CALGARY - University of Calgary researchers say a newly discovered type of cell appears to repair heart damage in mice.

The scientists say they've found the same type of cell in humans and believe it could foster new therapies for heart disease.

Researcher and cardiac surgeon Paul Fedak says it is located in a sack of fluid that surrounds the heart and "may hold the secret to repair and regeneration of new heart muscle."

He says the fluid is often discarded during surgery but when scientists induced heart attacks in mice and left the fluid intact, the mice appeared to fare better than those without the fluid.

Fedak adds that the research is at a very early stage and requires further work to determine any therapeutic potential in humans.

The research was supported by the Heart and Stroke Foundation of Canada, the Canadian Institutes of Health Research, the Canada Research Chairs Program, and the National Institutes of Health. The study is published today in the journal Immunity.

"This fluid that surrounds the heart, we don't really think much of it. In fact, I suck it away and throw it in the garbage when I do heart surgery," Fedak said of how little had been known of the material, which contains different cell populations but is largely comprised of one cell in particular.

"Maybe we should be trying to keep that intact or replacing that fluid or developing new therapies where we can take those cells out, expand them and then reinject them into that space to enhance repairs. There's a lot of therapeutic implications of this study for the future."

The research began with the work of physiology and pharmacology professor Paul Kubes, who says he first discovered similar reparative cells around the liver and intestines in 2016.

When Kubes realized the cells appeared to help repair those organs, he and Fedak wondered if similar cells exist near the heart and lungs.

It turns out these cells exist around many organs, says Kubes, but it's not clear how they function during a heart attack.

"One possibility is that these cells need to be replenished or we need to add more of these cells to help better heal the heart," says Kubes, who is director of the university's Snyder Institute for Chronic Diseases.

Fedak says the cells seem to reduce scar formation, which itself is a big problem.

"If you get scar formed in your heart, the scar is not functional, it can't contract or contribute to heart function," notes Fedak, the incoming director of the Libin Cardiovascular Institute of Alberta.

In fact, the very act of removing pericardial fluid could actually cause scarring, said Fedak, noting that he's observed scarring on the outside of the heart when he's had to operate on a patient who's previously undergone heart surgery.

"It's all scarred in there. And possibly that's because of the loss of this fluid and healing cells and other molecules and things that are in that fluid."

Fedak called this research "step one" towards identifying the potential of this cell, described as a Gata6+ pericardial cavity macrophage.

While he says studies in mice are useful as "proof of concept," determining real-world applications requires moving the study to larger animal subjects, such as rats, pigs and then humans.

A possible next step would be to reintroduce a large number of cells to see how it affects healing in mice, rats or pigs.

Kubes says the need for such research is great.

"People with a heart attack afterwards have limited capacity to live a normal life — walking can be a problem, just daily activity can be very strenuous and tiring. If we can help heal more of the heart, their life could be greatly improved."

- By Cassandra Szklarski in Toronto

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