Scientists have turned back the hands of a biological clock to rejuvenate ageing and damaged human heart cells.
Using stem cells, they reset a molecular mechanism that determines the rate at which cells age.
Although the work on human cells was confined to the laboratory, the same technique has been successfully tested in mice and pigs.
Researchers in the US managed to get new heart tissue to grow in the animals in just four weeks.
They hope the advance will lead to new treatments for heart failure, which often follows a heart attack.
"Modifying aged human cardiac cells from elderly patients adds to the cell's ability to regenerate damaged heart muscle, making stem cell engineering a viable option," said lead scientist Dr Sadia Mohsin, from San Diego State University in California.
During heart failure the damaged heart is not strong enough to pump blood around the body efficiently, leading to rapid exhaustion.
In the laboratory studies, Dr Mohsin's team worked on heart tissue surgically removed from elderly patients.
Stem cells from the samples were treated with a growth protein called PIM-1.
The effect was to boost activity of an enzyme called telomerase, which has a direct impact on ageing.
The enzyme increases the length of telomeres, "caps" on the ends of chromosomes that shorten each time a cell divides.
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Eventually the chromosomes become so short that their DNA is scrambled and cell division is halted. Cells in this "senescent" state not only stop growing but undergo age-related changes which may, for instance, lead to wrinkled skin.
Keeping telomeres long effectively holds back the ageing process.
The research was presented at a meeting of the American Heart Association in New Orleans and published in the Journal of the American College of Cardiology.
"Since patients with heart failure are normally elderly, their cardiac stem cells aren't very healthy," said Dr Mohsin. "We modified these biopsied stem cells and made them healthier. It's like turning back the clock so these cells can thrive again."
She added: "This is an especially exciting finding for heart failure patients. Right now we can only offer medication, heart transplantation or stem cell therapies with modest regenerative potential, but PIM-1 modification offers a significant advance for clinical treatment."