The Wnt1g177c/G177c Mutation Impairs Fracture Healing in Mice

Wnt1 is essential for bone development and remodeling, with pathogenic variants associated with osteogenesis imperfecta type XV (OI-XV) and early-onset osteoporosis (EOOP) in humans and mice. However, the impact of Wnt1 variants on fracture healing remains unclear. This study investigates how the Wnt1 G177C/G177C variant, associated with OI in humans, affects fracture repair processes, including inflammation, bone formation, and remodeling. A standardized femur osteotomy was performed in 12-week-old female Wnt1 +/+ and Wnt1 G177C/G177C mice, stabilized using an external fixator. At day 21 post-fracture, three-point bending test assessed the mechanical properties of fractured and unfractured femora. Bone quality was analyzed using microcomputed tomography (µCT), and histomorphometric analysis of the fracture callus was conducted on day 10. Early inflammatory responses, including immune cell populations, chemokines, and cytokines, were quantified on day 2 post-fracture using flow cytometry and a 36-plex cytokine/chemokine assay. Wnt1 G177C/G177C mice exhibited significantly reduced mechanical strength (N.mm 2 ) in unfractured (2688.4±486.7 vs 1660.3±350.3, P < 0.001) and fractured femora (1358.3±645.0 vs 439.3±257.5, P < 0.01) compared to Wnt1 +/+ controls. µCT revealed decreased cortical thickness (µm) in unfractured femora (204.7±13.1 vs 163.5±9.5, P < 0.001) and reduced bone volume fraction (%) in the fracture callus of Wnt1 G177C/G177C mice (12.1±3.9 vs 6.9±2.8, P < 0.05) Histomorphometric analysis showed increased cartilage area (%) (14.1±4.4 vs 22.0±5.9, P < 0.05) and a trend towards reduced bone area (%) within the fracture callus (13.4±3.4 vs 8.7±4.5, P = 0.06) The early inflammatory phase was compromised in Wnt1 G177C/G177C mice, evidenced by reduced macrophage numbers and lower levels of chemokines CCL5 and CCL7 The Wnt1 G177C/G177C variant impairs bone repair by disrupting bone formation and the inflammatory response critical for effective healing. Targeting Wnt1 signaling pathways presents a promising therapeutic approach to improve fracture repair in Wnt1-related bone disorders and other conditions with compromised bone healing.