Experiments in mice with a bone disorder similar to that in women after menopause show that a scientifically overlooked group of cells are likely crucial to the process of bone loss caused by the disorder, according to Johns Hopkins researchers. Their discovery, they say, not only raises the research profile of the cells, called preosteoclasts, but also explains the success and activity of an experimental osteoporosis drug with promising results in phase III clinical trials. A summary of the researchers’ work was published online on October 5, 2014 in Nature Medicine. "We didn't know that the drug affects preosteoclasts, nor did we understand how important preosteoclasts are in maintaining healthy bones," says Xu Cao, Ph.D., the Lee H. Riley Jr., M.D., Professor of Orthopaedic Surgery. "Now drug companies hoping to reverse osteoporosis can look for even more drugs that make use of and target these interesting cells." The bones of mice, people, and all land animals are not only necessary for strength and structure, but also as warehouses for calcium, which cells throughout the body use continuously for everyday tasks like cell-to-cell communication, muscle strength, and even embryo fertilization and hormone balance. Calcium is taken from digested food and stored in the semi-hollow space inside bones. To access the stored calcium, the inner bone goes through a process called resorption, in which cells called osteoclasts attach to the bone and dissolve the calcium and other stored minerals. Nearby, specialized blood vessels pick up the calcium and send it throughout the body. They also bring in nutrients needed for new bone formation. Under normal conditions, bone resorption is carefully balanced with bone rebuilding to maintain bone strength.
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