bone up. mice lacking leptin (right) vertebrae with 40% more mass than mice with an overactive nervous system (left).
A new skeletal control mode is out of the closet. A study concluded that the hormone leptin, long known to be involved in obesity, is by the sympathetic - "fight or flight" or - branch of the nervous system to suppress bone formation. The results provide the first evidence that the nervous system regulates bone cells and suggest that beta blockers, high blood pressure medications commonly prescribed to suppress the sympathetic nervous system, could also fight against osteoporosis.
The first indication of a link between leptin and bone came from the observation that obese people, who tend to be less sensitive to leptin, have strong bones. Studies conducted by geneticist Gerard Karsenty at Baylor College of Medicine in Houston confirmed the connection in mice, showing that mice deficient in leptin accumulate their bones and their body weight ( Science NOW, 18 January, 00). But how the hormone delivered his message remained mysterious.
The reports now Karsenty team in the November 1st issue of cell that the nervous system plays a key role. Researchers have joined the systemic circulation of two mouse leptin less and perfused leptin in the brain of a. Bone cells responded that in the mice that received leptin, a result involving the nervous system rather than a message carrying blood. Leptin appears to act through sympathetic nervous system: The mouse bone devoid of norepinephrine - the neurotransmitter of the signing of the sympathetic system - didnt respond to leptin treatment, the team found. Finally, mice treated with beta-blockers maintained normal bone mass, even with their ovaries removed. This condition normally stimulates bone loss, thus increasing the possibility that drugs could fight against osteoporosis.
"It is the elegant science," says immunologist Steven Teitelbaum of Washington University in St. Louis. The work creates a "whole new vision of how bone cells are regulated." However, Teitelbaum warns if the results in mice will apply to humans is still open to question. If the results generalize adds Gideon Rodan, a biologist bone cells in the Merck research laboratories in West Point, Pennsylvania, it might be possible to develop beta blockers that increase bone strength without adverse effects on blood pressure.
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