The director of the Children’s Medical Center Research Institute, Dr. Sean Morrison, told KERA’s Sam Baker it all begins with a niche in the bone marrow.
INTERVIEW HIGHLIGHTS:
If you think about when you run, there's a load placed on your leg bones. We know when somebody runs those load-bearing bones become thicker and stronger. It's been thought the load acts on the bones themselves and that the soft bone marrow inside the bones was insulated from those mechanical forces.
We discovered in this study that the mechanical forces get transmitted into the bone marrow and that part of the way that we form new bone cells that would thicken the bones is by transmitting those movement-induced mechanical forces along a specialized type of blood vessel into the bone marrow and bone-forming progenitors live around the margin of those blood vessels. The mechanical forces caused these cells to start dividing, to make more bone cells.
Any kind of movement enhances your heart health. But we think to maintain bone strength and bone thickness, you particularly benefit from load-bearing exercise: walking, running, that sort of thing.
The other interesting thing that we discovered is not just that these bone-forming progenitors live inside the bone marrow and are able to sense the mechanical forces on the bones, but that those cells also secrete factors that help maintain the cells that make new lymphocytes. Lymphocytes are T cells and B cells that are part of our immune system that fights infection.
And we found that we could strengthen a mouse's immune system by letting the mouse exercise, because in this specialized environment, along these blood vessels, not only are there new bone-forming cells, but there are also lymphocyte-forming cells.
When the mice weren't running this niche declined with age, and there were fewer bone-forming cells and fewer immune cells forming as the mice got older.
But if we put a running wheel in the cage with the mice — mice love to run — and the older mice had the running wheels, there were more bone-forming cells and more immune-forming cells. So we think this is also something likely to happen in humans.
For example, we know when astronauts go up into space, their bones get thinner and they have less immune function. Multiple things probably contribute to that. But we think one thing is that this specialized environment in the bone marrow actually needs mechanical stimulation or movement-induced mechanical in order to be maintained.
Yeah. I think it's one of the reasons it's important to exercise when you get older. And, for example, go on long walks.
There could be, but we didn't see it in mice. We did these experiments in mice that are 18 months old. Now that's not crazy old, but that probably corresponds to maybe a 60-year-old human. So, my prediction would be the benefit from this would last quite into old age.
We're going to continue trying to understand the exact mechanisms by which these bone-forming cells increase their division, because if we could better control it, maybe there would be ways of improving treatment of osteoporosis, for example.
RESOURCES:
The compelling link between physical activity and the body's defense system
Interview highlights were lightly edited for clarity.
Got a tip? Email Sam Baker at sbaker@kera.org. You can follow Sam on Twitter @srbkera.
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