Dual Regulation of Myocardin Expression by Tumor Necrosis Factor-α in Vascular Smooth Muscle Cells

De-differentiation of vascular smooth muscle cells (VSMCs) plays a critical role in the development of atherosclerosis, a chronic inflammatory disease involving various cytokines such as tumor necrosis factor-α (TNFα). Myocardin is a co-factor of serum response factor (SRF) and is considered to be the master regulator of VSMC differentiation. It binds to SRF and regulates the expression of contractile proteins in VSMCs. Myocardin is also known to inhibit VSMC proliferation by inhibiting the NF-κB pathway, whereas TNFα is known to activate the NF-κB pathway in VSMCs. NF-κB activation has also been shown to inhibit myocardin expression and smooth muscle contractile marker genes. However, it is not definitively known whether TNFα regulates the expression and activity of myocardin in VSMCs. The current study aimed to investigate the role of TNFα in regulating myocardin and VSMC function. Our studies showed that TNFα down-regulated myocardin expression and activity in cultured VSMCs by activating the NF-κB pathway, resulting in decreased VSMC contractility and increased VSMC proliferation. Surprisingly, we also found that TNFα prevented myocardin mRNA degradation, and resulted in a further significant increase in myocardin expression and activity in differentiated VSMCs. Both the NF-κB and p44/42 MAPK pathways were involved in TNFα regulation of myocardin, which further increased the contractility of VSMCs. These differential effects of TNFα on myocardin seemingly depended on whether VSMCs were in a differentiated or de-differentiated state. Taken together, our results demonstrate that TNFα differentially regulates myocardin expression and activity, which may play a key role in regulating VSMC functions.     

Atorvastatin Calcium Inhibits Phenotypic Modulation of PDGF-BB-Induced VSMCs via Down-Regulation the Akt Signaling Pathway

Plasticity of vascular smooth muscle cells (VSMCs) plays a central role in the onset and progression of proliferative vascular diseases. In adult tissue, VSMCs exist in a physiological contractile-quiescent phenotype, which is defined by lack of the ability of proliferation and migration, while high expression of contractile marker proteins. After injury to the vessel, VSMC shifts from a contractile phenotype to a pathological synthetic phenotype, associated with increased proliferation, migration and matrix secretion. It has been demonstrated that PDGF-BB is a critical mediator of VSMCs phenotypic switch. Atorvastatin calcium, a selective inhibitor of 3-hydroxy-3-methyl-glutaryl l coenzyme A (HMG-CoA) reductase, exhibits various protective effects against VSMCs. In this study, we investigated the effects of atorvastatin calcium on phenotype modulation of PDGF-BB-induced VSMCs and the related intracellular signal transduction pathways. Treatment of VSMCs with atorvastatin calcium showed dose-dependent inhibition of PDGF-BB-induced proliferation. Atorvastatin calcium co-treatment inhibited the phenotype modulation and cytoskeleton rearrangements and improved the expression of contractile phenotype marker proteins such as α-SM actin, SM22α and calponin in comparison with PDGF-BB alone stimulated VSMCs. Although Akt phosphorylation was strongly elicited by PDGF-BB, Akt activation was attenuated when PDGF-BB was co-administrated with atorvastatin calcium. In conclusion, atorvastatin calcium inhibits phenotype modulation of PDGF-BB-induced VSMCs and activation of the Akt signaling pathway, indicating that Akt might play a vital role in the modulation of phenotype.     

FGFR1 forms an FRS2-dependent complex with mTOR to regulate smooth muscle marker gene expression

Vascular smooth muscle cells (VSMCs) switch from a contractile to a synthetic phenotype in human cardiovascular disease such as atherosclerosis and restenosis after angioplasty. VSMCs show reduced expression of contractile proteins and are capable of responding to mitogens by increasing expression of growth factor receptors. Fibroblast growth factor receptor-1 (FGFR1) signaling is one of several signaling pathways involved in this VSMC phenotypic switching. The aim of this study was to examine the signaling pathway downstream of FGFR1 in the regulation of SM marker gene expression. We found that FGFR1 activated Akt/mTOR pathway and that the mTOR inhibitor rapamycin partially reversed FGFR1-mediated downregulation of SM marker gene expression. Furthermore, we showed that mTOR forms a multi-protein complex with FGFR1 in VSMCs. These findings provide novel information for future development of therapeutic strategies for the treatment of human cardiovascular disease.     

TRPV1 activation impedes foam cell formation by inducing autophagy in oxLDL-treated vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) are an important origin of foam cells besides macrophages. The mechanisms underlying VSMC foam cell formation are relatively little known. Activation of transient receptor potential vanilloid subfamily 1 (TRPV1) and autophagy have a potential role in regulating foam cell formation. Our study demonstrated that autophagy protected against foam cell formation in oxidized low-density lipoprotein (oxLDL)-treated VSMCs; activation of TRPV1 by capsaicin rescued the autophagy impaired by oxLDL and activated autophagy–lysosome pathway in VSMCs; activation of TRPV1 by capsaicin impeded foam cell formation of VSMCs through autophagy induction; activation of TRPV1 by capsaicin induced autophagy through AMP-activated protein kinase (AMPK) signaling pathway. This study provides evidence that autophagy plays an important role in VSMC foam cell formation and highlights TRPV1 as a promising therapeutic target in atherosclerosis.     

Mechanical Stretch Suppresses microRNA-145 Expression by Activating Extracellular Signal-Regulated Kinase 1/2 and Upregulating Angiotensin-Converting Enzyme to Alter Vascular Smooth Muscle Cell Phenotype

Phenotype modulation of vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of various vascular diseases, including hypertension and atherosclerosis. Several microRNAs (miRNAs) were found involved in regulating the VSMC phenotype with platelet-derived growth factor (PDGF) treatment, but the role of miRNAs in the mechanical stretch-altered VSMC phenotype is not clear. Here, we identified miR-145 as a major miRNA contributing to stretch-altered VSMC phenotype by miRNA array, quantitative RT-PCR and gain- and loss-of-function methods. Our data demonstrated that 16% stretch suppressed miR-145 expression, with reduced expression of contractile markers of VSMCs cultured on collagenI; overexpression of miR-145 could partially recover the expression in stretched cells. Serum response factor (SRF), myocardin, and Kruppel-like factor 4 (KLF4) are major regulators of the VSMC phenotype. The effect of stretch on myocardin and KLF4 protein expression was altered by miR-145 mimics, but SRF expression was not affected. In addition, stretch-activated extracellular signal-regulated kinase 1/2 (ERK1/2) and up-regulated angiotensin-converting enzyme (ACE) were confirmed to be responsible for the inhibition of miR-145 expression. Mechanical stretch inhibits miR-145 expression by activating the ERK1/2 signaling pathway and promoting ACE expression, thus modulating the VSMC phenotype.     

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.     

The role of SIRT6 in the differentiation of vascular smooth muscle cells in response to cyclic strain

Vascular smooth muscle cells (VSMCs) may switch their phenotype between a quiescent contractile phenotype and a synthetic phenotype in response to cyclic strain, and this switch may contribute to hypertension, atherosclerosis, and restenosis. SIRT 6 is a member of the sirtuin family, and plays an important role in different cell processes, including differentiation. We hypothesized that cyclic strain modulates the differentiation of VSMCs via a transforming growth factor-β1 (TGF-β1)-Smad-SIRT6 pathway. VSMCs were subjected to cyclic strain using a Flexercell strain unit. It was demonstrated that the strain stimulated the secretion of TGF-β1 into the supernatant of VSMCs. After exposed to the strain, the expressions of contractile phenotype markers, including smooth muscle protein 22 alpha, alpha-actin, and calponin, and phosphorylated Smad2, phosphorylated Smad5, SIRT6 and c-fos were up-regulated in VSMCs by western blot and immunofluorescence. And the expression of intercellular-adhesion molecule-1 (ICAM-1) was also increased detected by flow cytometry. The strained-induced up-regulation of SIRT6 was blocked by a TGF-β1 neutralizing antibody. Furthermore, the effects of strain on VSMCs were abrogated by SIRT6-specific siRNA transfection via the suppression c-fos and ICAM-1. These results suggest that SIRT6 may play a critical role in the regulation of VSMC differentiation in response to the cyclic strain.     

Phenotypic switching of vascular smooth muscle cells in atherosclerosis,hypertension, and aortic dissection

Vascular smooth muscle cells (VSMCs) play a critical role in regulating vasotone, and their phenotypic plasticity is a key contributor to the pathogenesis of various vascular diseases. Two main VSMC phenotypes have been well described: contractile and synthetic. Contractile VSMCs are typically found in the tunica media of the vessel wall, and are responsible for regulating vascular tone and diameter. Synthetic VSMCs, on the other hand, are typically found in the tunica intima and adventitia, and are involved in vascular repair and remodeling. Switching between contractile and synthetic phenotypes occurs in response to various insults and stimuli, such as injury or inflammation, and this allows VSMCs to adapt to changing environmental cues and regulate vascular tone, growth, and repair. Furthermore, VSMCs can also switch to osteoblast-like and chondrocyte-like cell phenotypes, which may contribute to vascular calcification and other pathological processes like the formation of atherosclerotic plaques. This provides discusses the mechanisms that regulate VSMC phenotypic switching and its role in the development of vascular diseases. A better understanding of these processes is essential for the development of effective diagnostic and therapeutic strategies.     

Shear Stress Induces Phenotypic Modulation of Vascular Smooth Muscle Cells via AMPK/mTOR/ULK1-Mediated Autophagy

Phenotypic modulation of vascular smooth muscle cells (VSMCs) is involved in the pathophysiological processes of the intracranial aneurysms (IAs). Although shear stress has been implicated in the proliferation, migration, and phenotypic conversion of VSMCs, the molecular mechanisms underlying these events are currently unknown. In this study, we investigated whether shear stress(SS)-induced VSMC phenotypic modulation was mediated by autophagy involved in adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR)/Unc-51-like kinase 1 (ULK1) pathway. The results show that shear stress could inhibit the expression of key VSMC contractile genes and induce pro-inflammatory/matrix-remodeling genes levels, contributing to VSMCs phenotypic switching from a contractile to a synthetic phenotype. More importantly, Shear stress also markedly increased the levels of the autophagy marker microtubule-associated protein light chain 3-II (LC3II), Beclin-1, and p62 degradation. The autophagy inhibitor 3-methyladenine (3-MA) significantly blocked shear-induced phenotypic modulation of VSMCs. To further explore the molecular mechanism involved in shear-induced autophagy, we found that shear stress could activate AMPK/mTOR/ULK1 signaling pathway in VSMCs. Compound C, a pharmacological inhibitor of AMPK, significantly reduced the levels of p-AMPK and p-ULK, enhanced p-mTOR level, and finally decreased LC3II and Beclin-1 level, which suggested that activated AMPK/mTOR/ULK1 signaling was related to shear-mediated autophagy. These results indicate that shear stress promotes VSMC phenotypic modulation through the induction of autophagy involved in activating the AMPK/mTOR/ULK1 pathway.     

Akt1 isoform modulates phenotypic conversion of vascular smooth muscle cells

In this study, we investigated the role of Akt1 isoform in phenotypic change of vascular smooth muscle cells (VSMCs) and neointima formation. Laminin-induced conversion of synthetic VSMCs into contractile VSMCs was measured by expression of marker proteins for contractile VSMCs and collagen gel contraction assay. Culture of synthetic VSMCs on laminin-coated plates induced expression of marker proteins for contractile VSMCs and showed contraction in response to angiotensin II (AngII) stimulation. Silencing integrin-linked kinase attenuated activation of Akt and blocked phenotypic conversion of VSMCs resulting in the loss of AngII-dependent contraction. Laminin-induced phenotypic conversion of VSMCs was abrogated by phosphatidylinositol 3-kinase inhibitor or in cells silencing Akt1 but not Akt2. Proliferation of contractile VSMCs on laminin-coated plate was enhanced in cells silencing Akt1 whereas silencing Akt2 did not affect. Promoter activity of myocardin and SM22α was enhanced in contractile phenotype and overexpression of myocardin stimulated promoter activity of SM22α in synthetic phenotype. Promoter activity of myocardin and SM22α was reduced in cells silencing Akt1 and promoter activity of SM22α was restored by overexpression of myocardin in cells silencing Akt1. However, silencing of Akt2 affected neither promoter activity of myocardin nor SM22α. Finally, neointima formation in carotid artery ligation and high fat-diet-induced atherosclerosis was facilitated in mice lacking Akt1. This study demonstrates that Akt1 isoform stimulates laminin-induced phenotypic conversion of synthetic VSMCs by regulating the expression of myocardin. VSMCs become susceptible to shifting from contractile to synthetic phenotype by the loss of Akt1 in pathological conditions.     

Transforming Growth Factor β Inhibits Platelet Derived Growth Factor-Induced Vascular Smooth Muscle Cell Proliferation via Akt-Independent,Smad-Mediated Cyclin D1 Downregulation

In adult tissue, vascular smooth muscle cells (VSMCs) exist in a differentiated phenotype, which is defined by the expression of contractile proteins and lack of proliferation. After vascular injury, VSMC adopt a synthetic phenotype associated with proliferation, migration and matrix secretion. The transition between phenotypes is a consequence of the extracellular environment, and in particular, is regulated by agonists such as the pro-differentiating cytokine transforming growth factor β (TGFβ) and the pro-proliferative cytokine platelet derived growth factor (PDGF). In this study, we investigated the interplay between TGFβ and PDGF with respect to their ability to regulate VSMC proliferation. Stimulation of human aortic VSMC with TGFβ completely blocked proliferation induced by all isoforms of PDGF, as measured by DNA synthesis and total cell number. Mechanistically, PDGF-induced Cyclin D1 mRNA and protein expression was inhibited by TGFβ. TGFβ had no effect on PDGF activation of its receptor and ERK1/2, but inhibited Akt activation. However, constitutively active Akt did not reverse the inhibitory effect of TGFβ on Cyclin D1 expression even though inhibition of the proteasome blocked the effect of TGFβ. siRNA against Smad4 completely reversed the inhibitory effect of TGFβ on PDGF-induced Cyclin D1 expression and restored proliferation in response to PDGF. Moreover, siRNA against KLF5 prevented Cyclin D1 upregulation by PDGF and overexpression of KLF5 partially reversed TGFβ-induced inhibition of Cyclin D1 expression. Taken together, our results demonstrate that KLF5 is required for PDGF-induced Cyclin D1 expression, which is inhibited by TGFβ via a Smad dependent mechanism, resulting in arrest of VSMCs in the G1 phase of the cell cycle.     

SCD1 activation impedes foam cell formation by inducing lipophagy in oxLDL‐treated human vascular smooth muscle cells

The formation of fat‐laden foam cells, which contributes to the fatty streaks in the plaques of atheromas, is an important process in atherosclerosis. Vascular smooth muscle cells (VSMCs) are a critical origin of foam cells. However, the mechanisms that underlie VSMC foam cell formation are not yet completely understood. Here, we demonstrated that oxidized low‐density lipoprotein (oxLDL) inhibited lipophagy by suppressing lipid droplet (LD)‐lysosome fusion and increased VSMC foam cell formation. Moreover, although oxLDL treatment inhibited lysosomal biogenesis, it had no significant effect on lysosomal proteolysis and lysosomal pH. Notably, through TMT‐based quantitative proteomic analysis and database searching, 94 differentially expressed proteins were identified, of which 54 were increased and 40 were decreased in the oxLDL group compared with those in the control group. Subsequently, SCD1, a protein of interest, was further investigated. SCD1 levels in the VSMCs were down‐regulated by exposure to oxLDL in a time‐dependent manner and the interaction between SCD1 and LDs was also disrupted by oxLDL. Importantly, SCD1 overexpression enhanced LD‐lysosome fusion, increased lysosomal biogenesis and inhibited VSMC foam cell formation by activating TFEB nuclear translocation and its reporter activity. Modulation of the SCD1/TFEB‐mediated lipophagy machinery may offer novel therapeutic approaches for the treatment of atherosclerosis.     

Invited review: cGMP-dependent protein kinase signaling mechanisms in smooth muscle: from the regulation of tone to gene expression.

cGMP is a second messenger that produces its effects by interacting with intracellular receptor proteins. In smooth muscle cells, one of the major receptors for cGMP is the serine/threonine protein kinase, cGMP-dependent protein kinase (PKG). PKG has been shown to catalyze the phosphorylation of a number of physiologically relevant proteins whose function it is to regulate the contractile activity of the smooth muscle cell. These include proteins that regulate free intracellular calcium levels, the cytoskeleton, and the phosphorylation state of the regulatory light chain of smooth muscle myosin. Other studies have shown that vascular smooth muscle cells (VSMCs) that are cultured in vitro may cease to express PKG and will, coincidentally, acquire a noncontractile, synthetic phenotype. The restoration of PKG expression to the synthetic phenotype VSMC results in the cells acquiring a more contractile phenotype. These more recent studies suggest that PKG controls VSMC gene expression that, in turn, regulates phenotypic modulation of the cells. Therefore, the regulation of PKG gene expression appears to be linked to phenotypic modulation of VSMC. Because several vascular disorders are related to the accumulation of synthetic, fibroproliferative VSMC in the vessel wall, it is likely that changes in the activity of the nitric oxide/cGMP/PKG pathway is involved the development of these diseases.     

SM22α在细胞骨架组构及血管重塑中的作用

血管平滑肌细胞（VSMC）表型转化是动脉粥样硬化、高血压和血管成形术后再狭窄等血管重塑性疾病的共同病理生理过程。VSMC表型转化过程中平滑肌特异基因的表达变化和细胞骨架的组构是当前研究的热点问题之一。平滑肌22α（SM22α）是近年发现的一种VSMC分化标志物,其表达具有平滑肌组织特异性和细胞表型特异性,该蛋白作为一种肌动蛋白细胞骨架相关蛋白参与VSMC骨架组构和收缩调节。本文就SM22α的结构特征及其在VSMC骨架组构和血管重塑中的作用机制进行综述。     

TLR4-mediated inflammation promotes foam cell formation of vascular smooth muscle cell by upregulating ACAT1 expression

Vascular smooth muscle cell (VSMC) foam cell formation is an important hallmark, especially in advanced atherosclerosis lesions. Acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT1) promotes foam cell formation by promoting intracellular cholesteryl ester synthesis. The present study tests the hypothesis that oxidized low-density lipoprotein (oxLDL) increases the ACAT1 expression by activating the Toll-like receptor 4 (TLR4)-mediated inflammation, and ultimately promotes VSMC foam cell formation. Wild-type, ApoE^−/−, TLR4^−/− and ACAT1^−/− mice on a C57BL/6J background were used. Increased TLR4, proinflammatory cytokines and ACAT1 were observed in high-fat (HF) diet-induced atherosclerotic plaque formation and in oxLDL-stimulated VSMCs. ACAT1 deficiency impeded the HF diet-induced atherosclerotic plaque formation and impaired the TLR4-manipulated VSMC foam cell formation in response to oxLDL. TLR4 deficiency inhibited the upregulation of myeloid-differentiating factor 88 (MyD88), nuclear factor-κB (NF-κB), proinflammatory cytokines and ACAT1, and eventually attenuated the HF diet-induced atherosclerotic plaque formation and suppressed the oxLDL-induced VSMC foam cell formation. Knockdown of MyD88 and NF-κB, respectively, impaired the TLR4-manipulated VSMC foam cell formation in response to oxLDL. Rosiglitazone (RSG) attenuated HF diet-induced atherosclerotic plaque formation in ApoE^−/− mice, accompanied by reduced expression of TLR4, proinflammatory cytokines and ACAT1 accordingly. Activation of peroxisome proliferator-activated receptor γ (PPARγ) suppressed oxLDL-induced VSMC foam cell formation and inhibited the expression of TLR4, MyD88, NF-κB, proinflammatory cytokines and ACAT1, whereas inhibition of PPARγ exerted the opposite effect. TLR4^−/− mice and VSMCs showed impaired atherosclerotic plaque formation and foam cell formation, and displayed no response to PPARγ manipulation. In conclusion, our data showed that oxLDL stimulation can activate the TLR4/MyD88/NF-κB inflammatory signaling pathway in VSMCs, which in turn upregulates the ACAT1 expression and finally promotes VSMC foam cell formation.Atherosclerosis remains the major cause of deaths worldwide, with deteriorated clinical consequence of cardiovascular diseases including myocardial infarction and stroke.¹ In 2008, for example, 17.3 million deaths were caused by cardiovascular diseases, and this number will increase to 23.3 million by 2030.² Therefore, a better understanding of mechanisms involved in atherosclerosis may advance the development of comprehensive therapeutic regimens.Foam cell formation from macrophages or vascular smooth muscle cells (VSMCs) is a crucial event in the development of atherosclerosis. Acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT1) is an intracellular enzyme that converts free cholesterol into cholesteryl esters for storage in lipid droplets, and promotes foam cell formation in atherosclerotic lesions.^{3, 4, 5} ACAT1 activity is present in a variety of cells and tissues, including the macrophages, neurons, cardiomyocytes, VSMCs, mesothelial cells, alveolar and intestinal epithelial cells and hepatocytes.⁶ In macrophages, the involvement of ACAT1 in foam cell formation has been demonstrated by studies, and multiple molecular mechanisms have been put forward. A well-accepted mechanism is that inflammation increases the expression of ACAT1, promotes the intracellular lipid accumulation and ultimately leads to foam cell formation.⁷ However, in contrast, the mechanisms underlying VSMC foam cell formation, especially the role of ACAT1 in this process, remain largely unelucidated.It is widely accepted that atherosclerosis involves chronic inflammatory reaction.⁸ Toll-like receptor 4 (TLR4), one intensively investigated member of the TLR family, has a critical role in initiating inflammation, and participates in VSMC activation.^{9, 10} Lipopolysaccharide (LPS) is a TLR4-specific ligand that can trigger TLR4-mediated inflammation. A previous study showed that Chlamydia pneumoniae, which contains LPS in its outer membrane, promotes low-density lipoprotein-induced macrophage-derived foam cell formation via upregulation of the expression of ACAT1.¹¹ This further enhanced the association between inflammation and intracellular lipid disorder. However, considering that VSMCs in normal conditions do not have inflammatory properties similar to macrophages, it is unclear whether the TLR4-mediated inflammatory mechanism is also involved in the regulation of ACAT1 in VSMC foam cell formation. Herein, the present study tests the hypothesis that oxidized low-density lipoprotein (oxLDL) increases the ACAT1 expression by activating the TLR4-mediated inflammation, and ultimately promotes VSMC foam cell formation.     

Implications of autophagy for vascular smooth muscle cell function and plasticity

Vascular smooth muscle cells (VSMCs) are fundamental in regulating blood pressure and distributing oxygen and nutrients to peripheral tissues. They also possess remarkable plasticity, with the capacity to switch to synthetic, macrophage-like, or osteochondrogenic phenotypes when cued by external stimuli. In arterial diseases such as atherosclerosis and restenosis, this plasticity seems to be critical and, depending on the disease context, can be deleterious or beneficial. Therefore, understanding the mechanisms regulating VSMC phenotype and survival is essential for developing new therapies for vascular disease as well as understanding how secondary complications due to surgical interventions develop. In this regard, the cellular process of autophagy is increasingly being recognized as a major player in vascular biology and a critical determinant of VSMC phenotype and survival. Although autophagy was identified in lesional VSMCs in the 1960s, our understanding of the implications of autophagy in arterial diseases and the stimuli promoting its activation in VSMCs is only now being elucidated. In this review, we highlight the evidence for autophagy occurring in VSMCs in vivo, elaborate on the stimuli and processes regulating autophagy, and discuss the current understanding of the role of autophagy in vascular disease.