通过抑制筛选鉴定促进多囊肾病囊肿发生生长的信号通路

Autosomal dominant polycystic kidney disease (ADPKD) is an adult-onset, chronic disease characterized by progressive enlargement of numerous fluid filled sacs in the kidney and liver. ADKPD affects 2 million individuals in China alone and over 12.5 million people worldwide. Half of the population reach end stage renal disease by age 60 years. There is no approved therapy, except kidney transplantation and dialysis. Polycystin-1 and Polycystin- 2, the protein products for causative ADPKD genes PKD1 and PKD2 respectively, were recently demonstrated to encode inhibitory signal that suppress an unknown cyst activation signal requiring the presence of intact cilia; loss of the inhibition of this cilia dependent signal by Polycystins in ADPKD leads to unfettered activation of the “pro-cyst” signal and cyst formation. Moreover, our unpublished data reveal that tubule specific knock out of Fibronectin, an extracellular matrix protein, attenuates the cystic burden in ADPKD models. These results demonstrate that majority of the signaling pathways and cell compartments that drive cyst progression in ADPKD haven’t been identified. We plan to perform forward mouse genetic screening to isolate mutants that suppress cyst growth, which will uncover genes in cyst-driving pathways without prior knowledge of their products. We will identify the cyst suppressor genes through whole exome sequencing of multiple mutants with reduced cyst growth mutant mice, with the candidate gene exhibiting a recessive mutation shared by all suppressed cyst formation mutants. We will study the gene function for cyst formation by genetic, biochemical and cell biological approaches. Identification of a novel gene has the potential to shed light on whole pathways/compartments. Furthermore, it may yield therapeutical targets for the treatment of ADPKD and other form of cystic kidney diseases.

常染色体显性遗传多囊肾病(ADPKD)是人类最大单基因遗传病之一，中国病人超过约200万。至60岁左右，一半病人进展到终末期肾病。除透析和换肾外，ADPKD目前还没有有效的治疗手段。ADPKD的致病基因是PKD1和PKD2，他们编码的蛋白产物是Polycystin1和Polycystin2, 表达在纤毛的膜上。最新的研究表明Polycystin1/2编码一个抑制性信号，抑制纤毛上一个未知信号的开启或活化。在ADPKD的上皮细胞纤毛上，由于Polycystin1或Polycystin2功能缺失导致该未知信号活化，进而囊肿细胞失控性增生，管腔直径变大到形成囊肿。目前ADPKD的研究重点是寻找促进囊肿生长的信号通路。在不了解这些信号的前提下，本研究将使用无偏的方法，在囊肿模型中筛选可抑制囊肿生长的突变体，再使用新一代测序技术鉴定突变基因/信号通路，进而研究这些信号通路促进囊肿生长的机理。

常染色体显性遗传多囊肾病（Autosomal Dominant Polycystic Kidney Disease, ADPKD）是人类最大的单基因遗传病，其在人群中的发病率是1:1000至1:500。全世界约有1200万病人，中国约有病人200万。除透析和肾脏移植外目前没有针对性的治疗手段。在ADPKD的治疗上，国家医疗体系每年花费约20-30亿人民币，ADPKD给病人家庭和国家带来沉重负担。ADPKD的致病基因是PKD1和PKD2, 编码多次跨膜的蛋白命名为polycystin1 (简称PC1) 和polycystin2（简称PC2）。PC1/2形成复合体，表达在纤毛膜上。PKD1和PKD2基因功能的缺失如何导致囊肿发生的机制还不十分清楚。小鼠Pkd1 和Pkd2条件性敲除模型与ADPKD临床症状一致。本课题利用ADPKD小鼠模型，通过抑制筛选的方法，从346个ENU诱导的家系中筛选到46个减缓囊肿生长的家系。其中12个家系在F4和F5代已稳定遗传。通过全外显子和全基因组测序分析，发现潜在的候选基因。我们发现固醇调节元件结合蛋白2（Srebf2）和胆汁酸受体Nr1h4参与囊肿的生长。本项目发现Srebf2 和Nr1h4两个重要的促进囊肿发生生长的关键因子，筛选的突变体为后续研究ADPKD发病机理以及开发治疗手段提供了重要的遗传材料。本项目目前共发表论文1篇，后续2篇论文将于今年投稿。