'Mighty Mice' to Fight Weak Bones

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'Mighty mice' to fight weak bones

http://news.bbc.co.uk/1/hi/health/4281709.stm

By

BBC News health reporter, in Washington DC

US scientists have made a " mighty mouse " whose big muscles could help

find a way to prevent bones weakening.

It has 70% more muscle mass than normal mice as it lacks the

myostatin gene that ensures muscles do not overgrow.

Six years ago, a German boy was born with a myostatin mutation and

had muscles twice the normal size.

A Medical College of Georgia team says bones may respond to the

stress placed on them by extra muscle by forming more bone - helping

to fight osteoporosis.

Bone density

Dr Mark Hamrick, who is leading the work on the " mighty mouse " ,

said: " We are interested in kids.

" We want to know how to maximise their bone during peaks of growth

while they still can, " he told the annual meeting of the American

Association for the Advancement of Science (AAAS).

He said bone mass by the end of the pubescent growth spurt was a good

predictor of a person's future risk of osteoporosis.

The way to increase bone density and strength is force.

The myostatin gene is expressed at highest levels as babies and

children grow, tapering off in adulthood. Its job is to make sure the

muscles do not overgrow.

By knocking out myostatin, Dr Hamrick's team will be able to see what

effect this has on the bones to which the muscles are attached.

" People have argued for many years that the way to increase bone

density and strength is force. "

He said bones responded to stress and strain placed on them by

forming more bone.

" The best way to increase that force is muscles. "

Fit not fat

Some studies have suggested that fat can have the same effect, but Dr

Hamrick said the increasing number of obese children in the US tended

to have lower bone masses which went against this theory.

In addition to their big muscles, mighty mice essentially have no fat

because they lack myostatin.

Since the summer, Dr Hamrick's team has been comparing the mice with

other ones that are overfed to become obese.

" We can look at whether muscle has more of an impact on bone mass

than fat because our mighty mice don't gain fat, " he said.

The other thing they want to find out is whether increasing muscle

mass by exercise alone would have the same effect as knocking out

myostatin.

Dr Hamrick said his early findings showed exercise did not benefit

the bones of mighty mice as much as normal mice.

" There is no easy way out. The best way to make our kids strong,

healthy and happy is a good diet and exercise, " he said.

He is also examining mice with a disorder similar to Duchenne

muscular dystrophy in humans.

These mice have big muscles but the muscles themselves are weak.

" This allows us to tease apart how muscle size affects bone versus

muscle strength, " he said.

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Carruthers

Wakefield, UK