Huntington's disease (HD) pathology is well understood at a histological level but a comprehensive molecular analysis of the effect of the disease in the human brain has not previously been available. To elucidate the molecular phenotype of HD on a genome-wide scale, we compared mRNA profiles from 44 human HD brains with those from 36 unaffected controls using microarray analysis. Four brain regions were analyzed: caudate nucleus, cerebellum, prefrontal association cortex [Brodmann's area 9 (BA9)] and motor cortex [Brodmann's area 4 (BA4)]. The greatest number and magnitude of differentially expressed mRNAs were detected in the caudate nucleus, followed by motor cortex, then cerebellum. Thus, the molecular phenotype of HD generally parallels established neuropathology. Surprisingly, no mRNA changes were detected in prefrontal association cortex, thereby revealing subtleties of pathology not previously disclosed by histological methods. To establish that the observed changes were not simply the result of cell loss, we examined mRNA levels in laser-capture microdissected neurons from Grade 1 HD caudate compared to control. These analyses confirmed changes in expression seen in tissue homogenates; we thus conclude that mRNA changes are not attributable to cell loss alone. These data from bona fide HD brains comprise an important reference for hypotheses related to HD and other neurodegenerative diseases.

We previously demonstrated that sodium butyrate is neuroprotective in Huntington’s disease (HD) mice and that this therapeutic effect is associated with increased expression of mitogen-activated protein kinase/dual-specificity phosphatase 1 (MKP-1/DUSP1). Here we show that enhancing MKP-1 expression is sufficient to achieve neuroprotection in lentiviral models of HD. Wild-type MKP-1 overexpression inhibited apoptosis in primary striatal neurons exposed to an N-terminal fragment of polyglutamine-expanded huntingtin (Htt171-82Q), blocking caspase-3 activation and significantly reducing neuronal cell death. This neuroprotective effect of MKP-1 was demonstrated to be dependent on its enzymatic activity, being ablated by mutation of its phosphatase domain and being attributed to inhibition of specific MAP kinases (MAPKs). Overexpression of MKP-1 prevented the polyglutamine-expanded huntingtin-induced activation of c-Jun N-terminal kinases (JNKs) and p38 MAPKs, whereas extracellular signal-regulated kinase 1/2 (ERK1/2) activation was not altered by either polyglutamine-expanded Htt or MKP-1. Moreover, mutants of MKP-1 that selectively prevented p38 or JNK binding confirmed the important dual contributions of p38 and JNK regulation to MKP-1-mediated neuroprotection. These results demonstrate additive effects of p38 and JNK MAPK inhibition by MKP-1 without consequence to ERK activation in this striatal neuron-based paradigm. MKP-1 also provided neuroprotection in vivo in a lentiviral model of HD neuropathology in rat striatum. Taken together, these data extend previous evidence that JNK- and p38-mediated pathways contribute to HD pathogenesis and, importantly, show that therapies simultaneously inhibiting both JNK and p38 signalling pathways may lead to improved neuroprotective outcomes.

Factor X deficiency is a rare haemorrhagic condition, normally inherited as an autosomal recessive trait, in which a variable clinical presentation correlates poorly with laboratory phenotype. The factor X (F10) genes of 14 unrelated individuals with factor X deficiency (12 familial and two sporadic cases) were sequenced yielding a total of 13 novel mutations. Family studies were performed in order to distinguish the contributions of individual mutant F10 alleles to the clinical and laboratory phenotypes. Missense mutations were studied by means of molecular modelling, whereas single basepair substitutions in splice sites and the 5' flanking region were examined by in vitro splicing assay and luciferase reporter gene assay respectively. The deletion allele of a novel hexanucleotide insertion/deletion polymorphism in the F10 gene promoter region was shown by reporter gene assay, to reduce promoter activity by approximately 20%. One family manifesting an autosomal dominant pattern of inheritance possessed three clinically affected members who were heterozygous for a splice-site mutation that was predicted to lead to the production of a truncated protein product. A model which accounts for the dominant negative effect of this lesion is presented. Variation in the antigen level of heterozygous relatives of probands was found to be significantly higher between families than within families, consistent with the view that the nature of the F10 lesion(s) segregating in a given family is a prime determinant of the laboratory phenotype. By contrast, no such relationship could be discerned between laboratory phenotype and polymorphism genotype.

Huntington's disease (HD) is an inherited neurodegeneration that causes a severe progressive illness and early death. Several animal models of the disease have been generated carrying the causative mutation and these have shown that one of the earliest molecular signs of the disease process is a substantial transcriptional deficit. We examined the alterations in brain gene expression in the R6/1 mouse line over the course of the development of phenotypic signs from 18 to 27 weeks. Changes in R6/1 mice were similar to those previously reported in R6/2 mice, and gene ontology analysis shows that pathways related to intracellular and electrical signaling are altered among downregulated genes and lipid biosynthesis and RNA processes among upregulated genes. The R6/1 mice showed deficits in rotarod performance, locomotor activity and exploratory behavior over the time-course. We have correlated the alterations in gene expression with changes in behavior seen in the mice and find that few alterations in gene expression correlate with all behavioral changes but rather that different subsets of the changes are uniquely correlated with one behavior only. This indicates that multiple behavioral tasks assessing different behavioral domains are likely to be necessary in therapeutic trials in mouse models of HD.

The age at onset of motor symptoms in Huntington’s disease (HD) is driven by HTT CAG repeat length but modified by other genes. In this study, we used exome sequencing of 683 patients with HD with extremes of onset or phenotype relative to CAG length to identify rare variants associated with clinical effect. We discovered damaging coding variants in candidate modifier genes identified in previous genome-wide association studies associated with altered HD onset or severity. Variants in FAN1 clustered in its DNA-binding and nuclease domains and were associated predominantly with earlier-onset HD. Nuclease activities of purified variants in vitro correlated with residual age at motor onset of HD. Mutating endogenous FAN1 to a nuclease-inactive form in an induced pluripotent stem cell model of HD led to rates of CAG expansion similar to those observed with complete FAN1 knockout. Together, these data implicate FAN1 nuclease activity in slowing somatic repeat expansion and hence onset of HD.