Epigenetic Regulation of Phenotypic Plasticity of Vascular Smooth Muscle Cells

血管平滑肌细胞（Vascular smooth muscle cells, SMCs）没有终末分化，具有表型可塑性：分化后，收缩的SMCs可以去分化，也可以合成和增殖，反之亦然。心肌素是一种血清反应因子（SRF）的转录辅激活因子，控制SMC收缩蛋白和microrna （miRs）的表达，促进SMC分化，抑制细胞增殖。包括激素、生长因子和细胞因子在内的许多因素调节SMC的可塑性，但它们如何触发细胞内信号传导以赋予表型转换尚不清楚。有证据表明，表观遗传修饰参与SMC表型调节。例如，DNA甲基化会抑制心肌素基因的表达。DNA甲基化和去甲基化分别由甲基转移酶（DNMT1、3A、3B）和10 - 11易位酶（TET1、2、3）催化。心肌素与其靶基因的去甲基化有关，其中TET2与启动子中的CArG盒结合。然而，SMC表型的表观遗传调控的确切机制在很大程度上仍然未知。基本原理和假设。我们的初步结果显示DNA甲基化在心肌素表达和功能中的作用。我们之前的研究结果也揭示了心肌素诱导miR-1的表达和抑制细胞增殖。因此，我们假设心肌素基因的甲基化和去甲基化决定了心肌素基因的表达，并且心肌素还诱导其靶基因的DNA去甲基化，从而驱动SMC分化并抑制细胞增殖。目标。为了验证上述假设，我们在5年内设定了两个目标：1)研究心肌素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DNMTs和TETs，这些DNMTs和TETs决定了心肌素基因的DNA甲基化水平，有助于调节SMC表型可塑性。2)确定心肌素如何调节其靶基因的DNA甲基化，包括SM收缩蛋白和miRs。我们希望揭示心肌素诱导其靶基因（如SM收缩蛋白和miRs）的去甲基化及其潜在机制。的意义。我们的研究将揭示SMC表型可塑性的一种新的表观遗传机制，这是血管生物学的一项重大进展。

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.