ABSTRACT
The important function of the endplate is to transmit stress and supply nutrition. Endplate degeneration might induce or promote degeneration of the intervertebral disc, causing a series of spine diseases that seriously impair people’s health and life quality. Endplate chondrocytes can respond to mechanical stimulation, which is an important factor affecting endplate degeneration. Inappropriate mechanical stimulation will accelerate endplate degeneration. This review summarized the effects of mechanical stimulation on vertebral endplate chondrocyte apoptosis, synthesis inhibition, calcification, and extracellular matrix degradation. The endplate degeneration induced by mechanical stimulation is regulated by a complex network of signal pathways composed of various signal transduction factors. The signal pathways involved in this review included NF-κB, Wnt, Hedgehog, MAPK, RhoA/Rock-1, AKT/mTOR, TGF-β signaling pathway and miRNA related signals. The interconnection of these pathways was highlighted and summarized. Multiple signaling pathways work together to regulate endplate chondrocyte metabolism, which ultimately leads to the endplate degeneration. This review might shed light on early diagnosis and precise treatment of cartilage endplate degeneration.
ABSTRACT
Objective To study fluid flow within alveolar bone under orthodontic and occlusal loading, so as to provide references for understanding the regulatory mechanism of bone remodeling during orthodontics. Methods An animal model for orthodontic tooth movement on rats was first constructed. The finite element model of tooth-periodontal ligament-alveolar bone was established based on micro-CT images and the strain field in alveolar bone under orthodontic or constant occlusal loading was analyzed. Then finite element model of alveolar bone was constructed from the bone near the cervical margin or apical root of mesial root. The fluid flow in this model under orthodontic and cyclic occlusal loading was further predicted by using fluid-solid coupling numerical simulation. Results The fluid velocity within alveolar bone cavity mainly distributed at 0-10 μm/s, and the fluid shear stress (FSS) was mainly distributed at 0-10 Pa. FSS on the surface of alveolar bone near the apical root was higher than that close to the cervical margin. Conclusions FSS at different levels could be produced at different location within alveolar bone cavity under orthodontic and cyclic occlusal loading, which might further activate biological response of bone cells on the surface of trabeculae and finally regulate the remodeling of alveolar bone and orthodontic movement of tooth. The results provide theoretical guidance for the clinical treatment of orthodontics.
ABSTRACT
Fluid shear stress (FSS) caused by interstitial fluid flow within trabecular bone cavities under mechanical loading is the key factor of stimulating biological response of bone cells. Therefore, to investigate the FSS distribution within cancellous bone is important for understanding the transduction process of mechanical forces within alveolar bone and the regulatory mechanism at cell level during tooth development and orthodontics. In the present study, the orthodontic tooth movement experiment on rats was first performed. Finite element model of tooth-periodontal ligament-alveolar bone based on micro computed tomography (micro-CT) images was established and the strain field in alveolar bone was analyzed. An ideal model was constructed mimicking the porous structure of actual rat alveolar bone. Fluid flow in bone was predicted by using fluid-solid coupling numerical simulation. Dynamic occlusal loading with orthodontic tension loading or compression loading was applied on the ideal model. The results showed that FSS on the surface of the trabeculae along occlusal direction was higher than that along perpendicular to occlusal direction, and orthodontic force has little effect on FSS within alveolar bone. This study suggests that the orientation of occlusal loading can be changed clinically by adjusting the shape of occlusal surface, then FSS with different level could be produced on trabecular surface, which further activates the biological response of bone cells and finally regulates the remodeling of alveolar bone.
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Objective To investigate the role of vitamin D in the synthesis and degradation of aggrecan in rat articular chondrocytes at cellular level. Methods Rat articular chondrocytes were stimulated by IL-1α, IL-1β and TNF-α, respectively. Normal and inflammatory chondrocytes were treated with different doses of vitamin D, respectively. CCK8, Flow cytometry, real time-PCR and western blot analysis were used to examine the proliferation activity and apoptosis level of chondrocytes, and the expression of aggrecan, ADAMTS-4 and ADAMTS-5 at both mRNA and protein levels. Results IL-1α,IL-1β and TNF-α significantly decreased the proliferation activity and increased the apoptosis level of the chondrocytes. Furthermore, IL-1α, IL-1β and TNF-α significantly decreased the expression of aggrecan, and increased the expressions of ADAMTS-4 and ADAMTS-5 at both mRNA and protein levels in the chondrocytes. 1α,25 (OH)2D3supplementation significantly increased the proliferation activity and decreased the apoptosis level of chondrocytes stimulated by IL-1α, IL-1β and TNF-α in a dose-dependent manner, but not affected the normal chondrocytes. Meanwhile, 1α,25(OH)2D3also significantly increased the expression of aggrecan, and decreased the expressions of ADAMTS-4 and ADAMTS-5 at both mRNA and protein levels in the chondrocytes under inflammatory conditions. Conclusions Vitamin D may promote the anabolism of aggrecan and inhibit aggrecanase activity in chondrocytes under inflammatory conditions, which may impact overall protection for articular cartilage.
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Objective To investigate whether TG2 plays an important role in the osteoblast differentiation and mineralization.Methods TG2 mRNA of SaOS-2 cells was knocked down using a lentivirus stably expressing short-hairpin ( sh) RNA targeting TG2.Then the cells were cultured in osteo-inductive medium for 14 d to measure mineralization and for 7 d to measure the levels of osteoblastic differentiation markers including ALP activity and mRNA of collagen I, osteocalcin ( OCN) and BMP-2.The wild-type SaOS-2 cells and scrambled shRNA-transducted SaOS-2 cells served as the controls. Results The controls displayed an increasing trend of the level of ALP activity and mRNA of collagen I, osteocalcin and BMP-2,and notable mineralization at 14 d.When TG2 was knocked down, ALP activity, mRNA of collagen I, osteocalcin and BMP-2 at 7d,and mineralization at 14 d were all significantly lower in comparison with the corresponding values in the controls.Conclusion TG2 is involved in the differentiation and mineralization of osteoblasts in vitro.
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ObjectiveTo explore the bone anabolic effects after a single local injection of simvastatin into femoral cavities of osteoporotic rats.MethodsThirty-six female SD rats(3 months old,body weight 250-300 g) were ovariectomized(OVX) and low-calcium-diet fed for 3 months,OVX rats were randomized into 3 groups(n=12).Left femurs of group A,B and C were injected with 0,5 and 10 mg simvastatin,respectively.Half of the rats in each group were randomly euthanized separately 1 and 5 months after simvastatin injection.Left femurs were taken out for bone mineral density (BMD) assessment with dual energy X-ray absorptiometry,bone histomorphometic changes were analysized by Micro-CT,and two kinds of biomechanical tests were used to evaluate the osteogenic effects.ResultsOne and five months after injection,BMD in mid-diaphysis significantly increased in simvastatin-injected groups compared to the control group.For Micro-CT analysis,significant increase in total bone volume/total tissue volume,cortical wall thickness,trabecular thickness,trabecular number,and a significant decrease in trabecular spacing were observed in simvastatin-injected groups compared to the control group.For both biomechanics (the three-pointbreaking test of condyles and axial compressive testing of proximal femur),the values were significantly higher in simvastatin-injected groups than the control group.ConclusionLocal simvastatin treatment showed a positive effect on improving mechanical strength,structure of osteopenic femurs and BMD.Our findings may provide a new strategy for the prevention and treatment of osteoporosis,especially for osteoporotic fractures.