Effects of hydrostatic pressure on cytoskeleton and BMP-2, TGF-beta, SOX-9 production in rat temporomandibular synovial fibroblasts

The relationship between the size of temporomandibular joint condyle and the sagittal disc-condyle position in adults

OBJECTIVE

To explore the relationship between the size of temporomandibular joint (TMJ) condyle and the sagittal disc-condyle position and the relationship between the condylar size and craniofacial structure.

METHODS

Seventy-four subjects (23.82 ± 3.77 years) underwent cone beam computed tomography (CBCT) and lateral cephalograms for orthodontics and volunteered to undergo magnetic resonance imaging (MRI). Mimics was used to calculate the volume and surface area of the condyle. MRI was used to evaluate the sagittal disc-condyle position. The lateral cephalograms were analyzed by Jarabak analysis.

RESULTS

The condylar volume and surface area were negatively correlated with the sagittal disc-condyle position. The condylar volume and surface area were positively correlated with Ar-Go, S-Go, and S-Go/N-Me*100% (p < 0.05) and negatively correlated with ∠Ar-Go-Me and ∠N-Go-Me (p < 0.05).

CONCLUSION

Condylar size was negatively correlated with the sagittal disc-condyle position. The condylar size was correlated with the vertical skeletal pattern.

Challenges and Possibilities of Cell-Based Tissue-Engineered Vascular Grafts

There is urgent demand for biologically compatible vascular grafts for both adult and pediatric patients. The utility of conventional nonbiodegradable materials is limited because of their thrombogenicity and inability to grow, while autologous vascular grafts involve considerable disadvantages, including the invasive procedures required to obtain these healthy vessels from patients and insufficient availability in patients with systemic atherosclerosis. All of these issues could be overcome by tissue-engineered vascular grafts (TEVGs). A large body of evidence has recently emerged in support of TEVG technologies, introducing diverse cell sources (e.g., somatic cells and stem cells) and novel fabrication methods (e.g., scaffold-guided and self-assembled approaches). Before TEVG can be applied in a clinical setting, however, several aspects of the technology must be improved, such as the feasibility of obtaining cells, their biocompatibility and mechanical properties, and the time needed for fabrication, while the safety of supplemented materials, the patency and nonthrombogenicity of TEVGs, their growth potential, and the long-term influence of implanted TEVGs in the body must be assessed. Although recent advances in TEVG fabrication have yielded promising results, more research is needed to achieve the most feasible methods for generating optimal TEVGs. This article reviews multiple aspects of TEVG fabrication, including mechanical requirements, extracellular matrix components, cell sources, and tissue engineering approaches. The potential of periodic hydrostatic pressurization in the production of scaffold-free TEVGs with optimal elasticity and stiffness is also discussed. In the future, the integration of multiple technologies is expected to enable improved TEVG performance.

Arterial graft with elastic layer structure grown from cells

Shortage of autologous blood vessel sources and disadvantages of synthetic grafts have increased interest in the development of tissue-engineered vascular grafts. However, tunica media, which comprises layered elastic laminae, largely determines arterial elasticity, and is difficult to synthesize. Here, we describe a method for fabrication of arterial grafts with elastic layer structure from cultured human vascular SMCs by periodic exposure to extremely high hydrostatic pressure (HP) during repeated cell seeding. Repeated slow cycles (0.002 Hz) between 110 and 180 kPa increased stress-fiber polymerization and fibronectin fibrillogenesis on SMCs, which is required for elastic fiber formation. To fabricate arterial grafts, seeding of rat vascular SMCs and exposure to the periodic HP were repeated alternatively ten times. The obtained medial grafts were highly elastic and tensile rupture strength was 1451 ± 159 mmHg, in which elastic fibers were abundantly formed. The patch medial grafts were sutured at the rat aorta and found to be completely patent and endothelialized after 2.5 months, although tubular medial constructs implanted in rats as interpositional aortic grafts withstood arterial blood pressure only in early acute phase. This novel organized self-assembly method would enable mass production of scaffold-free arterial grafts in vitro and have potential therapeutic applications for cardiovascular diseases.

Hydrostatic Compress Force Enhances the Viability and Decreases the Apoptosis of Condylar Chondrocytes through Integrin-FAK-ERK/PI3K Pathway

Reduced mechanical stimuli in many pathological cases, such as hemimastication and limited masticatory movements, can significantly affect the metabolic activity of mandibular condylar chondrocytes and the growth of mandibles. However, the molecular mechanisms for these phenomena remain unclear. In this study, we hypothesized that integrin-focal adhesion kinase (FAK)-ERK (extracellular signal-regulated kinase)/PI3K (phosphatidylinositol-3-kinase) signaling pathway mediated the cellular response of condylar chondrocytes to mechanical loading. Primary condylar chondrocytes were exposed to hydrostatic compressive forces (HCFs) of different magnitudes (0, 50, 100, 150, 200, and 250 kPa) for 2 h. We measured the viability, morphology, and apoptosis of the chondrocytes with different treatments as well as the gene, protein expression, and phosphorylation of mechanosensitivity-related molecules, such as integrin α2, integrin α5, integrin β1, FAK, ERK, and PI3K. HCFs could significantly increase the viability and surface area of condylar chondrocytes and decrease their apoptosis in a dose-dependent manner. HCF of 250 kPa resulted in a 1.51 ± 0.02-fold increase of cell viability and reduced the ratio of apoptotic cells from 18.10% ± 0.56% to 7.30% ± 1.43%. HCFs could significantly enhance the mRNA and protein expression of integrin α2, integrin α5, and integrin β1 in a dose-dependent manner, but not ERK1, ERK2, or PI3K. Instead, HCF could significantly increase phosphorylation levels of FAK, ERK1/2, and PI3K in a dose-dependent manner. Cilengitide, the potent integrin inhibitor, could dose-dependently block such effects of HCFs. HCFs enhances the viability and decreases the apoptosis of condylar chondrocytes through the integrin-FAK-ERK/PI3K pathway.

Observing the development of the temporomandibular joint in embryonic and post-natal mice using various staining methods

The temporomandibular joint (TMJ) is a specialized synovial joint that is essential for the movement and function of the mammalian jaw. The TMJ develops from two mesenchymal condensations, and is composed of the glenoid fossa that originates from the otic capsule by intramembranous ossification, the mandibular condyle of the temporal bone and a fibrocartilagenous articular disc derived from a secondary cartilaginous joint by endochondral ossification. However, the development of the TMJ remains unclear. In the present study, the formation and development of the mouse TMJ was investigated between embryonic day 13.5 and post-natal day 180 in order to elucidate the morphological and molecular alterations that occur during this period. TMJ formation appeared to proceed in three stages: Initiation or blastema stage; growth and cavitation stage; and the maturation or completion stage. In order to investigate the activity of certain transcription factors on TMJ formation and development, the expression of extracellular matrix (ECM), sex determining region Y-box 9, runt-related transcription factor 2, Indian hedgehog homolog, Osterix, collagen I, collagen II, aggrecan, total matrix metalloproteinase (MMP), MMP-9 and MMP-13 were detected in the TMJ using in situ and/or immunohistochemistry. The results indicate that the transcription factors, ECM and MMP serve critical functions in the formation and development of the mouse TMJ. In summary, the development of the mouse TMJ was investigated, and the molecular regulation of mouse TMJ formation was partially characterized. The results of the present study may aid the systematic understanding of the physiological processes underlying TMJ formation and development in mice.

Pressure and inflammatory stimulation induced increase of cadherin-11 is mediated by PI3K/Akt pathway in synovial fibroblasts from temporomandibular joint

OBJECTIVE

The goal of the study was to investigate the expression of cadherin-11 in synovial fibroblasts (SFs) under mechanical or inflammatory stimuli, and its potential relationship with PI3K/Akt signaling pathway.

METHODS

SFs separated from rat temporomandibular joint (TMJ) were treated with hydrostatic pressures (HP) of 30, 60, 90, and 120 kPa, as well as tumor necrosis factor-α (TNF-α) for 12, 24, 48, and 72 h. The location of cadherin-11 was observed by immunofluorescence microscopy, and its expression was detected by real-time PCR and Western blot. We also studied the activation of PI3K/Akt signaling pathway in SFs with HP or TNF-α stimulation.

RESULTS

The results showed that increased expression of cadherin-11 could be found in the cell-cell contact site of SFs in response to HP and inflammatory stimulation. The mRNA and protein expression of cadherin-11 was positively correlated with the intensity of HP and the duration time of TNF-α treatment. Increased expression of vascular endothelial growth factor-D (VEGF-D) and activation of Akt were also found. Treatment with PI3K inhibitor LY294002 attenuated the pressure or inflammatory cytokine induction increases of cadherin-11, VEGF-D, and FGF-2 both in mRNA and protein levels.

CONCLUSIONS

These findings suggest that cadherin-11 may play important roles in SFs following exposure to mechanical loading and inflammatory stimulation. In addition, PI3K/Akt pathway was associated with pressure or inflammation-induced cadherin-11 expression, which may involve in the pathogenesis of temporomandibular diseases.

Effect of in vitro chondrogenic differentiation of autologous mesenchymal stem cells on cartilage and subchondral cancellous bone repair in osteoarthritis of temporomandibular joint

This study investigated the effects of in vitro chondrogenic differentiated mesenchymal stem cells (MSCs) on cartilage and subchondral cancellous bone in temporomandibular joint osteoarthritis (TMJOA). Four weeks after induction of osteoarthritis (OA), the joints received hylartin solution, non-chondrogenic MSCs or in vitro chondrogenic differentiated MSCs. The changes in cartilage and subchondral cancellous bone were evaluated by histology, reverse transcription polymerase chain reaction and micro-computed tomography (CT). Implanted cells were tracked using Adeno-LacZ labelling. The differentiated MSC-treated group had better histology than the MSC-treated group at 4 and 12 weeks, but no difference at 24 weeks. Increased mRNA expression of collegan II, aggeran, Sox9 and decreased matrix metalloproteinase 13 (MMP13) were observed in differentiated MSC-treated groups compared to the undifferentiated MSC-treated group at 4 weeks. The differentiated MSC-treated group had decreased bone volume fraction, trabecular thickness and bone surface density, and increased trabecular spacing in the subchondral cancellous bone than the undifferentiated MSC-treated group. Transplanted cells were observed at cartilage, subchondral bone, and the synovial membrane lining at 4 weeks. Intra-articular injection of MSCs could delay the progression of TMJOA, and in vitro chondrogenic induction of MSCs could enhance the therapeutic effects. This provides new insights into the role of MSCs in cell-based therapies for TMJOA.

Mandibular lateral shift induces the increased expression of TGF-β, VEGF, and Col-II in the condyle of rat temporomandibular joints

OBJECTIVE

The present study evaluates histologic changes to and expression of angiogenic factors in rats with mandibular functional shift (MFS).

STUDY DESIGN

After 1, 2, and 4 weeks of MFS, rats in the experimental and control groups were killed. Histologic micrographs of the ipsilateral condyle cartilage were obtained. The localization and expression of vascular endothelial growth factor (VEGF), transforming growth factor beta (TGF-β), and type-II collagen (Col-II) in temporomandibular joints (TMJs) were evaluated through immunohistochemical staining.

RESULTS

The results showed that structural changes in the condyle cartilage could be observed 2 weeks after MFS. TGF-β expression reached its peak 2 weeks post-MFS, whereas VEGF and Col-II reached their peaks 4 weeks posttreatment.

CONCLUSIONS

Compressive forces applied to the TMJ could enhance the expressions of VEGF, TGF-β, and Col-II, and activate angiogenesis. The proteins appear to play important roles in the remodeling of the TMJ.

Combination of intermittent hydrostatic pressure linking TGF-β1, TNF-α on modulation of proteoglycan 4 metabolism in rat temporomandibular synovial fibroblasts

OBJECTIVE

This study was designed to evaluate the combined effects of intermittent hydrostatic pressure (IHP) and TGF-β1 or TNF-α on proteoglycan4 (PRG4) expression in rat temporomandibular synovial fibroblasts (SFs).

STUDY DESIGN

Rat SFs were isolated and expanded in monolayer cultures and subjected to IHP in the presence of TGF-β1 or TNF-α. Quantitative real-time RT-PCR was applied to analyze the PRG4 expression levels. Enzyme-linked immunosorbent assay was also used for the quantification of PRG4 accumulation in the culture medium while immunofluorescence staining was used to detect intracellular PRG4 protein expression.

RESULTS

The combination of IHP and TGF-β1 induced greater PRG4 expression than either stimulus alone. In contrast, TNF-α inhibited PRG4 expression, and this was partially alleviated by IHP.

CONCLUSIONS

Our study demonstrates a beneficial role of IHP, which can be used successfully in combination with TGF-β1 to enhance PRG4 production, and can partially counteract TNF-α-induced PRG4 inhibition in isolated rat SFs.

NEL-like molecule-1-modified bone marrow mesenchymal stem cells/poly lactic-co-glycolic acid composite improves repair of large osteochondral defects in mandibular condyle

OBJECTIVE

Articular cartilage of the mandibular condyle has limited ability to regenerate itself after injury. This study was to investigate whether osteochondral defects in mandibular condyle could be repaired by NELL-1(NEL-like molecule-1)-modified autogenous bone marrow mesenchymal stem cells (BMMSCs) and poly lactic-co-glycolic acid (PLGA) composite.

METHODS

Osteochondral defects of 3mm-diameter × 5mm-depth were created unilaterally in the central part of the condyle in 50 adult goats. The injury sites were treated with NELL-1-modified BMMSCs/PLGA, BMMSCs/PLGA, PLGA alone, or left empty. The defect area was monitored using gross examination, histology, immunohistochemistry, and micro-computed tomography (μ-CT). Implanted BMMSCs were tracked using Adeno-LacZ labeling.

RESULTS

The NELL-1-modified BMMSCs/PLGA group showed vigorous and rapid repair leading to regeneration of fibrocartilage at 6 weeks and to complete repair of native articular cartilage and subchondral bone at 24 weeks. The BMMSCs/PLGA group also completely repaired the defect with fibrocartilage at 24 weeks, but the cartilage in the BMMSCs/PLGA group was less well-organized than the NELL-1-modified BMMSCs/PLGA. The osteochondral defects in the PLGA and empty defect groups were poorly repaired, and no cartilage in the empty defect group or only small portion of cartilage in the PLGA group was found. In vivo viability of implanted cells was demonstrated by the retention for 6 weeks in the defects.

CONCLUSION

These findings demonstrated that NELL-1-modified BMMSCs/PLGA composite can rapidly repair large osteochondral defect in the mandibular condyle with regeneration of native fibrocartilage and subchondral bone.

Effects of cyclic hydraulic pressure on osteocytes

Bone is able to adapt its composition and structure in order to suit its mechanical environment. Osteocytes, bone cells embedded in the calcified matrix, are believed to be the mechanosensors and responsible for orchestrating the bone remodeling process. Recent in vitro studies have shown that osteocytes are able to sense and respond to substrate strain and fluid shear. However the capacity of osteocytes to sense cyclic hydraulic pressure (CHP) associated with physiological mechanical loading is not well understood. In this study, we subjected osteocyte-like MLO-Y4 cells to controlled CHP of 68 kPa at 0.5 Hz, and investigated the effects of CHP on intracellular calcium concentration, cytoskeleton organization, mRNA expression of genes related to bone remodeling, and osteocyte apoptosis. We found that osteocytes were able to sense CHP and respond by increased intracellular calcium concentration, altered microtubule organization, a time-dependent increase in COX-2 mRNA level and RANKL/OPG mRNA ratio, and decreased apoptosis. These findings support the hypothesis that loading induced cyclic hydraulic pressure in bone serves as a mechanical stimulus to osteocytes and may play a role in regulating bone remodeling in vivo.