Dr. Meliha Karsak from the Bonn-based Life & Brain Center has found that mice with a particular gene defect have a lower bone density. "We know two types of cannabinoidreceptors, CB1 and CB2," explains Karsak. "The CB1 receptor is formed by nerve cells in the brain and is responsible for, among other things, the mental effect of cannabis. The CB2 receptor, on the other hand, does not occur in nerve cells; its function was previously unknown."
To explore this function the scientists working with Bonn's senior brain expert Professor Dr. Andreas Zimmer have made genetic modifications in mice in order to switch off their CB2 receptor. Karsak summarises what happened: "The animals gradually lost their stabilising trabeculae. We found in these mice that the number of osteoclasts increases by almost 50 per cent."
Karsak was able to demonstrate that osteoclasts, as well as their opposite number, the osteoblasts, which are responsible for building bone, carry CB2 receptors on their surface. "We treated mice with an active substance that bonds specifically to the CB2 receptor. In this way we were able to diminish the bone loss caused by ovary removal," explains the molecular biologist.
"We found that a specific variant of the CB2 gene occurs more frequently among the patients than among the healthy control group," says Karsak. Individuals who carry this defect in their genetic make-up are not destined to have problems. However, as she points out, "Women with this mutation have a three-fold higher risk of osteoporosis."
The results show not only that the CB2 receptor is essential for the maintenance of a normal bone mass: "In many women with osteoporosis the CB2 receptor functions, so in their cases the disease has other causes. For them we could consider stimulating the receptor through medication and in this way slow down their bone loss, " Karsak hopes.
MEDICA.de; Source: University of Bonn