Osteoporosis Linked to Immune Response
Scientists have found a link between the risk of developing osteoporosis high cholesterol, and immune response. Researchers from UCLA have discovered that the immune system acts in a way to promote osteoporosis (loss of bone density), that increases risk of fracture and disability in both men and women.
Rita Effros, professor of pathology at the David Geffen School of Medicine at UCLA says, "We've known that osteoporosis patients have higher cholesterol levels, more severe clogging of the heart arteries and increased risk of stroke. We also knew that drugs that lower cholesterol reduce bone fractures too. "What we didn't understand was why."
The research team studied cells in the lab to discover that T cells exposed to oxidized LDL (low density lipoprotein), considered “bad” cholesterol released a chemical that destroyed bone tissue. High LDL cholesterol seemed to cause osteoporosis because it activated a chemical released by immune cells.
Next they fed one group of mice a high fat diet, and the other a regular diet. The chemical that destroyed bone, called RANKL, was activated by a gene in the mice fed the high fat diet. The result suggests that high LDL cholesterol changes cellular activity to produce bone loss seen in osteoporosis.
"It's normal for our T cells to produce small amounts of RANKL during an immune response," Effros said. "But when RANKL is manufactured for long periods or at the wrong time, it results in excessive bone damage. …The animals' high cholesterol increased their levels of oxidized LDL, which told the T cells to keep generating RANKL. This discovery revealed to us how the immune system might play an entirely new role in bone loss."
The researchers hope to find a way to moderate the response of the immune system when oxidized LDL is present to help prevent bone loss and osteoporosis. The findings come on the heels of a study from Chinese researchers showing that oxycholesterol (oxidized cholesterol) is the most harmful, but little known, type of cholesterol.