精子数量低可能是骨骼惹得祸
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。众所周知，性激素对维持骨骼健康影响很大，而且可能反之亦然。新的证据表明骨骼也能影响控制睾丸激素的水平。
纽约哥伦比亚大学的杰拉德•卡森蒂和同事将造骨细胞植入老鼠睾丸或卵巢细胞的培养基里。结果发现植入有造骨细胞的睾丸细胞产生的性激素数量是原先的三倍，然而卵巢细胞产生的孕酮和雌二醇几乎没有发生变化。
卡森蒂的研究组进一步研究了造骨细胞分泌的一种名为骨钙素的激素，发现植入了该激素的睾丸细胞分泌了睾丸激素，而且植入的骨钙素越多，分泌的睾丸激素也更多。
活老鼠注入骨钙素后血液里的睾丸激素含量也提升了。
为查明骨钙素对睾丸激素的影响是否会影响老师的生育能力，该研究组将一组老鼠的骨钙素基因取出。这些基因改良后的老鼠睾丸变小，而且精子含量也比正常老鼠低。而且研究人员发现当该组老鼠与正常雌性老鼠交配时，睾丸偏小的老鼠仅有一半表现正常。
老鼠和人
卡森蒂对此结果非常震惊，他说：“太意外了。为什么它只对男性有影响，我也不清楚。”
由于研究发现许多激素对鼠类和人类都有类似的作用，他推测这种激素也能提高男性的生育能力。该研究组正在研究是否可以利用造骨细胞治疗男性不育。
骨骼分泌激素的说法已是为人熟知。几年前，该研究组就发现造骨细胞影响了人体的葡萄糖含量水平。
