Watch: How are blood vessels made?

Growing new blood vessels is one of many quiet miracles our bodies perform. Understanding more about this process could help people with heart and circulatory disease. Our video explains how arteries and veins are formed.

A four-week-old human embryo already has miles of blood vessels. By adulthood, we each have 60,000 miles of blood vessels inside our bodies – that’s more than twice the distance around the world.

Those vessels keep blood flowing, supplying your tissues with oxygen and nutrients, and keeping your organs, including the heart, healthy.

In the embryo, specialised cells form the blood vessel lining, while other cells build up into the layers of the blood vessel.

The vessels are constructed all around the body, then join together to make the whole circulatory system. This activity is much slower in adulthood, but we never lose the ability to grow new blood vessels.

...we never lose the ability to grow new blood vessels.

It’s a process that helps the body heal when we get an injury but also has the potential to treat many conditions where something goes wrong with the blood vessels – including heart failure after a heart attack, diabetes, peripheral arterial disease and some types of stroke.

When part of your body needs a new blood supply, something starts to happen in a nearby blood vessel. The endothelial cells – which form the lining of the blood vessel – start to multiply. Then they become shape-shifters.

Instead of flat cells, tightly bound together like bricks in a tunnel wall, they form a line, which heads off to where it is needed. Once the line reaches its destination, the cells rearrange back into tunnels.

This becomes the blood vessel, and the cells remake the tight bonds that stop any blood leaking out.

How do the blood vessel cells know what to do?

That’s what Professor Harry Mellor and his team are trying to find out.

Scientists already know vascular endothelial growth factor (VEGF) plays an important role. Scientists have tried injecting VEGF into tissues that have been damaged, to try to encourage new blood vessels to grow. But it turns out it’s more complicated than this, explains Professor Mellor.

“You get new blood vessels if you do this but they are not very good blood vessels – they don’t really last. If we have a more sophisticated understanding of the processes, then we can find drugs to target those processes, so we have been focusing on trying to understand the shape changes and movement of the cells.”

Thanks to BHF funding, the team has discovered the role played by two proteins that allow cells to change shape.

Professor Mellor and his team are experts in the cytoskeleton – the framework of every cell. Like our own skeleton, it controls the shape of the cell and its ability to move, but it’s more flexible than a human skeleton, able to expand, shrink or change shape as needed.

Thanks to BHF funding, the team has discovered the role played by two proteins that allow cells to change shape. They’ve teamed up with international collaborators to study one of these in more detail: a protein with the snappy name of FMNL3.

How could research into blood vessels help those with heart and circulatory conditions?

What do we know about FMNL3?

“FMNL3 is part of a family of proteins that you find in nearly every living organism from yeast upwards – all plants and everything in the animal kingdom has them,” says Professor Mellor.

A small plant shoot growing out of the soil

FMNL3 is found in every living organism, from plants through to human nerve cells.

“These proteins seem to have a general function to allow cells to stretch and elongate. When plants produce long shoots, those are made by these proteins. When human nerve cells (which are incredibly long cells) stretch out, this occurs through these proteins. Now we know that this family of proteins are involved in blood vessels, too.”

If new blood vessels could be produced quickly, before the heart muscle dies, this research could even help repair hearts that have been damaged by a heart attack.

To the researchers’ surprise, there is a form of this protein that controls blood vessels specifically. “It seems that evolution has designed some proteins that are specialised to help blood vessels change shape,” says Professor Mellor.

“This is good news because it’s easier to develop a drug to help this process if there is a specific protein that you can target, which isn’t also involved in all the other kinds of cells in your body.”

In future, they hope to work with other scientists on a drug that could improve this process, which could help people with damage to blood vessels, especially those with diabetes.

And there’s a bigger challenge for the future – if new blood vessels could be produced quickly, before the heart muscle dies, this research could even help repair hearts that have been damaged by a heart attack.

How the BHF makes this research possible

Professor Mellor says that none of these discoveries would have happened without the BHF.

“The BHF has been absolutely amazing,” he says. “If we hadn’t had this funding from them, we would be working in a different area and none of the contributions we’ve made would have happened.

"I am incredibly grateful to the BHF for funding this. I don’t think we would have got funding from anywhere else.”

We fund scientists of all types to find answers that will help people with heart and circulatory diseases, and scientists from different backgrounds have an important role.

It makes you very humble to realise that the £200 you spend on an experiment might have come from someone doing a sponsored run

Professor Harry Mellor

This includes Professor Mellor, who is an expert in the cytoskeleton (the internal structure of cells).

“Through BHF funding and working with cardiovascular colleagues, we have been a fresh pair of eyes and brought fresh information to this area, increasing our own understanding of how these cells are controlled.”

Professor Mellor says that working on this project gives him purpose, knowing it could help future patients.

“It is nice to work on something that matters in a real situation,” he says. “On a personal level, that makes me feel more motivated about coming into work.”

He also enjoys meeting local volunteers and fundraisers.

“People come in from BHF shops and the local office and we explain our research,” he says.

“It makes you very humble to realise that the £200 you spend on an experiment might have come from someone doing a sponsored run and asking all their friends and family to help them, or from selling lots of items of clothing in a BHF shop. You get an incredible sense of responsibility about how the money is spent and we try to live up to that.”

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