DLL4/Notch blockade disrupts mandibular advancement‐induced condylar osteogenesis by inhibiting H‐type angiogenesis

Abstract Background Blocking Delta‐like 4 (DLL4)/Notch has emerged as a promising therapeutic target for the treatment of tumours by deregulating angiogenesis. However, DLL4/Notch serves as a negative regulator of angiogenesis in multiple organs while acting as a positive regulator of H‐type angiogenesis in postnatal long bones. Therefore, the effect of DLL4/Notch signalling blockade on mandibular condylar osteogenesis attracted our attention. Objective To explore the effect of blocking DLL4/Notch on mandibular advancement (MA)‐induced condylar osteogenesis. Methods Six‐week‐old young male C57BL/6J mice ( n = 40) were randomly divided into four groups: control group, MA group, MA + Anti‐DLL4 group and MA + IgG group. Of note, IgG served as the isotype control for the anti‐DLL4. The femurs, tibias and mandibular condyles were collected after sacrificing mice on Day 31 for morphology, micro‐computed tomography, immunofluorescence, histology and immunohistochemistry evaluation. Results First, DLL4/Notch blockade shortened femoral length and reduced bone mass by inhibiting H‐type angiogenesis. Second, DLL4/Notch blockade disrupted MA‐induced condylar head volume and quality by inhibiting H‐type angiogenesis. Mechanistically, blocking DLL4/Notch reduced the number of runt‐related transcription factor 2 + (RUNX2 + ) early osteoprogenitors and the expression of Noggin protein in the condylar subchondral bone by inhibiting H‐type angiogenesis. In addition, blockade of DLL4/Notch also destroyed the condylar cartilage layer. Conclusion DLL4/Notch blockade results in shortened femurs and osteopenia, as well as impaired MA‐induced condylar osteogenic volume and quality in growing mice by inhibiting H‐type angiogenesis. Therefore, when blocking DLL4/Notch is used as a treatment target for diseases, attention should be paid to its impact on the bone mass of mandibular condyle.