Loss of Estrogen Receptors Linked to Osteoporosis

by Patricia Reaney
Reuters Health, Wednesday, July 23, 2003

LONDON (Reuters) - Older women may be more prone to suffer from osteoporosis because they do not have enough receptors, or chemical doorways, for the female hormone estrogen, scientists said on Wednesday.

Osteoporosis, or brittle bone disease, affects about one in three women and is more common after the menopause when the body makes less estrogen.

Normally when a bone is subjected to repeated mechanical stress, new bone cells compensate for the load. But Professor Lance Lanyon and researchers at The Royal Veterinary College in London have discovered that in transgenic mice lacking an estrogen receptor called ER-alpha, this does not happen.

"It is the first time ER-alpha has been implicated in bones' normal adaptive response to mechanical loading," Lanyon said in an interview.

"The estrogen receptor is involved in the response to mechanical loading which is responsible for establishing and maintaining bone mass. We think that is the critical link why when you take away the reproductive hormone, you lose bone," he added.

Hormone replacement therapy (HRT), which replenishes the hormone loss after menopause, is prescribed to prevent osteoporosis but it can increase the risk of heart disease, strokes and some cancers.

"The rationale for why hormone replacement therapy prevents osteoporosis is that if it has estrogen in it, it maintains estrogen receptor numbers," said Lanyon.

But the disadvantage is that high estrogen receptors in breast or uterine tissue could increase the likelihood of developing cancer in those areas.

Lanyon believes his findings, which are reported in the science journal Nature, could lead to the development of new drugs that could enhance the performance of the receptor for bone density without increasing cancer risk.

"The future trick would be to get an organ or tissue-specific enhancement of estrogen receptor activity just for the bones and not for the other tissues," he added.

Lanyon said the research points to a specific therapeutic strategy to prevent osteoporosis and answers the long-standing puzzle about why removing a reproductive hormone results in bone loss.

SOURCE: Nature, 2003.

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