Myocardin在肝星状细胞激活中的转录调控及生物学意义研究

英文摘要.Liver injuries are inflicted by genetic, environmental, and dietary stresses. Liver fibrosis is the excessive accumulation of extracellular matrix (ECM) proteins due to sustained liver injury. Cirrhosis represents a typical end-stage hepatic pathology in most types of chronic liver diseases，accounting for a majority of deaths among patients with liver disease. Activation of hepatic stellate cells (HSCs) is a pivotal process in the pathogenesis of liver fibrosis. Activated HSCs undergo phenotype change and increase ECM synthesis in parallel with profound alterations of their gene expression profile. The transcriptional regulation of the gene profile is considered as a key process during the activation of HSCs. Our previous data suggest that knocking down Myocardin represses the expression of several fibrogenic genes in cultured primary HSCs. Myocardin can interact with various transcripton factors, which plays a crucial role in the regulation of gene transcription. The integrated mechanism of transcriptional regulation by Myocardin during the transdifferentiation of HSCs remains to be elucidated. Therefore, we hypothesize that Myocardin regulates the gene expression during the transdifferentiation of HSCs, promoting the transformation from a quiescent to a myofibroblast-like phenotype. We hope to unearth the mechanism and exact role of Myocardin in the transcriptional regulation in HSC transdifferentiation, in the meantime providing a new target for cirrhosis intervention.

肝硬化是许多慢性肝脏疾病发展的终末期，是导致肝病患者死亡的主要原因。肝纤维化是肝脏疾病向肝硬化转变的必经阶段。肝星状细胞激活（HSC）是肝脏纤维化发生发展中的重要事件。激活后的HSC基因发生表型改变并分泌大量细胞外基质。基因表达调控被认为是HSC激活过程中的关键步骤。我们前期预实验结果显示，用小干扰RNA敲低Myocardin后能够降低HSC激活时纤维化相关基因的mRNA表达水平。Myocardin能够与多种转录因子相互作用，与基因的表达调控密切相关。而对于Myocardin参与HSC激活的确切机制还有待阐明。因此，我们提出假说，Myocardin通过调节HSC的基因表达，促进其由静息状态向肌成纤维样表型转变。我们希望通过研究Myocardin在HSC激活中的转录调控机制及其作用，为临床上防治肝纤维化提供新的药物靶标。

肝星状细胞由静息状态转变为激活状态（肌成纤维样细胞）是肝纤维化过程中的关键生物学事件，其中的分子生物学机制尚未完全阐明。心肌素Myocardin最初在心肌细胞中发现的转录因子，既有研究显示其在平滑肌分化过程中的重要作用 ，然而其在肝星状细胞激活中的调控机制尚未完全清楚。我们发现，在激活的肝星状细胞和纤维化肝脏中Myocardin的表达水平显著上调。课题组通过敲低Myocardin后发现，肝星状细胞的激活明显受到抑制，纤维化相关基因的表达水平显著下调。而在小鼠体内敲低Myocd同样能够减轻CCl4诱导的肝脏纤维化程度。通过二代测序发现，敲低Myocd后能够显著改变肝星状细胞的表达谱。进一步研究发现，Myocardin对相关靶基因的调控是依赖与BRG1的。最后，Myocardin能够影响靶基因启动子组蛋白的H3K4的三甲基化水平。我们的研究进一步揭示了Myocardin参与调控肝星状细胞激活和肝脏纤维化过程中的作用机制，为临床防治肝脏纤维化提供了理论依据。