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The stem cell pluripotency genes Klf4 and Oct4 regulate complex SMC phenotypic changes critical in late-stage atherosclerotic lesion pathogenesis

ABSTRACT: Background Rupture or erosion of advanced atherosclerotic lesions with a resultant myocardial infarction or stroke are the leading worldwide cause of death. However, we have a very 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 and Results Using RNAseq and ChIPseq of advanced atherosclerotic lesions from mice, we provide evidence SMC-specific Klf4- versus Oct4-knockout ApoE-/- mice showed virtually opposite genomic signatures and putative SMC Klf4 or Oct4 target genes play an important role regulating SMC phenotypic changes. Further, we conducted a comprehensive single-cell RNA-seq of advanced human carotid endarterectomy samples and compared these with scRNAseq from murine micro-dissected advanced atherosclerotic lesions with SMC and endothelial lineage tracing to survey all plaque cell types and rigorously determine their origin. This analysis revealed remarkable similarity of transcriptomic clusters between mouse and human lesions and extensive plasticity of SMC- and EC-derived lesion cells. The latter included 7 distinct clusters of SMC- and EC-derived cells, 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-specific conditional knockout of Klf4. To study these cells and the mechanisms of their transition, we developed an innovative dual lineage tracing mouse that can uniquely label and genetically target Myh11+ SMC that subsequently activate Lgals3. We observed that SMC that activate Lgals3 comprise up to 2/3 of all SMC in advanced plaques. 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+, ECM-remodeling, “pioneer” cell phenotype that are the first to invest within lesions and subsequently give 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE150644 | GEO | 2020/07/23

REPOSITORIES: GEO

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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:Recent smooth muscle cell (SMC) lineage tracing studies have demonstrated that SMCs undergo remarkable changes in phenotype during development of atherosclerosis, including loss of typical SMC markers such as ACTA2 and Klf4 dependent activation of multiple markers of macrophages and mesenchymal stem cells. Of major interest, we showed Klf4 in SMC is critical for overall lesion pathogenesis as SMC-specific conditional knockout (KO) of Klf4 resulted in smaller, more stable lesions that exhibited marked reductions in the numbers of SMC-derived macrophage-like and mesenchymal stem cell like cells. Herein we tested the hypothesis that Klf4 dependent SMC transitions are beneficial following myocardial infarction (MI). Utilizing SMC-specific lineage tracing mice +/- simultaneous SMC-specific conditional KO of Klf4, we demonstrate that SMCs express Klf4 and transition to a Klf4 dependent macrophage-like state as well as a Klf4 independent myofibroblast-like state. SMC specific, conditional KO of Klf4 resulted in marked exacerbation of heart failure following MI. Surprisingly, significant cardiac dilation was seen in SMC-Klf4 KO mice prior to MI. This cardiac dilation was accompanied by a reduction in peripheral resistance, as evidenced by a reduction in blood pressure, an increase in blood flow, and a larger passive diameter of mesenteric resistance arteries as measured by pressure myography. Klf4 ChIP-Seq analysis on the mesenteric resistance arteries identified potential Klf4 target genes in SMC at baseline in pathways including PDGF and FGF signaling previously shown to be important for perivascular cell investment. Interestingly, examination of microvascular tissue beds revealed gaps in lineage traced SMC coverage along the resistance arteries. Taken together, these results provide novel evidence that Klf4 has a critical maintenance role within microvascular SMCs, including being required for normal SMC coverage of resistance arteries as well as their function.

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The stem cell pluripotency genes Klf4 and Oct4 regulate complex SMC phenotypic changes critical in late-stage atherosclerotic lesion pathogenesis

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