Day-Old Mice Grow Back New Heart Tissue After Injury

Experiments done on laboratory mice suggest it might one day be possible for the human heart to repair itself. Right now, when humans have a heart attack, heart muscles die after being cut off from their blood supply. But what if the heart could grow new muscle to replace the dead tissue?

Some amphibians can regrow body parts, even entire limbs. But humans and other higher animals mostly lack that ability, called regeneration. There are exceptions. Liver tissue, for example, will regrow after part of the organ is removed in surgery. But that's not true with most other organs, including the heart.

In a new study at the University of Texas Southwestern Medical Center, researchers cut off a piece of the heart in tiny, day-old mice. Hesham Sadek explains the procedure.

"We cut off the tip until we see the chamber of the heart. And amazingly enough, the animals survive and they form a blood clot and they don't bleed to death. And within three weeks, that tip grows back."

Grows back as normal, functioning heart muscle, not just closed up with scar tissue.

The mice retain the ability to grow back functioning heart tissue only during their first week of life, and Sadek says it's important to identify exactly when the mouse stops being able to regenerate heart tissue, to see what other changes happen at that point "so we can identify potential factors that are either on or off at this window that we can reintroduce them or block them and have the heart regain this capacity again."

What is encouraging, Sadek says, is that the heart - or at least the mouse heart - is born with this ability to regenerate.

"We discovered that the heart can do this by itself," he says. "It just forgets how to do that or turns it off for some reason. And the question now is, can we remind the heart to do this again?"

And not just after a week or two - but decades later, when a person suffers a heart attack.

"If we can develop actual therapies from this model, the goal would be to convince the heart, instead of forming a scar, the heart now will basically just fill it back up with contractile cells, cells that will contract and pump blood, and the heart will regain its function again."