Gene dysregulation in Huntington's disease: REST, microRNAs and beyond

Huntington's disease (HD) is an incurable, fatal neurodegenerative disorder that is caused by a polyglutamine expansion in the huntingtin (Htt) protein. Neuronal death in the striatum-the most obvious manifestation of the disease-is likely to result from widespread dysregulation of gene expression in various brain regions. To date, several potential mechanisms for this have been discovered, including one involving REST (RE1-Silencing Transcription Factor), a master regulator of neuronal genes. Recently, independent studies have demonstrated that post-transcriptional gene regulation by microRNAs is also disrupted in HD. Expression of key neuronal microRNAs-including mir-9/9*, mir-124 and mir-132-is repressed in the brains of human HD patients and mouse models. These changes occur downstream of REST, and are likely to result in major disruption of mRNA regulation and neuronal function. In this study we will discuss these findings and their implications for our understanding of HD. Using updated bioinformatic analysis, we predict 21 new candidate microRNAs in HD. We propose future strategies for unifying large-scale transcriptional and microRNA datasets with the aim of explaining HD aetiology. By way of example, we show how available genomic datasets can be integrated to provide independent, analytical validation for dysregulation of REST and microRNA mir-124 in HD. As a consequence, gene ontology analysis indicates that HD is characterised by a broad-based depression of neural genes in the caudate and motor cortex. Thus, we propose that a combination of REST, microRNAs and possibly other non-coding RNAs profoundly affect the neuronal transcriptome in HD.