apolipoprotein A-I Binding Are Impaired in Intima-Type Arterial Smooth Muscle Cells

Accumulation of excess cholesterol by intimal arterial smooth muscle cells (SMCs) contributes to the formation of foam cells in atherosclerotic lesions. The purpose of this study was to examine the expression and activity of ATP-binding cassette transporter A1 (ABCA1) in model intimal and medial arterial SMCs, in human atherosclerotic coronary artery intimal and medial layers, and in human intimal and medial SMCs. Model intimal arterial SMCs showed increased cholesteryl ester accumulation, absence of apolipoprotein A-I-mediated lipid efflux, markedly diminished ABCA1 expression, and poor apoA-I binding compared with medial-layer SMCs. Total ABCA1 mRNA and SMC-specific ABCA1 protein levels were diminished in the intimal layer compared with the medial layer of atherosclerotic human coronary arteries. Increased expression of ABCA1 by liver X receptor agonist treatment or gene transfection failed to correct apolipoprotein A-I binding, lipid efflux, or high-density lipoprotein particle formation by intima-type SMCs. In addition to impaired ABCA1 expression, intima-type SMCs appear to lack a critical binding factor or factors required for the apolipoprotein A-I-ABCA1 interaction, cholesterol efflux, and high-density lipoprotein particle formation. ABCA1 expression is reduced in cultured model intimal and human atherosclerotic lesion SMCs, suggesting that reduced ABCA1 activity contributes to smooth muscle foam cell formation in the intima.

Function of scavenger receptor class A type I/II is not important for smooth muscle foam cell formation

Macrophages (MΦ) and smooth muscle cells (SMC) are transformed into foam cells by massive accumulation of modified lipoproteins during atherogenesis. It is known that class AI/II scavenger receptors participate in the foam cell formation of MΦ. The mechanism of lipid accumulation in SMC is however unknown. Therefore, we investigated if class AI/II scavenger receptors mediate the uptake of modified lipoproteins in SMC. Additionally, we examined the influence of MΦ and proinflammatory cytokines in this process. Our flow cytometric experiments revealed significant uptake of DiI-AcLDL in SMC. This uptake was markedly enhanced by IL-1 α and TNF- α, whereas cocultured MΦ decreased the uptake of DiI-AcLDL in SMC. Competition and blocking experiments were performed to enlighten the role of class AI/II scavenger receptors. The competition experiments showed that surplus NatLDL, a ligand not known to interact with class AI/II scavenger receptors, caused a drastically decreased uptake of DiI-AcLDL in SMC. Additionally, blocking of class AI/II scavenger receptors with antibody 2F8 did not influence the uptake of DiI-AcLDL in SMC. Furthermore, fluorescence microscopic double staining of human coronary arteries with early, intermediate and advanced atherosclerotic lesions showed no colocalization of class AI scavenger receptors with SMC. These results indicate that class AI/II scavenger receptors play only a minor role in the uptake of modified lipoproteins in SMC. We suggest that SMC foam cell formation is mainly mediated by other receptors than class AI/II scavenger receptors.

Acyl-CoenzymeA (CoA):Cholesterol Acyltransferase Inhibition in Rat and Human Aortic Smooth Muscle Cells Is Nontoxic and Retards Foam Cell Formation

Studies in vitro and in vivo of macrophage foam cells have shown evidence of cytotoxicity after acyl-CoA:cholesterol acyltransferase (ACAT) inhibition. Foam cells of smooth muscle origin are also found in human and animal atherosclerotic lesions. To study whether cytotoxicity from ACAT inhibition is independent of cell type, we first established a protocol to conveniently induce aortic smooth muscle foam cell formation using cholesterol-cyclodextrin complexes (CCC). Rat aortic smooth muscle cells (ASMCs) treated for 48 hours with CCC (20 microg/mL) became foam cells by morphological (oil-red-O staining) and biochemical (approximately 1200% and approximately 180% increase in cellular esterified and free cholesterol, respectively) criteria. ACAT activity increased 500% (P<0.01 versus untreated). Similar results were obtained in human ASMC, but ACAT activity increased to an even greater extent (3200%; P<0.01 versus untreated). Western blots indicated that CCC treatment increased human (to 380+/-20% of untreated, P<0.001), but not rat, ACAT protein expression. ACAT inhibition by Fujirebio compound F1394 suppressed CCC-induced foam cell formation in rat and human ASMC, but, notably, did not induce significant cytotoxicity. ASMC might be more resistant to FC-induced adverse effects than are macrophages.

Lipid liberated from dead macrophages is responsible for smooth muscle foam cell formation in a co-culture system

Lipid liberated from dead macrophages is responsible for smooth muscle foam cell formation in a co-culture system