Robert J Ferrante, Isabelle Denghien, Sebastien Holbert, Jean Dausset, Tamara Kiechle, Christopher A Ross, Christian Neri, Cheryll Wellington, Michael R Hayden, Adam Rosenblatt, Russell L Margolis
[
International C. elegans Meeting,
2001]
Huntington's disease (HD) is a neurodegenerative disease caused by polyglutamine (polyQ) expansion in the protein huntingtin (htt). Pathogenesis in HD appears to involve the formation of ubiquitinated neuronal intranuclear inclusions containing N-terminal mutated htt, abnormal protein interactions, and the aggregate sequestration of a variety of proteins (noticeably transcription factors). To identify novel htt-interacting proteins in a simple model system, we used a yeast two-hybrid screen with a Caenorhabditis elegans activation domain library (R. Barstead, ORMF, Oklahoma City, OK). We found a predicted WW domain protein (ZK1127.9) that interacts with N-terminal fragments of htt in two-hybrid tests. A human homologue of ZK1127.9 is CA150, a transcriptional coactivator with a N-terminal insertion that contains an unperfect (Gln-Ala)38 tract encoded by a polymorphic repeat DNA. CA150 interacted in vitro with full length htt from lymphoblastoid cells. The immunohistochemical expression of CA150 was markedly increased in human HD brain tissue, in comparison to normal age-matched human brain tissue, and showed aggregate formation with colocalization to ubiquitin-positive aggregates. In 432 HD patients, the CA150 repeat length explains a small but statistically significant amount of the variability in HD onset age. Our data suggest that abnormal expression of CA150, as mediated by interaction with polyQ-expanded htt, may alter transcription, and have a role in HD pathogenesis. Our data illustrate the value of using C. elegans for the direct identifcation of novel biochemical and genetic modifiers of human neurodegenerative disease pathogenesis [Holbert et al. (2001) Proc. Natl. Acad. Sci. USA 98 1811-1816].
[
International Worm Meeting,
2003]
C. elegans amenability to genetic analyses and pharmacological screens may uncover aspects of the toxicity of human disease-associated proteins difficult to manipulate in vivo by other means. We have validated a worm-based approach to the study of Huntington's disease pathogenesis. We have observed that huntingtin, the HD protein, is able to interact with C. elegans proteins, and that human homologs of huntingtin interactors in worms may be involved in HD pathogenesis, as shown for the transcriptional regulator CA150, a candidate modifier gene in HD. We have described a transgenic C. elegans model of polyglutamine-dependent neuronal dysfunction without cell death. In this model, polyQ-expanded N-terminal huntingtin fused to fluorescent reporter proteins produces a significant mechanosensory defect at the tail. This phenotype partially correlates with aggregation of fusion proteins in neuronal processes and abnormal morphology of neuronal cell axons. This phenotype can be genetically suppressed with or without a reduction of aggregation, and genetic suppressors are being characterized. As part of a multi-assay neurodegeneration drug screening program coordinated by the NINDS, we have tested a collection of 1040 drugs in our transgenic animals. We have detected a manageable number of confirmed hits that show a dose-dependent restoration of touch sensitivity at the tail. One of these compounds appeared to significantly reduce aggregation in neuronal processes and abnormal morphology of axons in a dose-dependent manner. Our drug screening data suggest that the use of worm mechanosensation allows for a sensitive detection and validation of active compounds, which may be instructive in selecting drug leads.