Striatal specificity of gene expression dysregulation in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by an expanded CAG repeat region in exon 1 of the HD gene. This mutation results in the presence of an abnormally long polyglutamine tract in the encoded protein, huntingtin (htt). A major question in this field is how the mutant htt protein, which is expressed ubiquitously throughout the brain and body, causes severe neuropathologic changes predominantly in the striatum. The mechanisms accounting for this specificity are unknown. The role of transcriptional dysregulation in the pathophysiology of HD has gained much attention in recent years, however, this theory has been unable to explain the specificity of dysfunction and degeneration in HD. Microarray studies have showed hundreds of gene expression changes in mouse models of HD and in post-mortem brain samples from HD subjects. Among the genes whose expression levels are preferentially altered are those that exhibit enriched expression in the striatum, which we have argued are the most relevant to disease pathology. These "striatal-enriched" genes are associated with several systems previously implicated in HD pathology, especially disturbances in transcriptional processes and calcium homeostasis. Large-scale changes in striatal gene expression in this manner would likely have particularly devastating effects to normal striatal function and could explain the specificity of striatal dysfunction and ultimate neurodegeneration observed in HD.