Mutant huntingtin activates Nrf2-responsive genes and impairs dopamine synthesis in a PC12 model of Huntington's disease.
BACKGROUND
Huntington's disease is a progressive autosomal dominant neurodegenerative disorder that is caused by a CAG repeat expansion in the HD or Huntington's disease gene. Although micro array studies on patient and animal tissue provide valuable information, the primary effect of mutant huntingtin will inevitably be masked by secondary processes in advanced stages of the disease. Thus, cell models are instrumental to study early, direct effects of mutant huntingtin. mRNA changes were studied in an inducible PC12 model of Huntington's disease, before and after aggregates became visible, to identify groups of genes that could play a role in the early pathology of Huntington's disease.


RESULTS
Before aggregation, up-regulation of gene expression predominated, while after aggregates became visible, down-regulation and up-regulation occurred to the same extent. After aggregates became visible there was a down-regulation of dopamine biosynthesis genes accompanied by down-regulation of dopamine levels in culture, indicating the utility of this model to identify functionally relevant pathways. Furthermore, genes of the anti-oxidant Nrf2-ARE pathway were up-regulated, possibly as a protective mechanism. In parallel, we discovered alterations in genes which may result in increased oxidative stress and damage.


CONCLUSIONS
Up-regulation of gene expression may be more important in HD pathology than previously appreciated. In addition, given the pathogenic impact of oxidative stress and neuroinflammation, the Nrf2-ARE signaling pathway constitutes a new attractive therapeutic target for HD.
Center for Human and Clinical Genetics, Leiden, the Netherlands. w.vanroon@lumc.nl
Willeke M C
WM
van Roon-Mom
Barry A
BA
Pepers
Peter A C
PA
't Hoen
Carola A C M
CA
Verwijmeren
Johan T
JT
den Dunnen
Josephine C
JC
Dorsman
Gertjan B
GB
van Ommen
D000818:Animals; D004195:Disease Models, Animal; D004298:Dopamine / Q000096:biosynthesis*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D018384:Oxidative Stress; D016716:PC12 Cells; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015854:Up-Regulation
C499524:Htt protein, rat; D000071058:Huntingtin Protein; D051267:NF-E2-Related Factor 2; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins; D004298:Dopamine