Targeting injury-triggered grancalcin from senescent macrophages enhances aged bone healing

Age-related decline in bone regenerative capacity poses a significant challenge for craniofacial skeleton repair in elderly patients. Grancalcin (GCA), a calcium-binding protein secreted by myeloid cells, has been identified as a potential contributor to the process of skeletal aging. However, its specific role in age-related craniofacial bone regeneration remains poorly understood. Using a mouse model of tooth extraction socket healing, we show that GCA from bone marrow-derived macrophages (BMDMs) regulates both cellular senescence and osteogenic differentiation of bone marrow stromal cells (BMSCs) during bone regeneration in aged mice. Mechanistically, the injury-responsive transcription factors c-Jun and SPI1 act synergistically to drive Gca expression in senescent BMDMs, thereby impairing mitochondrial function and osteogenesis in BMSCs via the Plxnb2-Arg2 axis. Furthermore, we engineered a gelatin methacryloyl (GelMA) hydrogel for the sustained local delivery of a GCA-neutralizing antibody (GelMA-GCA-NAb). Local application of this hydrogel markedly enhanced jaw bone healing in aged mice. Our findings identify injury-induced GCA as a key mediator connecting immune senescence to deficient bone regeneration and propose local GCA neutralization via hydrogel as a promising immunotherapeutic strategy to improve bone healing in the elderly. STATEMENT OF SIGNIFICANCE: Current conventional therapies for age-related bone healing face limitations in addressing aging-impaired biological processes, while hydrogels delivering targeted factors show significant promise by enabling precise modulation of the local microenvironment. This study reveals that c-Jun/SPI1-driven GCA from senescent macrophages promotes BMSCs senescence and impairs osteogenesis via Plxnb2-Arg2 in age-related jawbone injury. Importantly, local delivery of a GCA-neutralizing antibody via GelMA hydrogel accelerates healing, offering an emerging therapeutic strategy.