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Yuriko Minegishi, XunLun Sheng, Kazuho Ikeo, Yuri V Sergeev, Takeshi Iwata; Novel compound heterozygous mutations of Leber congenital amaurosis in CCT2. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5424.
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© ARVO (1962-2015); The Authors (2016-present)
Leber Congenital Amaurosis (LCA) is a hereditary early-onset retinal dystrophy, which pathoetiology remains to be elucidated. We performed a whole-exome sequencing (WES) analysis on single Chinese LCA family and identified novel compound heterozygous mutations in CCT2. We further investigated the physiological impact of both mutations that leads to disease onset.
WES analysis was performed on 8 members of LCA pedigree. The mutant proteins were subjected for 3D structure prediction. Protein dynamics were monitored by using patient specific-iPSCs and over expression studies. LC-MS/MS proteomics identified the distinct protein interaction of CCTβ and the mutants. Cell growth was assayed under Si-RNA knock down with lenti-virus rescue. Retinal localization of CCTβ and the associating proteins were examined by immunohistochemistry.
We identified novel compound heterozygous mutations (T400P and R516H) in CCT2, which function as molecular chaperone CCTβ. Two children who have both T400P and R516H mutation exhibited macular degeneration, a hallmark of LCA, with retinal hypoplasia. Other family members having either one of these mutation showed normal macula and retinal structure. Protein structure prediction pointed out structural decay(s) in both mutants. Rapid degradation of T400P and R516H mutants were observed. LC-MS/MS proteomics and the immunoprecipitation and western blotting revealed that T400P has higher affinity to CCTγ, while the R516H exhibited less affinity to CCTγ than wild type CCTβ. Knock down of CCT2 decreased cell growth in 661W, a mouse photoreceptor cell line. Stable expression of CCTβ by lenti-virus in 661W rescued the growth phenotype while the T400P and R516H were less effective. Both CCTβ and CCTγ were expressed in retinal ganglion cells and the photoreceptors. Long term knock down of CCT2 decreased the Gβ1 protein amount in 661W.
We identified novel compound heterozygous mutations in CCT2. The mutants decreased the cell proliferation and Gβ1 supply, which thought to be the fundamental cause for hypoplastic retinal development and macular degeneration in the LCA patients. The CCT2-associating chaperon activity is crucial for retinal homeostasis. The further elucidation of specific clients for each CCT subunits will become increasingly important to understanding the molecular mechanism of LCA onsets.
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