Your bones secrete a hormone that can make you panic, say scientists

Anyone who said they were afraid of their bones could have spoken more literally than we knew. A new study released Thursday seems to show that both in mice and in humans, the bones secrete a hormone in response to stressful situations. In addition, this bone hormone seems crucial for our response to combat or flight, in a completely different way from other well-known stress chemicals like adrenaline.

Gerard Karsenty, a geneticist at Columbia University, and his colleagues have long been interested in how our skeleton keeps us alive and well – not just by physically supporting us, but through its interactions with the rest of the body. Their work has focused on osteocalcin, a hormone produced by some of the same cells that make up the bone. His previous research, among others, suggest that osteocalcin helps to regulate various functions such as metabolism, muscle function during exercise and fertility.

"What we have found is that you do not necessarily need an ounce of adrenal glands to produce this acute stress response, at least in mice."

In this sense, osteocalcin works like many other hormones produced by the glands and organs that make up our endocrine system. For this reason, Karsenty and his team argued that the skeleton should be considered an endocrine organ. This line of thinking has led the Karsenty team to think that our skeletons could have evolved to help us cope better with stress, as this is another essential function of the endocrine system. And if so, then osteocalcin should also play a leading role.

To test this theory, they first experimented with mice. They exposed the poor rodents to various sources of acute stress, such as controlling them or making them sniff the urine of foxes, a common predator. Judging by their blood tests, the team found that stressed mice produced more osteocalcin within minutes of their test.

They are then passed to people. But since fox urine does not have the same effect on us, Karsenty instead asked volunteers to speak in public and then answer questions. As expected, people's blood pressure and heart rate increased, as well as their osteocalcin levels.

The team's conclusions were published Thursday in Cell Metabolism.

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Other genetic experiments on mice have suggested that osteocalcin directly affects a part of the brain called the amygdala, a region well known to help us deal with emotions like fear. But above all, this passage from our bones to our brain does not seem to involve the adrenal glands – the organ located above our kidneys, long considered the key to the response to combat or theft.

It might even prove that osteocalcin is more important than our adrenal glands for us to light a fire in the face of danger. In mice conceived to be unable to respond to osteocalcin, their response to combat or theft was drastically reduced, but it was not the same when the mice had no adrenal glands . These mice were still able to feel quickly stressed.

"What we've found is that you do not necessarily need an ounce of adrenal glands to produce this acute stress response, at least in mice," Karsenty said. "And that may explain why even people without adrenaline can still have an answer intact."

According to Karsenty's theory, adrenaline and other hormones are of no value to our fight or flight response. On the one hand, some of our nerve cells produce adrenaline and a related hormone called norepinephrine. His team believes that the production of osteocalcin triggers the release of these hormones in the brain, which then regulate other aspects of our response to acute stress. Our adrenal glands probably still play their own part, even if it's not the starting gun that sends us when we see a tiger in the grass or a spider on the wall.

There is still a lot of work to do before we can rewrite the book on stress and adrenaline. This will involve new experiments with other test animals as well as humans. But nothing else, this is the latest research that shows that the body is even more complicated and interconnected than we had supposed.

"We have not studied the body as long as people think. We studied groups of cells isolated from each other, "said Karsenty. "But what the genetics of mice now allow us to do is to examine the function of organs and to determine how hormones and molecules mediate their function in a complete complex organism."