Fly embryos teach scientists about human scars

Most of us have at least one scar. Some people think they are unsightly, while others believe they each tell a story. For scientists at the University of Toronto, scars are a mystery to be solved.

A new study in Nature Physics examines how fruit fly embryos heal and avoid scars altogether. It turns out that flies and humans aren't that different when it comes to wound healing. So studying fruit flies, and particularly the embryos, is an opportunity to explore healing in humans too. This new study is significantly advancing the science of wound healing and scarring.

How a scar forms

A scar is a collection of tissue, mostly the crucial collagen fibers that make up part of the lining of your cells and keep them arranged in the right pattern. When we have a wound, our bodies react to try and close that wound as fast as possible. A large immune reaction takes place to clot the blood, recruit immune cells and close the gap of the wound as quickly as possible to avoid infection. As part of that response, cells produce collagen in a dense matrix that closes the gap in the wound and creates the thick tissue that we call a scar.

Once you develop a scar, you often lose the use of that area of the tissue. Many scars are numb to touch and can also compromise the use of that organ. For example, the scarring that can result from a heart attack can decrease the function of the heart and compromise the efficiency of the heart.

Fly embryos don't have scars

But, a fly embryo heals without scarring. 

"Embryos sometimes get wounds, because of friction with the amnion, with the liquid that kind of surrounds the fetus or the embryo. But when they are born, they don't have any scars," says Teresa Zulueta-Coarasa, lead author on the study from the University of Toronto. "So that's one of the main reasons why we are trying to understand how this process is happening in embryos. Because maybe we could figure out the strategies to be able to improve healthcare in adults."

Studying this phenomenon could help us understand how to help prevent the type of scarring that can have lasting consequences.

That's one of the main reasons why we are trying to understand how this process is happening in embryos. Because maybe we could figure out the strategies to be able to improve healthcare in adults.- Teresa Zulueta-Coarasa

The mechanics of the forces in the fly embryo cell that help close the wound involves similar molecules to those that generate force in our muscle, called actin and myosin. These molecules assemble into cables and motors to pull the wound closed.

The difference with the embryo is that the wound closes asymmetrically—different sides of the wound have different amounts of tension in the cables that are closing the wound. That could be important for understanding why embryos are so good at sealing wounds without scarring.

Adult organisms react to their environment

The next phase of research will examine how much adult organisms—flies, humans, or anything else—have to deal with in their atmosphere. For a human embryo or fetus, they exist in a placenta that is sterile, so there is no need to worry about exposure to germs that could cause an infection. 

For adults, there is a need to close the wound differently because of threats in the environment. But we don't know yet what genes are involved in the healing of embryos to create scarless wounds, or if the adult is capable of this without risking infection.

"For many, many years, people have been trying to apply mechanical stimuli to wounds," says Rodrigo Fernandez-Gonzalez, senior author on the study from the University of Toronto. "And some of those treatments help wounds close fast, but they are black boxes. We don't know how they were working and why they were promoting faster wound closure."

More work to do to prevent scarring

This basic research can't help prevent scarring yet. This work is the first step to explaining why we scar, the mechanics of how wounds close and how to avoid scarring under certain conditions. It can also help us understand what methods are best for healing a cut and what techniques are best to prevent scarring.

Now it's up to the clinical scientists and researchers to put into practice some of the basic science discovered with this new work.