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Background: The Myh11 promoter is extensively used as a smooth muscle cell (SMC) Cre-driver and is regarded as the most restrictive and specific promoter available to study SMCs. Unfortunately, in the existing Myh11-CreER T2 mouse, the transgene was inserted on the Y chromosome precluding the study of female mice. Given the importance of including sex as a biological variable and that numerous SMC-based diseases have a sex-dependent bias, the field has been tremendously limited by the lack of a model to study both sexes. Here, we describe a new autosomal Myh11-CreER T2 mouse (referred to as Myh11-CreER T2 -RAD ), which allows for SMC-specific lineage tracing and gene knockout studies in vivo using both male and female mice. Methods: A Myh11-CreER T2 -RAD transgenic C57BL/6 mouse line was generated using bacterial artificial chromosome clone RP23-151J22 modified to contain a Cre-ER T2 after the Myh11 start codon. Myh11-CreER T2 -RAD mice were crossed with 2 different fluorescent reporter mice and tested for SMC-specific labeling by flow cytometric and immunofluorescence analyses. Results: Myh11-CreER T2 -RAD transgene insertion was determined to be on mouse chromosome 2. Myh11-CreER T2 -RAD fluorescent reporter mice showed Cre-dependent, tamoxifen-inducible labeling of SMCs equivalent to the widely used Myh11-CreER T2 mice. Labeling was equivalent in both male and female Cre + mice and was limited to vascular and visceral SMCs and pericytes in various tissues as assessed by immunofluorescence. Conclusions: We generated and validated the function of an autosomal Myh11-CreER T2 -RAD mouse that can be used to assess sex as a biological variable with respect to the normal and pathophysiological functions of SMCs.

Background: Smooth muscle cells (SMCs) in atherosclerotic plaque take on multiple nonclassical phenotypes that may affect plaque stability and, therefore, the likelihood of myocardial infarction or stroke. However, the mechanisms by which these cells affect stability are only beginning to be explored. Methods: In this study, we investigated the contribution of inflammatory MCP1 (monocyte chemoattractant protein 1) produced by both classical Myh11 (myosin heavy chain 11) + SMCs and SMCs that have transitioned through an Lgals3 (galectin 3) + state in atherosclerosis using smooth muscle lineage tracing mice that label all Myh11 + cells and a dual lineage tracing system that targets Lgals3-transitioned SMC only. Results: We show that loss of MCP1 in all Myh11 + smooth muscle results in a paradoxical increase in plaque size and macrophage content, driven by a baseline systemic monocytosis early in atherosclerosis pathogenesis. In contrast, knockout of MCP1 in Lgals3-transitioned SMCs using a complex dual lineage tracing system resulted in lesions with an increased Acta2 (actin alpha 2, smooth muscle) + fibrous cap and decreased investment of Lgals3-transitioned SMCs, consistent with increased plaque stability. Finally, using flow cytometry and single-cell RNA sequencing, we show that MCP1 produced by Lgals3-transitioned SMCs influences multiple populations of inflammatory cells in late-stage plaques. Conclusions: MCP1 produced by classical SMCs influences monocyte levels beginning early in disease and was atheroprotective, while MCP1 produced by the Lgals3-transitioned subset of SMCs exacerbated plaque pathogenesis in late-stage disease. Results are the first to determine the function of Lgals3-transitioned inflammatory SMCs in atherosclerosis and highlight the need for caution when considering therapeutic interventions involving MCP1.

Women presenting with coronary artery disease (CAD) more often present with fibrous atherosclerotic plaques, which are currently understudied. Phenotypically modulated smooth muscle cells (SMCs) contribute to atherosclerosis in women. How these phenotypically modulated SMCs shape female versus male plaques is unknown. Here, we show sex-stratified gene regulatory networks (GRNs) from human carotid atherosclerotic tissue. Prioritization of these networks identified two main SMC GRNs in late-stage atherosclerosis. Single-cell RNA-sequencing mapped these GRNs to two SMC phenotypes: a phenotypically modulated myofibroblast-like SMC network and a contractile SMC network. The myofibroblast-like GRN was mostly expressed in plaques that were vulnerable in females. Finally, mice orthologs of the female myofibroblast-like genes showed retained expression in advanced plaques from female mice but were downregulated in male mice during atherosclerosis progression. Female atherosclerosis is driven by GRNs that promote a fibrous vulnerable plaque rich in myofibroblast-like SMCs.

TheAWe generated and validated the function of an autosomal

Rationale: Plaque instability remains poorly understood and new therapeutic approaches to reduce plaque rupture and subsequent clinical events are of great interest. Recent studies revealed an important role of phenotypic switching of smooth muscle cells (SMC) in controlling plaque stability, including ECM (extracellular matrix) deposition. Objective: The aim of this study was to elucidate the role of hyaluronan derived from SMC–hyaluronan synthase 3 ( Has3 ), in phenotypic switching and plaque stability in an animal model of atherosclerosis. Methods and Results: A mouse line with SMC-specific deletion of Has3 and simultaneous SMC-lineage tracing ( e YFP [enhanced yellow fluorescent protein]) on an Apoe −/− background was used. Lineage tracing of SMC with e YFP revealed that SMC-specific deletion of Has3 significantly increased the number of LGALS3 + (galectin-3) transition state SMC and decreased ACTA2 + (alpha-smooth muscle actin) SMC. Notably, SMC- Has3 deletion led to significantly increased collagen deposition and maturation within the fibrous cap and the whole lesion, as evidenced by picrosirius red staining and LC-PolScope analysis. Single-cell RNA sequencing of brachiocephalic artery lesions demonstrated that the loss of SMC- Has3 enhanced the transition of SMC to a Lgals3 + , ECM-producing phenotype with elevated acute-phase response gene expression. Experiments using cultured murine aortic SMC revealed that blocking CD44 (cluster of differentiation-44), an important hyaluronan binding receptor, recapitulated the enhanced acute-phase response, and synthesis of fibrous ECM. Conclusions: These studies provide evidence that the deletion of SMC- Has3 results in an ECM-producing transition state SMC phenotype (characterized by LGALS3 + expression), likely via reduced CD44 signaling, resulting in increased collagen formation and maturation, an index consistent with increased plaque stability.

Background: Plaque rupture and erosion of advanced atherosclerotic lesions resulting in ischemic heart disease or stroke are the leading worldwide cause of death. Multiple studies have shown that senescent cells are present in human atherosclerotic lesions, and recent animal studies have claimed that removing senescent cells from the lesions using senolytic agents has some beneficial effects but also limitations. Although these mouse studies have important implications for using senolytic agents to treat atherosclerosis, due to the lack of lineage tracing models and relying on markers not specific for various lesion cell types, it is difficult to ascertain the mechanisms that underline the beneficial effects shown by previous studies. Hypothesis: Treatment of western diet (WD) fed Apoe -/- mice with the senolytic agent ABT-263 (Navitoclax) will reduce lesion size and induce changes consistent with increased plaque stability including a thicker collagen-rich ACTA2 fibrous cap. Methods: SMC (Myh11-ERT2-Cre-eYFP+) and EC (Cdh5-ERT2-Cre-eYFP+) lineage tracing Apoe -/- were fed a WD for 18 weeks, followed by ABT-263 (100MG or 50MG /KG/BW) treatment for six to nine weeks on WD and analyzed for the indices of stability. Results: ABT-263 treatment did not result in changes in lesion size, lumen area, or outward remodeling of the brachiocephalic artery (BCA). However, surprisingly, ABT-263 treatment was associated with an 80% reduction in SMC (Myh11-eYFP+) but a 50-60% increase in endothelial cell (EC) contributions to lesions via EC to mesenchymal transition (EndoMT) (Chd5-eYFP+). ABT-263 treatment also reduced ACTA2 cap thickness by 50-75% and collagen content by 50%, but increased mortality by 50-60%. Conclusions: Taken together, contrary to our hypothesis, the senolytic agent ABT-263 treatment on advanced atherosclerosis showed multiple detrimental effects, including reduced indices of stability, increased Endo-MT, and increased mortality.

Supplemental Digital Content is available in the text., Background: Rupture and erosion of advanced atherosclerotic lesions with a resultant myocardial infarction or stroke are the leading worldwide cause of death. However, we have a limited understanding of the identity, origin, and function of many cells that make up late-stage atherosclerotic lesions, as well as the mechanisms by which they control plaque stability. Methods: We conducted a comprehensive single-cell RNA sequencing of advanced human carotid endarterectomy samples and compared these with single-cell RNA sequencing from murine microdissected advanced atherosclerotic lesions with smooth muscle cell (SMC) and endothelial lineage tracing to survey all plaque cell types and rigorously determine their origin. We further used chromatin immunoprecipitation sequencing (ChIP-seq), bulk RNA sequencing, and an innovative dual lineage tracing mouse to understand the mechanism by which SMC phenotypic transitions affect lesion pathogenesis. Results: We provide evidence that SMC-specific Klf4- versus Oct4-knockout showed virtually opposite genomic signatures, and their putative target genes play an important role regulating SMC phenotypic changes. Single-cell RNA sequencing revealed remarkable similarity of transcriptomic clusters between mouse and human lesions and extensive plasticity of SMC- and endothelial cell-derived cells including 7 distinct clusters, most negative for traditional markers. In particular, SMC contributed to a Myh11-, Lgals3+ population with a chondrocyte-like gene signature that was markedly reduced with SMC-Klf4 knockout. We observed that SMCs that activate Lgals3 compose up to two thirds of all SMC in lesions. However, initial activation of Lgals3 in these cells does not represent conversion to a terminally differentiated state, but rather represents transition of these cells to a unique stem cell marker gene–positive, extracellular matrix-remodeling, “pioneer” cell phenotype that is the first to invest within lesions and subsequently gives rise to at least 3 other SMC phenotypes within advanced lesions, including Klf4-dependent osteogenic phenotypes likely to contribute to plaque calcification and plaque destabilization. Conclusions: Taken together, these results provide evidence that SMC-derived cells within advanced mouse and human atherosclerotic lesions exhibit far greater phenotypic plasticity than generally believed, with Klf4 regulating transition to multiple phenotypes including Lgals3+ osteogenic cells likely to be detrimental for late-stage atherosclerosis plaque pathogenesis.

Aims Until recently, the pluripotency factor Octamer (ATGCAAAT)-binding transcriptional factor 4 (OCT4) was believed to be dispensable in adult somatic cells. However, our recent studies provided clear evidence that OCT4 has a critical atheroprotective role in smooth muscle cells. Here, we asked if OCT4 might play a functional role in regulating endothelial cell (EC) phenotypic modulations in atherosclerosis. Methods and results Specifically, we show that EC-specific Oct4 knockout resulted in increased lipid, LGALS3+ cell accumulation, and altered plaque characteristics consistent with decreased plaque stability. A combination of single-cell RNA sequencing and EC-lineage-tracing studies revealed increased EC activation, endothelial-to-mesenchymal transitions, plaque neovascularization, and mitochondrial dysfunction in the absence of OCT4. Furthermore, we show that the adenosine triphosphate (ATP) transporter, ATP-binding cassette (ABC) transporter G2 (ABCG2), is a direct target of OCT4 in EC and establish for the first time that the OCT4/ABCG2 axis maintains EC metabolic homeostasis by regulating intracellular heme accumulation and related reactive oxygen species production, which, in turn, contributes to atherogenesis. Conclusions These results provide the first direct evidence that OCT4 has a protective metabolic function in EC and identifies vascular OCT4 and its signalling axis as a potential target for novel therapeutics.

Histopathological studies have revealed key processes of atherosclerotic plaque thrombosis. However, the diversity and complexity of lesion types highlight the need for improved sub- phenotyping. We hypothesized that unbiased clustering of plaques based on gene expression results in an alternative categorization of late-stage atherosclerotic lesions.We analyzed the gene expression profiles of 654 advanced human carotid plaques. The unsupervised, transcriptome-driven clustering revealed five dominant plaque types. These novel plaque phenotypes associated with clinical presentation (pIn conclusion, the definition of the plaque at risk for a thrombotic event can be fine-tuned by in- depth transcriptomic based phenotyping. These differential plaque phenotypes prove clinically relevant for both carotid and coronary artery plaques and point to differential underlying biology of symptomatic lesions.

Background and aims The atherosclerotic plaque microenvironment is highly complex, and selective agents that modulate plaque stability are not yet available. We sought to develop a scRNA-seq analysis workflow to investigate this environment and uncover potential therapeutic approaches. We designed a user-friendly, reproducible workflow that will be applicable to other disease-specific scRNA-seq datasets. Methods Here we incorporated automated cell labeling, pseudotemporal ordering, ligand-receptor evaluation, and drug-gene interaction analysis into a ready-to-deploy workflow. We applied this pipeline to further investigate a previously published human coronary single-cell dataset by Wirka et al. Notably, we developed an interactive web application to enable further exploration and analysis of this and other cardiovascular single-cell datasets. Results We revealed distinct derivations of fibroblast-like cells from smooth muscle cells (SMCs), and showed the key changes in gene expression along their de-differentiation path. We highlighted several key ligand-receptor interactions within the atherosclerotic environment through functional expression profiling and revealed several avenues for future pharmacological development for precision medicine. Further, our interactive web application, PlaqView ( www.plaqview.com ), allows lay scientists to explore this and other datasets and compare scRNA-seq tools without prior coding knowledge. Conclusions This publicly available workflow and application will allow for more systematic and user-friendly analysis of scRNA datasets in other disease and developmental systems. Our analysis pipeline provides many hypothesis-generating tools to unravel the etiology of coronary artery disease. We also highlight potential mechanisms for several drugs in the atherosclerotic cellular environment. Future releases of PlaqView will feature more scRNA-seq and scATAC-seq atherosclerosis-related datasets to provide a critical resource for the field, and to promote data harmonization and biological interpretation.

The stem cell pluripotency factor Oct4 serves a critical protective role during atherosclerotic plaque development by promoting smooth muscle cell (SMC) investment. Here, we show using Myh11-CreERT2 lineage-tracing with inducible SMC and pericyte (SMC-P) knockout of Oct4 that Oct4 regulates perivascular cell migration and recruitment during angiogenesis. Knockout of Oct4 in perivascular cells significantly impairs perivascular cell migration, increases perivascular cell death, delays endothelial cell migration, and promotes vascular leakage following corneal angiogenic stimulus. Knockout of Oct4 in perivascular cells also impairs perfusion recovery and decreases angiogenesis following hindlimb ischemia. Transcriptomic analyses demonstrate that expression of the migratory gene Slit3 is reduced following loss of Oct4 in cultured SMCs, and in Oct4-deficient perivascular cells in ischemic hindlimb muscle. Together, these results provide evidence that Oct4 plays an essential role within perivascular cells in injury- and hypoxia-induced angiogenesis., Perivascular cells are essential to the formation and stabilization of new blood vessels during angiogenesis. Here, Hess and Kelly-Goss et al. show that the stem cell pluripotency factor Oct4 promotes perivascular cell survival and migration required for angiogenesis in contexts of tissue injury and hypoxia.

Objective— The goal of this study was to determine the role of ZFP148 (zinc-finger protein 148) in aneurysm formation. Approach and Results— ZFP148 mRNA expression increased at day 3, 7, 14, 21, and 28 after during abdominal aortic aneurysm formation in C57BL/6 mice. Loss of ZFP148 conferred abdominal aortic aneurysm protection using ERTCre+ ZFP148 flx/flx mice. In a third set of experiments, smooth muscle-specific loss of ZFP148 alleles resulted in progressively greater protection using novel transgenic mice (MYH [myosin heavy chain 11] Cre+ flx/flx, flx/wt, and wt/wt). Elastin degradation, LGAL3, and neutrophil staining were significantly attenuated, while α-actin staining was increased in ZFP148 knockout mice. Results were verified in total cell ZFP148 and smooth muscle-specific knockout mice using an angiotensin II model. ZFP148 smooth muscle-specific conditional mice demonstrated increased proliferation and ZFP148 was shown to bind to the p21 promoter during abdominal aortic aneurysm formation. ZFP148 smooth muscle-specific conditional knockout mice also demonstrated decreased apoptosis as measured by decreased cleaved caspase-3 staining. ZFP148 bound smooth muscle marker genes via chromatin immunoprecipitation analysis mediated by NF-1 (neurofibromin 1) promote histone H3K4 deacetylation via histone deacetylase 5. Transient transfections and chromatin immunoprecipitation analyses demonstrated that NF-1 was required for ZFP148 protein binding to smooth muscle marker genes promoters during aneurysm formation. Elimination of NF-1 using shRNA approaches demonstrated that NF-1 is required for binding and elimination of NF-1 increased BRG1 recruitment, the ATPase subunit of the SWI/SWF complex, and increased histone acetylation. Conclusions— ZFP148 plays a critical role in multiple murine models of aneurysm formation. These results suggest that ZFP148 is important in the regulation of proliferation, smooth muscle gene downregulation, and apoptosis in aneurysm development.

Stable atherosclerotic plaques are characterized by a thick, extracellular matrix-rich fibrous cap populated by protective ACTA2+ myofibroblast (MF)-like cells, assumed to be almost exclusively derived from smooth muscle cells (SMCs). Herein, we show that in murine and human lesions, 20% to 40% of ACTA2+ fibrous cap cells, respectively, are derived from non-SMC sources, including endothelial cells (ECs) or macrophages that have undergone an endothelial-to-mesenchymal transition (EndoMT) or a macrophage-to-mesenchymal transition (MMT). In addition, we show that SMC-specific knockout of the Pdgfrb gene, which encodes platelet-derived growth factor receptor beta (PDGFRβ), in Apoe-/- mice fed a Western diet for 18 weeks resulted in brachiocephalic artery lesions nearly devoid of SMCs but with no changes in lesion size, remodelling or indices of stability, including the percentage of ACTA2+ fibrous cap cells. However, prolonged Western diet 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-sequencing analyses of the brachiocephalic artery region and in vitro models, we provide evidence that SMC-to-MF transitions are induced by PDGF and transforming growth factor-β and dependent on aerobic glycolysis, while EndoMT is induced by interleukin-1β and transforming growth factor-β. Together, we provide evidence that the ACTA2+ fibrous cap originates from a tapestry of cell types, which transition to an MF-like state through distinct signalling pathways that are either dependent on or associated with extensive metabolic reprogramming.

Objective:Smooth muscle cells and pericytes display remarkable plasticity during injury and disease progression. Here, we tested the hypothesis that perivascular cells give rise toKlf4-dependent macrophage-like cells that augment adipose tissue (AT) inflammation and metabolic dysfunction associated with diet-induced obesity (DIO).Approach and Results:UsingMyh11-CreERT2eYFP (enhanced yellow fluorescent protein) mice and flow cytometry of the stromovascular fraction of epididymal AT, we observed a large fraction of smooth muscle cells and pericytes lineage traced eYFP+cells expressing macrophage markers. Subsequent single-cell RNA sequencing, however, showed that the majority of these cells had no detectable eYFP transcript. Further exploration revealed that intraperitoneal injection of tamoxifen in peanut oil, used for generating conditional knockout or reporter mice in thousands of previous studies, resulted in large increase in the autofluorescence and false identification of macrophages within epididymal AT as being eYFP+; and unintended proinflammatory consequences. Using newly generatedMyh11-DreERT2tdTomato mice given oral tamoxifen, we virtually eliminated the problem with autofluorescence and identified 8 perivascular cell dominated clusters, half of which were altered upon DIO. Given that perivascular cell KLF4 (kruppel-like factor 4) can have beneficial or detrimental effects, we tested its role in obesity-associated AT inflammation. While smooth muscle cells and pericytes-specificKlf4knockout (smooth muscle cells and pericytesKlf4Δ/Δ) mice were not protected from DIO, they displayed improved glucose tolerance upon DIO, and showed marked decreases in proinflammatory macrophages and increases in LYVE1+lymphatic endothelial cells in the epididymal AT.Conclusions:Perivascular cells within the AT microvasculature dynamically respond to DIO and modulate tissue inflammation and metabolism in a KLF4-dependent manner.

Rationale: Coronary artery disease (CAD) is a major cause of morbidity and mortality worldwide. Recent genome-wide association studies revealed 163 loci associated with CAD. However, the precise molecular mechanisms by which the majority of these loci increase CAD risk are not known. Vascular smooth muscle cells (VSMCs) are critical in the development of CAD. They can play either beneficial or detrimental roles in lesion pathogenesis, depending on the nature of their phenotypic changes. Objective: To identify genetic variants associated with atherosclerosis-relevant phenotypes in VSMCs. Methods and Results: We quantified 12 atherosclerosis-relevant phenotypes related to calcification, proliferation, and migration in VSMCs isolated from 151 multiethnic heart transplant donors. After genotyping and imputation, we performed association mapping using 6.3 million genetic variants. We demonstrated significant variations in calcification, proliferation, and migration. These phenotypes were not correlated with each other. We performed genome-wide association studies for 12 atherosclerosis-relevant phenotypes and identified 4 genome-wide significant loci associated with at least one VSMC phenotype. We overlapped the previously identified CAD loci with our data set and found nominally significant associations at 79 loci. One of them was the chromosome 1q41 locus, which harbors MIA3 . The G allele of the lead risk single nucleotide polymorphism (SNP) rs67180937 was associated with lower VSMC MIA3 expression and lower proliferation. Lentivirus-mediated silencing of MIA3 (melanoma inhibitory activity protein 3) in VSMCs resulted in lower proliferation, consistent with human genetics findings. Furthermore, we observed a significant reduction of MIA3 protein in VSMCs in thin fibrous caps of late-stage atherosclerotic plaques compared to early fibroatheroma with thick and protective fibrous caps in mice and humans. Conclusions: Our data demonstrate that genetic variants have significant influences on VSMC function relevant to the development of atherosclerosis. Furthermore, high MIA3 expression may promote atheroprotective VSMC phenotypic transitions, including increased proliferation, which is essential in the formation or maintenance of a protective fibrous cap.

Atherosclerosis is the process underlying heart attack and stroke. Despite decades of research, its pathogenesis remains unclear. Dogma suggests that atherosclerotic plaques expand primarily via the accumulation of cholesterol and inflammatory cells. However, recent evidence suggests that a substantial portion of the plaque may arise from a subset of “dedifferentiated” vascular smooth muscle cells (SMCs) which proliferate in a clonal fashion. Herein we use multicolor lineage-tracing models to confirm that the mature SMC can give rise to a hyperproliferative cell which appears to promote inflammation via elaboration of complement-dependent anaphylatoxins. Despite being extensively opsonized with prophagocytic complement fragments, we find that this cell also escapes immune surveillance by neighboring macrophages, thereby exacerbating its relative survival advantage. Mechanistic studies indicate this phenomenon results from a generalized opsonin-sensing defect acquired by macrophages during polarization. This defect coincides with the noncanonical up-regulation of so-called don’t eat me molecules on inflamed phagocytes, which reduces their capacity for programmed cell removal (PrCR). Knockdown or knockout of the key antiphagocytic molecule CD47 restores the ability of macrophages to sense and clear opsonized targets in vitro, allowing for potent and targeted suppression of clonal SMC expansion in the plaque in vivo. Because integrated clinical and genomic analyses indicate that similar pathways are active in humans with cardiovascular disease, these studies suggest that the clonally expanding SMC may represent a translational target for treating atherosclerosis.

Retinal diseases are frequently characterized by the accumulation of excessive scar tissue found throughout the neural retina. However, the pathophysiology of retinal fibrosis remains poorly understood, and the cell types that contribute to the fibrotic response are incompletely defined. Here, we show that myofibroblast differentiation of mural cells contributes directly to retinal fibrosis. Using lineage tracing technology, we demonstrate that after chemical ocular injury, Myh11+ mural cells detach from the retinal microvasculature and differentiate into myofibroblasts to form an epiretinal membrane. Inhibition of TGFβR attenuates Myh11+ retinal mural cell myofibroblast differentiation, and diminishes the subsequent formation of scar tissue on the surface of the retina. We demonstrate retinal fibrosis within a murine model of oxygen-induced retinopathy resulting from the intravitreal injection of adipose Myh11-derived mesenchymal stem cells, with ensuing myofibroblast differentiation. In this model, inhibiting TGFβR signaling does not significantly alter myofibroblast differentiation and collagen secretion within the retina. This work shows the complexity of retinal fibrosis, where scar formation is regulated both by TGFβR and non-TGFβR dependent processes involving mural cells and derived mesenchymal stem cells. It also offers a cautionary note on the potential deleterious, pro-fibrotic effects of exogenous MSCs once intravitreally injected into clinical patients.

Thromboembolic events secondary to rupture or erosion of advanced atherosclerotic plaques represent the leading cause of death worldwide. However, the mechanisms that regulate plaque stability are poorly understood. Human pathology studies show that lesions containing a high ratio of ACTA2+ (SM alpha-actin) to CD68+ (cluster of differentiation 68) cells and a thicker ECM (extracellular matrix)-rich fibrous cap are more stable, but there are major ambiguities regarding the origins and functions of ACTA2+ cells within lesions, as well as the mechanisms that regulate their investment and retention in the protective fibrous cap. The overall hypothesis of our Leducq Fondation PlaqOmics Transatlantic Network is that detrimental reprogramming of smooth muscle cells (SMCs) and other ACTA2+ fibrous cap cells destabilizes atherosclerotic plaques and that there are critical genetic determinants of coronary artery disease (CAD) risk that act, in part, by impacting phenotypic transitions of fibrous cap cells. Our ultimate goals are to (1) define distinct SMC phenotypes within human lesions and how these change as a function of lesion severity and vulnerability for rupture or erosion and (2) to use complementary human and mouse studies to determine mechanisms by which these cells impact lesion pathogenesis and to identify novel therapeutic targets that promote beneficial (plaque stabilizing) changes in the phenotype of SMC and other ECM-producing lesion cells.

Epigenetic mechanisms contribute to the regulation of cell differentiation and function. Vascular smooth muscle cells (SMCs) are specialized contractile cells that retain phenotypic plasticity even after differentiation. Here, by performing selective demethylation of histone H3 lysine 4 di-methylation (H3K4me2) at SMC-specific genes, we uncovered that H3K4me2 governs SMC lineage identity. Removal of H3K4me2 via selective editing in cultured vascular SMCs and in murine arterial vasculature led to loss of differentiation and reduced contractility due to impaired recruitment of the DNA methylcytosine dioxygenase TET2. H3K4me2 editing altered SMC adaptative capacities during vascular remodeling due to loss of miR-145 expression. Finally, H3K4me2 editing induced a profound alteration of SMC lineage identity by redistributing H3K4me2 towards genes associated with stemness and developmental programs, thus exacerbating plasticity. Our studies identify the H3K4me2-TET2-miR145 axis as a central epigenetic memory mechanism controlling cell identity and function, whose alteration could contribute to various pathophysiological processes.

Diabetic retinopathy threatens the vision of a third of diabetic patients. Progression of the disease is attributed to the dropout of pericytes, a cell type that enwraps and stabilizes the microvasculature. In tandem with this presumptive pericyte dropout, there is enriched formation of structures assumed to be remnants of collapsed or regressed vessels, previously classified as acellular capillaries, string vessels, and basement membrane bridges. Instead of endothelial cells, we show that pericytes colocalize with basement membrane bridges, and both bridging structures are enriched by cell-specific knockout of KLF4 and reversibly enriched with elevation of Ang-2, PDGF-BB, and blood sugar. Our data suggests that pericyte counts from retinal digests have misclassified pericyte bridges as endothelial structures and have exaggerated the role of pericyte loss in DR progression. In vivo imaging of corneal limbal vessels demonstrates pericyte migration off-vessel, implicating pericyte movement in formation of pericyte bridges and pathogenesis of diabetic retinopathy.

Diabetic retinopathy is a potentially blinding eye disease that threatens the vision of one-ninth of patients with diabetes. Progression of the disease has long been attributed to an initial dropout of pericytes that enwrap the retinal microvasculature. Revealed through retinal vascular digests, a subsequent increase in basement membrane bridges was also observed. Using cell-specific markers, we demonstrate that pericytes rather than endothelial cells colocalize with these bridges. We show that the density of bridges transiently increases with elevation of Ang-2, PDGF-BB, and blood glucose; is rapidly reversed on a timescale of days; and is often associated with a pericyte cell body located off vessel. Cell-specific knockout of KLF4 in pericytes fully replicates this phenotype. In vivo imaging of limbal vessels demonstrates pericyte migration off vessel, with rapid pericyte filopodial-like process formation between adjacent vessels. Accounting for off-vessel and on-vessel pericytes, we observed no pericyte loss relative to nondiabetic control retina. These findings reveal the possibility that pericyte perturbations in location and process formation may play a role in the development of pathological vascular remodeling in diabetic retinopathy.

Objective- Smooth muscle cells (SMCs) are the most abundant cells in human atherosclerotic lesions and are suggested to contribute at least 50% of atheroma foam cells. In mice, SMCs contribute fewer total lesional cells. The purpose of this study was to determine the contribution of SMCs to total foam cells in apolipoprotein E-deficient (ApoE

The results of the CANTOS trial provide exciting evidence in support of the inflammatory hypothesis of atherosclerosis in humans, and is the first phase III clinical trial to show clinical benefit of a targeted anti-inflammatory therapy. However, the modest overall clinical benefit and safety concerns with increased susceptibility to fatal infections indicate that we need much more work in this critical area.

Although somatic cell activation of the embryonic stem cell (ESC) pluripotency factor OCT4 has been reported, this previous work has been controversial and has not demonstrated a functional role for OCT4 in somatic cells. Here we demonstrate that smooth muscle cell (SMC)-specific conditional knockout of Oct4 in Apoe(-/-) mice resulted in increased lesion size and changes in lesion composition that are consistent with decreased plaque stability, including a thinner fibrous cap, increased necrotic core area, and increased intraplaque hemorrhage. Results of SMC-lineage-tracing studies showed that these effects were probably the result of marked reductions in SMC numbers within lesions and SMC investment within the fibrous cap, which may result from impaired SMC migration. The reactivation of Oct4 within SMCs was associated with hydroxymethylation of the Oct4 promoter and was hypoxia inducible factor-1α (HIF-1α, encoded by HIF1A) and Kruppel-like factor-4 (KLF4)-dependent. These results provide the first direct evidence that OCT4 has a functional role in somatic cells, and they highlight the potential role of OCT4 in normal and diseased somatic cells.

The historical view of vascular smooth muscle cells (VSMCs) in atherosclerosis is that aberrant proliferation of VSMCs promotes plaque formation, but that VSMCs in advanced plaques are entirely beneficial, for example preventing rupture of the fibrous cap. However, this view has been based on ideas that there is a homogenous population of VSMCs within the plaque, that can be identified separate from other plaque cells (particularly macrophages) using standard VSMC and macrophage immunohistochemical markers. More recent genetic lineage tracing studies have shown that VSMC phenotypic switching results in less-differentiated forms that lack VSMC markers including macrophage-like cells, and this switching directly promotes atherosclerosis. In addition, VSMC proliferation may be beneficial throughout atherogenesis, and not just in advanced lesions, whereas VSMC apoptosis, cell senescence, and VSMC-derived macrophage-like cells may promote inflammation. We review the effect of embryological origin on VSMC behavior in atherosclerosis, the role, regulation and consequences of phenotypic switching, the evidence for different origins of VSMCs, and the role of individual processes that VSMCs undergo in atherosclerosis in regard to plaque formation and the structure of advanced lesions. We think there is now compelling evidence that a full understanding of VSMC behavior in atherosclerosis is critical to identify therapeutic targets to both prevent and treat atherosclerosis.

Various hypertensive stimuli lead to exuberant adventitial collagen deposition in large arteries, exacerbating blood pressure elevation and end-organ damage. Collagen production is generally attributed to resident fibroblasts; however, other cells, including resident and bone marrow-derived stem cell antigen positive (Sca-1 + ) cells and endothelial and vascular smooth muscle cells, can produce collagen and contribute to vascular stiffening. Using flow cytometry and immunofluorescence, we found that adventitial Sca-1 + progenitor cells begin to produce collagen and acquire a fibroblast-like phenotype in hypertension. We also found that bone marrow-derived cells represent more than half of the matrix-producing cells in hypertension, and that one-third of these are Sca-1 + . Cell sorting and lineage-tracing studies showed that cells of endothelial origin contribute to no more than one fourth of adventitial collagen I + cells, whereas those of vascular smooth muscle lineage do not contribute. Our findings indicate that Sca-1 + progenitor cells and bone marrow-derived infiltrating fibrocytes are major sources of arterial fibrosis in hypertension. Endothelial to mesenchymal transition likely also contributes, albeit to a lesser extent and pre-existing resident fibroblasts represent a minority of aortic collagen-producing cells in hypertension. This study shows that vascular stiffening represents a complex process involving recruitment and transformation of multiple cells types that ultimately elaborate adventitial extracellular matrix.

Vascular smooth muscle cells (SMCs), like all cells, acquire a cell-specific epigenetic signature during development that includes acquisition of a unique repertoire of histone and DNA modifications. These changes are postulated to induce an open chromatin state (referred to as euchromatin) on the repertoire of genes that are expressed in differentiated SMC, including SMC-selective marker genes like Acta2 and Myh11, as well as housekeeping genes expressed by most cell types. In contrast, genes that are silenced in differentiated SMC acquire modifications associated with a closed chromatin state (ie, heterochromatin) and transcriptional silencing. Herein, we review mechanisms that regulate epigenetic control of the differentiated state of SMC. In addition, we identify some of the major limitations in the field and future challenges, including development of innovative new tools and approaches, for performing single-cell epigenetic assays and locus-selective editing of the epigenome that will allow direct studies of the functional role of specific epigenetic controls during development, injury repair, and disease, including major cardiovascular diseases, such as atherosclerosis, hypertension, and microvascular disease, associated with diabetes mellitus.

Many studies have noted similarities between atherosclerosis and cancer including pronounced cellular plasticity, clonal expansion of cellular subtypes, increased DNA mutations, defective efferocytosis pathways, and an important role for proto-oncogenes in disease development. Although it is clear that these 2 diseases have disparate causes, noting the parallels between atherosclerosis and cancer may help us identify unique, targeted therapeutic strategies. Early articles described atheromas as benign neoplasms of the blood vessel comprised primarily of fibrous smooth muscle cells (SMCs). However, additional studies soon noted the presence of macrophages and other cell types, thereby promoting controversy as to which cells actually give rise to the atherosclerotic plaque. Much of this controversy results from the promiscuity of the so-called lineage-specific markers.1 For example, bone marrow–derived cells can migrate into plaques and begin to express certain SMC markers,2 whereas SMCs can upregulate macrophage-specific markers such as galectin-3, CD11b, and F4/80 as they migrate into the plaque.3,4 In addition, recent lineage tracing studies suggest that endothelial cells can acquire mesenchymal cell characteristics, and some adventitial cells may have the capability of forming SMC-like cells. Collectively, these studies demonstrate the impressive capacity of many vascular cell types to dedifferentiate or transdifferentiate in response to the atherosclerotic environment and suggest that plaques may arise from multiple vascular and circulating cell types. Clearly, cellular plasticity is a major theme in atherosclerotic plaque development—as it is in cancer—and methods to reprogram proatherosclerotic cells could have tremendous therapeutic potential. The clonal evolution theory of cancer development posits that certain tumors arise from a single cell that expands in response to a series of acquired mutations. In 1973, Benditt and Benditt5 performed X-inactivation studies on human atherosclerotic lesions and found evidence that atherosclerotic plaques could be derived from a single cell that underwent monoclonal expansion, …

Atherosclerosis is a disease of chronic inflammation and the leading cause of morbidity and mortality worldwide. Despite decades of research, our understanding of the mechanisms regulating plaque stability remains poor. Until recently, smooth muscle cells (SMCs) were thought to play an athero-protective role in lesion pathogenesis. However, rigorous lineage tracing has shown a significant portion (>80%) of SMC-derived cells within an advanced atherosclerotic lesion did not express detectable SMC markers. Furthermore, SMC-specific conditional KO of Klf4 resulted in reduction of several indices of plaque instability and SMC-derived macrophage-like cells. In contrast, conditional KO of Oct4 in SMCs presented a reduction of SMC and increased of Lgals3+ cells within lesions, as well as increase of several indices of plaque instability. Taken together, SMCs can have a beneficial or detrimental effect in lesion pathogenesis. Hypothesis: Combinatorial analysis of Oct4/Klf4 ChIP-seq and RNA-seq of advanced atherosclerotic lesions from our SMC-Klf4 and SMC-Oct4 mice provide a unique opportunity to identify genes that play a critical role in regulating beneficial or detrimental changes in SMC phenotype. Results: SMC-Oct4 target genes are enriched for migration pathways, while SMC-Klf4 target genes are enriched for inflammation pathways. Further, atherosclerosis pathway, among others, presented significant opposite patterns (SMC-Oct4-KO up-regulation and SMC-Klf4-KO down-regulation), and presented strong significant gene anti-correlation, corroborating our phenotypic observations. Remarkably, we cross-reference our ChIP-seq datasets with CAD GWAS and found that 54 of the 161 human loci were either Klf4 and/or Oct4 SMC targets, highly suggesting that CAD GWAS genes might be affecting SMC function in lesion development/pathogenesis. To validate our results, we used the STARNET dataset, and we observed that both Oct4 and Klf4 are significantly up-regulated in aorta of CAD patients compared to controls. In addition, co-expression analysis shows that one of the Klf4 network is highly related to human GWAS CAD, including genes such as LDLR, APOE, PCSK9, TRIB1, and others. Surprisingly, more than 35% of genes in this network also are present in our SMC Klf4 ChIP-seq dataset. Conclusions: our results suggests that: late stage atherosclerotic lesions of mouse and humans seems to be more similar than previously thought; and nearly 1/3 of CAD GWAS loci appear to be affecting SMC function and are potentially Klf4/Oct4-dependent.

Despite decades of research, our understanding of the processes controlling late-stage atherosclerotic plaque stability remains poor. A prevailing hypothesis is that reducing inflammation may improve advanced plaque stability, as recently tested in the Canakinumab Anti-inflammatory Thrombosis Outcome Study (CANTOS) trial, in which post-myocardial infarction subjects were treated with an IL-1β antibody. Here, we performed intervention studies in which smooth muscle cell (SMC) lineage-tracing Apoe-/- mice with advanced atherosclerosis were treated with anti-IL-1β or IgG control antibodies. Surprisingly, we found that IL-1β antibody treatment between 18 and 26 weeks of Western diet feeding induced a marked reduction in SMC and collagen content, but increased macrophage numbers in the fibrous cap. Moreover, although IL-1β antibody treatment had no effect on lesion size, it completely inhibited beneficial outward remodeling. We also found that SMC-specific knockout of Il1r1 (encoding IL-1 receptor type 1) resulted in smaller lesions nearly devoid of SMCs and lacking a fibrous cap, whereas macrophage-selective loss of IL-1R1 had no effect on lesion size or composition. Taken together, these results show that IL-1β has multiple beneficial effects in late-stage murine atherosclerosis, including promotion of outward remodeling and formation and maintenance of an SMC- and collagen-rich fibrous cap.

Smooth muscle cells (SMC) are conventionally thought to promote atherosclerotic plaque stability by investing within the fibrous cap and protecting the blood flow from the harmful inflammatory plaque core. However, lineage tracing studies have shown that SMC in plaque can undergo a Klf4-dependent transition in vivo to a macrophage-like state, characterized by loss of SMC markers and expression of multiple macrophage markers, lipid accumulation, and phagocytic activity. Of major interest, SMC induced to the macrophage state in vitro by cholesterol loading also show increased production of the atheropromoting cytokine MCP1 (Monocyte chemoattractant protein 1). These results are surprising since it has been largely assumed that monocyte derived macrophages are the major source of MCP1 and that this acts to exacerbate lesion pathogenesis by inducing recruitment of additional circulating monocytes. Using MCP1-mCherry reporter mice on an ApoE -/- background, we show that MCP1 is highly expressed by medial and fibrous cap SMC. Further, we show that SMC-specific KLF4 knockout mice, which show marked reductions in the frequency of SMC-derived macrophages, show a 50% decrease in MCP1 immunostaining in late stage atherosclerotic lesions, suggesting that these cells are a major source of MCP-1 and produce it via a Klf4-dependent mechanism. Consistent with this possibility, we demonstrated that SMC-specific tamoxifen conditional MCP1 knockout mice on an ApoE -/- background (Myh11-CreERT2 eYFP ApoE -/- MCP1-mCherry), showed greatly decreased total MCP1 protein level within the aorta. We are currently completing examination of the effects of SMC specific MCP1 KO on late stage lesion pathogenesis in our Myh11-CreERT2 eYFP ApoE -/- MCP1-mCherry mice following 18 weeks of Western diet feeding. Taken together results provide evidence that SMC derived cells are an unexpected major source of MCP1 within lesions.

Objective: Angiogenesis requires coordinated migration of endothelial cells (EC) and perivascular cells, including smooth muscle cells and pericytes (SMC-P). Perivascular cell-specific mechanisms by which SMC-P migrate and invest EC remain largely unknown. Herein, we used Myh11-CreER T2 SMC-P lineage tracing, combined with SMC-P specific knockout of the stem cell pluripotency gene Oct4, to test the hypothesis that SMC-P derived Oct4 regulates perivascular cell migration and recruitment necessary for angiogenesis. Methods and Results: Myh11-CreER T2 ROSA floxed STOP eYFP Oct4 WT/WT and Myh11-CreER T2 ROSA floxed STOP eYFP Oct4 FL/FL littermate mice were injected with tamoxifen from 6-8 weeks of age to permanently label Myh11-expressing cells with eYFP, without or with Oct4 KO, respectively. Mice were subjected to either corneal alkali burn or hindlimb ischemia (HLI), monitored by live confocal imaging and laser doppler perfusion respectively, and sacrificed for tissue analysis. SMC-P Oct4 KO resulted in markedly impaired eYFP+ (SMC-P derived) migration and increased vascular leak following corneal alkali burn. EC neovascular area and migration distance were also significantly decreased in SMC-P specific Oct4 KO mice. Following HLI, SMC-P Oct4 KO mice had impaired perfusion recovery and decreased capillary density. Slit3 was expressed in eYFP+ cells of the microvasculature in both cornea and muscle and was downregulated following Oct4 KO. RNA-seq and qRT-PCR analysis of cultured SMC revealed dysregulation of Slit3 as well as additional members of the Slit-Robo pathway of guidance genes, including downregulation of the receptors Robo1 and Robo2 and upregulation of Slit2 following loss of Oct4. Conclusions: Taken together, we demonstrate that SMC-P derived Oct4 is essential for angiogenesis in both corneal alkali burn and HLI models. These effects are at least partially due to Oct4-dependent regulation of the Slit-Robo pathway in SMC-P, with Oct4 KO resulting in dysregulated migration of both EC and SMC-P. To our knowledge, this is the first direct evidence that loss of a single gene exclusively in SMC-P impacts angiogenesis following injury.

Recent smooth muscle cell (SMC) lineage-tracing studies have revealed that SMCs undergo remarkable changes in phenotype during development of atherosclerosis. Of major interest, we demonstrated that Kruppel-like factor 4 (KLF4) in SMCs is detrimental for overall lesion pathogenesis, in that SMC-specific conditional knockout of the KLF4 gene ( Klf4) resulted in smaller, more-stable lesions that exhibited marked reductions in the numbers of SMC-derived macrophage- and mesenchymal stem cell-like cells. However, since the clinical consequences of atherosclerosis typically occur well after our reproductive years, we sought to identify beneficial KLF4-dependent SMC functions that were likely to be evolutionarily conserved. We tested the hypothesis that KLF4-dependent SMC transitions play an important role in the tissue injury-repair process. Using SMC-specific lineage-tracing mice positive and negative for simultaneous SMC-specific conditional knockout of Klf4, we demonstrate that SMCs in the remodeling heart after ischemia-reperfusion injury (IRI) express KLF4 and transition to a KLF4-dependent macrophage-like state and a KLF4-independent myofibroblast-like state. Moreover, heart failure after IRI was exacerbated in SMC Klf4 knockout mice. Surprisingly, we observed a significant cardiac dilation in SMC Klf4 knockout mice before IRI as well as a reduction in peripheral resistance. KLF4 chromatin immunoprecipitation-sequencing analysis on mesenteric vascular beds identified potential baseline SMC KLF4 target genes in numerous pathways, including PDGF and FGF. Moreover, microvascular tissue beds in SMC Klf4 knockout mice had gaps in lineage-traced SMC coverage along the resistance arteries and exhibited increased permeability. Together, these results provide novel evidence that Klf4 has a critical maintenance role within microvascular SMCs: it is required for normal SMC function and coverage of resistance arteries. NEW & NOTEWORTHY We report novel evidence that the Kruppel-like factor 4 gene ( Klf4) has a critical maintenance role within microvascular smooth muscle cells (SMCs). SMC-specific Klf4 knockout at baseline resulted in a loss of lineage-traced SMC coverage of resistance arteries, dilation of resistance arteries, increased blood flow, and cardiac dilation.

The long-term adverse effects of radiotherapy on cardiovascular disease are well documented. However, the underlying mechanisms responsible for this increased risk are poorly understood. Previous studies using rigorous smooth muscle cell (SMC) lineage tracing have shown abundant SMC investment into atherosclerotic lesions, where SMCs contribute to the formation of a protective fibrous cap. Studies herein tested whether radiation impairs protective adaptive SMC responses during vascular disease. To do this, we exposed SMC lineage tracing (Myh11-ERT2Cre YFP+) mice to lethal radiation (1,200 cGy) followed by bone marrow transplantation prior to atherosclerosis development or vessel injury. Surprisingly, following irradiation, we observed a complete loss of SMC investment in 100% of brachiocephalic artery (BCA), carotid artery, and aortic arch lesions. Importantly, this was associated with a decrease in multiple indices of atherosclerotic lesion stability within the BCA. Interestingly, we observed anatomic heterogeneity, as SMCs accumulated normally into lesions of the aortic root and abdominal aorta, suggesting that SMC sensitivity to lethal irradiation occurs in blood vessels of neural crest origin. Taken together, these results reveal an undefined and unintended variable in previous studies using lethal irradiation and may help explain why patients exposed to radiation have increased risk for cardiovascular disease.

Atherosclerosis occurs in the subendothelial space (intima) of medium-sized arteries at regions of disturbed blood flow and is triggered by an interplay between endothelial dysfunction and subendothelial lipoprotein retention. Over time, this process stimulates a nonresolving inflammatory response that can cause intimal destruction, arterial thrombosis, and end-organ ischemia. Recent advances highlight important cell biological atherogenic processes, including mechanotransduction and inflammatory processes in endothelial cells, origins and contributions of lesional macrophages, and origins and phenotypic switching of lesional smooth muscle cells. These advances illustrate how in-depth mechanistic knowledge of the cellular pathobiology of atherosclerosis can lead to new ideas for therapy.

Objective— The impact of leukotriene production by the 5-lipoxygenase (5-LO) pathway in the pathophysiology of abdominal aortic aneurysms (AAAs) has been debated. Moreover, a clear mechanism through which 5-LO influences AAA remains unclear. Approach and Results— Aneurysm formation was attenuated in 5-LO –/– mice, and in lethally irradiated wild-type mice reconstituted with 5-LO –/– bone marrow in an elastase perfusion model. Pharmacological inhibition of 5-LO–attenuated aneurysm formation in both aortic elastase perfused wild-type and angiotensin II–treated LDLr –/– (low-density lipoprotein receptor) mice, with resultant preservation of elastin and fewer 5-LO and MMP9 (matrix metalloproteinase)-producing cells. Separately, analysis of wild-type mice 7 days after elastase perfusion showed that 5-LO inhibition was associated with reduced polymorphonuclear leukocyte infiltration to the aortic wall. Importantly, 5-LO inhibition initiated 3 days after elastase perfusion in wild-type mice arrested progression of small AAA. Human AAA and control aorta corroborated these elastin and 5-LO expression patterns. Conclusions— Inhibition of 5-LO by pharmacological or genetic approaches attenuates aneurysm formation and prevents fragmentation of the medial layer in 2 unique AAA models. Administration of 5-LO inhibitor in small AAA slows progression of AAA. Targeted interruption of the 5-LO pathway is a potential treatment strategy in AAA.

Objective— Cigarette smoke exposure (CSE) is a risk factor for cerebral aneurysm (CA) formation, but the molecular mechanisms are unclear. Although CSE is known to contribute to excess reactive oxygen species generation, the role of oxidative stress on vascular smooth muscle cell (VSMC) phenotypic modulation and pathogenesis of CAs is unknown. The goal of this study was to investigate whether CSE activates a NOX (NADPH oxidase)-dependent pathway leading to VSMC phenotypic modulation and CA formation and rupture. Approach and Results— In cultured cerebral VSMCs, CSE increased expression of NOX1 and reactive oxygen species which preceded upregulation of proinflammatory/matrix remodeling genes (MCP-1, MMPs [matrix metalloproteinase], TNF-α, IL-1β, NF-κB, KLF4 [Kruppel-like factor 4]) and downregulation of contractile genes (SM-α-actin [smooth muscle α actin], SM-22α [smooth muscle 22α], SM-MHC [smooth muscle myosin heavy chain]) and myocardin. Inhibition of reactive oxygen species production and knockdown of NOX1 with siRNA or antisense decreased CSE-induced upregulation of NOX1 and inflammatory genes and downregulation of VSMC contractile genes and myocardin. p47phox −/− NOX knockout mice, or pretreatment with the NOX inhibitor, apocynin, significantly decreased CA formation and rupture compared with controls. NOX1 protein and mRNA expression were similar in p47phox −/− mice and those pretreated with apocynin but were elevated in unruptured and ruptured CAs. CSE increased CA formation and rupture, which was diminished with apocynin pretreatment. Similarly, NOX1 protein and mRNA and reactive oxygen species were elevated by CSE, and in unruptured and ruptured CAs. Conclusions— CSE initiates oxidative stress-induced phenotypic modulation of VSMCs and CA formation and rupture. These molecular changes implicate oxidative stress in the pathogenesis of CAs and may provide a potential target for future therapeutic strategies.

Atherosclerosis is the leading cause of death in Western civilization accounting for more than 40% of all deaths. Despite reduced death rates due in part to statin treatment, there is little understanding of the molecular and cellular mechanisms that can help to reverse atherosclerotic development and/or decrease the chances of plaque rupture with associated clinical sequelae such as myocardial infarction or stroke. We recently demonstrated a functional role of the pluripotency factor OCT4 in smooth muscle cells (SMCs) during atherosclerosis, in that SMC-specific conditional Oct4 knockout mice exhibit marked alterations in lesion size and cellular composition within atherosclerotic lesions of Apoe -/- high-fat diet fed mice, including a thinner fibrous cap, increased necrotic core and increased intra-plaque hemorrhage. Results of SMC-lineage tracing studies show that these changes were likely due to marked reductions in SMC number within lesions including in the fibrous cap area, as well as significant increases in macrophage-like (LGALS3 + ) SMCs within the tunica media. Further studies show that inactivation of Oct4 in SMCs nearly completely abrogated the pro-atherogenic oxidized phospholipid POVPC-induced migration of SMCs in vitro and outgrowth of SMCs from aortic explants ex vivo. RNA-seq and ChIP-seq analyses of lesion specimens from Apoe -/- high-fat diet fed mice and cultured SMCs treated with POVPC or 1% O 2 hypoxia show that loss of Oct4 in SMCs was associated with marked activation of genes associated with inflammation and phagocytosis, and suppression of genes associated with cell migration, including extracellular matrix proteins, matrix metalloproteinases and multiple axon guidance molecules. Moreover, loss of Oct4 significantly increased ability of SMCs to phagocyte red blood cells in response to oxidized LDL treatment in vitro . Results advance our understanding of mechanisms by which OCT4 expression in SMCs impacts atherosclerosis lesion development and may help identify novel potential therapeutic targets for treatment of atherosclerosis.

Atherosclerotic plaque rupture with subsequent embolic events is a major cause of sudden death from myocardial infarction or stroke. Although smooth muscle cells (SMCs) produce and respond to collagens in vitro, there is no direct evidence in vivo that SMCs are a crucial source of collagens and that this impacts lesion development or fibrous cap formation. We sought to determine how conditional SMC-specific knockout of collagen type XV (COL15A1) in SMC lineage tracing mice affects advanced lesion formation given that 1) we have previously identified a Col15a1 sequence variant associated with age-related atherosclerosis, 2) COL15A1 is a matrix organizer enhancing tissue structural integrity, and 3) small interfering RNA-mediated Col15a1 knockdown increased migration and decreased proliferation of cultured human SMCs. We hypothesized that SMC-derived COL15A1 is critical in advanced lesions, specifically in fibrous cap formation. Surprisingly, we demonstrated that SMC-specific Col15a1 knockout mice fed a Western diet for 18 wk failed to form advanced lesions. SMC-specific Col15a1 knockout resulted in lesions reduced in size by 78%, with marked reductions in numbers and proliferating SMCs, and lacked a SMC and extracellular matrix-rich lesion or fibrous cap. In vivo RNA-seq analyses on SMC Col15a1 knockout and wild-type lesions suggested that a mechanism for these effects is through global repression of multiple proatherogenic inflammatory pathways involved in lesion development. These results provide the first direct evidence that a SMC-derived collagen, COL15A1, is critical during lesion pathogenesis, but, contrary to expectations, its loss resulted in marked attenuation rather than exacerbation of lesion pathogenesis. NEW & NOTEWORTHY We report the first direct in vivo evidence that a smooth muscle cell (SMC)-produced collagen, collagen type XV (COL15A1), is critical for atherosclerotic lesion development. SMC Col15a1 knockout markedly attenuated advanced lesion formation, likely through reducing SMC proliferation and impairing multiple proatherogenic inflammatory processes.

Could improving the design of preclinical murine atherosclerosis studies help increase the success rate of cardiovascular clinical trials? In this Viewpoint, the authors advocate for a change from prevention to intervention study designs and rigorous lesion analyses that they argue will enhance the translational potential of murine atherosclerosis studies. Clinical management of patients with coronary artery disease (CAD) has made great progress by reducing risk factors like low-density lipoprotein cholesterol level, hypertension, and diabetes mellitus. However, late-stage events associated with coronary atherosclerosis including myocardial infarction still account for ≈16% of worldwide mortality and are forecasted to increase in prevalence.1 These events arise from 3 main processes: plaque rupture, plaque erosion, and shedding of calcific nodules. Plaque rupture accounts for the majority of CAD and typically occurs in vulnerable atherosclerotic lesions termed thin-capped fibroatheromas,2 characterized by thin fibrous caps (