Related Experiment Videos
Calpain activation in Huntington's disease
Juliette Gafni1, Lisa M Ellerby
1Buck Institute for Age Research, Novato, California 94945, USA.
Insights
Activated calpain protease cleaves huntingtin protein fragments, a key step in Huntington's disease (HD) pathogenesis. This finding implicates calpain in the neurodegenerative process of HD.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Huntington's disease (HD) is a neurodegenerative disorder.
- It is caused by a CAG expansion in the huntingtin (Htt) gene.
- Abnormal processing of mutant Htt is critical in HD initiation.
Purpose of the Study:
- To identify the protease responsible for abnormal Htt processing in HD.
- To investigate the role of calpain in Htt cleavage.
Main Methods:
- Detection of activated calpain in human HD caudate tissue.
- Analysis of N-terminal Htt proteolytic fragments in HD tissue.
- In vitro cleavage of Htt by exogenous calpain.
Main Results:
- Activated calpain was detected in human HD tissue, but not in controls.
- A major N-terminal Htt fragment in HD tissue resulted from calpain cleavage.
- Calpain cleavage of Htt is dependent on polyglutamine tract length.
Conclusions:
- Calpain plays a role in the proteolytic processing of Htt in HD.
- Calpain-mediated cleavage of Htt is implicated in the pathogenesis of Huntington's disease.
Abstract:
Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG expansion that results in elongation of the polyglutamine tract at the N terminus of huntingtin (Htt). Abnormal proteolytic processing of mutant Htt has been implicated as a critical step in the initiation of HD. The protease(s) involved in this process has not been fully characterized. Here we report that activated calpain was detected in the caudate of human HD tissue but not in age-matched controls. In addition, one of the major N-terminal Htt proteolytic fragments found in human HD tissue appears to be derived from calpain cleavage. Htt fragments in HD lysates were similar in size to those produced by exposure of in vitro-translated Htt to exogenous calpain. Incubation of in vitro-translated Htt with calpain generated a cascade of cleavage events with an initial intermediate cleavage product at 72 kDa and a final cleavage product at 47 kDa. The rate of cleavage of Htt by calpain was polyglutamine-length-dependent. These results suggest that cleavage of Htt in human HD tissue is mediated in part by the Ca2+-activated neutral protease, calpain.