Stemming Heart Damage

Stem cells are often seen as panacean in cardiovascular circles, known for repairing and renewing heart muscle after a heart attack. But how and why they work is still up for debate.

New research out of a laboratory group headed by Victor Dzau, president and CEO of the health system and chancellor for health affairs, suggests that the chemical signals secreted by stem cells, and not the cells themselves, are likely responsible for the restorative effects. The findings were published in Circulation Research.

After a heart attack, a patient can lose anywhere from 20 to 30 percent of heart muscle cells. Regenerating those cells takes time, according to Dzau. He realized that a genetic sequence producing a protein called Akt could protect heart tissue. "When we used stem cells engineered to overproduce the Akt protein in heart muscle, we saw dramatic protective effects over what we found using regular stem cells," Dzau says.

Damage caused by heart attacks was reduced as early as seventy-two hours after injecting the Akt-enriched cells. "Improvement in cell numbers during that brief a time could not be explained by the growth of completely new cells," Dzau says. "The plausible hypothesis had to be that the stem cells were releasing biological factors that protected injured cells so that they survived."

The Dzau lab is now studying several other novel proteins that may help repair heart tissue. "Rather than giving patients stem cells, we may be able someday to give specific proteins produced by these cells to help protect heart cells," Dzau says.

Paracrine factors, proteins that act as chemical signals working over short distances between cells, are one example of what the lab is looking into. They seem to improve blood-vessel formation and may also positively influence heart tissue's metabolism and ability to contract.

Ultimately, Dzau and his colleagues aim to learn how paracrine factors might contribute to the growth of new cells.