February 26, 2011

Regrowing The Damaged Heart

US scientists have found that newborn mice can repair themselves after an injury, an important discovery that brings hopes that healing can occur with damaged hearts in people.

Scientists removed large chunks of heart out of mice that were only a day old, only to find that their hearts were restored within three weeks.

Fish and amphibians are known to have the power to re-grow parts of their hearts after major injuries, but the study, published in the journal Science, is the first time the process has been seen in mammals.

In the study, US researchers at the University of Texas Southwestern Medical Center, showed that one-day-old mice could regenerate 15 percent of their heart tissue within three weeks, an ability that was lost if the procedure had been done when the mice were a week old. Heart scans showed that parts of the organ that had been surgically removed had not only grown back, but were functioning normally.

The researchers believe that heart cells within the mouse have a narrow window after birth that allows them to replicate and repair cells. Subsequent tests suggested that these repair cells were stemming from within the heart muscle.

The research holds high hopes that the human heart may also have a natural ability to heal itself. If this could be turned on in adults it could potentially save millions of people living with heart damage.

"When a person has a heart attack and heart muscle cells are lost, the heart loses pump function, causing heart failure and eventual death," said Eric Olson, a molecular biologist at Southwestern Medical Center in Dallas, Texas.

"Now that we know that the mammalian heart indeed possesses the potential to regenerate, at least early in life, we can begin to search for drugs or genes or other things that might reawaken this potential in the adult heart of mice and eventually of humans," Olson told The Guardian newspaper.

Many amphibian and fish species, most notably the zebrafish, have the ability to regenerate heart muscle right into adulthood. The new study suggests that mammals too have such capacity for self-repair, albeit for a short period.

Olson thinks future research will show humans have a similar capacity, although no experiments involving human heart tissue are currently planned. "There's no reason to believe that the same window would not exist in the human heart."

"Everything we know about development and early function of the mouse heart is comparable to the human heart so we're quite confident that this process does exist in humans, although that of course still has to be shown," said Olson.

Jeremy Pearson, associate medical director at the British Heart Foundation, todl the Guardian's Ian Sample that the finding is exciting and "strengthens the view that understanding how this happens could provide the key to healing adult human hearts."

"If you get somebody to hospital immediately after a heart attack, you might well start thinking of a treatment that starts this repair process very quickly," he said. "But for a lot of other people, the main trouble is heart failure when they have had some mild damage for years and years and it slowly gets worse. At that point, you might think of more complicated interventions, to reduce the amount of scarring before inducing the heart to repair itself. It's a long way off, but these are probably the world leaders in the field."

The team is now focusing on finding ways to "reawaken" this capacity for self-repair in adult mice, with the ultimate goal of someday potentially doing the same in humans to repair damage sustained during heart attacks.

"We've identified a micro-RNA (a small piece of genetic material) which regulates this process so we're trying to use that as a way of further enhancing cardiac regeneration later in life and we're also screening for new drugs which can re-awaken this mechanism in adult mice," said Olson.

Olson admits there will be problems ahead. What works in the low-pressured heart of a zebrafish, might not work in the high-pressured multi-chambered heart of humans. Interfering with heart muscle cells could trigger arrhythmias in the heart, he said.


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