The HD iPSC Consortium: Repeat Length Dependent Phenotypes for Assay Development

Huntington’s disease (HD) is a significant neurodegenerative disease with unique genetic features. A CAG expansion in Huntington gene is correlated with severity and onset of sub-clinical and overt clinical symptoms, make it particularly suited to therapeutic development . The single genetic cause offers the opportunity to understand the pathological process triggered in all individuals with a CAG expansion, as emerging evidence suggests effects of the mutation in all cell types, though striatal neurons are most vulnerable to degeneration. Moreover, by virtue of a molecular test for the mutation, a unique opportunity exists to intervene/treat before the onset of overt clinical symptoms utilizing sub-clinical phenotypes emerging in pre-manifest individuals. Since human induced pluripotent stem cells (iPSCs) have the power to make any cell type in the human body, we are utilizing the technology to make patients iPSCs and study the effects of different number of CAG repeats on the neurons we generate from the patient iPS cells. Preliminary studies indicate that CAG length–dependent phenotypes occur at all stages of differentiation, from iPSC through to mature neurons and are likely to occur in non-neuronal cells as well, which can also be investigated using the iPSC that we are creating. The non-integrating technology (avoids integration of potentially deleterious reprogramming factors in the cell DNA) for producing iPSC lines is crucial to obtaining reproducible disease traits from patient cells. The Cedars-Sinai RMI iPSC Core is part of the Huntington’s Disease (HD) consortium. In the past year the iPSC Core has made many new non-integrating induced pluripotent stem (iPSC) cell lines from HD patients with different numbers of CAG repeat expansions. The grant application proposed generation of 18 HD and Control iPSC lines. Instead we are generating 20 iPSC lines. So far we have already generated 17 iPSC lines from individuals with Huntington’s disease and controls (10 HD patients and 7 controls). In order to have the disease trait reproducible across multiple groups, three clonal iPSC lines were generated from each subject. Some of these lines have (or are in process) of expansion for distribution to consortium members. We are now in the process of making the last 3 lines as part of this grant application to generate a HD iPSC repository with total of 20 patient/control lines from subjects with multitude of CAG repeat numbers. Most of these lines have undergone rigorous battery of characterization for pluripotency determination, while some other lines are currently being validated through more characterization tests. Neural stem cell aggregates (EZ spheres) have been generated from few of the patient lines in the Svendsen lab (not supported by this grant). We have also submitted 6 patient iPSC lines to Coriell Cell Repository for larger banking and distribution of these important and resourceful lines to other academic investigators and industry. We strongly believe that this iPSC repository will enormously speed up the process of understanding the disease causing mechanisms in HD patient brain cells as well as discovering novel therapeutics or drugs that may one day be able to treat HD patients.

Huntington’s disease (HD) is a fatal neurodegenerative condition with no current treatment. This significant neurodegenerative disease, whose relatively simple and unique known genetic cause, a CAG expansion in the HD gene correlated with severity and onset of clinical symptoms, makes it particularly suited to therapeutic development. The Huntington’s disease (HD) iPS cell consortium, funded with NIH and CIRM support, brings together leading groups in stem cell and HD research to establish whether newly created iPS cell lines show HD related (i.e., CAG length-dependent) phenotypes. Human iPSC technology can be used to generate specific neuronal and glial cell types, permitting investigation of the effects of the genetic lesion in the susceptible human cell types in the context of HD. The monogenic nature of HD and the existence of allelic series of iPSCs with a range of CAG repeat lengths confer tremendous power to model HD. Through CIRM support this consortium has capitalized on new technologies to use non-integrating approaches for reprogramming and promising phenotypes in current HD iPS lines to develop robust and validated assays for drug development for HD. Significant progress has been made through CIRM-funded support of this proposal. Notably, the Cedars-Sinai Medical Center’s Board of iPSC core housed in the Board of Governors Regenerative Medicine Institute has taken skin cells from HD patients with a wide range of CAG repeats (43 to 180), and unaffected healthy controls (21 to 33) and reprogrammed then to pluripotency using the latest non-integrating iPS cell technology. So far 18 well-characterized patient-specific iPSC lines have been generated. These new iPSC lines have been rigorously characterized by our iPSC core and available to HD research community throughout California and the world. The Svendsen lab and the other HD iPSC Consortium laboratories have already used these lines and differentiated into relevant neuronal cell types to study the disease mechanisms as well develop new treatment. These cell lines will be an essential resource for academic groups and pharmaceutical companies for studying pathogenesis and for testing experimental therapeutics for HD. The ultimate goal is to develop and validate methods and assays using >96 well format for CAG repeat length-dependent phenotypes that are amenable to high content/throughput screening methods. Assays developed using these patient-specific iPSC lines and their neuronal derivatives will allow academic groups and pharmaceutical companies to study pathogenesis and test experimental therapeutics for HD, which will significantly advance both our understanding of HD and potential treatments for this devastating and currently untreatable disease.