BioEd Online

The heart contains cells that can divide and mature after birth, which might allow the organ to regenerate itself. This surprise discovery raises the possibility of transplanting these cells into hearts crippled by heart attack to mend the damage.

A heart attack kills off many cells in the heart. These are replaced by scar tissue, made up of connective-tissue cells, called fibroblasts. As a result, parts of the heart become thin and fail to beat properly.

Because fully developed heart cells do not divide, medical experts viewed the organ as unable to regenerate after injury. But Kenneth Chien, of the University of California, San Diego, and his colleagues now challenge this belief.

The researchers searched for 'cardiac progenitor cells', which are rare cells from the heart's early development that retain the ability to reproduce. They looked for cells containing the products of a gene called islet-1, which is expressed in these progenitor cells.

Tracing forward

By tracking cells in developing mice, Chien and his team linked adult cells expressing islet-1 with a population of embryonic cells that can give rise to heart muscle. The group also discovered these cell types in the human heart.

"These are very rare cells, which accounts for why they have not yet been reported," explains Chien. Only a few hundred progenitor cells remain in the heart after birth, and this number decreases with age, the researchers say.

In the lab, several hundred progenitor cells taken from animals after birth produced millions of cardiac-muscle cells. The progenitor cells are found mainly in the heart's pumping chambers, the team reports in Nature¹.

Unlike stem cells, which have a seemingly unlimited capacity for self-renewal, progenitor cells undergo a finite number of divisions. But both types of cells have potential for use in repairing heart damage.

And according to the researchers, cardiac progenitor cells have one considerable advantage over stem cells: scientists can easily coax them into becoming fully specialized heart-muscle cells, without chemical or hormonal stimuli.

In the future, doctors might be able to capture and grow progenitor cells and then transplant them back into the patient's heart. For now, however, isolating substantial numbers of these special cells remains a technical challenge. "Therapeutic use of these cells is many years away," says Chien.