Why Skull Bone is Special Bone

20 December 2009

Interview with

Dr Ian McKay, Queen Mary University of London

Ben -   Also on the news this week, scientists A human skullat Queen Mary University of London helped discover someof the fundamental differences between the bone in our skulls and the bones in our limbs.  And this could hold the key to tackling bone weakness and fractures in osteoporosis.  They have published their work in the journal PLoS ONE.  And we're joined by Dr. Ian McKay to explain a bit more.  Hi, Ian.  Thanks for joining us.

Ian -   Hello.

Ben -   So what does happen to bones over time?

Ian -   Well, there's a gradual and progressive loss of most bone structure and strength.  And that's what will ultimately lead to osteoporosis.

Ben -   And by osteoporosis of course it comes from from bone and pores or holes so essentially we think you have holes in the bone.

Ian -   That's right.  And it's so common, about 50% of all women over 50 are going to suffer from this condition in some form.

Ben -   So what is it that you've been looking at?

Ian -    Well, in one sense , it sounds like the science of the plainly obvious because we'll be comparing the bones from the skull to the arm.  But when you consider osteoporosis, what's interesting is that the skull really doesn't show the same vulnerability to osteoporosis as the rest of the skeleton.  What's more curious, you know, on that basis is that we know that you need mechanical forces to maintain most of your skeleton.  If you don't walk about, your bones will actually will dissolve and be less strong. But the same is not the case for the skull which doesn't actually experience the same mechanical forces as your arms and legs.  Probably, the forces on your arms and legs are maybe 20 to 30 times higher.  So it's rather interesting why the skull should be protected in this way.

Ben -   So is it not just the case that bones become weaker, such as the limb bones, because of the different mechanical stresses?

Ian -   Well, it is to a certain extent.  And you can maintain that by exercises as you get older.  But the skull really seems to be completely insensitive to that.  What we've been doing is looking at the genetic differences between the cells that make the bone in your skull and in your arm.  And we find that they are indeed quite different.

Ben -   So these are factors that occur in the womb, I assume?  So the genes, different genes are switched on.  Some say, "I'm going to make skull bone that will never end up with osteoporosis."  And others say, "I'm going to make arm bone.  It'll be under lots of tension.  And eventually, it may become weak."

Ian -   Well, yes.  I mean, I think this just emphasises the complex nature, people will look at a tissue like bone and they see its uniform over the whole body but in fact if you think about it, your arms and your legs actually are able to experience different forces and designed to respond to those forces differently.  And what we're looking at with the skull is a very dramatic difference between being very hard and protected in the absence of these normal mechanical stimuli.

Ben -   And as these are genetic factors, do they only really kick in the womb?  What happens when we damage our bones, and we have to grow back new bone to knit old broken ones together?

Ian -   Well, there's two aspects to that.  The first is that you obviously do,when regenerate bone, you regenerate bone in their appropriate character for the damaged tissue.  But another thing is that this mechanical responsiveness, that most of the skeleton seems to show, is something which seems to be acquired during development, before birth in the maternal environment. And there's increasing evidence that actually what happens before birth will determine your final mineral mass, your final bone density and strength when you're an adult.  And obviously the more bone you have, the less likely you are to be affected by osteoporosis later in life.

Ben -   And obviously this is something quite important for this time of year.  It's very icy out there, certainly in Cambridge at the moment.  And people will fall.  And when you're bones are weak, certainly in the elderly, you can do a lot of damage to yourself.  Are we learning anything from your work that can help to prevent this or help to protect people from damaging their bones?

Ian -   Well, clearly if there was a way of tricking or making most the skeleton, feel that they are a bit more like the skull.  Then we'll be able to improve and maintain mineral density.  But really we're at the very early stage.  I think it's quite as surprise to some people to show that these bone cells really are that different.  I think a lot consider that they are fundamentally the same.

Ben -   Well, it's fascinating.  So where should we go next?  Where's the next step for you?

Ian -   Well, I think the next important step is to find out when during development the mechanical responsiveness is being established.  I mean, there's quite good evidence  that you can direct or correlate changes in the maternal blood chemistry where the bone density of children who are eight or nine years old.  But what we don't know is when during pregnancy that very important set point is being established.

And I think that's the key element if we wanted to intervene and maybe manipulate bone density and this kind of the gene what we've done will identify some of the markers which I think will be important in that.

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