Study on the effects of gradient mechanical pressures on the proliferation, apoptosis, chondrogenesis and hypertrophy of mandibular condylar chondrocytes in vitro

Early changes in asporin levels in osteoarthritis of the temporomandibular joint

OBJECTIVES

The present study aimed to elucidate the pathogenesis of temporomandibular joint (TMJ) osteoarthritis (TMJ-OA) in a mouse model. We investigated morphological and histological changes in the head of mandible cartilage and early immunohistochemical (IHC) changes in transforming growth factor (TGF)-β, phosphorylated Smad-2/3 (p-Smad2/3), a TGF-β signaling molecule, and asporin.

METHODS

TMJ-OA was induced in a mouse model through unilateral partial discectomy. Micro-computed tomography (micro-CT) and safranin-O staining were performed to morphologically and histologically evaluate the degeneration of the head of mandible caused by TMJ-OA. IHC staining for TGF-β, p-Smad2/3, and asporin was performed to evaluate the changes in protein expression.

RESULTS

In the experimental group, three-dimensional (3D) morphometry revealed an enlarged head of mandible and safranin-O staining showed degeneration of cartilage tissue in the early stages of TMJ-OA compared to the control group. IHC staining revealed that TGF-β, p-Smad2/3, and asporin expression increased in the head of mandible cartilage before the degeneration of cartilage tissue, and subsequently decreased for a short period.

CONCLUSION

The findings suggested a negative feedback relationship between the expression of asporin and the TGF-β/Smad transduction pathway, which may be involved in the degeneration of the head of mandible in the early stages of TMJ-OA. Asporin is a potential biomarker of the early stages of TMJ-OA, which ultimately leads to the irreversible degeneration of TMJ tissues.

Electrical stimulation prevents condyle and subchondral degeneration following the masseter atrophy

OBJECTIVE

There is a strong relationship between masticatory muscle atrophy and condyle degeneration. Although electrical stimulation (ES) is an effective treatment for muscle atrophy, its influence on the underlying condyle is unclear. This study aimed to investigate whether ES can prevent condyle degradation during the stage of masseter muscle atrophy.

MATERIALS AND METHODS

Six-week-old rats were randomly divided into the control, botulinum toxin (BTX), or BTX + ES group. BTX was injected into the bilateral masseters of rats to induce masseter atrophy. The left-side masseters without ES treatment were served as BTX group, and the right-side masseters received ES with different parameters (5 mA/10 Hz, 5 mA/50 Hz, 6 mA/10 Hz, 6 mA/50 Hz, 7 mA/10 Hz, and 7 mA/50 Hz) were served as BTX + ES groups. After 4 weeks, micro-CT and qualitative or quantitative analysis of osteogenesis, chondrogenesis, and angiogenesis-related genes in condyles were conducted.

RESULTS

ES, especially at 7 mA/50 Hz, significantly attenuated masseter atrophy, condyle degeneration, and subchondral bone loss. Moreover, the upregulation of related proteins, including collagen 1, osteocalcin, bone morphogenetic protein 2, collagen 2a, and vascular endothelial growth factor were observed.

CONCLUSION

ES partly rescued condylar degeneration and subchondral bone loss following masseter atrophy.

Effect of arthroscopic discopexy on condylar growth in adolescents with temporomandibular joint disc displacement without reduction: A retrospective self-controlled case series study

This study was a retrospective self-controlled study that aimed to evaluate the effect of arthroscopic discopexy on condylar height and mandibular position in adolescents with temporomandibular joint (TMJ) anterior disc displacement without reduction (ADDwoR). Patients between 10 and 20 years of age and diagnosed with bilateral TMJ ADDwoR by magnetic resonance image (MRI) were included in this study. All patients underwent a period of natural course before arthroscopic surgery and then a follow-up period postoperatively. Changes in condylar height and mandibular position were measured by MRI and X-ray radiographs. Data were analyzed by paired t-test, Pearson correlation analysis, and generalized estimating equations. This study comprised a total of 40 patients with a mean age of 14.80 years. Pearson correlation analysis showed correlations between condylar height and mandibular position changes. The condylar height change during the post-operative period was significantly higher than that during natural course period (3.57 mm, p < 0.001). The changes in mandibular position (including ANB angle, SNB angle, and Pog-Np) were significant different (all p < 0.05) between the two periods. This study found that arthroscopic discopexy can promote condylar growth and correct dentofacial deformity in adolescents with bilateral TMJ ADDwoR.

Effect of occlusal stabilisation splint with or without arthroscopic disc repositioning on condylar bone remodelling in adolescent patients

The aim of this study was to investigate the treatment effects of a stabilisation splint (SS) with and without arthroscopic disc repositioning (ADR) on condylar bone remodelling in adolescent patients with anterior disc displacement without reduction (ADDwoR). Cone beam computed tomography and magnetic resonance imaging were used to analyse condylar bone remodelling, condyle position, and disc position. Twenty-two temporomandibular joints of 14 patients who underwent ADR (age range 12-20 years; mean follow-up 12.5 ± 7.8 months) and 21 temporomandibular joints of 14 patients who did not undergo ADR (age range 13-20 years; mean follow-up 11.1 ± 5.1 months) were included. The change in bone volume (P < 0.001), rate of bone volume change (P < 0.001), and change in condyle height (P = 0.031) were significantly greater in patients with ADR than in those without ADR. The changes in posterior joint space (P = 0.013), superior joint space (P = 0.020), and ratio of condyle sagittal position (P = 0.013) were significantly greater in patients with ADR than in those without ADR. All discs in patients who underwent ADR and one disc in those who did not undergo ADR were backward repositioned. In conclusion, in adolescent patients with ADDwoR, ADR with SS therapy achieved better condyle and disc position than SS therapy alone, and also induced bone generation.

Review of the studies on the relationship and treatment of anterior disc displacement and dentofacial deformity in adolescents

Anterior disk displacement (ADD) is a common type of temporomandibular joint (TMJ) internal derangement. In adolescents, the relationship between ADD and dentofacial deformities are brought into focus. Whether treatment is needed, or what kind of treatment are effective are still without a consensus. From the literature review, the consequences of ADD without treatment and the effect on disk repositioning were summarized. The results showed that after ADD, condylar height was prone to reduce that may lead to or aggravate dentofacial deformities in adolescents. Disk repositioning could promote the regeneration of condylar bone, thus improving the development of dentofacial deformities.

MECHANOBIOLOGICAL APPROACHES FOR STIMULATING CHONDROGENESIS OF STEM CELLS

Chondrogenesis is the process of differentiation of stem cells into mature chondrocytes. Such a process consists of chemical, functional, and structural changes which are initiated and mediated by the host environment of the cells. To date, the mechanobiology of chondrogenesis has not been fully elucidated. Hence, experimental activity is focused on recreating specific environmental conditions for stimulating chondrogenesis, and to look for a mechanistic interpretation of the mechanobiological response of cells in the cartilaginous tissues. There are a large number of studies on the topic that vary considerably in their experimental protocols used for providing environmental cues to cells for differentiation, making generalizable conclusions difficult to ascertain. The main objective of this contribution is to review the mechanobiological stimulation of stem cell chondrogenesis and methodological approaches utilized to date to promote chondrogenesis of stem cells in-vitro. In-vivo models will also be explored, but this area is currently limited. An overview of the experimental approaches used by different research groups may help the development of unified testing methods that could be used to overcome existing knowledge gaps, leading to an accelerated translation of experimental findings to clinical practice.

Creating Cartilage in Tissue-Engineered Chamber Using Platelet-Rich Plasma Without Cell Culture

Background: Clinically available cartilage, such as large-volume tissue-engineered cartilage, is urgently required for various clinical applications. Tissue engineering chamber (TEC) models are a promising organ-level strategy for efficient enlargement of cells or tissues within the chamber. The conventional TEC technology is not suitable for cartilage culture, because it lacks the necessary chondrogenic growth factor, which is present in platelet-rich plasma (PRP). In this study, we added autogenous auricular cartilage fragments mixed with PRP in a TEC to obtain a large amount of engineered cartilage. Experiment: To prove the efficacy of this method, 48 New Zealand white rabbits were randomly divided into 4 groups: PRP, vascularized (Ves), PRP, PRP+Ves, and control. Auricular cartilage was harvested from the rabbits, cut into fragments (2 mm), and then injected into TECs. Cartilage constructs were harvested at week 8, and construct volumes were measured. Histological morphology, immunochemical staining, and mechanical strength were evaluated. Results: At week 8, PRP+Ves constructs developed a white, cartilage-like appearance. The volume of cartilage increased by 600% the original volume from 0.30 to 1.8 ± 0.1789 mL. Histological staining showed proliferation of edge chondrocytes in the embedded cartilage in the PRP and PRP+Ves groups. Furthermore, the cartilage constructs in the PRP+Ves group show mechanical characteristics similar to those of normal cartilage. Conclusions: Auricular cartilage fragments mixed with PRP and vascularization of the TEC showed a significantly increased cartilage tissue volume after 8 weeks of incubation in rabbits. Impact Statement Repair of defects of ear cartilage tissue has always been a huge challenge to plastic surgeons. In this article, a new method is presented to produce within 8 weeks auricular cartilage in a tissue engineering chamber without cell culture. Having such a method is a valuable step toward creating a large volume of functional cartilage tissue, which may lead to successful construction of normal auricular structure with minimal donor-site morbidity.

Hydrostatic Pressure Regulates Oxidative Stress through microRNA in Human Osteoarthritic Chondrocytes

Hydrostatic pressure (HP) modulates chondrocytes metabolism, however, its ability to regulate oxidative stress and microRNAs (miRNA) has not been clarified. The aim of this study was to investigate the role of miR-34a, miR-146a, and miR-181a as possible mediators of HP effects on oxidative stress in human osteoarthritis (OA) chondrocytes. Chondrocytes were exposed to cyclic low HP (1–5 MPa) and continuous static HP (10 MPa) for 3~h. Metalloproteinases (MMPs), disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-5, type II collagen (Col2a1), miR-34a, miR-146a, miR-181a, antioxidant enzymes, and B-cell lymphoma 2 (BCL2) were evaluated by quantitative real-time polymerase chain reaction qRT-PCR, apoptosis and reactive oxygen species ROS production by cytometry, and β-catenin by immunofluorescence. The relationship among HP, the studied miRNA, and oxidative stress was assessed by transfection with miRNA specific inhibitors. Low cyclical HP significantly reduced apoptosis, the gene expression of MMP-13, ADAMTS5, miRNA, the production of superoxide anion, and mRNA levels of antioxidant enzymes. Conversely, an increased Col2a1 and BCL2 genes was observed. β-catenin protein expression was reduced in cells exposed to HP 1–5 MPa. Opposite results were obtained following continuous static HP application. Finally, miRNA silencing enhanced low HP and suppressed continuous HP-induced effects. Our data suggest miRNA as one of the mechanisms by which HP regulates chondrocyte metabolism and oxidative stress, via Wnt/β-catenin pathway.

Strontium stimulates alkaline phosphatase and bone morphogenetic protein-4 expression in rat chondrocytes cultured in vitro

The trace element strontium has a significant impact on cartilage metabolism. However, the direct effects of strontium on alkaline phosphatase (ALP), a marker of bone growth, and bone morphogenetic protein-4 (BMP-4), which plays a key role in the regulation of bone and cartilage development, are not entirely clear. In order to understand the mechanisms involved in these processes, the chondrocytes were isolated from Wistar rat articular cartilage by enzymatic digestion and cultured under standard conditions. They were then treated with strontium at 0.5, 1.0, 2.0, 5.0, 20.0 and 100.0 μg/mL for 72 h. The mRNA abundance and protein expression levels of ALP and BMP-4 were measured using real-time polymerase chain reaction (real-time PCR) and Western blot analysis. The results showed that the levels of expression of ALP and BMP-4 in chondrocytes increased as the concentration of strontium increased relative to the control group, and the difference became significant at 1.0 μg/mL strontium (P<0.05). These results indicated that strontium could be involved in cartilage development via regulating ALP and BMP-4 expression.

The effects of elevated fibroblast growth factor 23 on mandibular growth in rats

OBJECTIVE

The aim of this study is to elucidate the local effects of fibroblast growth factor 23 (FGF23) in on mandibular condylar growth in growing rats.

DESIGN

Growing Sprague-Dawley rats received intra-temporomandibular joint injections of phosphate buffer solution (PBS), adenovirus-mediated green fluorescent protein (Ad-GFP) or adenovirus-mediated fibroblast growth factor 23 (Ad-FGF23), which were marked as groups A, B, and C, respectively. In vitro, we treated rat mandibular cartilage chondrocytes with PBS, Ad-GFP, and Ad-FGF23.

RESULTS

The mandibular condyles in group C grew smaller sizes than those in the other control groups due to significant differences among the experimental and control groups with the value of C-D, Q-R (P ≤ 0.05), accompanied by diminished bone mass of sub-cartilage condyles via micro CT analysis. Histologically, the length of the hypertrophic zone was diminished and was associated with decreasing chondrocyte proliferation in group C. Quantitative real-time PCR indicated significant decreases in the expression of chondrogenesis marker genes, including Type X collagen (Col X) and SRY-type box 9 (Sox 9). Moreover, elevated Ad-FGF23 suppressed chondrocyte proliferation and the expression of the chondrogenic differentiation markers Col X and Sox 9 of in vitro.

CONCLUSIONS

Local injection of FGF23 suppressed the development and decreased the bone mass of condyles through the decreasing the formation of condylar cartilage, specifically by regulating condylar cartilage cell viability and chondrogenesis expression.

Condylar Degradation from Decreased Occlusal Loading following Masticatory Muscle Atrophy

Objective

The masticatory muscles are the most important contributor to bite force, and the temporomandibular joint (TMJ) receives direct occlusal loading. The present study aimed to investigate condylar remodeling after masseter muscle atrophy in rats.

Methods

Sixty 5-week-old female Sprague-Dawley rats were divided into the following 3 groups: the control group, soft diet (SD) group, and botulinum toxin (BTX) group. The cross-sectional area (CSA) of the masseter muscles was investigated as well as atrogin-1/MuRF-1 expression. Changes in the condylar head were evaluated by H-E, toluidine blue staining, and contour measurements. The biomechanical sensitive factors PTHrP Ihh, Col2a1, and ColX of condylar cartilage were detected by immunohistochemical staining and western blotting. Furthermore, micro-CT and tartrate-resistant acid phosphatase (TRAP) staining were performed to determine the osteopenia in subchondral bone.

Results

The histological and protein analysis demonstrated muscle hypofunction in the SD and BTX groups. Condylar cartilage contour was diminished due to different treatments; the immunohistochemistry and protein examination showed that the expressions of PTHrP, Ihh, Col2a1, and ColX were suppressed in condylar cartilage. A steady osteoporosis in subchondral bone was found only in the BTX group.

Conclusion

The current results suggested that a steady relationship between muscular dysfunction and condylar remodeling exists.

A Prognostic Nomogram for Postoperative Bone Remodeling in Patients with ADDWoR

This study aimed to establish an effective prognostic nomogram for predicting the probability of postoperative bone remodeling of patients with anterior disc displacement without reduction (ADDWoR). The nomogram was based on a retrospective study on patients underwent surgical approaches for ADDWoR at Shanghai Ninth People’s Hospital, Shanghai Jiao Tong University from January, 2007 to January, 2017. A multivariate logistic regression analysis was used to develop variables suitable for probability estimation model. The predictive accuracy and discriminative ability were determined by ROC (AUC-index) and calibration curve. Results were validated using bootstrap resampling with all statistical tests two-sided. 1110 patients were included in the analysis. The probability of postoperative bone remodeling in ADDWoR was 0.51. Six independent prognostic factors including age of onset, nocturnal bruxism, disc morphology, BMD, Wilkes’ classification, and postoperative splint therapy were integrated to construct the nomogram. The probability estimation model showed good discrimination in both internal and external validation with AUC-index of 0.84. The calibration curves for probability of postoperative bone remodeling showed optimal agreement with actual observation. In conclusion, a nomogram was established to provide individual prediction of postoperative bone remodeling for patients with ADDWoR treated by arthroscopy surgery.

Effects of connective tissue growth factor (CTGF/CCN2) on condylar chondrocyte proliferation, migration, maturation, differentiation and signalling pathway

CCN2, also known as connective tissue growth factor (CTGF), is a 38 kDa cysteine-rich extracellular matrix protein that regulates a sequence of cellular functions and participates in multiple complex biological processes, such as chondrogenesis and osteogenesis. In the present study, we provided the first evidence describing the physiological role of CCN2 in condylar chondrocyte proliferation, migration, maturation and differentiation. CCN2 was widely expressed throughout the whole layers of condylar cartilage and predominantly distributed in the proliferative zone. Recombinant CCN2 promoted the proliferation, migration, proteoglycan synthesis and differentiation capacity of isolated condylar chondrocytes. The stimulatory effect of CCN2 on chondrocyte proliferation was associated with the activation of phosphatidylinositol 3-kinase/Akt signalling pathway. The blocking of this pathway by its inhibitor LY294002 impaired the proliferative effect of CCN2 on chondrocytes. These results suggested a novel physiological role of CCN2 in the development of condylar cartilage.