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Science News

New Hope For Parkinsonís Stem Cell Therapy

Someday doctors may be able to transplant healthy dopamine-producing cells into the brains of people with Parkinson’s disease (PD), replacing cells lost to disease.  Scientists funded by the Parkinson’s Disease Foundation announced in the November issue of Nature, that they have made an important step towards this goal by transforming pluripotent stem cells into dopamine neurons and implanting them into the brains of animals.

Pluripotent stem cells, such as those derived from embryos and more recently induced from adult skin cells, have the potential to develop into nearly any cell type.  For this reason, stem cells could potentially serve as unlimited sources of healthy new cells to treat a variety of injuries and diseases, including Parkinson’s disease.  However, scientists have had trouble transforming these stem cells into the desired cell type.

So researchers led by Lorenz Studer, M.D., at the Memorial Sloan-Kettering Cancer Center worked out the precise conditions needed to transform pluripotent stem cells into dopamine-producing neurons.  Then, they transplanted the neurons into the brains of animal with brain lesions reminiscent of those observed in Parkinson’s.

Results:

  • The researchers found that they could make cultured human pluripotent stem cells differentiate into dopamine neurons by treating the cells with certain chemicals. The chemicals activate specific cell signaling pathways, known as the WNT and sonic hedgehog pathways.
  • The dopamine neurons produced by this method had the same characteristics as dopamine neurons from the brain region affected by Parkinson’s.
  • When the scientists transplanted the dopamine neurons into the brains of mice and rats with lesions reminiscent of Parkinson’s, the neurons survived for at least four and a half months and did not form tumors.
  • The transplanted dopamine neurons improved the performance of mice and rats in motor function tests for Parkinson’s.
  • Dopamine neurons transplanted into the brains of rhesus monkeys survived for at least one month.

What Does It Mean?

Pluripotent stem cells hold great promise to treat a wide range of serious injuries and diseases.  To realize this promise, however, scientists must establish efficient, reliable methods to transform stem cells into specific cell types and then safely transplant the cells into the human body.  A study out of Columbia University Medical Center, which implanted fetal transplant tissue, helped some Parkinson’s symptoms but also led to significant dyskinesia in those who responded well to the treatment.  Creating stem cells out of one’s own tissue may be more difficult.  In the past, scientists have struggled with doing so for the dopamine neurons lost in Parkinson’s disease.  Other cell types “contaminated” the stem cell cultures.  When transplanted into animal brains these stem cells would fail to thrive; and when they did survive, often overgrew or even produced tumors.

For the first time, Dr. Studer and his colleagues have appeared to identify the correct conditions necessary to transform pluripotent stem cells exclusively into dopamine neurons that resemble those lost from the same brain region affected by Parkinson’s, that grow and perform well in animals, and don’t produce tumors.  The fact that these transplanted neurons reduced some Parkinson’s symptoms in animals is a good sign for potential therapeutic applications in people living with Parkinson’s.

Before stem cell therapy for Parkinson’s becomes a reality, however, significant challenges remain.  Longer-term experiments in monkeys must be done to show that the neurons can survive and avoid tumor formation for longer than one month; and can alleviate PD symptoms.  Finally, animals in these experiments were given immune-suppressing drugs to prevent their bodies from rejecting the transplanted cells.  These drugs have substantial side effects when taken long-term, which must be balanced against the benefit of improved PD symptoms.  Furthermore, stem cells may replace the cells that are affected by PD, but they will probably not stop the neurodegenerative process.

Nevertheless, until a safe and effective stem cell replacement therapy has been demonstrated, this new protocol can been used in the laboratory to efficiently generate large quantities of the dopamine neurons necessary to screen and test new potential drug therapies currently under investigation.

Reference: Kriks S, Shim J-W, Piao J, Ganat YM, Wakeman DR, Xie Z, Carrillo-Reid L, Auyeung G, Antonacci C, Buch A, Yang L, Beal MF, Surmeier DJ, Kordower JH, Tabar V, Studer L. Dopamine neurons derived from human ES cells efficiently engraft in animal models of Parkinson's disease. Nature 2011 Nov. Ahead of Print;

Source Date: Nov 17 2011