Buried alive

Posted: 14th July 2020

Bone is made by cells called osteoblasts. 
As they secrete the components that make up bone, some osteoblasts become encased within the hard bone matrix – buried alive – and the resulting cells are called osteocytes. 
For many years it was thought that osteocytes were nothing more than passive placeholders, lying entombed, inactive and overlooked, within their bony coffins. However, recently it has been shown that the cells play a much more important role. 
Martha Blank is focused on understanding how osteocytes influence the strength of bone. 
“Osteocytes are really fascinating cells. They survive for up to 25 years, making them one of the longest living cells in the body. They also make up 90% of all the cells found in our bones, and yet we know very little about what they do,” says Martha. 
She explains that osteocytes reach out long finger-like connections through miniature tunnels to connect with other osteocytes, allowing them to maintain a sort of ‘helicopter overview’ of bone health. 
“This allows them to communicate with each other about where the skeleton is weak and needs to be strengthened, or where there is damage that needs to be fixed, and then direct other cells to get to work.” 
Martha’s work centres around a particular type of mouse that has a defect in its osteocytes. The bones of these mice look normal by bone density scan, but are in fact extremely brittle. Martha says that this mimics what can happen in people with osteoporosis. 
“We know that if your bone density is low you are more likely to have a fracture. But these tests are imperfect – 60% of fractures occur in people with normal bone density scans.” 
Martha explains that bone is made up mainly of collagen fibres and bone mineral. The amount and arrangement of collagen and mineral is thought to contribute to bone strength and flexibility. 
Martha and the team in SVI’s Bone Cell Biology & Disease Unit have shown that the osteocytes in her mice deposit more mineral in their bones than normal, making their bones more brittle. This means she has discovered a new function for osteocytes – they are not just overviewing what is going on, but actually controlling how much mineral is in the bone. 
One in two women and one in four men will break a bone in their lifetime. For women, this risk is greater than that of heart attack, stroke and breast cancer combined. A man is more likely to break a bone due to osteoporosis than he is to get prostate cancer. 
As our population ages, more people will be affected by osteoporosis, making them more vulnerable and putting further pressure on our healthcare system. 
“Simply put, if we understood better the factors that contribute to bone fragility, we would be able to better identify people at risk of fracture, and also use that knowledge to find ways to improve bone strength,” says Martha. 

For more information please see: Bone cell biology & disease