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Elisabetta Soragni, JIntang Du, Ross A Aleff, Keith H Baratz, Eric Wieben, Joel M Gottesfeld; RNA toxicity in corneal endothelial tissue in Fuchs dystrophy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1171.
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© ARVO (1962-2015); The Authors (2016-present)
The strongest genetic association of Fuchs endothelial corneal dystrophy (FECD) is with an expanded trinucleotide repeat (CTG·CAG) in an intron of the TCF4 gene. The same expanded repeat sequence in the 3’UTR of the DMPK gene causes Myotonic Dystrophy type 1 (DM1) via a RNA toxicity mechanism. In DM1, poly(CUG) transcripts accumulate in foci and sequester the splicing factor MBNL1, causing missplicing of essential transcripts in skeletal muscle. Our hypothesis is that the same molecular mechanism causes RNA toxicity in the corneal endothelium of FECD patients. Because FECD patients do not present signs or symptoms of DM1, we also ask whether the molecular signature of RNA toxicity is present in muscle cells derived from FECD patients.
Corneal endothelial tissue was obtained at the time of endothelial keratoplasty, and skin fibroblasts were derived from skin biopsy specimens from patients with FECD. Using fluorescence in situ hybridization (FISH), protein-RNA aggregates can be visualized as RNA foci in the nucleus of affected cells. Immunofluorescence studies in the same cell types allow for detection of protein sequestered by the toxic RNA. Induced pluripotent stem (iPS) cells were also derived from FECD fibroblasts and differentiated to muscle cells to investigate the presence of RNA foci in this cell type.
Our data show that poly(CUG)-containing transcripts form RNA foci in fibroblasts derived from FECD patient skin biopsies and in FECD corneal endothelium and that these RNA foci co-localize with the splicing factor MBNL1. FISH in muscle cells derived from DM1 and FECD patients shows that RNA foci are either absent or less abundant and smaller in size in FECD compared to DM1 muscle cells.
RNA toxicity may be the cause of FECD, in a manner similar to DM1. In FECD patients, signs of RNA toxicity are present in the affected tissue (corneal endothelium) but not (or to a lesser extent) in iPSC-derived muscle cells, suggesting the possibility that the expression pattern of TCF4 poly(CUG)-containing transcript variants determines the pathogenesis of FECD.
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