Human Germ Cells Counter Nerve Degeneration

Researchers studying degenerative nerve diseases such as amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease) have employed human embryonic germ cells to partially restore mobility in a group of rats with paralyzed hind limbs.

Investigators at Johns Hopkins University (Baltimore, MD, USA) selectively destroyed the nerve cells that control muscles in the hind limbs of a group of laboratory rats by infecting them with a genetically engineered Sindbis virus.

The paralyzed mice were separated into three groups, which were treated with either human embryonic germ cells, human cells lacking stem cell properties, or with hamster kidney cells. The results, published in the June 15, 2003, issue of the Journal of Neuroscience, showed that the pluripotent embryonic germ cells established themselves in the rats. The group that received the germ cells partially recovered motor function 12 and 24 weeks after transplantation, whereas the control animals remained paralyzed.

The effect of the germ cells was indirect--due to the production and secretion of transforming growth factor-alpha (TGF-alpha) and brain-derived neurotrophic factor (BDNF)--and not because the germ cells transformed into nervous tissue. These protein factors enhanced the function and survival of the rats' own neurons.

"Our first hypothesis was that functional recovery came from human cells reconstituting the nerve circuits destroyed by the paralysis-inducing virus we gave the rats,” explained first author Dr. Douglas Kerr, assistant professor of neurology at the Johns Hopkins School of Medicine. "Some of the tens of thousands of implanted primitive human stem cells did become nerve cells or the like, but not enough to account for the physical improvements. Instead, these human embryonic germ cells create an environment that protects and helps existing rat neurons--teetering on the brink of death--to survive.”



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