Epigenetic Regulation of Phenotypic Plasticity of Vascular Smooth Muscle Cells

血管平滑肌细胞(SMCs)不是终末分化的，具有表型可塑性：分化的、收缩的SMCs可以经历去分化、合成和增殖，反之亦然。Myocardin是血清反应因子(SRF)的转录共激活因子，调控SMC收缩蛋白和microRNAs(MiRs)的表达，促进SMC分化，抑制细胞增殖。许多因素包括激素、生长因子和细胞因子调节SMC的可塑性，但它们如何触发细胞内信号传递表型转换却知之甚少。 有证据表明表观遗传修饰参与了SMC的表型调控。例如，DNA甲基化抑制了myocardin基因的表达。DNA甲基化和去甲基化分别由甲基转移酶(DNMT1、3A、3B)和十-十一易位酶(TET1、2、3)催化。Myocardin与其目标基因的去甲基化有关，在该过程中，TET2与启动子中的Carg盒结合。然而，表观遗传调控SMC表型的确切机制在很大程度上仍不清楚。 理论基础和假设。我们的初步结果表明，DNA甲基化在肌钙蛋白的表达和功能中起到了作用。我们先前的发现还表明，myocardin诱导miR-1表达并抑制细胞增殖。因此，我们假设myocardin基因的甲基化和去甲基化决定了myocardin基因的表达，并且myocardin还诱导其靶基因的DNA去甲基化，从而促进SMC的分化和抑制细胞的增殖。 目标。为了检验上述假设，我们在5年内设定了两个目标： 1)探讨Myocardin基因甲基化和去甲基化在SMC表型可塑性中的作用。我们希望发现或揭示特定的DNMT和Tets，它们决定了myocardin基因的DNA甲基化水平，有助于调节SMC表型可塑性。 2)确定myocardin如何调节其靶基因的DNA甲基化，包括SM收缩蛋白和miRs。我们希望揭示Myocardin诱导其靶基因如SM收缩蛋白和miRs去甲基化及其潜在机制。 意义重大。我们的研究将揭示SMC表型可塑性背后的一种新的表观遗传学机制，代表着血管生物学的重大进展。

Vascular smooth muscle cells (SMCs) are not terminally differentiated and have phenotypic plasticity: differentiated, contractile SMCs can undergo dedifferentiation and become synthetic and proliferative, and vice versa. Myocardin, a transcriptional coactivator of serum response factor (SRF), controls the expression of SMC contractile proteins and microRNAs (miRs) to promote SMC differentiation and inhibit cell proliferation. Many factors including hormones, growth factors and cytokines regulate SMC plasticity, but how they trigger intracellular signaling to confer phenotypic switching is poorly understood. Evidence suggests that epigenetic modification participates in SMC phenotype regulation. DNA methylation, for example, inhibits myocardin gene expression. DNA methylation and demethylation are catalyzed by methyltransferases (DNMT1, 3A, 3B) and ten-eleven translocation (TET1, 2, 3) enzymes, respectively. Myocardin is associated with demethylation of its target genes, in which TET2 binds to CArG boxes in the promoters. However, the exact mechanisms underlying epigenetic regulation of SMC phenotypes remain largely unknown. Rationale and hypothesis. Our preliminary results showed a role for DNA methylation in myocardin expression and functions. Our previous findings also revealed myocardin induction of miR-1 expression and inhibition of cell proliferation. Therefore, we hypothesize that myocardin gene methylation and demethylation determines myocardin gene expression and that myocardin also induces DNA demethylation of its target genes, driving SMC differentiation and inhibiting cell proliferation. Objectives. To test the above hypotheses, we set up two aims over 5 years: 1) Investigate the roles for myocardin gene methylation and demethylation in SMC phenotypic plasticity. We expect to discover or reveal the specific DNMTs and TETs that dictate the DNA methylation level of the myocardin gene, contributing to the regulation of SMC phenotypic plasticity. 2) Determine how myocardin modulates DNA methylation of its target genes, including SM contractile proteins and miRs. We expect to reveal myocardin induction of demethylation of its target genes, such as SM contractile proteins and miRs, and the underlying mechanisms. Significance. Our studies will uncover a novel epigenetic mechanism underlying SMC phenotypic plasticity, representing a major advancement in vascular biology.