Aging and neurodegeneration: Molecular mechanisms of neuronal loss in Huntington's disease

Huntington's disease (HD) is a fatal, genetically based late-onset neurodegenerative disorder in which a loss of neostriatal neurons is a main characteristic. The CAG trinucleotide repeat expansion encoding polyglutamine tract induces progressive deficits in intra- and inter-cellular signalling, and subsequent clinical signs developed with aging process. CAG-induced neurodegeneration and disease-onset shows aging-dependent pattern. Proposed mechanism of neurodegeneration includes intranuclear or intracellular protein aggregates, proteolytic cleavage of huntingtin (cf. caspase, calpain), altered transcription or other neurotransmitter signalling deficits. Recently, stem cell transplantation is of benefit to protect neurons against neurodegeneration and recover the functional deficit in the experimental HD model. This review focuses on current knowledge of molecular mechanisms in neurodegeneration and potential therapeutic targets in HD.