Johns Hopkins researchers, working with an international consortium, say they have generated stem cells from skin cells from a person with a severe, early-onset form of Huntington's disease (HD), and turned them into neurons that degenerate just like those affected by the fatal inherited disorder.
By creating "HD in a dish," the researchers say they have taken a major step forward in efforts to better understand what disables and kills the cells in people with HD, and to test the effects of potential drug therapies on cells that are otherwise locked deep in the brain.
Although the autosomal dominant gene mutation responsible for HD was identified in 1993, there is no cure. No treatments are available even to slow its progression.
The research, published in the journal Cell Stem Cell, is the work of a Huntington's Disease iPSC Consortium, including scientists from the Johns Hopkins University School of Medicine in Baltimore, Cedars-Sinai Medical Center in Los Angeles and the University of California, Irvine, as well as six other groups. The consortium studied several other HD cell lines and control cell lines in order to make sure results were consistent and reproducible in different labs.
The general midlife onset and progressive brain damage of HD are especially cruel, slowly causing jerky, twitch-like movements, lack of muscle control, psychiatric disorders and dementia, and - eventually - death. In some cases (as in the patient who donated the material for the cells made at Johns Hopkins), the disease can strike earlier, even in childhood.
"Having these cells will allow us to screen for therapeutics in a way we haven't been able to before in Huntington's disease," says Christopher A. Ross, M.D., Ph.D., a professor of psychiatry and behavioral sciences, neurology, pharmacology and neuroscience at the Johns Hopkins University School of Medicine and one of the study's lead researchers. "For the first time, we will be able to study how drugs work on human HD neurons and hopefully take those findings directly to the clinic."
Ross and his team, as well as other collaborators at Johns Hopkins and Emory University, are already testing small molecules for the ability to block HD iPSC degeneration. These small molecules have the potential to be developed into novel drugs for HD.
The ability to generate from stem cells the same neurons found in Huntington's disease may also have implications for similar research in other neurodegenerative diseases such as Alzheimer's and Parkinson's.
To conduct their experiment, Ross took a skin biopsy from a patient with very early onset HD. When seen by Ross at the HD Center at Hopkins, the patient was just seven years old. She had a very severe form of the disease, which rarely appears in childhood, and of the mutation that causes it. Using cells from a patient with a more rapidly progressing form of the disease gave Ross' team the best tools with which to replicate HD in a way that is applicable to patients with all forms of HD.
Her skin cells were grown in culture and then reprogrammed by the lab of Hongjun Song, Ph.D., a professor at Johns Hopkins' Institute for Cell Engineering, into induced pluripotent stem cells. A second cell line was generated in an identical fashion in Dr. Ross's lab from someone without HD. Simultaneously, other HD and control iPS cell lines were generated as part of the NINDS funded HD iPS cell consortium.
Scientists at Johns Hopkins and other consortium labs converted those cells into generic neurons and then into medium spiny neurons, a process that took three months. What they found was that the medium spiny neurons deriving from HD cells behaved just as they expected medium spiny neurons from an HD patient would. They showed rapid degeneration when cultured in the lab using basic culture medium without extensive supporting nutrients. By contrast, control cell lines did not show neuronal degeneration.