Fibroblast-derived NEU1 as a therapeutic target for improving cortical bone integrity and fracture healing

<b>Rationale:</b> Bone fractures, particularly in aging populations, present significant clinical challenges due to prolonged healing times and increased risk of complications. A deeper understanding of the molecular mechanisms regulating bone metabolism and repair is essential for developing novel therapeutic strategies. <b>Methods:</b> Through performing immunohistochemical staining and observation on the hind limbs of mice, we evaluated the differences in the spatial distribution of osteoclasts and sialic acid-enriched regions, and further investigated the correlation between osteoclast activation and sialic acid levels in the bone microenvironment. Additionally, single-cell sequencing was conducted to infer the main cell subsets involved in the modification of sialic acid levels in the periosteum. Meanwhile, <i>in vitro</i> and <i>in vivo</i> models were employed to specifically interfere with neuraminidase 1 (NEU1) activity, so as to verify the effectiveness of targeted regulation of NEU1 in modulating local osteoclast activation, maintaining cortical bone homeostasis, and regulating fracture healing rate. <b>Results:</b> Through single-cell RNA sequencing of human periosteum, we discovered that NEU1 desialylates α2,3-linked sialic acid residues on osteoclasts, disrupting cell-cell recognition and maintaining osteoclasts in a mononuclear state. This mechanism contributes to the low metabolic activity and structural integrity of cortical bone while enhancing bone anabolic effects. Importantly, targeted inhibition of NEU1 in mouse models accelerated fracture healing, reducing healing time by up to 30% compared to controls and significantly improving bone quality and mechanical strength. <b>Conclusions:</b> Here, we identify a critical role for periosteal fibroblast-derived NEU1 in modulating osteoclast activity and bone homeostasis. These findings suggest that NEU1 is a promising therapeutic target for enhancing bone regeneration and treating metabolic bone diseases. Our study lays the groundwork for the development of NEU1-targeted therapies that could transform clinical practice by promoting faster and more effective bone healing.