The IFT80/Hedgehog Pathway Regulates the Osteogenic-adipogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Background: Steroid-induced avascular necrosis of the femoral head (SANFH) is a typical refractory disease that often progresses irreversibly and has a high disability rate. Numerous studies have confirmed that abnormal osteogenic-adipogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) is one of the major factors of SANFH. However, the mechanism remains to be elucidated. Objectives: This study aimed to investigate the function of the IFT80/Hedgehog pathway in the osteogenic-adipogenic differentiation of BM-MSCs. Methods: Femoral head specimens of SANFH patients and femoral neck fractures (FNFs) patients were collected to detect the expression of IFT80, Shh and osteogenic-adipogenic differentiation-related genes by immunohistochemistry (IHC), western blot (WB) and Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR). Based on the rabbit SANFH model, the mRNA expression and protein level of IFT80 and Shh were detected by RT-qPCR and WB. After the osteogenic-adipogenic differentiation based on rabbit BM-MSCs, the IFT80, Gli, PPAR-γ, and Runx2 expression were detected. Differences in alkaline phosphodiesterase activity, calcium nodule, quantification/distribution of lipid droplets, expression of IFT80/Hedgehog axis, and the level of osteogenic- adipogenic associated factors were determined after IFT80 overexpression. Results: RT-qPCR, WB and IHC revealed that IFT80 was highly expressed in the osteoblasts and intra-trabecular osteocytes at the edge of trabeculae and in the intercellular matrix of the bone marrow lumen; Shh was highly expressed in the osteoblasts and intra- trabecular osteocytes at the edge of trabeculae. The Runx2 expression was low, while the PPAR-γ expression was high in both human specimens and animal models of SANFH, suggesting that the balance of osteogenic-adipogenic differentiation was dysregulated. Rabbit BM-MSCs with stable overexpression of IFT80 showed increased alkaline phosphatase activity after induction of osteogenic differentiation, increased calcium nodule production, and decreased adipogenesis after induction of adipogenic differentiation. Conclusion: There is a dysregulation of the balance of osteogenic-adipogenic differentiation in SANFH. IFT80 may inhibit adipogenic differentiation while promoting osteogenic differentiation in rabbit BM-MSCs by activating the Hedgehog pathway.