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Huan Meng, Mario Matthaei, Albert S. Jun; Differential Modes of Cell Death in Mouse Models of Fuchs Dystrophy Harboring Homozygous L450W and Q455K Mutations in the Col8a2 Gene. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5991.
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Fuchs endothelial corneal dystrophy (FECD) is a leading cause of progressive vision loss, and the only effective treatment is corneal transplantation. Knock-in mice harboring homologous missense mutations, L450W or Q455K in the Col8a2 gene, closely recapitulate the disease and provide a useful animal model to study early disease pathogenesis and potential therapies.
In vivo endothelial cell (EC) counts were imaged and analyzed by confocal microscopy. Ultrastructural analysis of ECs was performed using transmission electron microscopy (TEM). Quantitative (q)RT-PCR profiling of 91 autophagy-related genes was performed on total RNA from stripped ECs.
In vivo clinical confocal microscopy of Col8a2L450W/L450W mice at 20, 40, and 80wks reveal a 10% (p<.05), 27% (p<.0001), and 41% (p<.0001) decrease in ECs, respectively, compared to age-matched WT mice. In comparison, Col8a2Q455K/Q455K mice show a 27% (p<.0001), 41% (p<.0001), and 75% (p<.0001) decrease in ECs, respectively, compared to age-matched WT mice. TEM reveals dilated rough endoplasmic reticulum (RER) in both the Col8a2L450W/L450W and Col8a2Q455K/Q455K mice at 20wks; however, by 40wks, the dilated RER of the Col8a2Q455K/Q455K mice persists while the Col8a2L450W/L450W mice show significantly less RER, which is replaced by dilated vacuoles with partially degraded organelles inside. In addition, TEM of Col8a2Q455K/Q455K mice reveals accumulation of abnormal mitochondria marked for degradation. qRT-PCR of Col8a2Q455K/Q455K mice shows a 23.1-fold (p<.05) increase in Eif2ak3 levels and a 16.3-fold (p<.05) increase in mTOR. Contrastingly, profiling of Col8a2L450W/L450W mice reveal a downward trend in Eif2ak3 and mTOR (p>.05) expression.
Both Col8a2L450W/L450W and Col8a2Q455K/Q455K mice exhibit the hallmarks of FECD - progressive EC loss and increased numbers of guttae; however, the Col8a2Q455K/Q455K mice have earlier disease onset and greater than double the cell death rate. Ultrastructural differences coupled with gene expression analysis suggest that impaired autophagy may play a role in the delayed turnover of stressed ER and mitochondria. Future studies testing mTOR inhibitors to stimulate autophagy may be a valuable therapeutic approach to restoring functional autophagy and delaying progressive EC death.
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