Loss of Stat3 in Osteoblasts Impaired the Bone Remodeling in Inflammatory Microenvironment

Introduction: Oral diseases including periodontitis, periapical periodontitis, and peri-implantitis are characterized by inflammation and loss of alveolar bone. Signal transducer and activator of transcription 3 (Stat3) involved in bone formation and maintenance. This study aimed to investigate the effect of Stat3 on the osteoblast-mediated bone remodeling in the inflammatory lesion.Methods: The conditional knockout of Stat3 in osteoblasts (Stat3 CKO) was generated via the Cre-loxP recombination system using Osterix-Cre (Osx-Cre) transgenic mice. The lipopolysaccharide (LPS)-induced calvarial bone inflammatory lesions were harvested at day 3, 7 and 14 for micro-CT scanning, histological staining, quantitative real-time PCR (qRT-PCR) and western blot to assess the bone remodeling. Osteoblasts were harvested from Stat3 CKO and wildtype mice and were cultured in vitro. In response to LPS-stimulation, the cells were subjected to alizarin red staining, qRT-PCR and western blot to examine the formation of calcium deposit, the expression of osteogenic markers (i.e. Runx2, OPN, COL1A1) and osteoclast-related markers (i.e. RANKL, OPG). The EdU and transwell assays were performed to assess the proliferation and migration of the cells.Results: Compared with the wildtype control, a decrease of bone mass and an increase of osteolysis were found in the inflammatory lesions on Stat3 CKO mice. More osteoclastic-like cells, as well as an increased expression of RANKL, were observed in the lesions on Stat3 CKO mice. Both mRNA and protein expressions of Stat3 and osteogenic markers in the lesions was significantly decreased on Stat3 CKO mice. After co-cultured with osteogenic medium, the Stat3-deficient osteoblasts were found with a significant decrease of calcium deposits and the expression of osteogenic markers, and with a significant increased expression of RANKL, when compared with the control osteoblasts. The impaired ossification of Stat3-deficient osteoblasts was even more pronounced with the presence of LPS in vitro. According to the EdU and transwell assays, the most decrease of cell proliferation and migration was found in Stat3-deficient osteoblasts in response to LPS. Conclusions: Loss of Stat3 in osteoblasts impaired bone regeneration in inflammatory microenvironment, which might be resulted from the effect of Stat3 on the ossification, activation of osteoclast activationic signals, proliferation and migration of osteoblasts.