Role of proteolysis in polyglutamine disorders

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Nine polyglutamine disorders, including Huntington's disease (HD), are characterized by expanded polyglutamine tracts.
• While a toxic gain of function is implicated, the precise mechanisms of neurotoxicity and specific neuronal damage patterns remain unclear.
• Ubiquitous expression of abnormal proteins contrasts with the characteristic distribution of neuronal damage in each disease.

Purpose of the Study:

• To investigate the role of proteolytic cleavage in the specific neuronal toxicity observed in polyglutamine disorders.
• To explore potential therapeutic strategies targeting protease inhibition.

Main Methods:

• Review of in vitro and in vivo evidence for proteolytic cleavage in HD, spinobulbar muscular atrophy (SBMA), dentatorubral-pallidoluysian atrophy (DRPLA), and spinocerebellar ataxias (SCAs) 2, 3, and 7.
• Examination of evidence for regionally specific cleavage in HD via caspase activation.
• Analysis of intraneuronal aggregates and their relationship with the ubiquitin-proteasome pathway.

Main Results:

• Proteolytic cleavage of expanded polyglutamine proteins is evidenced in multiple polyglutamine disorders.
• Cleavage in HD is regionally specific and mediated by caspase activation.
• Intraneuronal aggregates, potentially promoted by cleavage (e.g., ataxin-3), are observed and co-localize with the ubiquitin-proteasome pathway.

Conclusions:

• Proteolytic cleavage is a potential mechanism underlying the specific distribution of neuronal toxicity in polyglutamine disorders.
• The role of intraneuronal aggregates as pathogenic or markers requires further clarification.
• Inhibition of specific proteases presents a promising therapeutic avenue for these neurodegenerative diseases.