SIRT2 Ablation Has No Effect on Tubulin Acetylation in Brain, Cholesterol Biosynthesis or the Progression of Huntington's Disease Phenotypes In Vivo

Huntington's disease (HD) is a devastating neurodegenerative disorder for which there are no disease-modifying treatments. The molecular pathogenesis of HD is complex and many mechanisms and cellular processes have been proposed as potential sites of therapeutic intervention. However, prior to embarking on drug development initiatives, it is essential that therapeutic targets can be validated in mammalian models of HD. Previous studies in invertebrate and cell culture HD models have suggested that inhibition of SIRT2 could have beneficial consequences on disease progression. SIRT2 is a NAD[superscript +]-dependent deacetylase that has been proposed to deacetylate α-tubulin, histone H4 K16 and to regulate cholesterol biogenesis – a pathway which is dysregulated in HD patients and HD mouse models. We have utilized mice in which SIRT2 has been reduced or ablated to further explore the function of SIRT2 and to assess whether SIRT2 loss has a beneficial impact on disease progression in the R6/2 mouse model of HD. Surprisingly we found that reduction or loss of SIRT2 had no effect on the acetylation of α-tubulin or H4K16 or on cholesterol biosynthesis in the brains of wild type mice. Equally, genetic reduction or ablation of SIRT2 had no effect on HD progression as assessed by a battery of physiological and behavioural tests. Furthermore, we observed no change in aggregate load or levels of soluble mutant huntingtin transprotein. Intriguingly, neither the constitutive genetic loss nor acute pharmacological inhibition of SIRT2 affected the expression of cholesterol biosynthesis enzymes in the context of HD. Therefore, we conclude that SIRT2 inhibition does not modify disease progression in the R6/2 mouse model of HD and SIRT2 inhibition should not be prioritised as a therapeutic option for HD.American Parkinson Disease Association, Inc. (Fellowship)Johnson & Johnson. Pharmaceutical Research & Development (Fellowship

Protein homeostasis and aging in neurodegeneration

Genetic and environmental factors responsible for numerous neurodegenerative diseases vary between disorders, yet age remains a universal risk factor. Age-associated decline in protein homeostasis, or proteostasis, enables disease-linked proteins to adopt aberrant tertiary structures, accumulate as higher-ordered aggregates, and cause a myriad of cellular dysfunctions and neuronal death. However, recent findings suggest that the assembly of disease proteins into tightly ordered aggregates can significantly delay proteotoxic onset. Furthermore, manipulation of metabolic pathways through key signaling components extends lifespan, bolsters proteostasis networks, and delays the onset of proteotoxicity. Thus, understanding the relationship between proteostasis and aging has provided important insights into neurodegeneration

Neurodegenerative processes in Huntington's disease

Huntington's disease (HD) is a complex and severe disorder characterized by the gradual and the progressive loss of neurons, predominantly in the striatum, which leads to the typical motor and cognitive impairments associated with this pathology. HD is caused by a highly polymorphic CAG trinucleotide repeat expansion in the exon-1 of the gene encoding for huntingtin protein. Since the first discovery of the huntingtin gene, investigations with a consistent number of in-vitro and in-vivo models have provided insights into the toxic events related to the expression of the mutant protein. In this review, we will summarize the progress made in characterizing the signaling pathways that contribute to neuronal degeneration in HD. We will highlight the age-dependent loss of proteostasis that is primarily responsible for the formation of aggregates observed in HD patients. The most promising molecular targets for the development of pharmacological interventions will also be discussed

Interference to ongoing activities covaries with the characteristics of an event-based intention.

Previous studies of event-based prospective memory have demonstrated that the character of an ongoing task can affect cue detection. By contrast, this study demonstrated that there is a reciprocal relationship insofar as cue-verification and response-retrieval processes interfered with making a response in the ongoing task. The amount of interference was determined by the type of intention, which was manip-ulated to affect the complexity of verification and retrospective response retrieval. These relationships were true even when the interference caused by cue detection was separated from a more general effect to ongoing-task performance caused by shifts in attentional allocation policies. The results have theoretical implications for models that attempt to specify the cognitive microstructure of event-based prospective memory. People fulfill a variety of intentions in the course of everyday life. Some examples of different types of prospective-memory tasks include remembering to make a phone call after a certain duration has elapsed (a time-based task), performing an activity right after finishing a different one (an activity-based task), deliv-ering a message to an acquaintance (an event-based task), attend-ing a seminar on changes in health benefits (a novel task), taking vitamins or medication (a habitual intention), and so forth (Bran-dimonte, Einstein, & McDaniel, 1996). The particular cuing con-ditions associated with these different intentions vary along many dimensions, such as the amount of self-initiated processing that i

Mutant huntingtin alters MAPK signaling pathways in PC12 and striatal cells: ERK1/2 protects against mutant huntingtin-associated toxicity.

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by an expanded polyglutamine (polyQ) tract within the huntingtin protein (Htt). Identifying the pathways that are altered in response to the mutant protein is crucial for understanding the cellular processes impacted by the disease as well as for the rational development of effective pharmacological interventions. Here, expression profiling of a cellular HD model identifies genes that implicate altered mitogen-activated protein kinase (MAPK) signaling. Targeted biochemical studies and pharmacological modulation of these MAPK pathways suggest that mutant Htt affects signaling at upstream points such that both ERK and JNK are activated. Modulation of the ERK pathway suggests that this pathway is associated with cell survival, whereas inhibition of JNK was found to effectively suppress pathogenesis. These studies suggest that pharmacological intervention in MAPK pathways, particularly at the level of ERK activation, may be an appropriate approach to HD therapy

Mutant huntingtin alters MAPK signaling pathways in PC12 and striatal cells: ERK1/2 protects against mutant huntingtin-associated toxicity.

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by an expanded polyglutamine (polyQ) tract within the huntingtin protein (Htt). Identifying the pathways that are altered in response to the mutant protein is crucial for understanding the cellular processes impacted by the disease as well as for the rational development of effective pharmacological interventions. Here, expression profiling of a cellular HD model identifies genes that implicate altered mitogen-activated protein kinase (MAPK) signaling. Targeted biochemical studies and pharmacological modulation of these MAPK pathways suggest that mutant Htt affects signaling at upstream points such that both ERK and JNK are activated. Modulation of the ERK pathway suggests that this pathway is associated with cell survival, whereas inhibition of JNK was found to effectively suppress pathogenesis. These studies suggest that pharmacological intervention in MAPK pathways, particularly at the level of ERK activation, may be an appropriate approach to HD therapy

Histone deacetylase (HDAC) inhibitors targeting HDAC3 and HDAC1 ameliorate polyglutamine-elicited phenotypes in model systems of Huntington's disease.

We have previously demonstrated amelioration of Huntington's disease (HD)-related phenotypes in R6/2 transgenic mice in response to treatment with the novel histone deacetylase (HDAC) inhibitor 4b. Here we have measured the selectivity profiles of 4b and related compounds against class I and class II HDACs and have tested their ability to restore altered expression of genes related to HD pathology in mice and to rescue disease effects in cell culture and Drosophila models of HD. R6/2 transgenic and wild-type (wt) mice received daily injections of HDAC inhibitors for 3 days followed by real-time PCR analysis to detect expression differences for 13 HD-related genes. We find that HDACi 4b and 136, two compounds showing high potency for inhibiting HDAC3 were most effective in reversing the expression of genes relevant to HD, including Ppp1r1b, which encodes DARPP-32, a marker for medium spiny striatal neurons. In contrast, compounds targeting HDAC1 were less effective at correcting gene expression abnormalities in R6/2 transgenic mice, but did cause significant increases in the expression of selected genes. An additional panel of 4b-related compounds was tested in a Drosophila model of HD and in STHdhQ111 striatal cells to further distinguish HDAC selectivity. Significant improvement in huntingtin-elicited Drosophila eye neurodegeneration in the fly was observed in response to treatment with compounds targeting human HDAC1 and/or HDAC3. In STHdhQ111 striatal cells, the ability of HDAC inhibitors to improve huntingtin-elicited metabolic deficits correlated with the potency at inhibiting HDAC1 and HDAC3, although the IC50 values for HDAC1 inhibition were typically 10-fold higher than for inhibition of HDAC3. Assessment of HDAC protein localization in brain tissue by Western blot analysis revealed accumulation of HDAC1 and HDAC3 in the nucleus of HD transgenic mice compared to wt mice, with a concurrent decrease in cytoplasmic localization, suggesting that these HDACs contribute to a repressive chromatin environment in HD. No differences were detected in the localization of HDAC2, HDAC4 or HDAC7. These results suggest that inhibition of HDACs 1 and 3 can relieve HD-like phenotypes in model systems and that HDAC inhibitors targeting these isotypes might show therapeutic benefit in human HD

Histone deacetylase (HDAC) inhibitors targeting HDAC3 and HDAC1 ameliorate polyglutamine-elicited phenotypes in model systems of Huntington's disease.

We have previously demonstrated amelioration of Huntington's disease (HD)-related phenotypes in R6/2 transgenic mice in response to treatment with the novel histone deacetylase (HDAC) inhibitor 4b. Here we have measured the selectivity profiles of 4b and related compounds against class I and class II HDACs and have tested their ability to restore altered expression of genes related to HD pathology in mice and to rescue disease effects in cell culture and Drosophila models of HD. R6/2 transgenic and wild-type (wt) mice received daily injections of HDAC inhibitors for 3 days followed by real-time PCR analysis to detect expression differences for 13 HD-related genes. We find that HDACi 4b and 136, two compounds showing high potency for inhibiting HDAC3 were most effective in reversing the expression of genes relevant to HD, including Ppp1r1b, which encodes DARPP-32, a marker for medium spiny striatal neurons. In contrast, compounds targeting HDAC1 were less effective at correcting gene expression abnormalities in R6/2 transgenic mice, but did cause significant increases in the expression of selected genes. An additional panel of 4b-related compounds was tested in a Drosophila model of HD and in STHdhQ111 striatal cells to further distinguish HDAC selectivity. Significant improvement in huntingtin-elicited Drosophila eye neurodegeneration in the fly was observed in response to treatment with compounds targeting human HDAC1 and/or HDAC3. In STHdhQ111 striatal cells, the ability of HDAC inhibitors to improve huntingtin-elicited metabolic deficits correlated with the potency at inhibiting HDAC1 and HDAC3, although the IC50 values for HDAC1 inhibition were typically 10-fold higher than for inhibition of HDAC3. Assessment of HDAC protein localization in brain tissue by Western blot analysis revealed accumulation of HDAC1 and HDAC3 in the nucleus of HD transgenic mice compared to wt mice, with a concurrent decrease in cytoplasmic localization, suggesting that these HDACs contribute to a repressive chromatin environment in HD. No differences were detected in the localization of HDAC2, HDAC4 or HDAC7. These results suggest that inhibition of HDACs 1 and 3 can relieve HD-like phenotypes in model systems and that HDAC inhibitors targeting these isotypes might show therapeutic benefit in human HD