The secrets of bone remodelling: Our bones are designed to remodel themselves; this is a lifelong process involving the bones adjusting to maintain strength, repair damages, and react to specific stress
Bone remodelling involves two mechanisms with two different cell types: osteoblast, which builds new bone tissue and osteoclasts, which break down old bones.
New research by the Max Planck Institute for Molecular Biomedicine has looked into the key players of bone remodelling and has discovered a new type of capillary known as Type R capillaries, which could be a key player.
Type R capillaries
When looking into type R capillaries, the researchers found that it is present in the trabecular bone, which makes up much of the inner structure of long bones. Type R capillaries are blood vessels, and unlike usual capillaries that transport blood, they can play an active role in bone remodelling.
These blood vessels are also involved in maintaining oxygen levels in blood tissues. This is important for the function of osteoblasts and osteoclasts.
When areas of bone are experiencing low oxygen, these capillaries help to ensure they are properly oxygenated, ultimately allowing bone cells to carry out their normal functions of building and restoring blood tissues.
Bone remodelling in adulthood
Type R capillaries are particularly important in adulthood. Until this new research, understanding bone vasculature has been limited to capillaries found in growing bones, such as Type H capillaries in the growth plate and Type L capillaries in the inner bone.
Researchers have identified Type R capillaries’ importance in bone remodelling in mature and ageing bones. This shows that these are passive blood vessels and active participants in bone health.
Using imaging techniques for better results
The research team used advanced imaging techniques, including Second Harmonic Generation (SHG) microscopy, which provides high-resolution images of bone tissue without additional dyes or labels.
This further allowed the researchers to clearly identify the close spatial relationship between Type R capillaries and the cells involved in bone remodelling.
Their findings show that these capillaries help maintain a delicate balance between bone formation and resorption, an important process for keeping bones healthy and strong.
The process of ageing bones
As bones age, the number of Type R capillaries decreases, especially in trabecular bone, which would explain the reduction in bone mass that occurs with ageing.
The researchers also found that in aged bones, the compact bone, the denser outer layer of bone, undergoes significant changes, such as thinning and the development of small holes, which weaken the bone and make it more prone to fractures.
However, the researchers discovered that new Type R capillaries are formed in the cortical bone of ageing mice, helping to support the ongoing remodelling process and could possibly counteract some of the effects of bone degeneration.
The future of bone health
By discovering this, there are new possibilities for the future of bone health with new therapeutic strategies aimed at improving bone health, particularly in age-related bone loss and conditions like osteoporosis on the horizon.
By targeting the health and maintenance of Type R capillaries, it may be possible to develop treatments that can preserve bone strength better and prevent fractures, improving the quality of life for people as they age.
The study also shows the importance of vascular health in bone remodelling. Before this study, most of the focus has been on the cells that directly build and resorb bone, but this research shows the key role that blood vessels play in supporting bone function.
The specialised vascular structures, like Type R capillaries, ensure that the bone tissue receives the oxygen and nutrients it needs to stay strong and adaptable.
