Human Heart Grows New Cells

Drugs that enhance this innate capability might help heal injured hearts.

The human heart has a notorious reputation for being unable to heal itself, but new research suggests it is capable of at least some self-repair. Using carbon dating to gauge the age of heart cells, scientists have found that low numbers of new heart cells are continuously being created throughout a person's life. This raises the possibility that we may one day be able to use drugs to directly stimulate this regenerative capacity to patch up damaged hearts, rather than relying on cell-transplantation therapies.

Healing the heart: Heart muscle cells (shown above) can be grown from human embryonic stem cells, but new research suggests the adult heart can grow new cells, too. Credit: Cellular Dynamics

Scientists can make new cardiomyocytes--heart muscle cells--from stem cells in cell-culture experiments, and evidence for cardiac stem cells has been building. But it was unclear until now whether new heart muscle cells are ever born under real-life conditions inside the heart after birth.

Ratan Bhardwaj and his colleagues at the Karolinska Institute in Stockholm, Sweden, used radiocarbon dating, which is normally employed to establish the age of archaeological or geological remains, to work out the age of heart cells compared to the chronological age of the person from which they were isolated. To do this, the team took advantage of nuclear tests done during the 1950s and 1960s, which led to a sharp increase of radioactive Carbon 14 in the atmosphere. The radioactive material was captured by plants as CO₂ and then worked its way up the food chain and into the DNA of the human body. Soon after the tests were stopped, atmospheric C14 levels declined again, leading to a corresponding drop in the C14 concentration in human DNA.

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The team measured C14 levels in the heart tissue of twelve deceased patients aged between 19 and 73 at the time of death and found elevated C14 even in those subjects who had been born two decades before the nuclear tests started, indicating that the radioactive carbon must have been incorporated into heart muscle cells long after birth. Similarly, the C14 levels in the hearts of younger patients did not match the year of their birth but rather indicated a younger birthday for the cells. The research was published today in the journal Science.

"I am very excited about how they have used this novel technology to get something useful out of such a terrible environmental disaster," says Charles Murry, director of the Center for Cardiovascular Biology at the University of Washington in Seattle, who coauthored a commentary, also in Science, on Bhardwaj's research.