精子數量低可能是骨骼惹得禍

Sex hormones are already known to play an important role in maintaining healthy bones - but the relationship may be a two-way street. New evidence suggests that bones are important for controlling testosterone levels。

Gerard Karsenty at Columbia University in New York City and his colleagues applied osteoblasts - bone cells involved in building new bone - to cultures of cells taken from either the testes or ovaries of mice. They found that testis cells treated with bone cells increased their production of the hormone testosterone threefold. The cells from the ovaries, on the other hand, showed no change in their production of the hormones progesterone and oestradiol。

Karsenty's team then focused in closer by looking at osteocalcin - a hormone produced by osteoblasts. They found that testis cells treated with an active form of the hormone released testosterone - and the more of the hormone they got, the more testosterone they produced. Injecting live mice with the hormone similarly boosted levels of testosterone in their bloodstream。

To find out if this effect on testosterone production might affect mice's fertility, the team knocked out the gene for osteocalcin in a group of the rodents. These modified mice had significantly smaller testes and lower sperm counts than their normal counterparts - and when the group bred them with normal females, they found that the litter size was around half normal。

Mice and men

Karsenty is stumped. "We were flabbergasted," he says. "Don't ask me why it only affects males because I don't know."

He thinks the hormone might also boost fertility in men, as many hormones have been found to have the same effects in mice and humans. His team are currently exploring the possibility of osteocalcin as a treatment option for infertile men。

Bone is already known to release hormones. A few years ago, the same group found that osteocalcin plays a role in maintaining the body's glucose levels。衆所周知，性激素對維持骨骼健康影響很大，而且可能反之亦然。新的證據表明骨骼也能影響控制睾丸激素的水平。

紐約哥倫比亞大學的傑拉德•卡森蒂和同事將造骨細胞植入老鼠睾丸或卵巢細胞的培養基裏。結果發現植入有造骨細胞的睾丸細胞產生的性激素數量是原先的三倍，然而卵巢細胞產生的孕酮和雌二醇幾乎沒有發生變化。

卡森蒂的研究組進一步研究了造骨細胞分泌的一種名爲骨鈣素的激素，發現植入了該激素的睾丸細胞分泌了睾丸激素，而且植入的骨鈣素越多，分泌的睾丸激素也更多。

活老鼠注入骨鈣素後血液裏的睾丸激素含量也提升了。

爲查明骨鈣素對睾丸激素的影響是否會影響老師的生育能力，該研究組將一組老鼠的骨鈣素基因取出。這些基因改良後的老鼠睾丸變小，而且精子含量也比正常老鼠低。而且研究人員發現當該組老鼠與正常雌性老鼠交配時，睾丸偏小的老鼠僅有一半表現正常。

老鼠和人

卡森蒂對此結果非常震驚，他說：“太意外了。爲什麼它只對男性有影響，我也不清楚。”

由於研究發現許多激素對鼠類和人類都有類似的作用，他推測這種激素也能提高男性的生育能力。該研究組正在研究是否可以利用造骨細胞治療男性不育。

骨骼分泌激素的說法已是爲人熟知。幾年前，該研究組就發現造骨細胞影響了人體的葡萄糖含量水平。