"Swiss Army knife" bears reveal anti-blood-clotting secret
If you've ever taken a long airplane ride, you've no doubt heard that you should get up and move periodically to avoid developing blood clots. That's because when our bodies are stationary for long periods of time, the odds of our blood pooling, coagulating, and clotting go up. Yet bears can spend months in the same position in their caves while hibernating without this concern. New research has uncovered why that is, and the findings could have implications to create better anti-clotting treatments for people.
In a study that was over a decade long, a team led by researchers from German and Swedish institutions took blood samples from brown bears in Sweden during the depths of their hibernation phase in winter, as well as during their active periods in the summer months. They found that when the bears were hibernating, a protein known as HSP47 was nearly absent in the blood samples. This protein covers the surface of blood platelets, and helps attract and bind to white blood cells to create the net-like structures involved in clot formation. When the bears returned to their active periods, levels of HSP47 increased.
Building on this knowledge, the researchers genetically engineered mice to not produce HSP47. The result was that the mice's ability to form blood clots greatly diminished.
In a further step, the research team took blood samples from humans who had been rendered immobile through spinal cord injuries. Just like the bears, these people spend their life immobile, but tend not to experience excessive blood clots. Sure enough, the human patients also had low levels of HSP47. Likewise, when the researchers had 10 healthy volunteers undergo strict bed rest for 27 days, their HSP47 levels dropped.
While it's clear from the research that our bodies naturally downregulate this protein when we are immobilized for long periods of time, the researchers wonder if activating it before the body does so on its own could help reduce the risk of blood clots known as deep vein thrombosis. These occur in people who are suddenly immobilized by, for example, an injury. Also, the researchers say that using a gene-based solution to help with clotting could be safer than the current standard of using blood-thinning medications, which pose a bleeding danger to those who take them.
"The ideal treatment for deep vein thrombosis would prevent blood clots from forming where they aren’t supposed to, while not preventing your body’s normal blood clotting machinery," Kim Martinod, a biomedical scientist at Katholieke Universiteit Leuven in Belgium who was not involved in the study, told Science.org. "This has the potential to be just that."
While the current bear study opens a new route of investigation into combating potentially lethal blood clots, the researchers say there is still yet more to learn from the animals.
"We are also continuing our research on the bear model, as it may potentially prove to be a Swiss Army knife with solutions to a wide range of major challenges," said Ole Frøbert, of the Department of Clinical Medicine at Aarhus University in Sweden. "Currently, we are working to understand why bears – unlike inactive humans – do not lose muscle mass during hibernation."
The results of the study have been reported in the journal, Science.