Cells from the hearts of newborn mice can form tissue-like layers and start beating in petri dishes, according to new research. If the same kind of cells can be found in adults, they could potentially fix hearts damaged in heart attacks.
Heart attacks ravage cardiac muscle, and unlike easily repaired skeletal muscle, the heart does nothing to fix itself. Skeletal muscle's restorative properties lie in its satellite cells: progenitors that have the capacity to turn into and replace the damaged muscle. Scientists have been searching for such cells in hearts for several years. Although three types of cells have been found in rodents that can grow in culture and be triggered to turn into heart muscle, no one knows much about the cells, nor has anyone found any of them in people.
To look for other populations of heart muscle-producing cells, molecular oncologist Kenneth Chien at the University of California, San Diego, in La Jolla and colleagues took advantage of cells that express a gene called Isl1. Researchers know that mouse fetuses build the right half of their hearts from these cells, but no one knew if any Isl1-producing cells stick around after the heart is formed. By hooking up an easily measured protein to a copy of the Isl1 gene, the team found about 500 Isl1-producing cells that did give rise to other cells and lingered past birth.
The team then purified these Isl1 cells and grew them in culture. In less than a week, about a third of the cells developed into beating cells, and some also fused together, suggestive of real heart tissue. In addition, when the team added adrenaline to cultures of the thumping cells, the cells picked up the beat, just as a normal heart does. The team also identified Isl1 cells in heart tissues from newborn rats and human babies who had undergone heart surgery, they report in 10 February Nature. The researchers are now testing whether the Isl1 cells grown up in culture will move into and fix damaged cardiac muscle when injected into a wounded heart.
"What stands out about these cells is their ability to differentiate into real, mature cardiac [muscle cells]," says cardiologist Jon Epstein at the University of Pennsylvania. And unlike the other potential cardiac satellite cells that scientists have identified previously, these are found in humans. That's makes them more interesting, he says, although researchers have yet to show that the same cells can be found in adults.