Huntingtin loss-of-function contributes to transcriptional deregulation in Huntington's disease

Abstract

Huntingtons disease (HD) is a fatal neurodegenerative disorder that is caused by the expansion of CAG repeats in the HTT gene, which results in a long polyglutamine (polyQ) tract in the huntingtin protein (HTT). In this study, we searched for networks of deregulated RNAs that contribute to initial transcriptional changes in HD neuronal cells and HTT-deficient cells. We used RNA-seq (including small RNA sequencing) to analyze a set of isogenic, human induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs); and we observed numerous changes in gene expression and substantial dysregulation of miRNA expression in HD and HTT-knockout (HTT-KO) cell lines. The gene set that was upregulated in both HD and HTT-KO cells was enriched in genes that are associated with DNA binding and regulation of transcription. For both of these models, we confirmed the substantial upregulation of the transcription factors (TFs) TWIST1, SIX1, TBX1, TBX15, MSX2, MEOX2 and FOXD1 in NSCs and medium spiny neuron (MSN)-like cells. Moreover, we identified miRNAs that were consistently deregulated in HD and HTT-KO NSCs and MSN-like cells, including miR-214, miR-199, and miR-9. We suggest that these miRNAs function in the network that regulates TWIST1 and HTT expression via regulatory feed-forward loop (FFL) in HD. Additionally, we reported that the expression of selected TFs and miRNAs tended to progressively change during the neural differentiation of HD cells, what was not observed in HTT-KO model. Based on comparing the HD and HTT-KO cell lines, we propose that early transcriptional deregulation in HD is largely caused by loss of HTT function.