FGFR antagonists restore defective mandibular bone repair in a mouse model of osteochondrodysplasia

Gain-of-function mutations in fibroblast growth factor receptor (FGFR) genes lead to chondrodysplasia and craniosynostoses. FGFR signaling has a key role in the formation and repair of the craniofacial skeleton. Here, we analyzed the impact of Fgfr2- and Fgfr3-activating mutations on mandibular bone formation and endochondral bone repair after non-stabilized mandibular fractures in mouse models of Crouzon syndrome (Crz) and hypochondroplasia (Hch). Bone mineralization of the calluses was abnormally high in Crz mice and abnormally low in Hch mice. The latter model presented pseudarthrosis and impaired chondrocyte differentiation. Spatial transcriptomic analyses of the Hch callus revealed abnormally low expression of Col11, Col1a, Dmp1 genes in mature chondrocytes. We found that the expression of genes involved in autophagy and apoptosis (Smad1, Comp, Birc2) was significantly perturbed and that the Dusp3, Dusp9, and Socs3 genes controlling the mitogen-activated protein kinase pathway were overexpressed. Lastly, we found that treatment with a tyrosine kinase inhibitor (BGJ398, infigratinib) or a C-type natriuretic peptide (BMN111, vosoritide) fully rescued the defective endochondral bone repair observed in Hch mice. Taken as a whole, our findings show that FGFR3 is a critical orchestrator of bone repair and provide a rationale for the development of potential treatments for patients with FGFR3-osteochondrodysplasia.