Apoptosis prevents osteoporosis

Grandmothers everywhere know well that estrogen deficits lead to osteoporosis. Now, the molecular basis for this debilitating bone loss is finally identified. Estrogen is needed to kill off bone-destroying osteoclasts, show Takashi Nakamura, Shigeaki Kato (University of Tokyo, Japan), and colleagues.

The root cause of osteoporosis has been difficult to pin down, in part because bones are not frail in female mice lacking estrogen receptors. These mice make extra androgen, which builds bone in male mice and might compensate for bone loss in the mutant females.

To avoid the androgen rise, Kato's group knocked out estrogen receptors only in mature osteoclasts, which accumulate in osteoporotic bones. These female mutants developed rickety bones due to losses within the central bone shafts.

The authors then isolated osteoclasts...