After someone has had a heart attack, their heart's damaged muscle tissue is replaced by non-beating scar tissue. Unfortunately, this leaves the muscle permanently weakened, and thus susceptible to more problems. There could be new hope, however, as scientists have taken large strides toward understanding how a fish is able to heal its own heart.
About 1.5 million years ago, a variety of tetra fish known as Astyanax Mexicanus lived in the rivers of Northern Mexico – they're still found there today. Some of them would periodically get washed into caves by seasonal floods, and once those floods eventually stopped occurring, the fish were permanently trapped in those caves. Over time, they evolved to lose their eyesight and pigmentation. Their counterparts that were still in the rivers, however, remained as they always had been.
The present-day river-dwelling Astyanax Mexicanus is capable of regrowing beating heart tissue, after damage to its heart has occurred. When blind Astyanax Mexicanus from a certain cave were examined, though, it was found that they could not do so. Led by Dr. Mathilda Mommersteeg, a team from the University of Oxford set out to determine why this was so.
When the genetic activity of the river and cave fish were compared, it was found that two genes – lrrc10 and caveolin – were much more active in the river fish. In humans, lrrc10 has previously been linked to a heart condition called dilated cardiomyopathy, plus mouse studies have shown that it plays a role in how the heart cells contract with each heartbeat.
The scientists then looked to the zebrafish, which is commonly used in scientific studies. Like the river tetras, it's also ordinarily able to regrow its own heart. When the researchers inactivated lrrc10 in zebrafish, however, the animals lost that ability.
Based on these findings, is now hoped that eventually, treatment involving the gene could be used to help humans recover from heart attacks.
"A real challenge until now was comparing heart damage and repair in fish with what we see in humans. But by looking at river fish and cave fish side by side, we've been able to pick apart the genes responsible for heart regeneration," says Mommersteeg. "It's early days but we're incredibly excited about these remarkable fish and the potential to change the lives of people with damaged hearts."
A paper on the research was recently published in the journal Cell Reports.
Source: British Heart Foundation