The c.119-123dup5bp mutation in human γC-crystallin destabilizes the protein and activates the unfolded protein response to cause highly variable cataracts

Ordered cellular architecture and high concentrations of stable crystallins are required for the lens to maintain transparency. Here we investigate the molecular mechanism of cataractogenesis of the CRYGC c.119-123dupGCGGC (p.Cys42AlafsX63) (CRYGC5bpdup) mutation. Lenses were extracted from wild type and transgenic mice carrying the CRYGC5bpdup minigene and RNA was isolated and converted into cDNA. Expression of genes in the unfolded protein response (UPR) pathways was estimated by qRT-PCR and RNA seq and pathway analysis was carried out using the Qiagen IPA website. Postnatal 3 weeks (P3W) Transgenic mice exhibited phenotypic diversity with a dimorphic population of severe and clear lenses. PCA of RNA seq data showed separate clustering of wild-type, clear CRYGC5bpdup, and severe CRYGC5bpdup lenses. Transgenic mice showed differential upregulation in Master regulator Grp78 (Hspa5) and downstream targets in the PERK-dependent UPR pathway including Atf4 and Chop (Ddit3), but not GADD34 (Ppp1r15a). Thus, high levels of CRYGC5bpdup transgene expression in severely affected lenses induces UPRer and UPRmt stress responses primarily through the PERK-dependent and Atf4/Atf5/Ddit3 pathways respectively, inducing autophagy and apoptosis and thence congenital nuclear cataracts. This effect is correlated to CRYGC5bpdup transgene expression, offering insight into cataract pathogenic pathways and recapitulating the variation in cataract severity in humans.