Polyglutamine expansion causes neurodegeneration by altering the neuronal differentiation program

• Published in: Human molecular genetics Vol. 15; no. 5; pp. 691 - 703
• Main Authors: Abou-Sleymane, Gretta, Chalmel, Frédéric, Helmlinger, Dominique, Lardenois, Aurélie, Thibault, Christelle, Weber, Chantal, Mérienne, Karine, Mandel, Jean-Louis, Poch, Olivier, Devys, Didier, Trottier, Yvon
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.03.2006; Oxford Publishing Limited (England); Oxford University Press (OUP)
• Subjects: Animals; Biological and medical sciences; Blotting, Western; Cell Differentiation - genetics; Fluorescent Antibody Technique, Indirect; Fluorescent Dyes; Fundamental and applied biological sciences. Psychology; Gene Expression Profiling; Gene Expression Regulation, Developmental; Genetics of eukaryotes. Biological and molecular evolution; Indoles; Life Sciences; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; Microscopy, Confocal; Molecular and cellular biology; Nerve Degeneration - genetics; Nerve Degeneration - metabolism; Nerve Degeneration - pathology; Neurons - pathology; Oligonucleotide Array Sequence Analysis; Reproducibility of Results; Retina - pathology; Reverse Transcriptase Polymerase Chain Reaction; Transcription Factors - genetics; Transcription Factors - metabolism; Trinucleotide Repeat Expansion - genetics; Genetics; Degenerative disease; Neuron; Program; Differentiation
• ISSN: 0964-6906; 1460-2083
• DOI: 10.1093/hmg/ddi483

Huntington's disease (HD) and spinocerebellar ataxia type 7 (SCA7) belong to a group of inherited neurodegenerative diseases caused by polyglutamine (polyQ) expansion in corresponding proteins. Transcriptional alteration is a unifying feature of polyQ disorders; however, the relationship between polyQ-induced gene expression deregulation and degenerative processes remains unclear. R6/2 and R7E mouse models of HD and SCA7, respectively, present a comparable retinal degeneration characterized by progressive reduction of electroretinograph activity and important morphological changes of rod photoreceptors. The retina, which is a simple central nervous system tissue, allows correlating functional, morphological and molecular defects. Taking advantage of comparing polyQ-induced degeneration in two retina models, we combined gene expression profiling and molecular biology techniques to decipher the molecular pathways underlying polyQ expansion toxicity. We show that R7E and R6/2 retinal phenotype strongly correlates with loss of expression of a large cohort of genes specifically involved in phototransduction function and morphogenesis of differentiated rod photoreceptors. Accordingly, three key transcription factors (Nrl, Crx and Nr2e3) controlling rod differentiation genes, hence expression of photoreceptor specific traits, are down-regulated. Interestingly, other transcription factors known to cause inhibitory effects on photoreceptor differentiation when mis-expressed, such as Stat3, are aberrantly re-activated. Thus, our results suggest that independently from the protein context, polyQ expansion overrides the control of neuronal differentiation and maintenance, thereby causing dysfunction and degeneration.