Polyglutamine expansion causes neurodegeneration by altering the neuronal differentiation program.
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.
Abou-Sleymane
Gretta
G
Department of Molecular Pathology, Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC), CNRS/INSERM/ULP, BP10142, 67404 Illkirch Cédex, CU de Strasbourg, France.
Chalmel
Frédéric
F
Helmlinger
Dominique
D
Lardenois
Aurélie
A
Thibault
Christelle
C
Weber
Chantal
C
Mérienne
Karine
K
Mandel
Jean-Louis
JL
Poch
Olivier
O
Devys
Didier
D
Trottier
Yvon
Y
D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics*; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D007211:Indoles; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009410:Nerve Degeneration / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000473:pathology*; D020411:Oligonucleotide Array Sequence Analysis; D015203:Reproducibility of Results; D012160:Retina / Q000473:pathology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
D005456:Fluorescent Dyes; D007211:Indoles; D014157:Transcription Factors; C007293:DAPI