热休克因子4感应蛋白质内稳态调控晶状体发育的机制研究

Imbalance of lens protein homeostasis leads to cataract formation. As the master transcription factor to induce heat shock response in lens tissue, Hsf4 mutations are responsible for congenital cataract formation. The mechanism that heat shock response regulates the lens protein homeostasis is still masked. Our previous studies suggest that Hsf4 interacted with ubiquitin fusion protein Uba52, consisting of ubiquitin at the N terminus and ribosomal protein L40 at the C terminus. Proteotoxic stresses enhance the interaction between Hsf4 and Uba52, and Uba52 also increase the transcriptional activity of Hsf4. Meanwhile, Uba52 protein displayed a high expression levels in lens tissues and could formed functional ubiquitin molecules. The ubiquitin-proteasome pathway is the predominant system to regulate protein homeostasis by involved in protein folding, degradation and interactions. We infer that Hsf4 is involved in sustaining protein homeostasis through the interaction with Uba52 protein, and then regulates lens differentiation. Using lens epithelial cell lines and zebrafish models, this project aim to explore: 1. the molecular mechanism of Hsf4 activation induced by proteotoxic stresses; 2. the mechanism that Uba52 enhances the transcriptional activity of Hsf4; 3. the lens development and Hsf4’s transcriptional activity in Uba52 Knockout zebrafish models that constructed with CRISPR-Cas9 technology. This study could hint a novel strategy towards to cataract prevention and therapy.

晶状体内蛋白内稳态失调是白内障发生的重要原因。Hsf4是晶状体中执行热休克反应的主要转录因子，其功能失常导致白内障发生。Hsf4介导的热休克反应如何调控晶状体内的蛋白内稳态并不清楚。我们发现泛素融合蛋白Uba52互作Hsf4并上调其转录活性，蛋白毒性压力增强二者间互作。同时，Uba52在晶状体中可成熟为泛素分子。泛素-蛋白酶体系统调控蛋白有序折叠、降解及互作，是调控晶状体蛋白内稳态的关键通路。由此，我们推测Hsf4通过与Uba52互作感应晶状体细胞内的蛋白内稳态紊乱，调控晶状体发育过程。本课题利用细胞和斑马鱼模型揭示：①蛋白毒性压力激活Hsf4介导的热休克反应的分子机制；②晶状体细胞中Uba52增强Hsf4转录活性的分子机理；③斑马鱼中CRISPR-Cas9敲除Uba52对Hsf4介导的晶状体发育的调控。该立项将阐述Hsf4调控蛋白内稳态的分子机制，为靶向防治Hsf4相关白内障提供新方向。

晶状体内稳态失衡是先天性和老年性白内障发生的重要原因。HSF4为晶状体中执行热休克反应的主导转录因子，其功能缺失导致白内障发生。HSF4介导的热休克反应在晶状体的蛋白内稳态维持中的功能并不清楚。该项目我们利用野生型、HSF4敲除和过表达的晶状体上皮细胞系和HSF4敲除斑马鱼，构建了HSF4突变小鼠，UBA52敲除斑马鱼及DNase1l1l敲除斑马鱼等，研究了HSF4在晶状体上皮细胞内稳态维持及纤维细胞终末分化中的作用。我们发现1）晶状体中泛素融合蛋白UBA52互作HSF4并增强其转录活性。HSF4/UBA52可感应蛋白毒性压力，并调控HSF4下游基因的转录延伸过程。HSF4和UBA52敲除斑马鱼都具有晶状体分化障碍。2）晶状体上皮细胞中HSF4通过调控下游基因αB-crystallin表达，促进溶酶体膜上质子泵的组装，维持溶酶体酸性PH，进而维持溶酶体活性。3）晶状体上皮细胞中HSF4互作甲基转移酶EZH2调控组蛋白H3K27的甲基化修饰直接抑制p21的表达，进而抵抗晶状体衰老过程。4）HSF4转录调控晶状体特异性DNase（如人和鼠中的DNase2β，斑马鱼中DNase1l1l）促进晶状体纤维细胞终末分化过程中的细胞核降解。通过以上研究，我们解释了UBA52在晶状体中的功能，阐释了HSF4感应蛋白毒性压力的分子机制。同时我们揭示了晶状体上皮细胞中HSF4维持溶酶体活性和抵抗细胞衰老的分子机制，也阐明了HSF4调控晶状体分化中纤维细胞去核过程的分子机制。该项目系统研究了HSF4在晶状体稳态维持中的作用，为研发防治白内障的药物提供理论依据。