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

Reversible Effects of Functional Mandibular Lateral Shift on Masticatory Muscles in Growing Rats

In this study, we aimed to determine the effects of functional mandibular lateral shift (FMLS) on the muscle mass, fiber size, myosin heavy chain fiber type, and related gene expression in masticatory muscles (masseter and temporalis), as well as whether the baseline levels could be recovered after FMLS correction in growing rats. The FMLS appliance was placed to shift the mandible leftward by approximately 2 mm. After FMLS placement for 2 and 4 weeks, the muscles on the left side had significantly lower wet weight, mean cross-sectional area, and proportion of type IIa fibers than those on the right side or in the control groups (p < 0.05), with downregulation and upregulation of IGF-1 and GDF-8 gene expression, respectively (p < 0.05). Following 2 weeks devoted to recovery from FMLS, the muscle parameters in the recovery group were not significantly different to those of the control group, and IGF-1 expression in the left-side muscles was enhanced and GDF-8 expression was simultaneously suppressed. These findings indicate that the masticatory muscle changes induced via FMLS tend to revert to normal conditions if the intervention is eliminated at an early stage. Therefore, appropriate orthodontic treatment for FMLS during the growth period is advisable to prevent asymmetric alterations in masticatory muscles.

Effects of Twin Inclined Plane Device on Adaptation and Ultrastructure Variations in Condyle of Growing Rats

Objective

This study investigates the effects of using a twin inclined plane device (TIPD) on the remolding and ultrastructure variation of mandibular condyle in growing rats.

Materials and Methods

Forty-eight male Wistar rats (six weeks old, body weight of approximately 190–210 g) were divided into experimental group (wearing appliance, n = 32) and control group (no appliance, n = 16). Samples were collected on days 3, 14, 30, and 60. The immunohistochemical analysis for vascular endothelial growth factor (VEGF) and type II collagen was carried out. Tartrate-resistant acid phosphatase (TRAP) reaction was performed to evaluate the osteoclastic activity. Three-dimensional morphometric images were reconstructed for morphometric analysis by microcomputed tomography (micro-CT). The ultrastructure of the condylar surface was observed by scanning electron microscopy (SEM).

Results

The expression of VEGF significantly increased, while the expression of type II collagen decreased in the experimental group at days 30 and 60. Furthermore, the enhanced osteoclast activity was observed under the subchondral bone, which was highest at day 30, and decreased to the lowest at day 60 in the experimental group. In addition, adaptive subchondral bone remolding in the posterior part of the condyle was observed at day 60 in the experimental group, and the SEM revealed the ultrastructure variations after installation of the TIPD. However, these changes began to reverse after 30 days.

Conclusion

Condylar tissue changes point to the osteoclastic activity in the posterior region of the condyle. These adaptive changes point to bone resorption in the posterior condyle. Type II collagen and VEGF contribute to the MCC remolding induced by the TIPD. The ultrastructural changes in the posterior condylar area in response to mechanical stresses are recoverable at the initial stage.

Mandibular lateral deviation induces alteration in vascular endothelial growth factor expression and oxidative stress/nitric oxide generation in rat condyle, synovial membrane and masseter muscle

OBJECTIVE

We aimed to investigate alteration in cellular signaling mediated by vascular endothelial growth factor (VEGF) and parameters of oxidative stress/nitric oxide generation, superoxide dismutase (SOD) and neuronal nitric oxide synthase (nNOS), underlying altered functional mechanical loading of TMJ (temporomandibular joint) during lateral mandibular deviation.

DESIGN

Thirty-eight 5-week-old male Wistar rats were divided into experimental group, which received acrylic resin appliance that shifted mandible to the left during closure, and control group. Computed tomography and histomorphometry were used for condyle analyses, while samples of condyle, synovial membrane and m. masseter were analyzed with enzyme-linked immunosorbent assay and spectrophotometry to determine VEGF and nNOS protein concentrations, and SOD activity.

RESULTS

Experimental group of rats developed smaller and asymmetrical mandibles. Less of new bone and cartilage formation and larger bone marrow cavities area were found in the experimental group. Higher VEGF expression in condyle and m. masseter as well as higher nNOS expression in m. masseter and synovial membrane were found in the experimental compared to the control group. Alteration of SOD activity was found in m. masseter and synovial membrane in the experimental group.

CONCLUSIONS

Lateral mandibular deviation induces mandibular and condylar morphological changes as well as significant cellular signaling alterations in condyle, synovial membrane and masticatory muscle. Cellular VEGF protein overexpression and oxidative stress/nitric oxide disbalance could be the mechanisms underlying unbalanced functional TMJ loading due to mandibular deviation.

Effects of bisphosphonates on mandibular condyle of ovariectomized osteoporotic rats using micro-ct and histomorphometric analysis

OBJECTIVE

To evaluate microarchitectural changes in condylar cartilage and associated subchondral bone after bisphosphonates treatment using an ovariectomized (OVX) osteoporosis rat model.

METHODS

Thirty six-month-old female Sprague-Dawley rats were randomly divided into sham, OVX, and risedronate (RIS)-treated groups. Both OVX and RIS groups received bilateral ovariectomy. OVX group was treated subcutaneously with saline, whereas RIS group received risedronate treatment (2.4 μg/kg) subcutaneously for 3 months. At the end of 3 months, animals were sacrificed and the entire condyles were harvested for micro-CT and histological analyses. Immunohistochemistry (IHC) was performed to assess the expression of type I/II collagen protein by semiquantitative imaging analysis.

RESULTS

Micro-CT analysis showed OVX group had significant condylar subchondral bone loss compared to sham as shown by significant decrease in bone volume fraction (P = 0.028), trabecular thickness (P = 0.041), and significant increase in trabecular spacing (P = 0.003). In RIS group, partial inhibition of OVX-induced bone loss was detected. HE staining showed proliferative layer of condylar cartilage reduced, while hypertrophic chondrocyte layer increased significantly in RIS group compared to sham and OVX groups. IHC showed reduced expression of Col I in both the OVX and RIS groups, whereas expression of Col II was reduced in the OVX group but increased in the RIS group.

CONCLUSION

Our findings suggest that systemic bisphosphonate treatment influences the structure and ossification of condylar cartilage and it has a dual action on condyle in a postmenopausal osteoporosis rat model which raises the concerns for the potential side effects of BPs on condyle to elder patients.

Trend of Cadherin-11 expression and its impact on cartilage degradation in the temporomandibular joints of guinea pigs with spontaneous osteoarthritis

BACKGROUND

This study aims to investigate spatial and temporal changes in cadherin-11 (CAD-11) expression and their effects on cartilage degeneration in the temporomandibular joint (TMJ) of guinea pigs with spontaneous osteoarthritis (OA).

METHODS

Dunkin-Hartley (DH) and Bristol strain 2 (BS2) guinea pigs at ages of 1, 3, 6, 9, and 12 months were categorized into two groups and analyzed. The bilateral TMJ condyles of DH and BS2 guinea pigs were harvested and fixed. The distribution and expression profiles of CAD-11, collagen type II, and matrix metalloproteinase 3 (MMP-3) were detected by immunohistological assays. Histological micrographs of the condyle cartilage were obtained and analyzed.

RESULTS

Osteoarthritis can be spontaneously induced by mechanical stress in DH guinea pigs. The main histopathological changes in the TMJ structure and increased expression of MMP-3 occurred within 6-9 months of ages in DH guinea pigs with spontaneous OA. By contrast, minimal to mild cartilage degradations were observed in the TMJ of BS2 guinea pigs even at the age of 12 months. From as early as 3 months of age, the expression levels of CAD-11 were upregulated in the TMJ of DH guinea pigs compared with those in BS2 animals. CAD-11 expression differed between the two groups at 12 months of age.

CONCLUSIONS

Increased CAD-11 expression within cartilage is associated with the development and progression of OA between the two strains of guinea pigs. Therefore, CAD-11 expression in TMJ could be an important predisposing factor for the development of spontaneous OA.

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.