ABSTRACT
Objective@# To investigate the expression of the mTORC1 signaling pathway during the osteogenic differentiation of mouse bone marrow mesenchymal cells (BMMSCs) under cyclic uniaxial tension and explore its possible role.@*Methods @# The BMMSCs of mice were affected by uniaxial dynamic tensile force. Western blot was used to detect the expression changes of major molecules (mTOR, Raptor, S6K) in the endogenous mTORC1 signaling pathway at 0, 1, 2, 4, and 8 hours after stretching. Chemical colorimetry, ELISA and PCR were used to detect alkaline phosphatase (ALP), osteocalcin (OCN) and Runx2 mRNA, respectively. Then, inhibition, activation and control groups were established by administration of the drugs PP242, MHY1485 and PBS, respectively. Two hours after the stress, the expression of S6K was detected by western blot, and the expression of the osteogenic signal was continuously detected by the above methods.@*Results @#Western blot analysis showed that the main molecules of the mTORC1 signaling pathway were all expressed within 8 hours after traction, and the highest expression was 2 hours after the stress. Compared with those in the control group, the ALP activity and OCN expression decreased and the Runx2 mRNA levels increased after the mTORC1 signal pathway was inhibited (P ＜ 0.001); ALP activity and OCN expression increased after the mTORC1 signal pathway was activated, while the Runx2 mRNA levels decreased (P ＜ 0.001). @*Conclusion @#The mTORC1 signaling pathway participates in the osteogenic differentiation of mouse BMMSCs under tension. The osteogenesis of BMMSCs under cyclic uniaxial tension would be enhanced if the mTORC1 signaling pathway was activated.
ABSTRACT
Objective @#To explore the promoting effect of periostin on rapid distraction osteogenesis of the rabbit mandible and provide experimental evidence for the clinical use of periostin to promote osteogenesis.@*Methods@#Twenty-four New Zealand male white rabbits underwent distraction osteogenesis, and after 3 days of retention, they were rapidly stretched at a stretch rate of 2 mm/d (total 5 d). The animals were randomly divided into group A and group B (12 per group). On the last day of the stretch, 0.5 mL of normal saline containing 40 μg of recombinant periostin was given to group B or an equal volume of normal saline was added to the control group (group A) for 8 days. At 4 weeks and 8 weeks post-stretch, 8 animals were randomly selected from each group to undergo a CT scan under general anesthesia. The bone mineral density and bone mineral content were detected by dual energy X-ray absorptiometry. Eight weeks post-stretch, all of the experimental animals were sacrificed. Six animals were randomly selected from each group for micro-CT and a histological examination, and the remaining animals were subjected to biomechanical tests. @*Results @#CT images showed that the new bone formation in the distraction space of group B was significantly better than that of group A at 4 and 8 weeks post-stretch. At 4 weeks and 8 weeks post-stretch, the bone mineral density in group B was (0.157 ± 0.016) g/cm 2 and (0.234 ± 0.023) g/cm 2, respectively, and the bone mineral content was (0.096 ± 0.010) g and (0.204 ± 0.017) g, respectively. The above four means were significantly higher in group B than in group A (P < 0.001). The micro-CT images and data suggest that the stretch gap microstructure of group B has more mature features. Histological experiments showed that the trabecular bone of group B was thick and mature, with few chondrocytes. The biomechanical test results showed that the biomechanical strength of the distraction gap in group B was (228.47 ± 39.98) N, which was 1.24 times that of group A (P = 0.045).@*Conclusion@# Interstitial use of periosteal protein in the distraction space of the mandible in rabbits can promote local new bone formation and mineralization.