Distraction force promotes the osteogenic differentiation of Gli1+ cells in facial sutures via primary cilia-mediated Hedgehog signaling pathway

Background: Trans-sutural distraction osteogenesis (TSDO) involves the application of distraction force to facial sutures to stimulate osteogenesis. Gli1⁺ cells in the cranial sutures play an important role in bone growth. However, whether Gli1⁺ cells in facial sutures differentiate into bone under distraction force is unknown.

Methods: 4-week-old Gli1ER/Td and C57BL/6 mice were used to establish a TSDO model to explore osteogenesis of zygomaticomaxillary sutures. A Gli1⁺ cell lineage tracing model was used to observe the distribution of Gli1⁺ cells and explore the role of Gli1⁺ cells in facial bone remodeling.

Results: Distraction force promoted bone remodeling during TSDO. Fluorescence and two-photon scanning images revealed the distribution of Gli1⁺ cells. Under distraction force, Gli1-lineage cells proliferated significantly and co-localized with RUNX2⁺ cells. Hedgehog signaling was upregulated in Gli1⁺ cells. Inhibition of Hedgehog signaling suppresses the proliferation and osteogenesis of Gli1⁺ cells induced by distraction force. Subsequently, the stem cell characteristics of Gli1⁺ cells were identified. Cell-stretching experiments verified that mechanical force promoted the osteogenic differentiation of Gli1⁺ cells through Hh signaling. Furthermore, immunofluorescence staining and RT-qPCR experiments demonstrated that the primary cilia in Gli1⁺ cells exhibit Hedgehog-independent mechanosensitivity, which was required for the osteogenic differentiation induced by mechanical force.

Conclusions: Our study indicates that the primary cilia of Gli1⁺ cells sense mechanical stimuli, mediate Hedgehog signaling activation, and promote the osteogenic differentiation of Gli1⁺ cells in zygomaticomaxillary sutures.