Embryonic Stem Cells Yield Full Range of Heart Tissues

The finding brings experts a step closer to stem cell-based treatments

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By Steven Reinberg
HealthDay Reporter

WEDNESDAY, Nov. 22, 2006 (HealthDay News) -- In a discovery that highlights the promise of stem cell research, researchers say a "master" embryonic cardiac stem cell is able to produce all three types of cardiac tissue.

In experiments using mice, the Harvard University team was able to produce cardiac muscle, smooth muscle and "pacemaker" cardiac cells.

The findings are outlined in two reports published online Nov. 22 in the journal Cell.

"This is the beginning of unlocking the scientific and therapeutic potential of human embryonic stem cells," said the lead author of the first report, Dr. Kenneth R. Chien of the Harvard Stem Cell Institute.

According to experts, that potential includes the ability, someday, to repair hearts by growing new cardiac tissue from stem cells. Embryonic stems cells are unique in that they have the ability to develop into any type of cell.

The human heart is composed of a variety of cell types, but "what has not been clear is if all these different types of cells is due to the presence of a master cell that can decide what it wants to be when it grows up," Chien said.

However, in their experiments with embryonic mouse cells, Chien's team found that there is a common origin for the three major cell types in the heart. "We have discovered a single cell that can make that decision," Chien said. "Moreover, the single cell can be cloned and expanded into the three different cell types."

This finding may open the door to the use of these master stem cells in regenerating heart cells, Chien explained. "It's the beginning of being able to harness the power of embryonic stem cells for generating specific tissues," he said. "We have no reason to believe that this can't be transposed into the human context."

Chien noted that, so far, experiments using adult stem cells to grow heart muscle have not been conclusive. "We should start isolating the best cell type," he said. "Embryonic stem cells offer this potential, since these are the cells that actually form the heart, as opposed to adult stem cells, for which that is not their normal function."

A second paper -- also using embryonic mouse stem cells -- found once again that a single type of embryonic stem cell can make all types of cells in the heart.

In terms of therapy, it is easier to introduce a cell that gives rise to all the descendent cells that you need, rather than to have to isolate each different type of cell, said Dr. Stuart H. Orkin, also from the Harvard Stem Cell Institute, and author of the second study.

In mice, one can clone and expand these stem cells, Orkin said, and "we presume it would be the same in the human situation. The question in humans is, what is the source of the cells? In principal, it would simplify giving stem cells for regenerative purposes," he said.

Another expert believes applications in human patients are still a long way off, however.

"The finding of cardiac stem cells in adult hearts cannot be applied for the clinical implications, since we cannot [yet] directly isolate cardiac stem cells from patient's or donor's heart tissue for therapeutic stem cell transplantation," said Atsushi Asakura, an assistant professor at the University of Minnesota Medical School's Stem Cell Institute.

"One problem is that cells from outside one's own body face problems of rejection in the same way organ transplants do. However, it is possible that one can induce proliferation of [the patient's] cardiac stem cells in patient's heart by treatment with growth factors," Asakura said.

"In addition, we may be able to induce cardiac stem cell differentiation from other stem cells, including adult stem cells and embryonic stem cells," he said.

More information

There's more on cardiac stem cell research at the American Heart Association.

SOURCES: Stuart H. Orkin, M.D., Harvard Stem Cell Institute; Kenneth R. Chien, M.D., Ph.D., Harvard Stem Cell Institute, Boston; Atsushi Asakura, Ph.D., assistant professor, Stem Cell Institute, University of Minnesota Medical School, Minneapolis; Nov. 22, 2006, online edition, Cell

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