Progressive decrease in chaperone protein levels in a mouse model of Huntington's disease and induction of stress proteins as a therapeutic approach.

The manipulation of chaperone levels has been shown to inhibit aggregation and/or rescue cell death in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster and cell culture models of Huntington's disease (HD) and other polyglutamine (polyQ) disorders. We show here that a progressive decrease in Hdj1, Hdj2, Hsp70, alphaSGT and betaSGT brain levels likely contributes to disease pathogenesis in the R6/2 mouse model of HD. Despite a predominantly extranuclear location, Hdj1, Hdj2, Hsc70, alphaSGT and betaSGT were found to co-localize with nuclear but not with extranuclear aggregates. Quantification of Hdj1 and alphaSGT mRNA levels showed that these do not change and therefore the decrease in protein levels may be a consequence of their sequestration to aggregates, or an increase in protein turnover, possibly as a consequence of their relocation to the nucleus. We have used genetic and pharmacological approaches to assess the therapeutic potential of chaperone manipulation. Ubiquitous overexpression of Hsp70 in the R6/2 mouse (as a result of crossing to Hsp70 transgenics) delays aggregate formation by 1 week, has no effect on the detergent solubility of aggregates and does not alter the course of the neurological phenotype. We used an organotypic slice culture assay to show that pharmacological induction of the heat shock response might be a more useful approach. Radicicol and geldanamycin could both maintain chaperone induction for at least 3 weeks and alter the detergent soluble properties of polyQ aggregates over this time course.

Standardization and statistical approaches to therapeutic trials in the R6/2 mouse.

The R6/2 mouse is the most widely used animal model of Huntington's disease (HD), a genetic disorder causing movement disorders, personality changes, dementia, and premature death, for which there is currently no effective therapy. Use of animal models to assess novel therapeutic approaches to HD is currently a major focus of research. Progress in this field will depend upon careful standardization of experimental protocols, and a sophisticated statistical approach. Here we investigate the sources of phenotypic variability in R6/2, and make recommendations for the future use of such models in therapeutic trials.

Minocycline and doxycycline are not beneficial in a model of Huntington's disease.

Huntington's Disease (HD) is an inherited neurological disorder causing movement impairment, personality changes, dementia, and premature death, for which there is currently no effective therapy. The modified tetracycline antibiotic, minocycline, has been reported to ameliorate the disease phenotype in the R6/2 mouse model of HD. Because the tetracyclines have also been reported to inhibit aggregation in other amyloid disorders, we have investigated their ability to inhibit huntingtin aggregation and further explored their efficacy in preclinical mouse trials. We show that tetracyclines are potent inhibitors of huntingtin aggregation in a hippocampal slice culture model of HD at an effective concentration of 30 microM. However, despite achieving tissue levels approaching this concentration by oral treatment of R6/2 mice with minocycline, we observed no clear difference in their behavioral abnormalities, or in aggregate load postmortem. In the light of these new data, we would advise that caution be exercised in proceeding into human clinical trials of minocycline.

Suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, ameliorates motor deficits in a mouse model of Huntington's disease.

Huntington's disease (HD) is an inherited, progressive neurological disorder that is caused by a CAG/polyglutamine repeat expansion and for which there is no effective therapy. Recent evidence indicates that transcriptional dysregulation may contribute to the molecular pathogenesis of this disease. Supporting this view, administration of histone deacetylase (HDAC) inhibitors has been shown to rescue lethality and photoreceptor neurodegeneration in a Drosophila model of polyglutamine disease. To further explore the therapeutic potential of HDAC inhibitors, we have conducted preclinical trials with suberoylanilide hydroxamic acid (SAHA), a potent HDAC inhibitor, in the R6/2 HD mouse model. We show that SAHA crosses the blood-brain barrier and increases histone acetylation in the brain. We found that SAHA could be administered orally in drinking water when complexed with cyclodextrins. SAHA dramatically improved the motor impairment in R6/2 mice, clearly validating the pursuit of this class of compounds as HD therapeutics.

Abnormal phosphorylation of synapsin I predicts a neuronal transmission impairment in the R6/2 Huntington's disease transgenic mice.

Motor and cognitive deficits in Huntington's disease (HD) are likely caused by progressive neuronal dysfunction preceding neuronal cell death. Synapsin I is one of the major phosphoproteins regulating neurotransmitter release. We report here an abnormal phosphorylation state of synapsin I in the striatum and the cerebral cortex of R6/2 transgenic mice expressing the HD mutation. These changes are mostly characterized by an early overphosphorylation at sites 3-5, whereas phosphorylation at site 1 remains unchanged and at site 6 becomes reduced only close to the end stage of the disease. Such changes do not result from modification in protein expression levels. However, we show a decreased expression of the calcineurin regulatory subunit-B, which may contribute to an imbalance between kinase and phosphatase activities. Together the results suggest that an early impairment in synapsin phosphorylation-dephosphorylation may alter synaptic vesicle trafficking and lead to defective neurotransmission in HD.

Environmental enrichment slows disease progression in R6/2 Huntington's disease mice.

Huntington's disease is a genetic disorder that causes motor dysfunction, personality changes, dementia, and premature death. There is currently no effective therapy. Several transgenic models of Huntington's disease are available, the most widely used of which is the R6/2 mouse, because of its rapid disease progression. Environmental enrichment alters gene expression in the normal mouse brain, and modulates the course of several neurological disorders. Environmentally enriched mice may actually mimic human disease more accurately. We found that even limited environmental enrichment slows decline in RotaRod performance in R6/2 mice, despite rapid disease progression, whereas in normal littermates, maximal enrichment was required to induce a marked improvement in behavioral tests. Enrichment also delayed the loss of peristriatal cerebral volume in R6/2 brains. These results could provide the basis for a rational approach to ameliorate the effects of Huntington's disease.