Research Around the World

HD Research around the World: Canada

By: Lise Munsie, PhD

Canada-FlagInvestigators across Canada are heavily involved in HD research; these teams tackle a broad array of HD related research topics ranging from basic cell biology and biochemistry of the huntingtin (Htt) protein, to therapeutic leads and large clinical trials.

On the east coast, Dr. Eileen Denovan-Wright’s lab at the University of Dalhousie focuses on the cell biology of Htt in mouse models. Her group explores altered gene expression and its consequences in the brain. Their current research focuses on cannabanoid receptors. Dr. Denovan-Wright’s group recently published a manuscript that looks at the dysregulation of genes in the cytokine and endocannabinoid systems in HD. They posit that activation of p65/ RelA, which co-regulates expression of cytokine and endocannabinoid receptor genes, may prove beneficial in HD.1

In Ontario, Dr. Ray Truant’s lab at McMaster University is looking at the normal function of Htt and related dysfunction of mHtt, using cell models and biophotonic techniques.Dr. Truant’s lab uses advanced and elegant techniques, described in their recent paper published in Human Molecular Genetics, that looks at fluorescently tagged Htt, in aggregates, in live cells.2 Also in Ontario, Dr. Mark Guttman, a movement disorder neurologist affiliated with the University of Toronto, is heavily involved in PREDICT-HD, as well as caring for HD patients across the province.

In the prairies, Dr. Simonetta Sipione’s lab at the University of Alberta uses a multi-disciplinary approach to study mechanisms behind HD for the drug discovery pipeline. In the past year this group uncovered GM1 as a therapeutic lead for HD treatment.3

Finally, the west coast province of British Columbia is a hotbed for HD research.

The Centre for Molecular Medicine and Therapeutics, affiliated with the University of British Columbia (UBC), houses the labs of Dr. Michael Hayden (see HD Insights, vol. 4) and Dr. Blair Leavitt (see HD Insights, vol. 3). These multi-faceted labs perform advanced HD research, including elucidating molecular mechanisms involved in the progression of HD, using many different mouse models.4 Dr. Hayden’s group has been heavily involved in developing therapeutics for HD, specifically antisense oligonucleotide (ASO) development for in vivo Htt knockdown (see HD Insights, vol. 3).5 In addition to their laboratory work, both Dr. Leavitt and Dr. Hayden are heavily involved in clinical trials, including the TRACKHD study,6 patient-based research, and HD genetic research.7 Also at UBC, Dr. Lynn Raymond’s lab specializes in neuroscience-related techniques including electrophysiology.8 With respect to HD, her group investigates the role of neurotransmitter receptors and the neuron-specific role of Htt and related dysfunction in HD.9


1 Laprairie RB, Warford JR, Hutchings S, et al. The cytokine and endocannabinoid systems are co-regulated by NF-kappaB p65 RelA in cell culture and transgenic mouse models of Huntington’s disease and in striatal tissue from Huntington’s disease patients. J Neuroimmunol. 2013 Dec 12; pii: S0165-5728(13)00339-1. doi: 10.1016/j.jneuroim.2013.12.008.

2 Caron NS, Hung CL, Atwal RS, Truant R. Live cell FRET and protein dynamics reveal two types of mutant huntingtin inclusions. Hum Mol Genet. 2013 Dec 11; doi: 10.1093/hmg/ddt625.

3 Di Pardo A, Maglione V, Alpaugh M, et al. Ganglioside GM1 induces phosphorylation of mutant huntingtin and restores normal motor behavior in Huntington disease mice. Proc Natl Acad Sci USA. 2012 Feb 28; 109(9):3528-33. doi: 10.1073/pnas. 1114502109.

4 Mazarei G, Budac DP, Lu G, et al. Age-dependent alterations of the kynurenine pathway in the YAC128 mouse model of Huntington disease. J Neurochem. 2013 Dec; 127(6):852-67. doi:10.1111/jnc.12350.

5 Ostergaard ME, Southwell AL, Kordasiewicz H, et al. Rational design of antisense oligonucleotides targeting single nucleotide polymorphisms for potent and allele selective suppression of mutant Huntingtin in the CNS. Nucleic Acids Res. 2013 Nov; 41(21):9634-50.

6 Franciosi S, Shim Y, Lau M, Hayden MR, Leavitt BR. A systematic review and meta-analysis of clinical variables used in Huntington disease research. Mov Disord. 2013 Dec;28(14): 987-94. doi: 10.1002/mds.25663.

7 Semaka A, Hayden M. Evidence-based genetic counselling implications for Huntington disease intermediate allele predictive test results. Clin Genet. 2013 Nov 20; doi: 10.1111/ cge.12324.

8 Milnerwood AJ, Parsons MP, Young FB, et al. Memory and synaptic deficits in Hip14/DHHC17 knockout mice. Proc Natl Acad Sci USA. 2013 Nov 25; 110:20296-20301.

9 Parsons MP, Kang R, Buren C, et al. Bidirectional control of postsynaptic density-95 (PSD-95) clustering by huntingtin. J Biol Chem. 2013 Dec 17; doi: 10.1074/jbc.M113.513945jbc.M113.513945.

If you are interested in contributing a piece that highlights research in your part of the world, please contact us at editor@hdinsights.org.

HD Research Around the World: France

franceImaging Brain Metabolic Markers at the Institut du Cerveau et de la Moelle Épinière (ICM), Paris

By: Isaac M. Adanyeguh

In addition to the well-known neurological phenotype, HD presents with non-neurological symptoms that suggest hyper-catabolism in the early stage of the disease, leading to significant weight loss1. Metabolic dysfunction is therefore a major focus of HD research and may be easily amenable to therapeutic intervention2. Our team has shown that dietary anaplerotic therapy can improve peripheral energy metabolism in HD patients3. We also emphasized the potential of non-invasive 31- phosphorus magnetic resonance spectroscopy (31P MRS) in biomarker identification3. However, a sensitive biomarker of brain energy metabolism in HD patients has yet to be identified. Our team at ICM, Hôpital Pitié- Salpêtrière in Paris, led by Prof. Alexandra Durr and Dr. Fanny Mochel, is therefore interested in identifying biomarkers that reflect brain energy metabolism that could be used in therapeutic trials in HD patients.

To identify sensitive brain metabolic markers based on the results obtained in muscle3, we recruited 15 HD patients in the early stage of HD, but who were without significant cognitive impairment, and 15 age- and sex-matched controls, as subjects for brain 31P MRS on a 3T Siemens Magnetom Trio system. We targeted the visual cortex for the single-voxel functional MRS because it is easily stimulated and has high energy metabolism (Figure 1a). It is also very close to the scalp, giving an increased sensitivity to the small surface coils. A 6 cm 31P transmit/receive surface coil (Figure 1b) was used to detect signals (free induction decays – FIDs) from the visual cortex for 4 minutes at rest (baseline), 8 minutes during visual activation, and 8 minutes after visual stimulation (recovery), while limiting signals from other brain regions. A small sphere 10 mm in diameter filled with water and placed below the coil along the coil axis helped to verify and adjust the position of the 31P coil on T1 images (Figure 1a). Visual stimulation was performed with 6 Hz red and black checkerboard flashes (Figure 1c) generated in MATLAB and projected by a video projector onto a screen at the beginning of 8 minutes of stimulation. Subjects were able to focus on the flashes with a nonmagnetic mirror mounted above their eyes.

Figure 1: a) T1-weighted image with highlighted visual cortex showing the position of the sphere filled with water. The black square shows the region used for localized 1H shimming. The dashed white line indicates the sensitive volume of the coil encompassing most of the visual cortex.

Figure 1a:
T1-weighted image with highlighted visual cortex showing the position of the sphere filled with water. The black square shows the region used for localized 1H shimming. The dashed white line indicates the sensitive volume of the coil encompassing most of the visual cortex.

Figure 1: b) The 6 cm 31P transmit/receive coil in a holder with mounted mirror used in the lab.

Figure 1b:
The 6 cm 31P transmit/receive coil in a holder with mounted mirror used in the lab.

Figure 1: c) Red and black checkerboard used for visual stimulation

Figure 1c:
Red and black checkerboard used for visual stimulation.

 

 

 

 

 

 

 

 

 

 

 

We obtained 31P spectra from our MRS protocol in the brain (Figure 2). Analysis of the 31P spectra in the time domain using jMRUI software allowed the quantification of energy metabolites ATP, Pi and PCr. The ratio of Pi/PCr was then calculated to determine the brain response to cortical activation. The Pi/PCr ratio has been linked to mitochondrial activation and it provides an index of mitochondrial oxidative regulation4. At rest, there was no significant difference in Pi/ PCr ratio between HD patients and control subjects. Visual stimulation allowed us to analyse the evolution of the Pi/PCr ratio in HD and control subjects. The Bonferroni-corrected Wilcoxon signed-rank test indicated an 11% increase in Pi/PCr ratio between rest and activation (P = 0.024), followed by a decrease between activation and recovery (P = 0.012) in controls (Figure 3). In contrast, no difference was found between the three stages for the HD group for Pi/PCr ratio (Figure 3).

Figure 2: Representative 31P spectrum obtained at 3T with well-defined high-energy phosphate metabolites from the visual cortex of a control subject.

Figure 2:
Representative 31P spectrum obtained at 3T with well-defined high-energy phosphate metabolites from the visual cortex of a control subject.

Figure 3: Pi/PCr ratio before, during and after visual stimulation of 15 HD patients and 15 age- and sex-matched controls. Bonferroni-corrected Wilcoxon signedrank test indicated increased Pi/PCr between rest and activation (p = 0.024a) followed by a decrease between activation and recovery (p = 0.012b). No change was observed in patients (p > 0.05).

Figure 3:
Pi/PCr ratio before, during and after visual stimulation of 15 HD patients and 15 age- and sex-matched controls. Bonferroni-corrected Wilcoxon signedrank test indicated increased Pi/PCr between rest and activation (p = 0.024a) followed by a decrease between activation and recovery (p = 0.012b). No change was observed in patients (p > 0.05).

 

 

 

 

 

 

 

 

 

 

 

Because the observed changes were relatively small, a subsequent study will allow us to further explore the use of Pi/ PCr ratio as an outcome measure in HD clinical trials. Recruiting patients from the previous study will allow us to test the reproducibility of the initial findings in the same patient population and measure longitudinal changes. New patients at the early stage of the disease will also be recruited to validate our findings in an independent study population. In addition, we wish to include premanifest individuals to assess whether an abnormal brain energy profile can be identified before onset of overt HD symptoms, which is essential for development of future therapies.


 

1 Mochel F, Charles P, Seguin F, et al. Early energy deficit in Huntington disease: identification of a plasma biomarker traceable during disease progression. PLoS ONE. 2007 Jul 25; 2(7):e647. doi:10.1371/journal.pone.0000647.

2 Mochel F, Haller RG. Energy deficit in Huntington disease: why it matters. J Clin Invest. 2011 Feb 1;121(2):493–499. doi: 10.1172/JCI45691.

3 Mochel F, Duteil S, Marelli C, et al. Dietary anaplerotic therapy improves peripheral tissue energy metabolism in patients with Huntington’s disease. Eur J Hum Genet. 2010 Sep; 18(9):1057-60. doi: 10.1038/ejhg.2010.72. Epub 2010 May 26.

4 Weiner DH, Fink LI, Maris J, et al. Abnormal skeletal muscle bioenergetics during exercise in patients with heart failure: role of reduced muscle blood flow. Circulation. 1986 Jun; 73(6):1127-36.

HD Research Around the World: Australia

HD Down Under

By: Izelle Labuschagne, PhD

australiaApproximately 1,200 Australians have HD and 6,000 people are at risk1. HD got its start in our island state of Tasmania, where it was first introduced in 1842 by a woman from Somerset, England, who had 13 children, 11 of whom carried the HD gene.

The 1970s in Australia saw significant early developments for HD, thanks to psychiatrist and educator Professor Edmond Yu-Kuen Chiu. In 1972, Professor Chiu envisioned a plan that would eventually result in the opening of the first HD clinic in Australia at the Royal Melbourne Hospital, followed by his establishment in 1973 of the Australian HD Association. Since then, many more clinical services for HD have been established in other Australian states.

Our largest HD research efforts come from Melbourne-based researchers. Biochemist Dr. Danny Hatters from the University of Melbourne’s Bio21 Institute leads a team studying how clumps of huntingtin (Htt) form, and their role in disease pathogenesis. Dr Hatters’ group has developed tools for dissecting how Htt clumps accumulate at the molecular level. For example, sedimentation velocity analysis can measure the size and heterogeneity of all Htt molecules in a cell extract2, 3. Another more recently developed method can, for the first time, separate and recover cells enriched with mutant Htt in dispersed patterns relative to Htt in inclusions4, which allows detailed study of the aggregation and clumping process and how it relates to biological functioning of the cells that contain mutant Htt (Figure 1).

Figure 1. A new approach developed by Dr Hatters’ research team that enables cells with inclusions to be separated from those without4. a) The technique uses pulse shape information from a flow cytometer to separate diffuse patterns of Htt from inclusions. b) Analysis of a normal polyglutamine length (25Q) versus a HD length (46Q) shows a new population of cells (i), that have inclusions, as distinct from cells that have diffuse Htt (ni). c) The enrichment of these cells was verified by microscopy.

Figure 1. A new approach developed by Dr Hatters’ research team that enables cells with inclusions to be separated from those without4. a) The technique uses pulse shape information from a flow cytometer to separate diffuse patterns of Htt from inclusions. b) Analysis of a normal polyglutamine length (25Q) versus a HD length (46Q) shows a new population of cells (i), that have inclusions, as distinct from cells that have diffuse Htt (ni). c) The enrichment of these cells was verified by microscopy.

Professor Anthony Hannan and his team at the Florey Institute of Neuroscience and Mental Health in Melbourne have made exciting discoveries using the R6/1 transgenic mouse model of HD. A key discovery from their work was the finding that environmental enrichment has beneficial effects on the development of HD in the transgenic mice. Environmental enrichment resulted in a delay in onset and a slowing of disease progression in the mice5, and it also resulted in the rescue of abnormal stress response in the adrenal cells6 (Figure 2). Furthermore, increased physical activity delayed motor onset and slowed cognitive decline7. Hannan’s team was the first to demonstrate the beneficial effects of environmental stimulation in a genetic model of a brain disorder. These, and other findings from Hannan’s lab, provide a biological foundation for the potential of environmental enrichment as a treatment option for HD.

Our focus at Monash University in Melbourne is on clinical studies assessing cognition and structural brain changes in HD. Our work is well-integrated with the largest HD clinic in the state, run by Dr. Andrew Churchyard at the Calvary-Bethlehem Hospital.

Figure 2. Environmental enrichment changes the temporal dynamics of the stress response and strikingly implies that adrenal cells maintain an in vitro epigenetic memory of their previous in vivo environmental enrichment; the first evidence that environmental enrichment can act on such a peripheral organ6 .

Figure 2. Environmental enrichment changes the temporal dynamics of the stress response and strikingly implies that adrenal cells maintain an in vitro epigenetic memory of their previous in vivo environmental enrichment; the first evidence that environmental enrichment can act on such a peripheral organ6 .

My research team, led by Professor Julie Stout, uses tools for sensitive measurement of cognitive dysfunction to aid in the understnding and treatment of HD. Success in finding treatments to restore cognition or slow cognitive deterioration rests on the sensitivity of cognitive outcomes that can be tolerated during clinical trials and that are responsive to treatment. The Stoutlab recently developed and standardized a new Cognitive Assessment Battery, in conjunction with the CHDI Foundation, using a 20-site international study (unpublished data). Further, our group leads the cognitive component of the multinational longitudinal observational study, TrackHD8, in which we have been able to identify key cross-sectional and longitudinal markers of cognitive decline in large samples of HD patients.

Within the Stout lab, my own research addresses the social and emotional aspects of HD, and whether current medications impede socio-emotional outcomes9. I am currently leading an fMRI study in HD on whether intranasal oxytocin, a hormone associated with bonding, might improve neural responses to social-emotion cues, as has been observed in other disorders.

Figure 3. Longitudinal 30-month change in brain activity and functional connectivity in pre-HD during a working memory task (2-BACK). PreHD participants show an increased level of activation in corticostriatal networks over time (top images) despite the progressive loss of functional connectivity (bottom images) (unpublished data).

Figure 3. Longitudinal 30-month change in brain activity and functional connectivity in pre-HD during a working memory task (2-BACK). PreHD participants show an increased level of activation in corticostriatal networks over time (top images) despite the progressive loss of functional connectivity (bottom images) (unpublished data).

Professor Nellie Georgiou-Karistianis’s lab investigates motor and cognitive deficits in HD using a range of experimental paradigms. Georgiou-Karistianis leads the IMAGE-HD project, an Australia-based longitudinal multimodal biomarker development study, which followed a cohort of premanifest HD (pre-HD), early symptomatic HD (symp-HD) and healthy controls at three time points over 30 months. To date, this study has yielded cross-sectional and longitudinal reports on the impact of HD on multimodal magnetic resonance neuroimaging biomarkers of macrostructural, microstructural, and functional integrity10, 11, 12. Data from the 30-month functional imaging studies in working memory and set-shifting, although currently unpublished, shows dynamic changes in activity and connectivity in pre-HD and symp-HD, suggesting possible compensatory mechanisms occurring well in advance of disease onset (Figure 3).

Although I have highlighted the Melbourne, Victoria, research contribution, several colleagues in other states are making important contributions, notably Clement Loy and Elizabeth McCusker in New South Wales, and Peter Panegyres in Western Australia. And the kiwis in New Zealand are also punching above their weight, with collaborative projects in Adelaide, South Australia using a sheep model of HD, and other clinical research projects.

 

 

 


1 Conneally, PM. Huntington disease: genetics and epidemiology. Am J Hum Genet. 1984; 36(3):506-26. 2 Olshina, MA, et al. Tracking mutant huntingtin aggregation kinetics in cells reveals three major populations that include an invariant oligomer pool. J Biol Chem. 2010; 285(28):21807-16.

3 Hatters, DM. Putting huntingtin “aggregation” in view with windows into the cellular milieu. Curr Top Med Chem. 2012;12(22):2611-22.

4 Ramdzan, YM, et al. Tracking protein aggregation and mislocalization in cells with flow cytometry. Nat Methods. 2012;9(5):467-70.

5 van Dellen, A, et al. Delaying the onset of Huntington’s in mice. Nature. 2000;404(6779):721-2.

6 Du, X, et al. Environmental enrichment rescues femalespecific hyperactivity of the hypothalamic-pituitary-adrenal axis in a model of Huntington’s disease. Transl Psychiatry. 2012;2:133.

7 Pang, TY, et al. Differential effects of voluntary physical exercise on behavioral and brain-derived neurotrophic factor expression deficits in Huntington’s disease transgenic mice. Neurosci. 2006;141(2):569-84.

8 Tabrizi, SJ, et al. Predictors of phenotypic progression and disease onset in premanifest and early-stage Huntington’s disease in the TRACK-HD study: analysis of 36-month observational data. Lancet Neurol, 2013;12(7):637-49.

9 Labuschagne, I, et al. Emotional face recognition deficits and medication effects in pre-manifest through stage-II Huntington’s disease. Psychiatry Res. 2013; 207(1-2):118-26.

10 Georgiou-Karistianis, N, et al. Automated differentiation of pre-diagnosis Huntington’s disease from healthy control individuals based on quadratic discriminant analysis of the basal ganglia: The IMAGE-HD study. Neurobiol Dis. 2013;51:82-92.

11 Poudel, GR, et al. Abnormal synchrony of resting-state networks in premanifest and symptomatic Huntington’s disease: The IMAGE-HD Study. J Psychiatry Neurosci. Forthcoming 2013.

12 Georgiou-Karistianis, N, et al. Functional magnetic resonance imaging of working memory in Huntington’s disease: Cross-sectional data from the IMAGE-HD study. Hum Brain Mapp. Forthcoming 2013.

HD Research Around the World: Japan

Past, Present, and Future

japanBy: Hitoshi Okazawa, MD, PhD

Huntington disease (HD) is rare in Japan. Its incidence is one-tenth of that observed in western countries, and as a result, the number of researchers studying HD in Japan is relatively low.

Dr. Ichiro Kanazawa, former chair of the Department of Neurology at the University of Tokyo, was the first to initiate research on the molecular genetics and biology of HD in Japan. After Gusella and colleagues identified the HD causative gene in 1993, Dr. Kanazawa and Dr. Nobuyuki Nukina and colleagues used immunohistochemistry and western blot techniques to generate a polyclonal antibody against the expected mutant protein (mHtt), and confirmed the difference in length of the polyglutamine repeat sequence in mHtt compared to Htt, and its expression in the brain1.

When post-genome research on HD started, Nukina discovered the involvement of the heat shock protein 40 family (Hsp40) and heat shock protein 70 family (Hsp70) in the pathogenesis of HD2. He developed a unique therapeutic approach based on selective autophagy3, and discovered the regulation of selective autophagy via the phosphorylation of p624. My group studies the functional side of mHtt. The polyglutamine repeat sequence is important for transcription-related proteins. Oct-3/ Oct-4, an octamer transcription factor, is now recognized as the most important transcription factor for embryonic stem cells and induced pluripotent stem cells5. Many transcription factors possess these polyglutamine sequences, and the tract sequence has been suggested as a motif for protein–protein interaction. Using this knowledge, my group identified a novel mediator of polyglutamine diseases, namely polyglutamine-binding protein-16, 7, which the European Consortium of Xlinked Mental Retardation subsequently recognized as the cause of a spectrum of mental retardations8.

Much of the current HD research in Japan is focused on therapy. Therapeutic research trends include the activation of selective autophagy; inhibition of mHtt; functional recovery of target physiological proteins; and use of induced pluripotent stem cells. Some of these approaches have reached the preclinical stage. Dr. Nukinaʼs group has identified that trehalose has a therapeutic effect in HD9. Dr. Nagai (National Center of Neurology and Psychiatry) and colleagues discovered that polyglutamine-binding peptide-1 (an artificial peptide distinct from the endogenous polyglutamine-binding protein-1 referred to above) showed a protective effect against aggregation10, 11.

Meanwhile, my group has used genomics and proteomics to screen pathological mediators of HD. Using genomics, we determined that Hsp70 plays a critical role in neuron subtype-specific vulnerability12. Using proteomics, we found that high-mobility group protein B, a DNA architectural protein, is involved in HD pathology13. In collaboration with Dr. Erich Wanker (Max-Delbrück Center for Molecular Medicine, Germany) and by using an interactomics approach, we discovered that Ku70, a DNA damage repair protein, plays a role in HD pathology14. More recently, we discovered that DNA damage repair by VCP/TERA/p97 is involved in the pathology of many polyglutamine diseases15. These targets of mHtt are functionally disturbed in HD, and the foci of their functions cluster around transcription and DNA damage repair, although other functions of these molecules, such as autophagy, may also be relevant. Functional rescue of these molecular targets has proved very successful in mice models of HD. Viral vector-mediated supplementation of high-mobility group protein B1, Ku70, and some other molecules has been very successful in mice model treatment for HD, spinocerebellar ataxia type 1, and other diseases. Details of such research will be published in the future.

DNA double strand break is increased in striatal neurons of human HD patients.14

DNA double strand break is increased in striatal neurons of human HD patients.14

Lifespan elongation by Ku70. Double transgenic mice have a 30% longer lifespan.14

Lifespan elongation by Ku70. Double transgenic mice have a 30% longer lifespan.14

 Colocalization of mutant huntingtin and Ku70 in astriatal neuron of R6/2 mouse.14


Colocalization of mutant huntingtin and Ku70 in astriatal neuron of R6/2 mouse.14

 

 

 

 

 

 

 

 

 

 

Moreover, mice models of HD treated with the above-mentioned genes have shown longer survival than other reported treatments. Due to limited social and financial support for HD research in Japan, HD research groups collaborate closely with each other and with research groups studying other neurodegenerative diseases. In order to advance HD research in Japan, there must be closer collaboration with researchers in countries that have a higher incidence of HD and consequent stronger support for HD research. International collaboration with pharmaceutical companies is also essential.

Dr. Okazawa would like to thank all friends around the world for their current and future support.


 

1 Yazawa I, Nukina N, Hashida H, et al. Abnormal gene product identified in hereditary dentatorubralpallidoluysian atrophy (DRPLA) brain. Nat Genet 1995 May; 10(1):99-103.

2 Jana NR, Tanaka M, Wang GH, et al. Polyglutamine lengthdependent interaction of Hsp40 and Hsp70 family chaperones with truncated N-

3 Bauer PO, Goswami A, Wong HK, et al. Harnessing chaperone-mediated autophagy for the selective degradation of mutant huntingtin protein. Nat Biotechnol 2010 Mar;28(3): 256-63. doi: 10.1038/nbt.1608. Epub 2010 Feb 28.

4 Matsumoto G, Wada K, Okuno M, et al. Serine 403 phosphorylation of p62/SQSTM1 regulates selective autophagic clearance of ubiquitinated proteins. Mol Cell 2011 Oct;44(2):279-89.

5 Okamoto K, Okazawa H, Okuda A, et al. A novel octamer binding transcription factor is differentially expressed in mouse embryonic cells. Cell 1990 Feb;60(3):461-72.

6 Waragai M, Lammers CH, Takeuchi S, et al. PQBP-1, a novel polyglutamine tract-binding protein, inhibits transcription activation by Brn-2 and affects cell survival. Hum Mol Genet 1999 Jun; 8(6):977-87. 7 Okazawa H, Rich T, Chang A, et al. Interaction between mutant ataxin-1 and PQBP-1 affects transcription and cell death. Neuron 2002 May;34(5):701-13.

8 Kalscheuer VM, Freude K, Musante L, et al. Mutations in the polyglutamine binding protein 1 gene cause X-linked mental retardation. Nat Genet. 2003 Dec; 35(4):313-5. Epub 2003 Nov 23.

9 Tanaka M, Machida Y, Niu S, et al. Trehalose alleviates polyglutamine-mediated pathology in a mouse model of Huntington disease. Nat Med 2004 Feb;10(2):148-54.

10 Nagai Y, Tucker T, Ren H, et al. Inhibition of polyglutamine protein aggregation and cell death by novel peptides identified by phage display screening. J Biol Chem 2000 Apr; 275(14):10437-42.

11 Nagai Y, Fujikake N, Ohno K, et al. Prevention of polyglutamine oligomerization and neurodegeneration by the peptide inhibitor QBP1 in Drosophila. Hum Mol Genet 2003 Jun; 12(11):1253-9.

12 Tagawa K, Marubuchi S, Qi ML, et al. The induction levels of heat shock protein 70 differentiate the vulnerabilities to mutant huntingtin among neuronal subtypes. J Neurosci 2007 Jan; 27(4):868-80.

13 Qi ML, Tagawa K, Enokido Y, et al. Proteome analysis of soluble nuclear proteins reveals that HMGB1/2 suppress genotoxic stress in polyglutamine diseases. Nat Cell Biol 2007 Apr; 9(4):402-14.

14 Enokido Y, Tamura T, Ito H, et al. Mutant huntingtin impairs Ku70-mediated DNA repair. J Cell Biol 2010 May 3; 189(3):425-43.

15 Fujita K, Nakamura Y, Oka T, et al. A functional deficiency of TERA/VCP/p97 contributes to impaired DNA damage repair in multiple polyglutamine diseases. Nature Commun In press.

Research Around the World: Chile

Alleviating Secretory Pathway Stress in Huntington Disease

By: Rene Vidal, PhD and Claudio Hetz, PhD

chileMany clinical trials that use drugs validated in mouse models of HD have failed to alleviate disease progression in humans. Preclinical studies have been performed in transgenic mice of pure genetic backgrounds that overexpress high levels of truncated forms of mutant huntingtin (mHtt). This mouse model, and other HD mouse models, does not truly replicate HD in humans. Several HD mouse models are available, including many mHtt knock-in mice. However, these mouse models often require the use of homozygous mHtt alleles, because mice carrying only one mutant allele develop very minor phenotypes and fail to express most of the distinctive features of HD. Also, cellular processes known to be important for neuronal function are often altered in HD mouse models. Researchers are developing strategies to identify molecular events that transcend various HD cellular and animal models, and correlate these with alterations observed in human HD-derived samples.

A common molecular feature described in cellular and animal models of HD is the occurrence of protein folding stress responses in the brain, possibly caused by alterations of the protein secretory pathway. Defects in virtually every step of the secretory pathway are observed in HD neurons, such as perturbations in protein folding networks; vesicular transport; the endoplasmic reticulum (ER) and Golgi 3D patterning; protein quality control mechanisms (i.e. autophagy and the ER-associated degradation pathway); and ER calcium homeostasis. Many alterations of the of the protein secretory pathway generate alterations in the protein folding process and lead to a pathological condition known as ER stress.

Some investigators take a global view of mHtt pathogenesis and hypothesize that strategies aimed at alleviating secretory pathway stress may have beneficial effects in HD. Studies have documented activation of the unfolded protein response (UPR), an adaptive reaction against ER stress, in animal models of HD and human postmortem samples from HD patients. Studies in HD cellular models support the concept that chronic ER stress contributes to HD related neurodegeneration1. Lee and colleagues demonstrated that the ER stress sensor IRE1 may govern mHtt aggregation and neurotoxicity through a molecular crosstalk with autophagy, another homeostatic pathway2. IRE1 enhanced mHtt degradation by the lysosome-autophagy pathway. Targeting the stress networks involved in protein homeostasis is an interesting method of disease intervention. We investigated the possible contribution of ER stress to phenotypic HD in vivo using a recently generated strain of mice that selectively lack XBP1 in neurons (the downstream target of IRE1).

Despite predictions that XBP1 deficiency would increase the severity of experimental HD, we observed that this genetic manipulation triggered resistance to development of the disease. XBP1 deficiency enhanced neuronal survival and improved motor performance of a full-length mHtt transgenic mouse (the YAC128 model)3. We also validated the effects of XBP1 on mHtt levels in a heterozygous knock-in mouse HD model. The mechanism of protection appears to be related to the upregulation of autophagy and the degradation of full-length mHtt in the lysosomes. In collaboration with Dr. Ana Maria Cuervo (Albert Einstein College of Medicine), we showed that mHtt is delivered to autophagosomes and autophagolysosomes in vivo upon targeting XBP1 in the nervous system. This observation suggests that a homeostatic crosstalk between the UPR and autophagy is a response against mHtt pathogenesis that may be manipulated to provide protection against HD. At the molecular level, we found a negative regulation of the transcription factor FoxO1 by XBP1 in vivo. Fox01 is a major protein involved in ageing and operates as a macrostress integrator of metabolic and stress processes.

Secretory pathway stress in HD could be manipulated by targeting different components of this network, including homeostatic pathways such as the UPR and autophagy.

General pharmacological strategies may include administration of chemical chaperones such as TUDCA or 4-PBA, modulators of UPR components (i.e. available IRE1 inhibitors), or autophagy enhancers such as trehalose or rapamycin. The use of gene therapy to target proteinfolding stress has been applied to other neurodegenerative diseases with the aim of targeting protein homeostasis, and may be an approach to consider, since HD is a disease that progresses slowly.

The development of network modifying therapeutic interventions may lead to important protective advances in the HD field. Minor shifts in the protein homeostasis network may involve the alteration of hundreds of target genes that as a whole may result in beneficial effects in HD. Thus, modulating global homeostatic processes could have broad impact for chronic alterations observed in HD that involve multiple aspects of neuronal physiology and protein homeostasis.


 

1 Vidal R, Caballero B, Couve A, Hetz C. Converging pathways in the occurrence of endoplasmic reticulum (ER) stress in Huntington’s disease. Curr Mol Med. 2011 Feb; 11(1):1-12.

2 Lee H, Noh JY, Oh Y, et al. IRE1 plays an essential role in ER stress-mediated aggregation of mutant huntingtin via the inhibition of autophagy flux. Hum Mol Genet 2012 Jan; 21(1): 101-14.

3 Vidal RL, Figueroa A, Court FA, et al. Targeting the UPR transcription factor XBP1 protects against Huntington’s disease through the regulation of FoxO1 and autophagy. Hum Mol Genet 2012 May; 21(10):2245-62.