STAT3 is a transcription factor that can be activated by cytokine and growth factor stimulation by alteration of its phosphorylation and subcellular localisation, which in turn regulates gene expression. Aberrant STAT3 activity may therefore result in significant transcriptional dysregulation; which is a prominent pathogenic effect observed in many models of HD, as well as in human HD brain. We therefore aimed to elucidate the role of STAT3 signalling in transcriptional regulation in the StHdhQ111 immortalised embryonic striatal cell model of HD.

Epidermal growth factor stimulation was utilised to create a dynamic model, and various protein biochemistry techniques were utilised to characterise the localisation and expression of total STAT3 and phosphorylated STAT3 proteins in StHdhQ111 cell lines. This was coupled with microarray and qRTPCR analyses to investigate the transcriptional impact of dysregulated STAT3. Manipulation of STAT3 activation using phosphorylation and nuclear transport inhibitors is planned, as well as measures of cell stress and apoptosis in response to altered STAT3.

Preliminary results reveal increased STAT3 protein expression, as well as an increased STAT3 phosphorylation response to EGF stimulation in StHdhQ111 cells homozygous for the HD mutation. Immunofluorescence analyses also indicate enhanced nuclear localisation of both total and phosphorylated STAT3 in StHdhQ111 homozygous cells, which is consistent with the dysregulated expression of STAT3-regulated genes, such as Atf3, Fosl1 and Junb.

Dysregulation of STAT3 subcellular localisation may therefore be a potential mechanism for the transcriptional effects observed in HD that could have implications for brain development and maturation. Should STAT3 prove to have a development-associated impact on cellular function and survival, it could potentially provide a novel therapeutic target and biomarker for disease progression.