TCF4 Triplet Repeat Expansion and Nuclear RNA Foci in Fuchs' Endothelial Corneal Dystrophy.
OBJECTIVE
Expansion of the intronic CTG18.1 triplet repeat locus within TCF4 contributes significant risk to the development of Fuchs' endothelial corneal dystrophy (FECD) in Eurasian populations, but the mechanisms by which the expanded repeats result in degeneration of the endothelium have been hitherto unknown. The purpose of this study was to examine FECD endothelial samples for the presence of RNA nuclear foci, the hallmark of toxic RNA, as well as evidence of haploinsufficiency of TCF4.


METHODS
Using fluorescence in situ hybridization, we examined for the presence of nuclear RNA foci containing expanded CUG transcripts in corneal endothelial samples from FECD subjects with CTG18.1 expansion. We also examined for any changes in expression levels of TCF4 by quantitative real-time PCR.


RESULTS
Numerous discrete nuclear RNA foci were identified in endothelial samples of FECD subjects (n = 8) harboring the CTG18.1 expansion, but not in controls lacking the expansion (n = 5) (P = 7.8 × 10(-4)). Percentage of cells with foci in expansion-positive endothelial samples ranged from 33% to 88%. RNA foci were absent in endothelial samples from an FECD subject without CTG18.1 expansion and a subject with endothelial dysfunction without FECD. Expression of the constitutive TCF4 exon encoding the basic helix-loop-helix domain was unaltered with CTG18.1 expansion.


CONCLUSIONS
Our findings suggest that the RNA nuclear foci are pathognomonic for CTG18.1 expansion-mediated endothelial disease. The RNA nuclear foci have been previously found only in rare neurodegenerative disorders caused by repeat expansions. Our detection of abundant ribonuclear foci in FECD implicates a role for toxic RNA in this common disease.
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States McDermott Center for Human Growth and Development/Center for Human Genetics, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
V Vinod
VV
Mootha
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Imran
I
Hussain
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Khrishen
K
Cunnusamy
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Eric
E
Graham
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Xin
X
Gong
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Sudha
S
Neelam
McDermott Center for Human Growth and Development/Center for Human Genetics, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Chao
C
Xing
McDermott Center for Human Growth and Development/Center for Human Genetics, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
Ralf
R
Kittler
Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States.
W Matthew
WM
Petroll
D000368:Aged; D000369:Aged, 80 and over; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D004728:Endothelium, Corneal / Q000378:metabolism; D005260:Female; D005642:Fuchs' Endothelial Dystrophy / Q000235:genetics* / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008875:Middle Aged; D015138:RNA, Nuclear / Q000235:genetics*; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015138:RNA, Nuclear; C532096:TCF4 protein, human; D000073940:Transcription Factor 4; D014157:Transcription Factors
CTG18.1; Fuchs' endothelial corneal dystrophy; RNA nuclear foci; TCF4; triplet repeat expansion