Coaxing Human Embryonic Stem Cells to Make Dopamine
For all of the promise embryonic stem cells hold for therapies for neurodegenerative diseases such as Parkinson's disease, they are notoriously difficult to use. One problem is in coaxing them into becoming brain cells that make dopamine, which is in short supply in the brains of individuals with Parkinson's. Such cells might be used for transplantation in these patients, but current methods involve extremely complex growth media and potentially contaminating animal products.
Now, developmental biologist Lorraine Iacovitti, Ph.D., associate director of the Farber Institute for Neurosciences at Thomas Jefferson University in Philadelphia, and her co-workers have devised a quicker, simpler method.
Dr. Iacovitti, who is also professor of neurology at Jefferson Medical College of Thomas Jefferson University, and her co-workers devised a technique using only a few additives, "all chemically defined and of human origin" to get embryonic stem cells to become dopamine-producing in the laboratory dish in only three weeks, compared to the five-to-eight week period it commonly takes. She reports her group's results November 13, 2005 at the annual meeting of the Society for Neuroscience in Washington, D.C.
According to Dr. Iacovitti, scientists have been using blood serum, serum replacement products and cell conditioned media, all of which contain "undefined proprietary components and growth substances of animal origin." Such animal-derived substances can cause an immune reaction and result in the rejection of dopamine-producing cells transplanted into a patient's bdrain.
"The goal is to get the best source of dopamine neurons and the simplest reagent and media in which to grow cells," she says. "Everyone should be trying to use human cells that have seen only human reagents."
In the work, she and her co-workers used various cell markers to track changes in stem cell development, chronicling each of five steps to become a dopamine cell. They eventually were able to get the cells to form dopamine neurons, she says, but they could not harvest the cells from culture for transplantation.
Dr. Iacovitti decided to stop the process and revert back to an earlier developmental stage.
Shortening the differentiation process is important, she notes. The longer cells are grown and allowed to mature in culture before transplant, the less able they are to survive harvest for transplant. "We transplant cells at two weeks in stage four of development and not after three weeks and stage five for this reason," she says. "The brain can finish the process of differentiating cells into dopamine neurons.
"We have been able to show we could generate a process in the tissue culture dish that is simple, rapid, and uses defined reagents, most of which are human products. We can make them into dopamine neurons in a dish, and they are mature."
But because they used a pool of younger, stage four cells, which are not yet mature and still dividing, there could be a potential problem in overproduction of cells.
"We're trying to figure out a way to identify these stage 4 prospective dopamine neurons," she says. "We have to go back and try to use stage 4 markers that predict which cells will be dopamine neurons and use them to purify cells before they are put into the animal.
"That won't be easy, but this work gets us one step closer to it.".