The process is akin to removing a section of telephone cable, Zhang says. If you can find the correct route, you could wire the replacement from either end.
For the study, published in the current issue of Nature Biotechnology, Zhang and first author Yan Liu, a postdoctoral associate at the Waisman Center on campus, chemically directed the human embryonic stem cells to begin differentiation into neural cells, and then injected those intermediate cells. Ushering the cells through partial specialization prevented the formation of unwanted cell types in the mice.
Ensuring that nearly all of the transplanted cells became neural cells was critical, Zhang says. "That means you are able to predict what the progeny will be, and for any future use in therapy, you reduce the chance of injecting stem cells that could form tumors. In many other transplant experiments, injecting early progenitor cells resulted in masses of cells tumors. This didn't happen in our case because the transplanted cells are pure and committed to a particular fate so that they do not generate anything else. We need to be sure we do not inject the seeds of cancer."
Brain repair through cell replacement is a Holy Grail of stem cell transplant, and the two cell types are both critical to brain function, Zhang says. "Cholinergic neurons are involved in Alzheimer's and Down syndrome, but GABA neurons are involved in many additional disorders, including schizophrenia, epilepsy, depression and addiction."
Though tantalizing, stem-cell therapy is unlikely to be the immediate benefit. Zhang notes that "for many psychiatric disorders, you don't know which part of the brain has gone wrong." The new study, he says, is more likely to see immediate applic
|Contact: Su-Chun Zhang|
University of Wisconsin-Madison