To date, it has been assumed that bones lack lymphatic vessels, but new research published in the journal Cell not only mapped them within bone tissue, but demonstrated their role in bone and blood cell regeneration and reveals changes associated with ageing.
The network of vessels that form the lymphatic system plays an important role in draining excess fluid from tissues, clearing waste products and supporting immune responses.
The fine network of lymph vessels extends throughout the body, but a small number of sites such as the brain, eye and bone were previously assumed to lack lymph tissue. The hard tissue of bone in particular has traditionally made studying the distribution and role of blood and lymph more difficult.
Researchers used light-sheet imaging to identify and visualise the lymphatic vessels of bone in high-resolution 3D, revealing an active network of lymph vessels within bone. The researchers further identified some of the key signals happening between lymph vessels, blood stem cells and bone stem cells.
Dr Lincoln Biswas, co-first author of this study, said: ‘Interestingly after injury, lymphatic vessels in bone show dynamic crosstalk with blood stem cells and with specialised perivascular cells in order to accelerate bone healing. Such interactions between lymphatics and bone stem cells can harnessed to promote bone healing such as in fracture repair.’
The researchers found that lymphatic vessels in bone increase during injury via a signalling molecule called IL6, and trigger expansion of bone progenitor cells by secreting a different signal, called CXCL12. Dr Junyu Chen, a co-first author of the study now based at Sichuan University said: “Ageing is associated with diminished capacity for bone repair, and our findings show that lymphatic signalling is impaired in aged bones. Remarkably, the administration of young lymphatic endothelial cells restores healing of aged bones, thus providing a future direction to promote bone healing in elderly.”
Dr Anjali Kusumbe, who led the research said: “I am very excited as these findings not only demonstrate that lymphatic vessels do exist in bone but also reveal their critical interactions with blood stem cells and perivascular bone stem cells after injury to promote healing, thereby presenting lymphatics as a therapeutic avenue to stimulate bone and blood regeneration. Further, these findings are very fundamental, opening doors for understanding the impact of bone lymphatics on the immune system and their role in bone and blood diseases.”
Source: Oxford University
