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What prevents blood clots in hibernating bears?

A new study led by the University of Reading has found that reduction in a key protein can prevent the formation of dangerous blood clots – known as “deep vein thrombosis” – in hibernating bears, paralyzed humans, pigs kept in small enclosures and other animal species that are immobile for days, weeks, months, or even years at a time.

Although people forced to sit still for many hours during long haul flights are often warned about the risks of blood clotting and advised to occasionally get up and walk around or wear compression socks, most of them will not experience blood clots, if they are not genetically predisposed to such a condition. Now, the experts found that a protein known as “heat shock protein 47” (Hsp47) is dramatically reduced – by as much as 55 times – when someone is immobilized for extended periods of time.

“It seems counterintuitive that people who have severe paralysis don’t appear to be at higher risk of blood clots. This tells us that something interesting is happening. And it turns out that reducing levels of Hsp47 plays a key role in preventing clots, not just in humans, but in other mammals, including bears and pigs. When we see something like this in multiple species, that reinforces its importance. Having Hsp47 must have been an evolutionary advantage,” explained co-author Jon Gibbins, a professor of Cell Biology at Reading.

This protein is released by platelets – the sticky blood cells triggering clotting – in response to an injury, to help protect against blood loss. However, if released into the blood of healthy bears, mice, or humans, Hsp47 seems to promote conditions which may give rise to thrombosis.

By comparing blood samples from hibernating and non-hibernating bears, pigs kept in small enclosures and pigs free to move around in barns, and immobilized people and individuals who can move and walk, the researchers discovered that the absence of movement in all of these species was associated with having much less Hsp47.

“We aren’t totally sure how, but it appears that there is something about movement that keeps Hsp47 at an appropriate level. It could be that the mechanical forces involved in moving around actually have an impact on gene expression, dramatically increasing the amount of Hsp47 that circulates in the blood,” Gibbins said.

“Now that we know that Hsp47 is so important, we can begin to look for new or existing medicines that might be able to inhibit the function of this protein in blood clotting and protect mobile people who are prone to clots,” he concluded.

The study is published in the journal Science.

By Andrei Ionescu, Staff Writer

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