Mutations of RagA GTPase in mTORC1 Pathway Are Associated with Autosomal Dominant Cataracts

Cataracts are a significant public health problem with no proven methods for prevention. Discovery of novel disease mechanisms to delineate new therapeutic targets is of importance in cataract prevention and therapy. Herein, we report that mutations in the RagA GTPase (RRAGA), a key regulator of the mechanistic rapamycin complex 1 (mTORC1), are associated with autosomal dominant cataracts. We performed whole exome sequencing in a family with autosomal dominant juvenile-onset cataracts, and identified a novel p.Leu60Arg mutation in RRAGA that co-segregated with the disease, after filtering against the dbSNP database, and at least 123,000 control chromosomes from public and in-house exome databases. In a follow-up direct screening of RRAGA in another 22 families and 142 unrelated patients with congenital or juvenile-onset cataracts, RRAGA was found to be mutated in two unrelated patients (p.Leu60Arg and c.-16G>A respectively). Functional studies in human lens epithelial cells revealed that the RRAGA mutations exerted deleterious effects on mTORC1 signaling, including increased relocation of RRAGA to the lysosomes, up-regulated mTORC1 phosphorylation, down-regulated autophagy, altered cell growth or compromised promoter activity. These data indicate that the RRAGA mutations, associated with autosomal dominant cataracts, play a role in the disease by acting through disruption of mTORC1 signaling.

白内障是一类严重的公共卫生问题，目前尚无经证实的预防手段。阐明新型疾病机制以确定全新治疗靶点，对于白内障的预防与治疗具有重要意义。本研究报道，RagA GTP酶（RagA GTPase, RRAGA）作为雷帕霉素机制靶标复合物1（mechanistic rapamycin complex 1, mTORC1）的关键调控因子，其突变与常染色体显性遗传性白内障存在关联。我们对一个常染色体显性遗传性青少年发病型白内障家系开展全外显子组测序，在排除dbSNP数据库及公共与内部外显子组数据库中至少123000条对照染色体的变异后，鉴定出RRAGA基因上一处全新的p.Leu60Arg突变，该突变与疾病表型共分离。在针对另外22个家系及142名散发性先天性或青少年发病型白内障患者的RRAGA基因直接随访筛查中，我们在两名散发性患者体内分别发现了RRAGA突变：p.Leu60Arg与c.-16G>A。对人晶状体上皮细胞开展的功能研究显示，RRAGA突变会对mTORC1信号通路产生有害影响，具体表现为RRAGA向溶酶体的移位增多、mTORC1磷酸化水平上调、自噬活性下调、细胞生长异常或启动子活性受损。上述研究结果表明，与常染色体显性遗传性白内障相关的RRAGA突变，可通过破坏mTORC1信号通路参与疾病的发生发展。