Polyglutamine expansions cause decreased CRE-mediated transcription and early gene expression changes prior to cell death in an inducible cell model of Huntington's disease

Huntington's disease (HD) is one of 10 known diseases caused by a (CAG)(n) trinucleotide repeat expansion that is translated into an abnormally long p olyglutamine tract. We have developed stable inducible neuronal (PC12) cell lines that express huntingtin exon 1 with varying CAG repeat lengths under doxycycline (dox) control. The expression of expanded repeats is associate d with aggregate formation, caspase-dependent cell death and decreased neur ite outgrowth. Post-mitotic cells expressing mutant alleles were more prone to cell death compared with identical cycling cells. To determine early me tabolic changes induced by this mutation in cell models, we studied changes in gene expression after 18 h dox induction, using Affymetrix arrays, cDNA filters and adapter-tagged competitive PCR (ATAC-PCR). At this time point there were low rates of inclusion formation, no evidence of mitochondrial c ompromise and no excess cell death in the lines expressing expanded compare d with wildtype repeats. The expression profiles suggest novel targets for the HD mutation and were compatible with impaired cAMP response element (CR E)-mediated transcription, which we confirmed using CRE-luciferase reporter assays. Reduced CRE-mediated transcription may contribute to the loss of n eurite outgrowth and cell death in polyglutamine diseases, as these phenoty pes were partially rescued by treating cells with cAMP or forskolin.