组蛋白变异体H2A.Z在血管平滑肌细胞表型转化中的作用及其机制研究

Phenotypic switching of vascular smooth muscle cells (VSMCs) is a key event in vascular homeostasis and remodeling. Although recent studies uncovered critical roles of chromatin regulation in vascular development and diseases, it still remains to be elucidated how they form a cohesive regulatory network. In particular, how histone variants contribute to this network remains unknown. Our preliminary results showed that H2A.Z expression was markedly decreased in atherosclerotic lesions. In addition, H2A.Z selectively occupied VSMC marker genes, and its depletion resulted in a dramatic reduction in their expression. Therefore, we hypothesize that H2A.Z plays a pivotal role in vascular homeostasis, and that downregulation of H2A.Z is a key molecular event in vascular diseases. To test our hypothesis, we will first confirm the role of H2A.Z in VSMC phenotypic switching, and uncover the underlying mechanisms by genomic approaches. Then, we will dissect how H2A.Z incorporates into the molecular regulatory network in VSMC fate decisions. Finally, we will evaluate whether manipulation of H2A.Z is capable of ameliorating neointima formation in a mouse femur artery injury model. Findings from this study will reveal the role of histone variants in VSMC phenotypic switching, further our understanding of the molecular basis of vascular homeostasis and remodeling, and provide novel insights into the prevention and intervention of vascular diseases.

血管平滑肌细胞表型转化是血管稳态与重构中的关键分子事件。研究提示染色质调控在血管发育与疾病中发挥着重要作用，但是其作用机制并未系统阐明，尤其是组蛋白变异体的作用尚未报导。我们发现组蛋白变异体H2A.Z在人动脉粥样硬化斑块中表达明显降低，进一步发现H2A.Z选择性地结合在血管平滑肌细胞特异性基因的染色质，敲低H2A.Z导致这些基因表达显著下降。据此推测，H2A.Z在维持血管稳态中发挥着重要作用，其表达下降是血管疾病发生的重要分子事件。为验证此假设，拟首先确定H2A.Z在血管平滑肌细胞表型转化中的作用，并进一步通过基因组学方法明确其机制；接着阐明H2A.Z如何整合到动态的分子调控网络；最后在小鼠疾病模型中调控H2A.Z的表达量探讨干预疾病发生的可能。本研究将揭示组蛋白变异体如何影响血管平滑肌细胞的表型转化，完善我们对于血管稳态与重构的分子调控网络的理解，并为血管疾病的预防与治疗提供新的思路。

血管平滑肌表型转化在血管疾病如动脉粥样硬化中发挥着重要作用，尽管以往有研究提示转录因子、信号通路、细胞外基质等影响血管平滑肌细胞稳态，但是组蛋白变异体在血管平滑肌细胞中的作为远未明朗。为了更好的寻找调控血管稳态的分子，我们在人颈动脉斑块中利用单细胞测序技术，发现了组蛋白变异体H2AZ和平滑肌细胞稳态高度相关。进一步体内体外实验发现H2AZ可以促进平滑肌细胞标志性基因的转录、从而促进其表达，维持平滑肌细胞收缩表型和血管稳态。在机制方面，我们发现H2AZ可以促进核小体的重新组装、从而导致染色质结果相对松散，使得转录因子SMAD3、MED1的结合增加，从而促进了平滑肌细胞标志基因的表达，维持平滑肌细胞表型。当平滑肌细胞丧失表型了时候可以观察到H2AZ表达的显著降低，而在体和离体过表达H2AZ均可以有效促进平滑肌细胞标志基因的表达，维持平滑肌细胞收缩表型并且抑制新生内膜形成。这些发现可以帮我们更好的理解组蛋白变异体在维持血管平滑肌细胞稳态中的作用及机制，为我们防治血管疾病提供了新的思路和靶点。