Bone marrow stem cells, which are adult stem cells, are in their fifth decade of uncontroversial new discovery. But they can still surprise us. Our bones may be getting fatter as we age, and it could lead to osteoporosis, the condition where bone mineral density is 2.5 standard deviations below the mean (62%). The NIH estimates that up to 50% of women and 25% of men over the age of 50 will break a bone due to osteoporosis.
What's the connection? Bone marrow is that sponge-like tissue inside the bones, you will see animals crack bones open to get to it, and early humans likely did also.(2) Sucking out the marrow was likely done because early man discovered bone marrows had a lot of fat content. In some German restaurants today, you can still get soup with bone marrow in it. Markklößchen are bone marrow dumplings and a lot less work than running down a deer, stripping the meat and cracking the bones.
Mmmmm, bone marrow. Credit and link: oliver latus on flickr
That fat content may be an issue as we get older.
Bone marrow stem cells are produced all our lives and they can differentiate into various types of cells, like the red blood cells that distribute oxygen in our blood, white blood cells to fight infection and platelets that help our blood to clot after injury. Marrow is composed of red and yellow kinds; the red which become osteoblasts, and yellow, which has a lot of adipocytes, those fat cells that compose adipose tissue which store energy as the fat tissue most people know as white fat and brown fat.
Some studies have found that, in people with osteoporosis, stem cells are more likely to become adipocytes than osteoblasts. People with osteoporosis were also found to have more adipocytes in their bones, leading researchers to try and found out if bone marrow fat is a cause or effect of osteoporosis. One signaling molecule, vascular endothelial growth factor (VEGF), is known to decrease with age and a new study looked at the effect of changing VEGF on bone marrow stem cells in mice.
Result: The mice lacking VEGF had more adipocytes in their bone marrow and developed a condition similar to osteoporosis so now they want to see if an age-related decrease in VEGF may contribute to osteoporosis in humans.
Citation: Yanqiu Liu, Agnes D. Berendsen, Shidong Jia, Sutada Lotinun, Roland Baron, Napoleone Ferrara and Bjorn R. Olsen, 'Intracellular VEGF regulates the balance between osteoblast and adipocyte differentiation', J Clin Invest, doi:10.1172/JCI61209 (FREE TO READ)
(1) For international readers, the social authoritarians in New York City are blaming Big Gulps, a giant soda brand at 7-Elevens, for their obesity problem and want to ban them. If that makes as much sense to you as blaming spoons for people being fat, you now know why you are not a New York City politician.
(2) Anyone who has been to a crawdad party is witnessing similar ancient, tiresome food extraction at work.
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