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Background: Signal transducer and activator of transcription 3 (Stat3) is a cytoplasmic transcription factor that participates in various biologic processes. Loss of Stat3 causes hyperimmunoglobulin E syndrome, presenting with skeletal disorders including osteoporosis, recurrent fractures, scoliosis, and craniosynostosis. The objective of this study is to explore the effect and mechanism of Stat3 on osteogenesis of mesenchymal progenitors. Methods: Stat3 was conditionally knockout (CKO) in mesenchymal progenitors by crossing the pair-related homeobox gene 1-cre (Prx1-Cre) with Stat3-floxed strain mice. Whole-mount-skeletal staining, histology, and micro-CT were used to assess the differences between Stat3 CKO and control mice. Further, in vitro experiments were conducted to evaluate the osteogenesis potential of primary isolated bone marrow mesenchymal stem cells (BMSCs) from both control and Stat3 CKO mice. After osteogenic induction for 14d, alizarin red staining was used to show the calcium deposit, while the western blotting was applied to detect the expression of osteogenic markers. Results: Compared with the control, Stat3 CKO mice were present with shortened limbs, multiple fractures of long bone, and open calvarial fontanels. The abnormal growth plate structure and reduced collagen fiber were found in Stat3 CKO limbs. According to micro-CT analysis, the reduced cortical bone thickness and bone volume were found on Stat3 CKO mice. The in vitro osteogenic differentiation of BMSCs was inhibited in Stat3 CKO samples. After osteogenic induction for 14d, the significantly diminished calcium deposits were found in Stat3 CKO BMSCs. The decreased expression of osteogenic markers (OPN and COL1A1) was observed in Stat3 CKO BMSCs, compared with the control. Conclusions: Stat3 played a critical role in bone development and osteogenesis. Loss of Stat3 impaired the osteogenesis of mesenchymal progenitors in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Background: Receptor tyrosine kinase-like orphan receptor 2 (Ror2) plays a key role in bone formation, but its signaling pathway is not completely understood. Signal transducer and activator of transcription 3 (Stat3) takes part in maintaining bone homeostasis. The aim of this study is to reveal the role and mechanism of Ror2 in the osteogenic differentiation from mouse bone marrow mesenchymal stem cells (mBMSCs) and to explore the effect of Stat3 on Ror2-mediated osteogenesis. Methods: Ror2 CKO mice were generated via the Cre-loxp recombination system using Prrx1-Cre transgenic mice. Quantitative real-time PCR and western blot were performed to assess the expression of Stat3 and osteogenic markers in Ror2-knockdown mBMSCs (mBMSC-sh-Ror2). After being incubated in osteogenic induction medium for 3 weeks, Alizarin Red staining and western blot were used to examine the calcium deposit and osteogenic markers in Stat3 overexpression in mBMSC-sh-Ror2. Results: Loss of Ror2 in mesenchymal or osteoblast progenitor cells led to a dwarfism phenotype in vivo. The mRNA expression of osteogenic markers (osteocalcin, osteopontin (OPN), and collagen I) in the ulna proximal epiphysis of Ror2 CKO mice was significantly decreased (P < 0.05). The mRNA and protein expression of Stat3 and osteogenic markers (Runx2, osterix, and OPN) decreased in mBMSC-sh-Ror2 cells (P < 0.05). The overexpression of Stat3 in mBMSC-sh-Ror2 cells rescued the calcium deposit and expression of Runx2, osterix, and OPN to a level comparable to normal mBMSCs. Conclusions: Ror2 was essential for skeleton development by regulating mBMSCs' osteogenesis and osteoblast differentiation. Loss of Ror2 may impair the osteogenesis of mBMSCs by inhibiting Stat3. [ABSTRACT FROM AUTHOR]