HD Insights™

HD INSIGHTS TM HD INSIGHTS Research Round-Up By: Lise Munsie, PhD In the beginning... In the past year, researchers have published on the use of stem cells to model Huntington disease (HD) and on investigations of stem cell use as a treatment for HD. Sadan and colleagues1 induced mesenchymal stem cells into neurotrophic factor– secreting (NTF) cells, then transplanted the NTF cells into rats that had striatal lesions induced by quinolinic acid (QA). The NTF cells, whether derived from an HD patient or a control, survived transplantation and maintained an NTF- secreting phenotype leading to improved striatal volume and behavioural phenotypes. Ma and colleagues2 showed that human embryonic stem cells can be directed into an enriched population of GABA medium spiny neurons. When GABA neurons were implanted into the striatum of a QA lesion mouse model, they maintained functionality, leading to phenotypic improvements in the mice. An and colleagues3 corrected the genetic mutation in HD patient–derived induced pluripotent stem cell (iPSC) lines using homologous recombination, and found this also corrected many of the aberrant phenotypes associated with neural stem cells (NSC) derived from these iPSC lines. Genetically corrected NSCs were able to populate the striatum of the R6/2 mouse post-transplantation. Patient-specific cell replacement therapy with corrected mutant huntingtin (mHTT) CAG lengths may be feasible in the future. The HD iPSC consortium4 generated and studied 14 iPSC lines from HD patients and controls. Investigators in different labs found clear and reproducible phenotypes associated with the disease-causing mutation, consistent in multiple lineages. These cell lines may be used in future assay development and screening in HD drug discovery efforts. 1 Sadan O, Shemesh N, Barzilay R, et al. Mesenchymal stem cells induced to secrete neurotrophic factors attenuate quinolinic acid toxicity: a potential therapy for Huntington's disease. Experimental neurology. 2012 Apr;234(2):417-27. 2 Ma L, Hu B, Liu Y, et al. Human embryonic stem cell-derived GABA neurons correct locomotion deficits in quinolinic acid- lesioned mice. Cell stem cell. 2012 Apr;10(4):455-64. 3 An MC, Zhang N, Scott G, et al. Genetic correction of Huntington's disease phenotypes in induced pluripotent stem cells. Cell stem cell. 2012 Aug;11(2):253-63. 4 ThHD iPSC induced pluripotent stem cells from patients with Huntington's disease show CAG-repeat-expansion-associated phenotypes. Cell stem cell 2012 Aug;11(2):264-78. HD Insights, Vol. 3 In the lab... There is a vast breadth of recently published basic research in HD. Dong and colleagues5 recently identified additional post-translational modifications in huntingtin. They coupled tandem affinity purification and 2D nano-LC mass spectrometry and found novel phosphorylation sites at serines 431 and 432. Phosphorylation at these sites was specific to polyglutamine-expanded huntingtin when N-terminal fragments were overexpressed in 293 cells. Milnerwood and colleagues6 developed a new protocol for studying excitatory transmission onto GABAergic medium spiny neurons, with specific focus on the effects of mutant huntingtin on the cortico-striatal pathway. Using striatal and cortical co-cultures, NMDAR- induced cell death increased in cultures derived from YAC128 mice. The researchers further showed this is associated with the misregulation of phosphorylated cAMP response element binding protein (CREB) leading to decreased transcription of pro-survival factors. The dysfunction was significantly reduced using specific NMDAR subunit inhibitors. Kordasiewicz and colleagues7 used transiently administered antisense oligonucleotides (ASOs), designed to suppress the expression of huntingtin, in HD mouse models and in non-human primates. In mouse models, ASOs were administered into the lateral ventricle and led to specific knockdown of the mHtt transgene and some phenotypic reversal. The knockdown was sustained in both animal models for up to three months post treatment, suggesting that ASOs may provide a clinically relevant strategy for combating HD. 5 Dong G, Callegari E, Gloeckner CJ, et al. Mass spectrometric identification of novel posttranslational modification sites in Huntingtin. Proteomics. 2012 Jun;12(12):2060-4. 6 Milnerwood AJ, Kaufman AM, Sepers MD, et al. Mitigation of augmented extrasynaptic NMDAR signaling and apoptosis in cortico-striatal co-cultures from Huntington's disease mice. Neurobiol Dis. 2012 Oct;48(1):40-51. 7 Kordasiewicz HB, Stanek LM, Wancewicz EV, et al. Sustained therapeutic reversal of Huntington's disease by transient repression of huntingtin synthesis. Neuron. 2012 Jun;74(6):1031-44. In the clinic... Important studies reviewing and analyzing previously obtained clinical data give new insights into disease mechanisms and assess current treatments for HD. Ji and colleagues8 conducted a population-based study assessing the incidence of cancer in Swedish patients with HD and other neurological diseases. The standardized incidence of cancer was significantly lower in patients with polyglutamine disease. The largest difference (0.47) was associated with HD gene carriers. Polyglutamine disease seems to be protective against benign and metastatic cancer. Armstrong and Miyasaki9 looked at the data available for current pharmacological options for treating chorea. Their analysis showed that tetrabenazine, the only drug approved by the FDA specifically for the treatment of chorea, remains the best performing drug at a dose of 100 mg/day. Amantadine and rizuole give modest benefit. It is important to have multiple effective drugs available for HD patients due to tetrabenazine's potential adverse effects and the necessary close monitoring of patients who receive the drug. Unschuld and colleagues10 examined brain metabolite alterations, using magnetic resonance spectroscopy, in prodromal HD gene carriers with no gross brain morphological changes, and compared the metabolite alterations to controls. Eleven metabolites had decreases in N- acetyl aspartate and glutamate levels associated with prodromal HD. Future studies are needed to determine the utility of these results as longitudinal biomarkers for HD disease progression. 8 Ji J, Sundquist K, Sundquist J. Cancer incidence in patients with polyglutamine diseases: a population-based study in Sweden. Lancet Oncol. 2012 Jun;13(6):642-8. 9 Armstrong MJ, Miyasaki JM. Evidence-based guideline: Pharmacologic treatment of chorea in Huntington disease: Report of the Guideline Development Subcommittee of the American Academy of Neurology. Neurology2012 Aug 7;79(6):597-603. 10 Unschuld PG, Edden RA, Carass A, et al. Brain metabolite alterations and cognitive dysfunction in early Huntington's disease. Movement Disorders. 2012 Jun;27(7):895-902. Copyright © Huntington Study Group 2012. All rights reserved. 3

• Cover