Photo Credit: Pavel Danilyuk
Scientific Frontline: Extended "At a Glance" Summary: Collectin-11 and Bone Health
The Core Concept: Collectin-11 is an immune protein traditionally known for defending against infection that has now been discovered to play a critical role in maintaining healthy bones by supporting normal bone remodeling.
Key Distinction/Mechanism: While its primary immune function involves recognizing sugar patterns on pathogens to trigger defense responses, collectin-11 produced in the bone marrow specifically facilitates the formation and function of osteoclasts—specialized cells responsible for breaking down old or damaged bone so that new bone can form. Without it, stem cells fail to generate these necessary bone-resorbing cells.
Origin/History: The dual function of collectin-11 was discovered by researchers at King's College London and published in PNAS. The breakthrough emerged from cross-disciplinary research led by Professor Steven Sacks and Dr. Mark Howard, merging immunology and bone development studies.
Major Frameworks/Components:
- Collectin-11 Protein: Functions both as a first responder in the immune system and as a crucial communication bridge for the local immune environment within bone tissue.
- Osteoclasts: Specialized bone-resorbing cells that require collectin-11 to properly differentiate from bone marrow-derived stem cells.
- Bone Remodeling: The continuous biological cycle of bone breakdown and formation, which halts in the absence of collectin-11, leading to the accumulation of age-related bone damage and diminished skeletal strength.
Branch of Science: Immunology, Osteology (Bone Biology), Molecular Biology, and Pathology.
Future Application: The development of targeted pharmacological drugs designed to block collectin-11 interactions in specific disease contexts. This could offer an alternative or complementary approach to controlling abnormal osteoclast activity with fewer side effects than current suppressive treatments.
Why It Matters: This unexpected link between the immune system and skeletal health opens new therapeutic avenues for treating metabolic bone diseases, osteoporosis, erosive osteoarthritis, and bone damage associated with metastatic cancers (such as breast, prostate, and lung cancer). Furthermore, it helps explain the biology behind skeletal abnormalities seen in children with rare genetic mutations affecting collectin-11, such as 3MC syndrome.
The research published in PNAS, reveals that the protein collectin-11 supports normal bone remodeling by enabling the formation and function of osteoclasts – specialized cells responsible for breaking down old or damaged bone so that new bone can form.
Collectin-11 has an important role in the immune response. It acts as a first responder against infection by recognizing sugar patterns on bacteria and viruses and then triggering a sequence of other proteins that activate the immune response. Until now, its function outside of immune defense had not been fully understood. The researchers found that collectin-11 produced in the bone marrow plays a critical role in ensuring a healthy supply of osteoclasts.
Using mouse models, the researchers demonstrated that when collectin-11 is absent along with one other protein in the sequence that it activates as part of the immune response, osteoclast formation is impaired. As a result, normal bone remodeling fails, leading to the accumulation of age-related bone damage and reduced bone strength in mice.
In the lab, when collectin-11 was added back to stem cells derived from the bone marrow of mice lacking these proteins, the stem cells were able to generate osteoclasts. The researchers found this mechanism operated in the same way in human cells. Human stem cells lacking collectin-11 were unable to generate osteoclasts unless the missing protein was restored.
These findings could help to explain the biology behind skeletal abnormalities observed in children born with rare genetic mutations affecting collectin-11, including cleft palate and abnormal development of bones in the skull (known as 3MC syndrome).
At a molecular level, the research showed that osteoclasts depend on collectin-11 to communicate with part of the immune system that operates locally in bone. Targeting this communication could represent a potential new therapeutic avenue for conditions in which abnormal osteoclast activity contributes to bone pathology. These include osteoporosis, erosive osteoarthritis, and bone disease associated with metastatic cancers such as breast, prostate, and lung cancer.
Steven Sacks, Professor of Nephrology at King’s College London and senior author of the paper, said: “Our findings highlight an unexpected link between the immune system and bone health and identify a potential new target for treating osteoporosis and cancer-related bone disease, where excessive osteoclast activity can damage bone. The research also shows how immune proteins can play an unexpected but important role in maintaining long-term health.”
Dr Mark Howard, former Research Associate at King’s College London and first author of the paper, said: “It is an enjoyable coincidence that my earlier work in bone development should intersect with our current research in immunity. That a bone health mechanism would emerge from this convergence of knowledge is particularly satisfying. Even more exciting is the potential link to metabolic bone disease, which may open the door to entirely new therapeutic approaches.”
Current treatments that suppress osteoclast formation can be effective but may have significant side effects. The researchers are now working to develop drugs that block collectin-11 interactions in specific disease contexts. These treatments could provide an alternative or complementary approach, offering more targeted control of osteoclast activity.
Funding: The research was supported by the Medical Research Council.
Published in journal: Proceedings of the National Academy of Sciences
Title: Collectin-11 regulates osteoclastogenesis and bone maintenance via a complement-dependent mechanism
Authors: Mark C. Howard, Conrad A. Farrar, Christopher L. Nauser, Yusun Jeon, Anastasia Polycarpou, Dorota Smolarek, Roseanna Greenlaw, Martyn Foster, Peter Garred, Daniela A. Vizitiu, Subhankar Mukhopadhyay, and Steven H. Sacks
Source/Credit: King’s College London
Reference Number: imgy030626_01