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Taking tips from zebrafish

Zebrafish (Credit: Novartis AG)

Zebrafish can repair their own hearts (Copyright: Novartis AG)

At an MRC-sponsored session at the Cheltenham Science Festival in June, researchers discussed why scientists are taking lessons from the humble zebrafish when it comes to helping the body heal itself.

Scientists are pretty good at growing cells. They can take stem cells, a kind of cell that has the potential to develop into many — and sometimes any — cell types, and coax them into developing into heart cells, liver cells, retinal cells, nerve cells … the list is long.

The idea is that transplanting these healthy cells into damaged organs could cure disease. There are even attempts to grow entire organs; a new heart grown from a patient’s own cells wouldn’t be rejected so they wouldn’t need immune-suppressing drugs.

But growing heart cells in the lab is a million miles from building an entirely new heart, with its specific and complex structure of muscle and blood vessels. Wouldn’t it be better to fix the old one?

The secret for doing this may lie with zebrafish, tiny fish that have the ability to regenerate part of their heart.

Heart attacks happen when an artery that supplies blood to the heart is blocked. Without a blood supply, a section of the heart muscle dies and scars, meaning that healthy pumping muscle is replaced with fibrous, inactive tissue. If too much of the heart is lost in this way, people can suffer a second heart attack or even heart failure.

Not so for zebrafish. If around a fifth of a zebrafish heart is cut off, the wound will immediately clot but instead of scarring, the epicardium, a layer of cells that surrounds the heart, begins to grow around the clot. The epicardium then stimulates the production of new muscle and blood vessels. Within a couple of months, the heart is back up and running at full speed.

But what has this got to do with people?

The University of  Oxford’s Professor Paul Riley explained how we could encourage the human heart to do a similar thing. He has used a specific protein to encourage dormant cells in the mouse epicardium to ‘wake up’ and generate new heart tissue, and is exploring the biology of these cells in the hope of one day translating this into people.

This kind of research isn’t confined to the heart. Researchers in other areas are looking more and more at stimulating the cells that are already in damaged organs rather than transplanting them.

Paul and the other speakers at the session, MRC fellow Dr Fiona Wardle and Professor John Iredale, Director of the MRC/University of Edinburgh Centre for Inflammation Research, agreed that this approach — of stimulating cells already present in damaged organs rather than transplanting cells — is promising.

Researchers are continuing to work on growing cells and even whole organs. That’s important, said John, because through this work researchers will learn a lot about how organs grow. But his money’s on our bodies eventually being encouraged to repair from the inside.

Katherine Nightingale

Find out more about our regenerative medicine work.

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