Clayton Carey, a postdoctoral researcher in the Gagnon lab and lead author on the new study. Credit here and above: Brian Maffly

A heart attack will leave a permanent scar on a human heart, yet other animals, including some fish and amphibians, can clear cardiac scar tissue and regrow damaged muscle as adults.

Scientists have sought to figure out how special power works in hopes of advancing medical treatments for human cardiac patients, but the great physiological differences between fish and mammals make such inquiries difficult.

So University of Utah biologists, led by assistant professor Jamie Gagnon, tackled the problem by comparing two fish species: zebrafish, which can regenerate its heart, and medaka, which cannot.

A tale of two fish

The team identified a few possible explanations, mostly associated with the immune system, for how zebrafish fix cardiac tissue, according to newly published research.

“We thought by comparing these two fish that have similar heart morphology and live in similar habitats, we could have a better chance of actually finding what the main differences are,” said Clayton Carey, a postdoctoral researcher in the Gagnon lab and lead author on the new study.

Gagnon’s team wasn’t able to solve the mystery—yet—but their study shed new light on the molecular and cellular mechanisms at play in zebrafish’s heart regeneration.

“It told us these two hearts that look very similar are actually very different,” Gagnon said.

Both members of the teleost family of ray-finned fish, zebrafish (Danio rerio) and medaka (Oryzias latipes) descended from a common ancestor that lived millions of years ago. Both are about 1.5 inches long, inhabit freshwater and are equipped with two-chamber hearts. Medaka are native to Japan and zebrafish are native to the Ganges River basin.

According to the study, the existence of non-regenerating fish presents an opportunity to contrast the differing responses to injury to identify the cellular features unique to regenerating species. Gagnon suspects heart regeneration is an ancestral trait common to all teleosts.

Understanding the evolutionary path that led to the loss of this ability in some teleost species could offer parallel insights into why mammals cannot regenerate as adults.

With their distinctive horizontal stripes, zebrafish have long been popular as pets in the United States. In the 1970s zebrafish were embraced by biologists as a model organism for studying embryonic development of vertebrates.

Scientists like zebrafish because they can be propagated by the thousands quickly in labs, are easy to study and proved to be extremely hardy.

Read the full story by Brian Maffly in @The U.