Finding a Master Heart Cell

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hough embryonic stem cells have certainly grabbed most of the attention — and headlines — in the stem cell field in recent years, embryos aren't the only source of these versatile mother-cells. Political leanings aside, researchers are beginning to appreciate that many tissues in the body have their own stem cells. Blood cells, for example, derive from a single hematopoietic stem cell in the bone marrow, and now two groups of scientists from Boston report that they have identified a similar mother stem cell from which most heart cells arise. Working with mice, one group at Massachusetts General Hospital isolated a cardiac stem cell that generates the three major cell types of the mammalian heart, while another group at the hospital found a stem cell that gives rise to the contracting and smooth muscle cells found in heart vessel walls.

The findings are certainly exciting — these stem cells could form the basis of new heart therapies, and could become a source of healthy, replacement cells for heart tissue damaged after a heart attack or by heart disease. But they represent only the first step in what will be a long road. First, the studies were conducted in mice and rats, and while these animals can serve as a template for understanding how heart cells develop, any stem cell-based therapies that come out of them will have to go through more testing in larger mammals before doctors can even begin to think about trying them in human patients.

And even if the heart is created from these master stem cells, scientists still have to master the process of recreating the normal development of heart tissue in the lab. They have to understand the delicate and perfectly timed steps involved in coaxing some stem cells to develop into heart blood vessels, while guiding others on the path to becoming the steadily beating heart muscle that methodically pumps blood to the entire human body.

What these findings do promise, however, is the possibility of developing heart-based therapies without the need for using embryonic stem cells — a welcome prospect for researchers in the U.S. who are restricted from working with these cells unless they secure private, non-government funding.