Bone repair is a complex but carefully organised biological process that depends on stem and progenitor cells to rebuild damaged tissue. In younger people, these cells respond quickly after a fracture, maturing into osteoblasts, the specialised cells responsible for forming new bone. This rapid response allows broken bones to knit together efficiently and regain strength. With increasing age, however, this process becomes much slower and less reliable. Doctors have long recognised that fractures in older adults take longer to heal and are more likely to lead to complications, yet the underlying biological reasons have remained poorly understood.
This slowdown in healing is becoming an increasingly serious problem as populations age worldwide. Fractures among older adults often result in extended hospital stays, reduced mobility, and lasting loss of independence. Until recently, most treatments have focused on stabilising bones surgically rather than improving the body’s own ability to regenerate tissue. As a result, scientists have been searching for the molecular signals that actively interfere with bone repair during ageing, in the hope that targeting these signals could restore the body’s natural healing capacity.
Recent research has identified a key player in this age-related decline: apolipoprotein E, or ApoE. ApoE is a protein best known for its role in lipid transport and is produced mainly by the liver. The study found that levels of ApoE in the bloodstream rise with age and that this increase has a direct negative effect on bone healing. Rather than helping repair, ApoE acts as a systemic inhibitor, interfering with the signals that normally drive stem and progenitor cells to become bone-forming osteoblasts.
To understand how this happens, researchers compared fracture healing in young and aged animal models using a combination of molecular, cellular, and tissue-level analyses. They observed that higher ApoE levels in older subjects suppressed a key signalling pathway known as β-catenin signalling within bone marrow stromal cells. This pathway is essential for pushing immature cells towards an osteoblast fate. When β-catenin signalling is blocked, these progenitor cells stall before fully maturing, leaving the repair process incomplete and fragile.
The study also revealed how ApoE exerts this effect. ApoE binds to a receptor on bone marrow stromal cells called Lrp4, which disrupts downstream β-catenin activity and effectively places a molecular “brake” on bone formation. When researchers used antibodies to block ApoE, this brake was released. β-catenin signalling resumed, osteoblast formation increased, and fracture healing improved significantly. Notably, aged animals treated in this way formed stronger, more complete bone calluses, closely resembling the quality of healing normally seen in much younger individuals.
Perhaps most striking was how reversible the process appeared to be. Even in advanced age, bone-forming cells retained their ability to regenerate once the inhibitory influence of ApoE was removed. This suggests that ageing does not permanently damage the bone’s regenerative machinery but instead suppresses it through circulating signals. The findings also highlight the unexpected role of the liver in controlling skeletal repair, showing that organs far from the injury site can strongly influence healing outcomes.
Together, these results reshape how ageing-related bone repair is understood. By identifying a circulating protein that actively suppresses regeneration, the research opens the door to new, non-invasive therapies aimed at neutralising systemic inhibitors rather than directly manipulating bone tissue. Such approaches could significantly improve fracture healing in older adults, reduce complications, and help preserve mobility and quality of life in an ageing society.
More information: Mingjian Huang et al, Neutralizing hepatic apolipoprotein E enhances aged bone fracture healing, Bone Research. DOI: 10.1038/s41413-025-00489-y
Journal information: Bone Research Provided by Editorial Office of West China School of Stomatology, Sichuan University
