January 21, 2008

Stem Cells Restore Muscle Function in Mice

Researchers at University of Texas have successfully used embryonic stem cells to restore muscle function in genetically engineered mice with the most common form of muscular dystrophy.  

The research creates new hope for the treatment of Duchenne muscular dystrophy (DMD), one of  nine types of muscular dystrophy, a degenerative disease in which the cells can no longer regenerate after an injury.  The disease affects approximately 1 out of every 3,500 to 5,000 boys in the United States.

Stem cells are cells in the body from which other types of cells develop. When a stem cell divides, each new cell has the potential to either remain a stem cell or become one with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.  This process is called differentiation.  Embryonic stem cells, as their name suggests, are derived from embryos, and can produce virtually all of the body's various cell types.

Researchers have long sought ways to use stem cells to develop potential treatments for muscular dystrophy.   However, the results have often been inadequate.   The challenge has been in getting stem cells to properly differentiate into only certain cell types.

"The problem had been that embryonic stem cells make everything," said Dr. Rita Perlingeiro of the University of Texas Southwestern Medical Center, who led the study, in a telephone interview with Reuters.

"We know with embryonic stem cells you have to find a way to pull out the cells you want.  How to dig them out "“ that is the problem," she said.

In performing the study, Dr. Perlingeiro and her team wanted to isolate only the cells that would become muscle. They wanted to avoid results seen in previous studies in which transplanted stem cells had caused the mice to develop a type of cell tumor called a teratoma.    Dr. Perlingeiro's team chose instead to use stem cells taken from mouse embryos, and then developed the cells containing the gene Pax3.  This gene triggers cells to grow into muscle tissue that will produce dystrophin, the protein lacking in humans with muscular dystrophy.

Then, the team created a new technique using fluorescent dyes that allowed them to isolate only the cells that would go on to become muscle cells.  

The mice used in the study were genetically engineered to lack dystrophin. 

After injecting the special embryonic stem cells into the hindquarters of the mice, the researchers found that a month later the dyed cells had moved deeply into the muscle, suggesting they had differentiated into new muscle cells.    The researchers also observed that many of the new muscle fibers also contained dystrophin. 

Three months later, the mice showed no signs of tumors, and tests revealed the muscles were significantly stronger than in the untreated mice.  At four months out, there were still no signs of tumor formation. 

"Embryonic stem cells can make every tissue in the body. We instructed these cells to make more skeletal muscle," explained Dr. Rita Perlingeiro in a Washington Post article.  "We found a way to pull out only the ones destined to make muscle. These two steps combined resulted in a cell population capable of making muscle in a mouse with muscular dystrophy and, very importantly, the new muscle is stronger."

Dr. Perlingeiro said the research is promising, however it is still early.  Her hope is to eventually develop a stem-cell therapy for humans with muscular dystrophy using stem cells made from reprogrammed skin cells.  Although not yet perfected, this technique essentially tricks the skin cells into acting as embryonic stem cells.  

"You go brick by brick to build something," she said. 

The research appears in the Jan. 20 online issue of Nature Medicine.


On the Net:

Muscular Dystrophy Association