Photo: Plamen Petkov
Stem cells may soon allow doctors to turn back the clock on damage caused by heart disease.
Long before we feel a thumping beat in our chest, there is a moment when our heart first begins to take shape. At that point, it's hardly fair to call it a heart—it's just a speck-sized clump of cells without a pulse. But like a house being raised brick by brick, that clump, infused with cardiac stem cells—protean cells that are able to take the form of any heart tissue—expands into an elaborate structure. Some cells become muscle, aligning into four separate chambers. Others become valves and arteries, weaving intricately through muscle walls. With architectural precision, every kind of cell falls neatly into place.
Not long afterward, the stem cells that built the heart dwindle until they almost disappear. And later—decades after the builders have gone—the house itself begins to fall apart. Arteries clog with plaque, plaque causes heart attacks, heart attacks destroy ventricular muscle. In the worst cases, the damage is so great that the only option is a transplant.
Over the next decade, though, many stem cell researchers believe, doctors will be able to restore even "irreversibly" damaged hearts, at least in part. "The ability to replace dead heart muscle with new lab-grown muscle after a heart attack is one of the great goals in medicine today," says Deepak Srivastava, MD, director of the Gladstone Institute of Cardiovascular Disease in San Francisco. If scientists can manage to do so, it would be monumental. Cardiovascular disease affects an estimated 81 million Americans and is the leading cause of death for both women and men in the United States.
The leap forward has been driven by a series of startling breakthroughs. Among the most radical was the discovery, in 2007, of a way to transform ordinary human adult skin cells back into stem cells (known as induced pluripotent stem cells, or IPS cells), by manipulating a small piece of the genetic code. IPS cells can be chemically prodded to become almost any tissue, including bone, cartilage, or heart. And they neatly sidestep the political and ethical morass surrounding embryonic stem cells—which, unlike IPS cells, must be derived from human embryos left over from fertility treatments.
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