Miller, JRC; (2016) Immune and huntingtin biology in Huntington's disease. Doctoral thesis , UCL (University College London).

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Abstract

Huntington’s disease (HD) is a fatal, autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Expression of the mutant (m)HTT protein is the primary cause of disease pathology, so lowering intracellular levels of mHTT is a promising therapeutic strategy. The aim of this thesis was to achieve allele-selective suppression of mHTT using siRNA targeted to single nucleotide polymorphisms (SNPs) in the HTT gene. HD patients were genotyped for three SNPs before the mRNA and protein knockdown efficacy of a panel of siRNAs was tested in primary human myeloid cells. Functional validation was carried out by characterising the effects of selective siRNAs on the cells’ hyper-reactive cytokine profile. In parallel, RNA sequencing was used to carry out the first whole transcriptome analysis of primary human HD myeloid cells. HD myeloid cells are functionally abnormal, and there is mounting interest in the peripheral immune system as a modifier of HD progression. In contrast with previous studies that have required stimulation to elicit phenotypic abnormalities, this thesis demonstrates significant transcriptional changes in unstimulated HD monocytes, including increased resting expression of proinflammatory cytokines. Pathway analysis revealed enrichment of gene sets relating to innate immunity and inflammation, while upstream regulator analysis suggests this transcriptional dysregulation is mediated by abnormal basal activation of the NFĸB intracellular signalling pathway; this was later confirmed by western blotting. These data are consistent with a priming effect of mHTT, whereby resting dysfunction leads to an exaggerated response once a stimulus is encountered. Finally, the contribution of adaptive immunity to HD peripheral immune dysfunction is yet to be satisfactorily investigated. This thesis demonstrates that mHTT expression does not affect the intrinsic phenotype of human HD T lymphocytes, suggesting that HD peripheral immune disturbance is not universal but is primarily the result of altered innate immunity.

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