Epigenetic Regulation of αA-crystallin in High Myopia-Induced Dark Nuclear Cataract

PURPOSE To assess the etiology of early-onset dark nucleus in high-myopic patients and its relationship with the epigenetic regulation of αA-crystallin (CRYAA). METHODS We reviewed clinical data from patients who underwent cataract surgery at our center in 2012. Lens epithelial samples were collected during capsulorhexis, whereas young lens epithelium was donated. Cataract type and severity were graded according to the Lens Opacity Classification System III (LOCS III). DNA methylation was analyzed by pyrosequencing the CpG islands of the CRYAA promoter in the following groups: Age-Related Cataract (ARC) Nuclear Color (NC) 2-3; High-Myopic Cataract (HMC) NC2-3; ARC NC5-6; HMC NC5-6; and in young lenses graded NC1. We analyzed CRYAA expression by real-time polymerase chain reaction (PCR), reverse transcription PCR, and immunohistochemistry. RESULTS The odds ratio of dark nucleus in high-myopic patients was 5.16 (95% confidence interval: 3.98-6.69; p<0.001). CpG islands in lens epithelial CRYAA promoter in the HMC NC5-6 Group exhibited the highest methylation of all the groups, but no statistically significant differences were evident between the HMC NC2-3 and ARC NC2-3 Groups. Likewise, CRYAA mRNA and protein levels in the HMC NC5-6 Group were significantly lower than the ARC NC5-6 Group and high-myopic controls. CONCLUSIONS High myopia is a risk factor for dark nucleus. Downregulation of CRYAA via the hypermethylation of CpG islands in its promoter could underlie the earlier onset of dark nucleus in high-myopic patients.