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Helene Dollfus, Anais Mockel, Dominique Schlicht, Nadia Messaddeq, Vincent Marion; Bardet Biedl Syndrome Chaperonin-like Proteins Depletion Induces Photoreceptor Cells Death Due To Endoplasmic Reticulum Stress. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5414.
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© ARVO (1962-2015); The Authors (2016-present)
The photoreceptor connecting cilium function is known to be impaired in a growing number of inherited ciliopathies. Bardet-Biedl syndrome (BBS) is an emblematic ciliopathy defined by the following major clinical features: early onset retinitis pigmentosa, obesity, polydactyly, renal dysfunction, and cognitive impairment. 15 BBS genes have been identified to date. Seven BBS proteins form the BBSome involved in vesicle trafficking to the primary cilium and three BBS chaperonin-like proteins BBS6, BBS10 and BBS12 with CCT proteins form a chaperonin complex helping the BBSome assembly. To understand how BBS chaperonin-like proteins dysfunction can lead to retinal degeneration, we performed a functional study of BBS12 in photoreceptor cells by gene knock-down in mice retinal explants and analyzed the retinal phenotype of Bbs12 knock-out mice.
We performed organotypic culture of mice retinas . BBS12 knock-down was induced by lentiviral infections. To analyze photoreceptors functionality, we performed immunostaining and transmission electronic microscopy (TEM). We analyzed induced cell stress using quantitative PCR, western blotting, and TUNEL assay. Bbs12 null mice retinal phenotype was investigated using histological analysis and TEM.
In the ex-vivo model, BBS12 knock-down induces decrease of connecting cilium number . Illumination variations were performed on retinal explants to investigate light-dependent bidirectional movements of arrestin and transducin, both proteins were mislocalized after BBS12 depletion. Rhodopsin accumulation in the inner segment was also detected in shRNA Bbs12 treated explants, suggesting ciliary dysfunction. Moreover, BBS12 depletion induces photoreceptor cells apoptosis due to endoplasmic reticulum stress as demonstrated by up-regulation of caspase12, Chop10 and BIP mRNAs and phosphorylation of the translation factor eIF2alpha. In vivo, Bbs12 knock-out mice presented retinopathy as early as 8 weeks including outer nuclear layer thickness and outer segment degeneration.
Ex-vivo, BS12 knock-down in photoreceptor cells triggers apoptotic pathways mediated by Endoplasmic Reticulum stress due to proteins accumulation in the inner segment. Bbs12 null mice characterization reveals a strong retinal phenotype.
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