February 18, 2011

Male Bones Linked To Fertility

Researchers have discovered an unexpected connection between a hormone produced in bone and male fertility. 

The study shows that the skeletal hormone known as osteocalcin boosts testosterone production to support the survival of the germ cells that go on to become mature sperm.

The researchers said the findings, which were reported in the February 18th issue of Cell, provide the first evidence that the skeleton controls reproduction through the production of hormones.

According to Gerard Karsenty of Columbia University and his colleagues, bone was once thought of as a "mere assembly of inert calcified tubes."  However, in the last ten years scientists have gained a more dynamic picture of bone as a bona fide endocrine organ with links to energy metabolism and reproduction.

The team performed a prior study on skeletal ties to reproduction that focused primarily on the reproductive organs as a regulator of bone remodeling.  The results from that study led the team to wonder whether the influence might go the either way as well.

Karsenty said his team anticipated such a connection would more likely turn up in females, but that is not what they found at all.

"We found that the bones do control reproduction, but only in males," Karsenty said in a press release. "That was obviously a surprise, but that's the finding."

The researchers report that osteocalcin produced by the bone-building cells known as osteoblasts induces testosterone production by the testes, but fails to influence estrogen production by ovaries.

Mating between females and osteocalcin-deficient males produced smaller and less frequent litters than those between typical males and females.

Males who lack a second gene that inhibits osteocalcin's endocrine functions showed jus the opposite.

The team found that osteocalcin works through a receptor found on testosterone-producing Leydig cells in the testes.

The newly discovered osteocalcin receptor is already known to be expressed in human tests but not ovaries.

Osteocalcin has also been shown to influence glucose metabolism in mice and humans, which suggests that it acts as a hormone in humans.

The discovery may lead to answers for men who suffer from unexplained infertility.

"Male subfertility with no apparent cause is a well-known condition," Karsenty said in a statement.

He added that researchers may now begin looking for evidence that mutations in osteocalcin or its receptor might be responsible in some of those cases.

Karsenty said that his team intends to continue studying the effects of bone on male fertility in greater detail, and they may yet find another rink to female fertility that are independent of osteocalcin.


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