Blood Cells Made From Muscle Cells

Contrary to the belief that a specific type of cell can duplicate only its own cell type, researchers have produced blood cells from muscle cells.

This discovery at Baylor College of Medicine might provide scientists with an alternative to using embryonic cells for research, according to principal investigator Dr. Margaret A. Goodell. Her findings are published in the December 7 Proceedings of the National Academy of Sciences.

"Scientists used to think that blood cells came from blood cells only and muscle cells came from muscle cells only," says Dr. Goodell, assistant professor in the International Center for Cell and Gene Therapy at Baylor, The Methodist Hospital and Texas Children's Hospital. "We've now shown that there are stem cells in skeletal muscle that can generate blood. This suggests that the natural function of the muscle stem cells can be changed from becoming one type of cell to another."

Stem cells are immature cells that have not yet specialized to become a certain type of cell, such as nerve, blood or muscle. Blood cells usually originate from stem cells in bone marrow.

For the research, Dr. Goodell and colleagues injected two types of stem cells into the bloodstream of mice: muscle cells that had been taken from adult mice and "tagged" with genetic markers for tracing, and bone-marrow cells from other adult mice. Six and 12 weeks later, they analyzed adult blood cells from the mice to trace their origin.

Much to their surprise, the researchers found that more than 10 times as many blood cells had come from the specially marked muscle cells than from the bone-marrow cells. Placing the muscle cells in a different environment - the bloodstream - apparently affected the type of cell they became, Dr. Goodell says.

When bone-marrow cells that originated from muscle cells were transplanted into bone marrow of another group of mice, they continued to generate more blood cells. "This demonstrated they have the extremely primitive nature of natural bone-marrow stem cells," Dr. Goodell says.

The researchers found that a small portion of the muscle cells had some of the same characteristics as bone-marrow cells. This set of cells might be more vulnerable to the new environment than other cells in the muscle.

Further studies are needed to show whether muscle stem cells or other stem cells can be turned into heart, brain, nerve, skin or other cell types, and whether human cells will respond the way mice cells did, Dr. Goodell says. "Theoretically, we might be able to take cells from an adult human and turn them into other types of cells, opening the way for new therapies."

Dr. Goodell's study was supported by the Curtis Hankamer Basic Research Fund, Baylor, the National Institutes of Health and the American Society of Hematology. Her co-authors were Dr. Kathyjo Ann Jackson and Tiejuan Mi in the International Center for Cell and Gene Therapy.

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©2006 Texas Medical Center

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