Stem cells keep popping up in ever more kinds of tissues--even in unexpected organs such as the brain. Soon, the heart may join that list. Cardiovascular researchers in the United States and Italy have discovered that despite popular belief to the contrary, hearts can regenerate after transplantation, and stem cells may be responsible.
Some tissues in the body regenerate if damaged--the skin is one obvious example--but others do not. "We all thought that once you lose a chunk of heart, it's gone," says cardiologist Roberto Bolli of the University of Louisville, Kentucky. That finality would pose a particular problem to recipients of heart transplants, because many heart cells die during the hours the organ is out of the body waiting to be transplanted. But new research suggests that the donated organ may recover inside the transplant recipient.
Cardiovascular researcher Piero Anversa of New York Medical College in Valhalla, New York, along with colleagues at the University of Udine, Italy, examined eight hearts transplanted from female donors into male patients. Each patient had died between 4 days and 18 months after receiving the new heart. Up to 10% of cells in the transplanted hearts contained the male Y chromosome--a clear sign that cells from the recipient had taken up residence in the heart, the group reports in today's issue of The New England Journal of Medicine.
Anversa's group also searched the heart tissue for molecular markers signaling that some of the heart cells held the potential to specialize further. In the transplanted hearts, the team found markedly higher numbers of these so-called primitive cells, some of which had come from the donor and some from the recipient. Anversa suspects that these primitive cells are behind the heart's regeneration, but that has yet to be proven. The bigger question is whether these are in fact heart-specific stem cells, and if so, exactly how they promote regeneration of heart tissue.
"This is a very exciting finding," Bolli says. Discovering that the heart can regenerate itself could have important implications for treating heart failure--but that will take time, he says. "It's a conceptual breakthrough, but the practical application is still far away."