Shujuan Zou

Mechanical strain induces osteogenic differentiation: Cbfa1 and Ets-1 expression in stretched rat mesenchymal stem cells

Distraction osteogenesis is an active process of bone regeneration under controlled mechanical stimulation. Osteogenic differentiation of mesenchymal stem cells (MSCs) is essential for bone formation during this process. Cbfa1 and Ets-1 (core binding factor alpha 1 and v-ets erythroblastosis virus E26 oncogene homolog 1) are transcription factors that play important roles in the differentiation of MSCs to osteoblasts. In order to mimic a single activation of a clinical distraction device, a short period of cyclic mechanical strain (40 min and 2,000 microstrains) was applied to rat MSCs. Cellular proliferation and alkaline phosphatase (ALP) activity were examined. The mRNA expression of Cbfa1 and Ets-1, as well as ALP, a specific osteoblast marker, was detected using real-time quantitative reverse transcription polymerase chain reaction. The results showed that mechanical strain can promote MSC proliferation, increase ALP activity and up-regulate the expression of Cbfa1 and Ets-1. A significant increase in Ets-1 expression was detected immediately after mechanical stimulation, but Cbfa1 expression was elevated later. The temporal expression pattern of ALP coincided perfectly with that of Cbfa1. Mechanical strain may act as a stimulator to induce differentiation of mesenchymal stem cells into osteoblasts, which is vital for bone formation in distraction osteogenesis.

Effects of mandibular setback on the temporomandibular joint: A comparison of oblique and sagittal split ramus osteotomy

PURPOSEnThis investigation studied the changes in temporomandibular joint function and condylar position after mandibular setback using different ramus osteotomies.nnnPATIENTS AND METHODSnThe sample consisted of 50 Chinese adults with mandibular prognathism. Twenty-eight of the patients underwent intraoral oblique ramus osteotomy (IORO), and 22 received sagittal split ramus osteotomy (SSRO) with rigid internal fixation (RIF). TMJ symptoms and radiographic findings were evaluated preoperatively and postoperatively.nnnRESULTSnAfter surgery in the IORO group, the TMJ radiographs showed a significant anterior-inferior displacement of the condyle. Seventy-five percent of the preoperatively symptomatic patients reported fewer or no TMJ symptoms and no preoperatively asymptomatic patients developed new TMJ symptoms. In the SSRO group, the TMJ radiographs showed a posterior displacement of the condyle. Sixty percent of the preoperatively symptomatic patients had no improved TMJ function and 8% of asymptomatic patients developed TMJ symptoms after surgery.nnnCONCLUSIONnThe results of this study show that IORO with MMF appears to be more favorable to the TMJ than the SSRO with RIF; IORO is particularly good in orthognathic surgery patients with preoperative TMJ symptoms.

The effect of hydrofluoric acid treatment on titanium implant osseointegration in ovariectomized rats

This study aimed to investigate the effects of hydrofluoric acid (HF) treatment of grit-blasted Ti implants on osseointegration in ovariectomized (OVX) rats. After blasting with aluminium oxide particles, half implants were treated with 0.2 vol.% HF, and the other half were kept non-modified as control. The topographical and chemical changes of implant surface were determined by Scanning Electron Microscope, Atomic Force Microscope, and X-ray Photoemission Spectroscopy. 12 Weeks after bilateral ovariectomy, each rat accepted two implants in distal femora, with the control implant on the left and the fluoride-modified on the right. As a result, fluoride modification induced markedly changed surface topography and chemical composition. 12 Weeks after implant insertion, the fluoride-modified implants showed improved osseointegration compared to control, with the bone area ratio and bone-to-implant contact increased by 0.9- and 1.4-fold in histomorphometry, the bone volume ratio and percent osseointegration by 0.8- and 1.3-fold in micro-CT evaluation, and the maximal push-out force and ultimate shear strength by 1.2- and 2.0-fold in biomechanical test. These promising results indicated that HF treatment of Ti surface improved implant osseointegration in OVX rats, and suggested the feasibility of using fluoride modification to improve Ti implant osseointegration in osteoporotic bone.

Temporospatial expression of vascular endothelial growth factor and basic fibroblast growth factor during mandibular distraction osteogenesis

OBJECTIVEnDistraction osteogenesis is a vascular-dependent process. This study investigated expression patterns of two major angiogenic factors, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), in the distracted calluses following mandibular lengthening in a goat model.nnnMATERIAL AND METHODSnBilateral mandibular osteotomies were performed in 15 young adult goats. After a latency of 7 days, the mandibles were elongated using custom-made distractors with a rate of 1 mm/day for 10 days. Three animals each were sacrificed at the end of the delay phase, at 0, 7, 14, and 28 days after completion of distraction, respectively. The lengthened mandibles were harvested and processed for histological and immunohistochemical examinations.nnnRESULTSnElevated cellular expression of VEGF and bFGF, with neovascularization in the distraction gap, was observed following mandibular lengthening. VEGF staining was noted in the endothelial cells and osteoblasts. bFGF staining was seen in the fibroblast-like cells, osteoblasts and immature osteocytes. Their strongest expression was found 0-7 days after the end of distraction, and declined with maturation of the newly formed bone.nnnCONCLUSIONnA temporal and spatial expression pattern of VEGF and bFGF was found during distraction osteogenesis in goat mandibles. It suggests that distraction forces can stimulate the production of VEGF and bFGF, which contribute to neovascularization and new bone formation during gradual distraction of the mandible. Application of angiogenic factors may be considered as a potential method to enhance angiogenesis and osteogenesis in osteodistraction, especially in sites without enough vascularization.

Expression of bone-related genes in bone marrow MSCs after cyclic mechanical strain: implications for distraction osteogenesis.

AimUnderstanding the response of mesenchymal stem cells (MSCs) to mechanical strain and their consequent gene expression patterns will broaden our knowledge of the mechanobiology of distraction osteogenesis.MethodologyIn this study, a single period of cyclic mechanical stretch (0.5 Hz, 2,000 μɛ) was performed on rat bone marrow MSCs. Cellular proliferation and alkaline phosphatase (ALP) activity was examined. The mRNA expression of six bone‐related genes (Ets‐1, bFGF, IGF‐II, TGF‐β, Cbfa1 and ALP) was detected using real‐time quantitative RT‐PCR.ResultsThe results showed that mechanical strain can promote MSCs proliferation, increase ALP activity, and up‐regulate the expression of these genes. A significant increase in Ets‐1 expression was detected immediately after mechanical stimulation, but Cbfa1 expression becameelevated later. The temporal expression pattern of ALP coincided perfectly with Cbfa1.ConclusionThe results of this study suggest that mechanical strain may act as a stimulator to induce differentiation of MSCs into osteoblasts, and that these bone‐related genes may play different roles in the response of MSCs to mechanical stimulation.

Biomechanical Properties of the Condyle Created by Osteodistraction

A new condyle can be reconstructed by osteodistraction, but the biomechanical properties of the neocondyle remain unknown. This study examined the hypothesis that the biomechanical properties of neocondylar cancellous bone could reach control levels 24 weeks after its creation by osteodistraction. The right mandibular condyles were removed and reconstructed by osteo-distraction in 16 adult goats. Their contralateral condyles served as controls. Microstructural and mechanical properties were examined by microcomputed tomography and mechanical testing. At 24 weeks after distraction, the neocondyle grew larger in size, but the shape and histological features were similar to those of the controls. The cancellous bone of the neocondyle even appeared to be more dense and stiffer in comparison with the control condyle. The results of this study suggest that the neocondyle created by osteodistraction develops nearly normal biomechanical properties for functional loading by 24 weeks after creation.

The Effect of Uniaxial Mechanical Stretch on Wnt/β-Catenin Pathway in Bone Mesenchymal Stem Cells.

Abstract Wnt/&bgr;-catenin signal is required in bone formation and remodling, but little is known about whether Wnt/&bgr;-catenin signal could promote osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs) after uniaxial mechanical stretch. In this study, rat BMSCs were identified by flow cytometry and used for mechanical stretch. A custom-made uniaxial dynamic stretch apparatus was applied for rat BMSCs stretch. There were 2 groups in the study: the mechanical stretch group and the nonstretch control group. Cell morphology, alkaline phosphatase (ALP) activity, mRNA levels (Wnt3a, Lrp5, &bgr;-catenin, as well as Runx2 were evaluated using quantitative real-time reverse transcription-polymerase chain reaction) and protein levels (&bgr;-catenin and Runx2 were examined using western blot) were observed in both groups. The authors finally found that not only the cell proliferation, ALP activity, but also mRNA expression of Wnt3a, Lrp5, &bgr;-catenin, and Runx2 in BMSCs were markedly elevated by mechanical stretch than the controls. Protein levels of &bgr;-catenin and Runx2 were significantly higher than that of control as well. Activation of mechanical stretch was partially reversed by DKK-1, a classical inhibitor of Wnt/&bgr;-catenin signal. These results demonstrate that uniaxial mechanical stretch could stimulate osteogenic differentiation and proliferation of BMSCs by activating the Wnt/&bgr;-catenin signaling.

Effects of Intermittent Low-Dose Parathyroid Hormone Treatment on Rapid Mandibular Distraction Osteogenesis in Rabbits

PURPOSEnTo determine whether low-dose recombinant human parathyroid hormone (rhPTH) would have a beneficial effect on regenerate healing and surrounding bone in a rabbit model of rapid mandibular distraction osteogenesis (DO).nnnMATERIALS AND METHODSnTwenty-eight rabbits underwent unilateral mandibular lengthening at a rapid rate of 2xa0mm per day for 5xa0days. From the first day of DO, the experimental group received daily subcutaneous injections of rhPTH 10xa0μg/kg for 30xa0days and the control group received the same volume of saline (nxa0=xa014 in each group). At 6xa0weeks after completion of DO, the distracted callus was examined by micro-computed tomography (micro-CT), histology, and the 3-point bending test. Moreover, bone mineral density of the anterior pin region was evaluated by dual-energy x-ray absorptiometry.nnnRESULTSnUnder rapid distraction, poor bone healing was observed in the distracted callus from the control group. In contrast, more mature and abundant bone formation was found in the distracted callus from the experimental group by histologic and micro-CT examinations. Quantitatively, the PTH-treated animals had superior parameters in bone volume fraction, trabecular number, and trabecular thickness and mechanical properties compared with controls (Pxa0<xa0.05). Bone mineral density of the anterior pin region was greater in the experimental than in the control group (Pxa0<xa0.05).nnnCONCLUSIONnLow-dose intermittent rhPTH administration not only enhances new bone formation but also can prevent fixator-related osteoporosis of surrounding segments after rapid mandibular DO in rabbits.

Wnt/β-catenin signaling is required for distraction osteogenesis in rats

ABSTRACT Overview: The Wnt signaling pathway plays crucial roles in embryonic skeletal development and postnatal bone regeneration. However, mechanisms of Wnt signaling functioning in distraction osteogenesis (DO) haven’t been well characterized. Materials and Methods: We established a DO model using Sprague–Dawley rat tibia. And a Wnt signaling blocking agent, recombinant rat Dickkopf-related protein 1 (rrDkk1), was locally applied in the distracted gap to study the role of Wnt signaling during DO process. Animals in the experimental group received rrDkk1 injections (dose = 25 μg/kg) once daily during distraction period and every third day during consolidation stage (n = 48). Animals in the control group received saline under the same injection strategy (n = 48). Animals at different time points during DO process (1, 3, 6, 12 days after distraction, 10 days and 6 weeks after consolidation) were killed and tissues in the distraction region were harvested for radiography, dual energy X-ray absorptiometry, micro-computed tomography (micro-CT), and histological analyses. Results: Most Wnt ligands, cofactors, receptors, and antagonists were widely expressed in the distraction callus and were significantly upregulated during DO process. After rrDkk1 administration, the majority of these factors were downregulated at the mRNA level, except sFRP and GSK-3β. At the protein level, both β-catenin and Lef-1 were also suppressed by rrDkk1. In the long term, restricted bone healing was observed in the distracted callus in the rrDkk1 injection group. These findings were confirmed by histological and micro-CT analyses. Conclusions: Our findings suggest that Wnt signaling participates in the process of DO, and clinical therapeutic approaches of DO may do well to avoid Wnt pathway suppression.