Project description:Cardiovascular disease is the leading cause of death in developed countries and there is compelling evidence that the majority of these fatalities are secondary to rupture of unstable atherosclerotic plaques. However, the mechanisms that control plaque stability are poorly understood, although it is widely believed that plaques having a decreased ratio of cells positive for smooth muscle cell (SMC) markers such as ACTA2 relative to macrophage markers are more likely to rupture. Herein we employMyh11-CreERT2 ROSA floxed STOP eYFP Apoe-/- mice to trace SMC lineage and show that traditional methods for detecting SMCs based on immunostaining for SMC markers like ACTA2 are unable to detect 82% of SMC-derived cells within advanced atherosclerotic lesions. Moreover, we show that these SMC-derived cells within advanced lesions exhibit multiple phenotypes including activation of multiple markers of macrophages, mesenchymal stem cells (MSC), and myofibroblasts (MF). Importantly, we show that SMC-derived macrophage like cells are phagocytic based on electron microscope YFP immunolabeling. In addition, results of single cell epigenetic assays developed in our lab shows that nearly 20% of macrophage-like cells within human lesions are of SMC not myeloid origin. These phenotypic transitions appear to be critical in lesion pathogenesis, in that we show that SMC-specific conditional knockout (KO) of the pluripotency factor, Krüppel-like factor 4 (KLF4), resulted in marked reductions in lesion size, increases in multiple indices of plaque stability, and reduced numbers of SMC-derived MSC- and macrophage-like cells. Finally, we show that cholesterol loading of cultured SMC is associated with activation of multiple markers of macrophages and MSC, secretion of pro-inflammatory cytokines, and increased phagocytosis, all of which are Klf4 dependent. Taken together, results indicate that the contribution of SMCs within atherosclerotic plaques has been greatly underestimated, and that loss of Klf4 within SMC result in major changes in SMC phenotype and function that play a major role in lesion pathogenesis. Examination of KLF4 transcription factor in an atherosclerosis setting

Project description:Atherosclerotic plaques are complex tissues composed of a heterogeneous mixture of cells. However, our understanding of the comprehensive transcriptional and phenotypical landscape of the cells within these lesions is limited. To characterize the landscape of human carotid atherosclerosis in greater detail, we combined cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) and single-cell RNA sequencing (scRNA-seq) to classify all cell types within lesions (n=21; 13 symptomatic) to achieve a comprehensive multimodal understanding of the cellular identities of atherosclerosis and their association with clinical pathophysiology. We identified 25 cell populations, each with a unique multi-omic signature, including macrophages, T cells, NK cells, mast cells, B cells, plasma cells, neutrophils, dendritic cells, endothelial cells, fibroblasts, and smooth muscle cells (SMCs). Among the macrophages, we identified 2 proinflammatory subsets enriched in IL1B or C1Q expression, 2 TREM2 positive foam cells (one expressing inflammatory genes), and subpopulations with a proliferative gene signature and SMC-specific gene signature with fibrotic pathways upregulated. Further characterization revealed various subsets of SMCs and fibroblasts, including SMC-derived foam cells. These foamy SMCs were localized in the deep intima of coronary atherosclerotic lesions. Utilizing CITE-seq data, we developed a flow cytometry panel, using cell surface proteins CD29, CD142, and CD90, to isolate SMC-derived cells from lesions. Lastly, we observed reduced proportions of efferocytotic macrophages, classically activated endothelial cells, and contractile and modulated SMC-derived cells, while inflammatory SMCs were enriched in plaques of clinically symptomatic vs asymptomatic patients. Our multimodal atlas of cell populations within atherosclerosis provides novel insights into the diversity, phenotype, location, isolation, and clinical relevance of the unique cellular composition of human carotid atherosclerosis. These findings facilitate both the mapping of cardiovascular disease susceptibility loci to specific cell types as well as the identification of novel molecular and cellular therapeutic targets for the treatment of the disease.

Project description:BACKGROUND: Vascular smooth muscle cells (VSMC) are the most abundant cell type in the artery’s media layer and regulate vascular tone and lesion remodeling during atherogenesis. Like monocyte-derived macrophages, VSMCs accumulate excess lipids and contribute to the total intimal foam cell population in human coronary plaque and mouse aortic atheroma. While there are extensive studies characterizing the contribution of lipid metabolism in macrophage immunometabolic responses in atherosclerotic plaques, the role of VSMC lipid metabolism in regulating vascular function and lesion remodeling in vivo remains poorly understood. METHODS: We re-analyzed publicly available single-cell RNA sequencing (scRNA-seq) data from mouse atherosclerosis studies and found Liver X receptor (LXR) signaling in VSMCs was continuously activated during atherogenesis. We thus generated mice with an inducible SMC-specific knockout of LXR/LXR on a fate mapping background by crossbreeding LXRf/fLXRf/f mice with Myh11-CreERT2;mTmGf/f mice. Mice were administered with tamoxifen (1 mg/day) for 10 consecutive days and followed by a 2-week resting period to induce CreERT2 mediated recombination. To induce hypercholesterolemia and atherosclerosis, we injected Myh11-CreERT2;mT/mGf/f;LXRf/fLXRf/f mice and Myh11-CreERT2;mT/mGf/f mice with AAV8-PCSK9 and fed them with a Western diet (WD) for 16 weeks. Metabolic, immunocytochemistry and genomic analysis were conducted to assess lesion size and morphology and unravel the molecular mechanism by which LXR in VSMC contributes to lesion formation. RESULTS: Deficiency of LXR in SMCs under hypercholesterolemic condition influenced lesion remodeling by altering the fate of de-differentiated SMC and promoting the accumulation of VSMC-derived transitional cells. This phenotypic switching is accompanied with reduced index of plaque stability characterized by larger necrotic core area and reduced fibrous cap thickness. Moreover, SMC-specific LXR deficiency impaired vascular function and caused visceral myopathy characterized by bladder maladaptive remodeling and gut lipid malabsorption. CONCLUSIONS: We unveil an essential role of hypercholesterolemia-induced LXR signaling in atherosclerotic lesion remodeling, controlling the fate decision of VSMCs and regulating vascular and visceral SMCs functions.

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PRDM16 controls smooth muscle cell fate in atherosclerosis: Fixed-cell scRNAseq datasets [scRNA-seq]

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