“Aw Rats!” Says Lou, Stem Cells Show Promise
By Maggie Fox, Scientific American, October 16, 2006
Rats that were bred to duplicate Lou Gehrig’s Disease had the initiation of their nerve damage delayed (typical of the disease), and their lives extended slightly after having their spinal cords injected with human stem cells at John Hopkins. The grafted stem cells do not themselves give way to Lou Gehrig’s, which is also known as amyotrophic lateral sclerosis (ALS), but actually develop into nerve cells and make extensive connections with existing nerves. This week’s issue of Transplantation has published the study.
“We were extremely surprised to see that the grafted stem cells were not negatively affected by the degenerating cells around them, as many feared introducing healthy cells into a diseased environment would only kill them,” says Vassilis, M.D., an associate professor of pathology and neuroscience at Hopkins.
“We only injected cells in the lower spine, affecting only the nerves and muscles below the waist,” he noted. “The nerves and muscles above the waist, especially those in the chest responsible for breathing, were not helped by these transplanted stem cells.”
A more complete transplant of cells - already being planned -- along the full length of the spine to affect upper body nerves and muscles as well might lead to longer survival in the same rats says Vassilis. He believes his experiments present “proof of principle” for stem cell grafts, even though all the rats eventually died of ALS.
Animals engineered to carry a mutated human gene for an inherited form of ALS, also called SOD-1 rats, were used by the research team in their experiments. All the muscles in the body ultimately become paralyzed due to slow nerve cell death, just as it does in humans. The particular SOD-1 rats in the study developed an “especially aggressive” form of the disease.
Human neural stem cells - cells that can in theory become any type found in the nervous system, were injected into the lower spine of adult rats not yet exhibiting symptoms. Another group for comparison purposes was injected with dead human stem cells, which would not affect disease progression. To prevent transplant rejection, both groups of rats were treated with drugs.
Twice a week for 15 weeks, the rats were weighed and tested for strength. According to Vassilis, weight loss indicates disease onset. On average, weight loss started at 59 days for rats injected with live stem cells and they lived for 86 days after injection. The rats injected with dead stem cells (the control group) started losing weight at 52 days and lived for 75 days after injection.
To determine each rats overall strength, they were persuaded to crawl uphill on an angled plank. The highest angle each rat could cling to for 5 seconds without sliding backwards was recorded as an indictor of their strength. The rats injected with live cells grew weaker much more slowly than those injected with dead cells.
It was determined that 70 percent of the transplanted cells developed into nerve cells after close examination. Many of the nerve cells also grew new nerve endings connecting to other cells in the rat’s spinal cord.
“These stem cells differentiate massively into neurons,” says Vassilis, “a pleasant surprise given that the spinal cord has long been considered an environment unfavorable to this type of transformation.”
The cells aptitude to make nerve-cell-specific proteins and growth factors was another important characteristic. In the spinal cord fluid, researchers measured five times more GNDF (short for glial cell derived neurotrophic factor) than normal. Through physical connections, the transformed transplant cells may also deliver these growth factors to other cells in the spinal cord.
In an effort to learn as much as possible about how human stem cells behave when transplanted, Vassilis hopes to take further advantage of his rodents with ALS and possibly make discoveries that lead to clinical applications in the future.