[Molecular mechanism for spinocerebellar ataxias]

Recent advance of molecular biology reveals that quality control of intracellular environment takes an important role for maintaining the neuronal function. One is a quality control of protein and another is a quality control of nucleotide. Polyglutamine disease is a disease which caused by a failure of quality control of protein. Expanded polyglutamine repeats result in neurodegenerative disorders, but their cytotoxic structures remain to be elucidated. About the quality control of nucleotide in neuron, DNA single-strand breaks (SSBs) were continually produced by endogenous reactive oxygen species or exogenous genotoxic agents. These damaged ends posses damaged 3'-ends including 3'-phosphate, 3'-phosphoglycolate, or 3'-alpha, beta-unsaturated aldehyde ends, and should be restored to 3'-hydroxyl ends for subsequent repair processes. We have demonstrated by in vitro assay that aprataxin, the causative gene product for early-onset ataxia with ocular motor apraxia and hypoalbuminemia/ ataxia with oculomotor apraxia type 1 (EAOH/AOA1), specifically removes 3'-phosphoglycolate and 3'-phosphate ends at DNA 3'-ends, but not 3'-alpha, beta-unsaturated aldehyde ends. The findings indicate that aprataxin removes blocking molecules from 3'-ends, and that the accumulation of unrepaired SSBs with damaged 3'-ends underlies the pathogenesis of EAOH/AOA1. The findings will provide new insight into the mechanism underlying degeneration and DNA repair in neurons.