The neurofibromatosis type I gene promotes autophagy via mTORC1 signalling pathway to enhance new bone formation after fracture

Bone fracture is one of the most common injuries. Despite the high regenerative capacity of bones, failure of healing still occurs to near 10% of the patients. Herein, we aim to investigate the modulatory role of neurofibromatosis type I gene (NF1) to osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and new bone formation after fracture in a rat model. We studied theNF1gene expression in normal and non-union bone fracture models. Then, we evaluated howNF1overexpression modulated osteogenic differentiation of BMSCs, autophagy activity, mTORC1 signalling and osteoclastic bone resorption by qRT-PCR, Western blot and immunostaining assays. Finally, we injected lentivirus-NF1(Lv-NF1) to rat non-union bone fracture model and analysed the bone formation process. TheNF1gene expression was significantly down-regulated in non-union bone fracture group, indicatingNF1is critical in bone healing process. In theNF1overexpressing BMSCs, autophagy activity and osteogenic differentiation were significantly enhanced. Meanwhile, theNF1overexpression inhibited mTORC1 signalling and osteoclastic bone resorption. In rat non-union bone fracture model, theNF1overexpression significantly promoted bone formation during fracture healing. In summary, we proved theNF1gene is critical in non-union bone healing, andNF1overexpression promoted new bone formation after fracture by enhancing autophagy and inhibiting mTORC1 signalling. Our results may provide a novel therapeutic clue of promoting bone fracture healing.