Low frequency sinusoidal electromagnetic field accelerating intervertebral fusion through YAP/β-catenin axis

OBJECTIVE: Lumbar interbody fusion plays a crucial role in treating lumbar degenerative diseases, but its fusion rate is influenced by various factors. As a non-invasive physical therapy, low-frequency sinusoidal electromagnetic fields have been proven to promote bone tissue regeneration, although the specific molecular mechanisms remain incompletely understood. The aim of this study is to investigate whether low-frequency sinusoidal electromagnetic fields (LF-SEMF) can regulate the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts through YAP/β-catenin axis in vitro, and to evaluate the effect of LF-SEMF in assisting HA/Col I composite scaffold loaded with BMSCs in intervertebral fusion. METHODS: The impact of LF-SEMF on osteogenic differentiation and mineralization was studied using BMSCs through alkaline phosphatase (ALP) staining and Alizarin red staining. Techniques such as Western blot, immunofluorescence, and qRT-PCR were employed to detect the impact of LF-SEMF on the YAP/β-catenin signaling pathway and related osteogenic genes. Gene silencing was performed to validate the critical role of the YAP/β-catenin axis in the promotion of osteogenic differentiation by LF-SEMF. A rat intervertebral fusion model was established, and the effects of LF-SEMF on intervertebral fusion were evaluated using imaging techniques (X-ray, Micro-CT) and histological analysis (HE staining, Masson staining, and immunohistochemical staining). RESULTS: In vitro experiments demonstrated that exposure to LF-SEMF could facilitate the osteogenic differentiation of BMSCs, significantly upregulating the protein expression levels of YAP and β-catenin, and enhancing the expression of osteogenesis-related genes. Gene silencing experiments confirmed that the YAP/β-catenin axis played a critical role in the promotion of osteogenic differentiation by LF-SEMF. Additionally, animal studies showed that LF-SEMF could significantly promote new bone formation and increase bone strength in the fusion region of caudal vertebrae, while inhibition of YAP/β-catenin signaling pathway attenuated the fusion effect. CONCLUSIONS: LF-SEMF promotes the differentiation of bone marrow mesenchymal stem cells into osteoblasts through YAP/β-catenin signaling pathway. The hydroxyapatite/collagen I composite scaffold loaded with bone marrow mesenchymal stem cells can effectively improve the fusion effect of caudal vertebral fusion by LF-SEMF.