Alteration of structural and mechanical properties of the temporomandibular joint disc following elastase digestion.

The temporomandibular joint disc is a fibrocartilaginous structure, composed of collagen fibers, elastin fibers, and proteoglycans. Despite the crucial role of elastin fibers in load-bearing properties of connective tissues, its contribution in temporomandibular joint disc biomechanics has been disregarded. This study attempts to characterize the structural-functional contribution of elastin in the temporomandibular joint disc. Using elastase, we selectively perturbed the elastin fiber network in porcine temporomandibular joint discs and investigated the structural, compositional, and mechanical regional changes through: (a) analysis of collagen and elastin fibers by immunolabeling and transmission electron microscopy; (b) quantitative analysis of collagen tortuosity, cell shape, and disc volume; (c) biochemical quantification of collagen, glycosaminoglycan and elastin content; and (d) cyclic compression test. Following elastase treatment, microscopic examination revealed fragmentation of elastin fibers across the temporomandibular joint disc, with a more pronounced effect in the intermediate regions. Also, biochemical analyses of the intermediate regions showed significant depletion of elastin (50%), and substantial decrease in collagen (20%) and glycosaminoglycan (49%) content, likely due to non-specific activity of elastase. Degradation of elastin fibers affected the homeostatic configuration of the disc, reflected in its significant volume enlargement accompanied by remarkable reduction of collagen tortuosity and cell elongation. Mechanically, elastase treatment nearly doubled the maximal energy dissipation across the intermediate regions while the instantaneous modulus was not significantly affected. We conclude that elastin fibers contribute to the restoration and maintenance of the disc resting shape and actively interact with collagen fibers to provide mechanical resilience to the temporomandibular joint disc.

[Effects of staurosporine on the contraction of self-assembled constructs of goat temporomandibular joint disc cells].

OBJECTIVE: The effects of the staurosporine on contraction of self-assembled constructs and extracellular matrix syntheses of goat temporomandibular joint discs were investigated. METHODS: Goat temporomandibular joint disc cells were isolated and cultured to P3, and 5.5×106 cells were combined with different concentrations of staurosporine (0, 0.1, 1, 10, 100 nmol·L⁻¹) in agarose wells and cultured for one week. The samples were frozen and sectioned. Safranin-O,  Picro-sirius red and immunohistochemical staining were performed to observe the distributions of the extracellular matrix and the expression of alpha-smooth muscle actin (α-SMA). Enzyme linked immunosorbent assay (ELISA) and Blyscan kits were utilized to quan--titatively detect the contents of type Ⅰ collagen (ColⅠ) and glycosaminoglycans (GAGs). RESULTS: Each group of goat temporo-mandibular joint disc cells in the agarose wells were gathered to self-assemble into a disc-shaped base for 4 hours and then to gradually contract into a round shape. The Picro-sirius red staining was strong and indicated collagen distribution. The Safranin-O staining observed GAGs throughout the entire construct. The expression of ColⅠ was strongly posi-tive in the staurosporine groups; however, the expression of α-SMA was weak. ColⅠ and GAGs contents in the stau-rosporine groups were greater than that of the control group, especially in the 10 nmol·L⁻¹ group (P<0.01). CONCLUSIONS: Staurosporine has a certain effect on the shrinkage of self-assembled constructs; however, such effect is not prominent. Staurosporine contributes to the construction synthesis of extracellular matrix.

Tissue Engineering for the Temporomandibular Joint.

Tissue engineering potentially offers new treatments for disorders of the temporomandibular joint which frequently afflict patients. Damage or disease in this area adversely affects masticatory function and speaking, reducing patients' quality of life. Effective treatment options for patients suffering from severe temporomandibular joint disorders are in high demand because surgical options are restricted to removal of damaged tissue or complete replacement of the joint with prosthetics. Tissue engineering approaches for the temporomandibular joint are a promising alternative to the limited clinical treatment options. However, tissue engineering is still a developing field and only in its formative years for the temporomandibular joint. This review outlines the anatomical and physiological characteristics of the temporomandibular joint, clinical management of temporomandibular joint disorder, and current perspectives in the tissue engineering approach for the temporomandibular joint disorder. The tissue engineering perspectives have been categorized according to the primary structures of the temporomandibular joint: the disc, the mandibular condyle, and the glenoid fossa. In each section, contemporary approaches in cellularization, growth factor selection, and scaffold fabrication strategies are reviewed in detail along with their achievements and challenges.

Fibro/chondrogenic differentiation of dental stem cells into chitosan/alginate scaffolds towards temporomandibular joint disc regeneration.

Tissue engineering (TE) may provide effective alternative treatment for challenging temporomandibular joint (TMJ) pathologies associated with disc malpositioning or degeneration and leading to severe masticatory dysfunction. Aim of this study was to evaluate the potential of chitosan/alginate (Ch/Alg) scaffolds to promote fibro/chondrogenic differentiation of dental pulp stem cells (DPSCs) and production of fibrocartilage tissue, serving as a replacement of the natural TMJ disc. Ch/Alg scaffolds were fabricated by crosslinking with CaCl2 combined or not with glutaraldehyde, resulting in two scaffold types that were physicochemically characterized, seeded with DPSCs or human nucleus pulposus cells (hNPCs) used as control and evaluated for cell attachment, viability, and proliferation. The DPSCs/scaffold constructs were incubated for up to 8 weeks and assessed for extracellular matrix production by means of histology, immunofluorescence, and thermomechanical analysis. Both Ch/Alg scaffold types with a mass ratio of 1:1 presented a gel-like structure with interconnected pores. Scaffolds supported cell adhesion and long-term viability/proliferation of DPSCs and hNPCs. DPSCs cultured into Ch/Alg scaffolds demonstrated a significant increase of gene expression of fibrocartilaginous markers (COLI, COL X, SOX9, COM, ACAN) after up to 3 weeks in culture. Dynamic thermomechanical analysis revealed that scaffolds loaded with DPSCs significantly increased storage modulus and elastic response compared to cell-free scaffolds, obtaining values similar to those of native TMJ disc. Histological data and immunochemical staining for aggrecan after 4 to 8 weeks indicated that the scaffolds support abundant fibrocartilaginous tissue formation, thus providing a promising strategy for TMJ disc TE-based replacement.

Layering Poly (lactic-co-glycolic acid)-based electrospun membranes and co-culture cell sheets for engineering temporomandibular joint disc.

The temporomandibular joint disk (TMJD) lacks blood vessels and is characterized by slow self-repair. Qualitative lesions in TMJD are difficult to repair. In this study, electrospun poly (lactic-co-glycolic acid) (PLGA) scaffolds were used to reconstruct temporomandibular joint discs by tissue engineering. Rabbit temporomandibular joint disc cells (TMJDCs) and rabbit synovium-derived mesenchymal stem cells (SMSCs) were co-cultured in 1:1 ratios. Cell sheets were induced by ascorbic acid incubated with electrospun PLGA scaffolds for 14 days in the presence (10 ng/ml in culture medium) or absence of TGF-ß3. Dimethylmethylene Blue Assay (DMMB) was used to determine the content of glycosaminoglycans in the extracellular matrix. The expression of Col1a1, Col2a1, Sox-9 and Runx-2 was quantified by RT-PCR, and the expression of type II collagen was observed by immunofluorescent staining. After 14 days of cultivation, the electrospun PLGA scaffold-loaded cell sheets could form an articular disc tissue with certain morphological characteristics. The expression of chondrogenic-related genes (Col2a1, Sox-9) and the secretion of extracellular matrix (GAG, type II collagen) in the co-culture group were close to those in the TMJDC group alone. The results suggest that PLGA electrospun scaffold-loaded co-cultured cell membrane could be used in the tissue engineering reconstruction of the temporomandibular joint disc.

Effect of mechanical loading on the metabolic activity of cells in the temporomandibular joint: a systematic review.

OBJECTIVES: The purpose of this systematic review was to elucidate how different modalities and intensities of mechanical loading affect the metabolic activity of cells within the fibro-cartilage of the temporomandibular joint (TMJ). MATERIALS AND METHODS: A systematic review was conducted according to PRISMA guidelines using PubMed, Embase, and Web of Science databases. The articles were selected following a priori formulated inclusion criteria (viz., in vivo and in vitro studies, mechanical loading experiments on TMJ, and the response of the TMJ). A total of 254 records were identified. After removal of duplicates, 234 records were screened by assessing eligibility criteria for inclusion. Forty-nine articles were selected for full-text assessment. Of those, 23 were excluded because they presented high risk of bias or were reviews. Twenty-six experimental studies were included in this systematic review: 15 in vivo studies and 11 in vitro ones. CONCLUSION: The studies showed that dynamic mechanical loading is an important stimulus for mandibular growth and for the homeostasis of TMJ cartilage. When this loading is applied at a low intensity, it prevents breakdown of inflamed cartilage. Yet, frequent overloading at excessive levels induces accelerated cell death and an increased cartilage degradation. CLINICAL SIGNIFICANCE: Knowledge about the way temporomandibular joint (TMJ) fibrocartilage responds to different types and intensities of mechanical loading is important to improve existing treatment protocols of degenerative joint disease of the TMJ, and also to better understand the regenerative pathway of this particular type of cartilage.

[Analysis of factors related to the number of mesenchymal stem cells derived from synovial fluid of the temporomandibular joint].

Objective: To analyze related factors on the number of mesenchymal stem cells in the synovial fluid of the temporomandibular joint (TMJ) and provide an research basis for understanding of the source and biological role of mesenchymal stem cells derived from synovial fluid in TMJ. Methods: One hundred and twenty-two synovial fluid samples from 91 temporomandibular disorders (TMD) patients who visited in Department of TMJ Center, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University from March 2013 to December 2013 were collected in this study, and 6 TMJ synovial fluid samples from 6 normal volunteers who were studying in the North Campus of Sun Yat-sen University were also collected, so did their clinical information. Then the relation between the number of mesenchymal stem cells derived from synovial fluid and the health status of the joints, age of donor, disc perforation, condylar bony destruction, blood containing and visual analogue scale score of pain were investigated using Mann-Whitney U test and Spearman rank correlation test. Results: The number of mesenchymal stem cells derived from synovial fluid had no significant relation with visual analogue scale score of pain (r=0.041, P=0.672), blood containing (P=0.063), condylar bony destruction (P= 0.371). Linear correlation between the number of mesenchymal stem cells derived from synovial fluid and age of donor was very week (r=0.186, P=0.043). The number of mesenchymal stem cells up-regulated when the joint was in a disease state (P=0.001). The disc perforation group had more mesenchymal stem cells in synovial fluid than without disc perforation group (P=0.042). Conclusions: The number of mesenchymal stem cells derived from synovial fluid in TMJ has no correlation with peripheral blood circulation and condylar bony destruction, while has close relation with soft tissue structure damage of the joint.

[Effect of temporomandibular joint disc perforation on expression of type â collagen in temporomandibular joint disc cells].

Objective: To investigate the effect of temporomandibular joint (TMJ) disc perforation on expression of type Ⅰ collagen in TMJ disc cells. Methods: The fibroblastic-like cells from the surgical removed TMJ disc tissue (disc perforation or TMJ condyle hyperplasia) were cultured. The cultured cells were identified as fibroblastic-like cells by toluidine blue and immunofluorescence staining. The expression of type Ⅰ collagen was detected with Western blotting and the content of type Ⅰ collagen was examined by enzyme linked immunosorbent assay (ELISA). Results: Fibroblastic-like cells were cultured from TMJ disc cells and the controls. The collagen-Ⅰ and collagen-Ⅱ were positive in both toluidine blue and immunofluorescence staining. In Western blotting, the expression of typeⅠcollagen in cells from joints with disc perforation was lower than that from normal joints. The content of collagen-Ⅰ was (1.62±0.52) µg/L from controls, and (0.85±0.33) µg/L from disc perforation respectively (P=0.0134). Conclusions: The disc cells from TMJ with disc perforation expressed lower type Ⅰ collagen than that from controls, which may be related to the lower content of collagen-Ⅰ in TMJ disc and the formation of TMJ disc perforation.

Isolation and characterization of mesenchymal stromal progenitors from the temporomandibular joint disc.

Disorders of the temporomandibular joint (TMJ) complex affect 6-12% of the population; the joint's disc is usually involved. Tissue engineering and regenerative medicine may constitute a promising therapeutic approach, with resident stromal progenitor cells a key factor in the process. We hypothesized that the TMJ disc (TMJD) contains multipotent stromal progenitors that may play an important role in regeneration of the disc. TMJD cells were cultured and evaluated for growth kinetics and colony-forming units (CFUs). Single cell-derived clones were isolated and induced to differentiate toward the osteogenic, adipogenic and chondrogenic lineages by culturing in various induction media. Flow cytometry was used to identify multipotent stromal cell surface markers in additional cell samples, and reverse transcription-polymerase chain reaction (RT-PCR) was used to determine gene expression patterns within isolated cells. High numbers of CFUs were observed, indicating cell self-renewal. Biochemical assays showed significantly higher alkaline phosphatase (ALP) activity, lipid droplet concentration and glycosaminoglycan levels in cells cultured in osteogenic, adipogenic and chondrogenic induction medium, respectively. Approximately 1% of the total cell population demonstrated the capability to differentiate into all three mesenchymal lineages. Chondrogenic gene levels within TMJD-derived cells were significantly reduced in passaged culture. Our results support the hypothesis that multipotent stromal progenitor cells populate the TMJD and possess proliferation and differentiation capabilities. These cells may contribute to the regeneration potential of dysfunctional tissue and become the primary component in future attempts at tissue engineering or regeneration of this complex. Copyright © 2015 John Wiley & Sons, Ltd.

Choosing sheep (Ovis aries) as animal model for temporomandibular joint research: Morphological, histological and biomechanical characterization of the joint disc.

Preclinical trials are essential to the development of scientific technologies. Remarkable molecular and cellular research has been done using small animal models. However, significant differences exist regarding the articular behavior between these models and humans. Thus, large animal models may be more appropriate to perform trials involving the temporomandibular joint (TMJ). The aim of this work was to make a morphological (anatomic dissection and white light 3D scanning system), histological (TMJ in bloc was removed for histologic analysis) and biomechanical characterization (tension and compression tests) of sheep TMJ comparing the obtained results with human data. Results showed that sheep processus condylaris and fossa mandibularis are anatomically similar to the same human structures. TMJ disc has an elliptical perimeter, thinner in the center than in periphery. Peripheral area acts as a ring structure supporting the central zone. The disc cells display both fibroblast and chondrocyte-like morphology. Marginal area is formed by loose connective tissue, with some chondrocyte-like cells and collagen fibers in diverse orientations. Discs obtained a tensile modulus of 3.97±0.73MPa and 9.39±1.67MPa, for anteroposterior and mediolateral assessment. The TMJ discs presented a compressive modulus (E) of 446.41±5.16MPa and their maximum stress value (σmax) was 18.87±1.33MPa. Obtained results suggest that these animals should be considered as a prime model for TMJ research and procedural training. Further investigations in the field of oromaxillofacial surgery involving TMJ should consider sheep as a good animal model due to its resemblance of the same joint in humans.

Stem Cells for Temporomandibular Joint Repair and Regeneration.

Temporomandibular Disorders (TMD) represent a heterogeneous group of musculoskeletal and neuromuscular conditions involving the temporomandibular joint (TMJ), masticatory muscles and/or associated structures. They are a major cause of non-dental orofacial pain. As a group, they are often multi-factorial in nature and have no common etiology or biological explanations. TMD can be broadly divided into masticatory muscle and TMJ disorders. TMJ disorders are characterized by intra-articular positional and/or structural abnormalities. The most common type of TMJ disorders involves displacement of the TMJ articular disc that precedes progressive degenerative changes of the joint leading to osteoarthritis (OA). In the past decade, progress made in the development of stem cell-based therapies and tissue engineering have provided alternative methods to attenuate the disease symptoms and even replace the diseased tissue in the treatment of TMJ disorders. Resident mesenchymal stem cells (MSCs) have been isolated from the synovia of TMJ, suggesting an important role in the repair and regeneration of TMJ. The seminal discovery of pluripotent stem cells including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have provided promising cell sources for drug discovery, transplantation as well as for tissue engineering of TMJ condylar cartilage and disc. This review discusses the most recent advances in development of stem cell-based treatments for TMJ disorders through innovative approaches of cell-based therapeutics, tissue engineering and drug discovery.

The effects of oxygen level and glucose concentration on the metabolism of porcine TMJ disc cells.

OBJECTIVE: To determine the combined effect of oxygen level and glucose concentration on cell viability, ATP production, and matrix synthesis of temporomandibular joint (TMJ) disc cells. DESIGN: TMJ disc cells were isolated from pigs aged 6-8 months and cultured in a monolayer. Cell cultures were preconditioned for 48 h with 0, 1.5, 5, or 25 mM glucose DMEM under 1%, 5%, 10%, or 21% O2 level, respectively. The cell viability was measured using the WST-1 assay. ATP production was determined using the Luciferin-Luciferase assay. Collagen and proteoglycan synthesis were determined by measuring the incorporation of [2, 3-(3)H] proline and [(35)S] sulfate into the cells, respectively. RESULTS: TMJ disc cell viability significantly decreased (P < 0.0001) without glucose. With glucose present, decreased oxygen levels significantly increased viability (P < 0.0001), while a decrease in glucose concentration significantly decreased viability (P < 0.0001). With glucose present, decreasing oxygen levels significantly reduced ATP production (P < 0.0001) and matrix synthesis (P < 0.0001). A decreased glucose concentration significantly decreased collagen synthesis (P < 0.0001). The interaction between glucose and oxygen was significant in regards to cell viability (P < 0.0001), ATP production (P = 0.00015), and collagen (P = 0.0002) and proteoglycan synthesis (P < 0.0001). CONCLUSIONS: Although both glucose and oxygen are important, glucose is the limiting nutrient for TMJ disc cell survival. At low oxygen levels, the production of ATP, collagen, and proteoglycan are severely inhibited. These results suggest that steeper nutrient gradients may exist in the TMJ disc and it may be vulnerable to pathological events that impede nutrient supply.

Immortalization and characterization of mouse temporomandibular joint disc cell clones with capacity for multi-lineage differentiation.

OBJECTIVE: Despite the importance of temporomandibular joint (TMJ) disc in normal function and disease, studying the responses of its cells has been complicated by the lack of adequate characterization of the cell subtypes. The purpose of our investigation was to immortalize, clone, characterize and determine the multi-lineage potential of mouse TMJ disc cells. DESIGN: Cells from 12-week-old female mice were cultured and immortalized by stable transfection with human telomerase reverse transcriptase (hTERT). The immortalized cell clones were phenotyped for fibroblast- or chondrocyte-like characteristics and ability to undergo adipocytic, osteoblastic and chondrocytic differentiation. RESULTS: Of 36 isolated clones, four demonstrated successful immortalization and maintenance of stable protein expression for up to 50 passages. Two clones each were initially characterized as fibroblast-like and chondrocyte-like on the basis of cell morphology and growth rate. Further the chondrocyte-like clones had higher mRNA expression levels of cartilage oligomeric matrix protein (COMP) (>3.5-fold), collagen X (>11-fold), collagen II expression (2-fold) and collagen II:I ratio than the fibroblast-like clones. In contrast, the fibroblast-like clones had higher mRNA expression level of vimentin (>1.5-fold), and fibroblastic specific protein 1 (>2.5-fold) than the chondrocyte-like clones. Both cell types retained multi-lineage potential as demonstrated by their capacity to undergo robust adipogenic, osteogenic and chondrogenic differentiation. CONCLUSIONS: These studies are the first to immortalize TMJ disc cells and characterize chondrocyte-like and fibroblast-like clones with retained multi-differentiation potential that would be a valuable resource in studies to dissect the behavior of specific cell types in health and disease and for tissue engineering.

Transcriptional regulation of proteoglycan 4 by 17ß-estradiol in immortalized baboon temporomandibular joint disc cells.

Temporomandibular joint disorders (TMDs) affect a significant portion of the population of the USA, with the majority of those seeking treatment being women of childbearing age. Owing to this striking sexual dimorphism it has been postulated that sex hormones play a role in the maintenance of normal temporomandibular joint (TMJ) function. Proteoglycan 4 (PRG4) is a secreted lubricating molecule required for maintaining low frictional levels within articular joints; however, its role in the TMJ is not well characterized. In this study we describe the development of immortalized baboon cells isolated from specific regions of the TMJ disc and their use in the investigation of PRG4 expression and localization patterns in the TMJ. We identified conserved estrogen response elements within the 5' flanking region of the PRG4 gene of several species, and found that treatment of baboon TMJ disc cells with estrogen led to reduced PRG4 promoter activity and reduced expression of PRG4 mRNA in vitro. The observed negative regulation of PRG4 by estrogen could lead to increased friction and degradation of joint components over time. This study, for the first time, provides evidence of the regulatory potential of estrogen on PRG4 gene expression and suggests a novel etiology for the gender disparity observed among TMD patients.

A combined approach for the assessment of cell viability and cell functionality of human fibrochondrocytes for use in tissue engineering.

Temporo-mandibular joint disc disorders are highly prevalent in adult populations. Autologous chondrocyte implantation is a well-established method for the treatment of several chondral defects. However, very few studies have been carried out using human fibrous chondrocytes from the temporo-mandibular joint (TMJ). One of the main drawbacks associated to chondrocyte cell culture is the possibility that chondrocyte cells kept in culture tend to de-differentiate and to lose cell viability under in in-vitro conditions. In this work, we have isolated human temporo-mandibular joint fibrochondrocytes (TMJF) from human disc and we have used a highly-sensitive technique to determine cell viability, cell proliferation and gene expression of nine consecutive cell passages to determine the most appropriate cell passage for use in tissue engineering and future clinical use. Our results revealed that the most potentially viable and functional cell passages were P5-P6, in which an adequate equilibrium between cell viability and the capability to synthesize all major extracellular matrix components exists. The combined action of pro-apoptotic (TRAF5, PHLDA1) and anti-apoptotic genes (SON, HTT, FAIM2) may explain the differential cell viability levels that we found in this study. These results suggest that TMJF should be used at P5-P6 for cell therapy protocols.

[Effects of basic fibroblast growth factor on bone marrow mesenchymal stem cell differentiation into temporomandibular joint disc cells].

The present paper is aimed to observe the effects of basic fibroblast growth factor (bFGF) on bone marrow mesenchymal stem cell (BMSCs) differentiation. The bFGF was used to stimulate BMSCs and histology, immunohistochemistry and enzyme linked immunosorbent assay (ELISA) were used to examine the extracellular matrix produced by induced BMSCs, evaluated the feasibility of BMSCs being the seeding cells of temporomandibular joint (TMJ) disc tissue engineering. The results showed that having been induced with bFGF, the BMSCs could differentiate into fibroblast-like cells, which could synthesize GAG and collagen type I matrix. So it is feasible for BMSCs as seeding cells for engineered TMJ disc.

Modificación del líquido sinovial en diferentes afecciones articulares de la rodilla / Changes in synovial fluid in different knee-joint diseases

Objetivo. Analizar las modificaciones del líquido sinovial (LS) en las afecciones articulares más frecuentes de la rodilla y establecer una relación en función de su concentración. Material y métodos. Se analizaron 62 muestras de LS de rodillas con afección meniscal (32), rotura del ligamento cruzado anterior (LCA) (17) y lesión condral aislada (13). De cada muestra se realizó un estudio cuantitativo y cualitativo de las citocinas (IL-1, IL-2, IL-6, IL-10, TNF-alfa) y factores de crecimiento (IGF-1, TGF-Beta). Resultados. En la lesión del LCA, el ambiente del LS fue predominantemente anabólico e inflamatorio, con niveles elevados de IL1, IL6, significativos de TGF-Beta (p=0,02 y p=0,004), IL-10 (p=0,046 y p=0,047) y significativamente disminuidos de TNF-alfa (p=0,02 y p=0,004). En la afección condral y meniscal, predominó un ambiente catabólico, con elevación significativa del TNF-alfa y disminución significativa del TGF-Beta (p=0,02 y p=0,004). Las diferencias fueron mayores en el caso de la lesión condral aislada. Conclusión. Los cambios observados señalan que en la lesión articular, además de la alteración biomecánica, el LS influye negativamente en la homeostasis articular, variando su composición según el tipo de afección (AU)

Objective. To analyse the changes in synovial fluid (SF) in the most common knees joint diseases, and to establish a relationship according to its concentration. Material and methods. A total of 62 synovial fluids were analysed from knees with, meniscus disease (32), anterior cruciate ligament (ACL) (17) and isolated chondral injury (13). A quantitative and quality study was performed on each sample, which included cytokines IL-1, IL-2, IL-6, IL-10, TNF-alfa and growth factors, IGF-1 and TGF-Beta). Results. The SF environment in the ACL injury was mainly anabolic and inflammatory, with increased levels of IL1, IL6, significant levels of TGF-Beta (P=.02 and P=.004), IL-10 (P=.046 and P=.047) and significantly decreased levels of TNF-alfa (P=.02 and P=.004). There was mainly a catabolic environment in chondral and meniscal disease, with a significant increase in TNF-alfa and a significant decrease in TGF-Beta (P=.02 and P=.004). The differences were greater in the case of isolated chondral injury. Conclusion. The changes observed show that, as well as the biomechanical changes, the SF has a negative effect on joint homeostasis, it composition varying depending on the type of pathology (AU)

Alterations in intermediate filaments expression in disc cells from the rat temporomandibular joint following exposure to continuous compressive force.

The articular disc in the temporomandibular joint (TMJ) that serves in load relief and stabilizing in jaw movements is a dense collagenous tissue consisting of extracellular matrices and disc cells. The various morphological configurations of the disc cells have given us diverse names, such as fibroblasts, chondrocyte-like cells and fibrochondrocytes; however, the characteristics of these cells have remained to be elucidated in detail. The disc cells have been reported to exhibit heterogeneous immunoreaction patterns for intermediate filaments including glial fibrillary acidic protein (GFAP), nestin and vimentin in the adult rat TMJ. Because these intermediate filaments accumulate in the disc cells as tooth eruption proceeds during postnatal development, it might be surmised that the expression of these intermediate filaments in the disc cells closely relates to mechanical stress. The present study was therefore undertaken to examine the effect of a continuous compressive force on the immunoexpression of these intermediate filaments and an additional intermediate filament - muscle-specific desmin - in the disc cells of the TMJ disc using a rat experimental model. The rats wore an appliance that exerts a continuous compressive load on the TMJ. The experimental period with the appliance was 5 days as determined by previous studies, after which some experimental animals were allowed to survive another 5 days after removal of the appliance. Histological observations demonstrated that the compressive force provoked a remarkable acellular region and a decrease in the thickness of the condylar cartilage of the mandible, and a sparse collagen fiber distribution in the articular disc. The articular disc showed a significant increase in the number of desmin-positive cells as compared with the controls. In contrast, immunopositive cells for GFAP, nestin and vimentin remained unchanged in number as well as intensity. At 5 days after removal of the appliance, both the disc and cartilage exhibited immunohistological and histological features in a recovery process. These findings indicate that the mature articular cells are capable of producing desmin instead of the other intermediate filaments against mechanical stress. The desmin-positive disc cells lacked α-smooth muscle actin (α-SMA) in this study, even though desmin usually co-exists with α-SMA in the vascular smooth muscle cells or pericytes. Because the precursor of a pericyte has such an immunoexpression pattern during angiogenesis, there is a further possibility that the formation of new vessels commenced in response to the extraordinary compressive force.

The fracture toughness of soft tissues.

Fracture toughness is important for any material, but to date there have been few investigations of this mechanical property in soft mammalian tissues. This paper presents new data on porcine muscle tissue and a detailed analysis of all previous work. The conclusion is that, in most cases, fracture toughness has not in fact been measured for these tissues. Reanalysis of the previous work shows that failure of the test specimens generally occurred at the material's ultimate strength, implying that no information about toughness can be obtained from the results. This finding applied to work on cartilage, artificial neocartilage, muscle and the TMJ disc. Our own data, which was also found to be invalid, gave measured fracture toughness values which were highly variable and showed a strong dependence on the crack growth increment. The net-section failure stress and failure energy were relatively constant in large specimens, independent of crack length, whilst for smaller specimens they showed a strong size effect. These findings are explained by the fact that the process zone size, estimated here using the critical distance parameter L, was similar to, or larger than, critical specimen dimensions (crack length and specimen width). Whilst this analysis casts doubt on much of the published literature, a useful finding is that soft tissues are highly tolerant of defects, able to withstand the presence of cracks several millimetres in length without significant loss of strength.

Aquaporin 1 expression in human temporomandibular disc.

Aquaporins (AQPs) are a family of hydrophobic membrane channel proteins. The expression of several AQP isoforms has been investigated in different human tissues, including the orofacial region. However, information on the role and localization of AQP1 in joints is limited, and no data are available on aquaporins in the normal temporomandibular joint (TMJ) disc. Sixteen human TMJ discs without degenerative changes were taken from fresh cadavers to investigate the presence and distribution of AQP1 by immunohistochemistry. The aim of the study was to gain additional insights into the biomolecular composition of aquaporins and their role in homeostasis of the TMJ. Porcine TMJ discs were also studied by Western blotting for comparison. Scattered AQP1 immunoexpression was detected in human disc cells, documenting its constitutive expression, but differences amongst the three disc regions were not significant. AQP1 expression was demonstrated in porcine TMJ disc by Western blotting. Our findings suggest that AQP1 is normally expressed in the TMJ disc and confirm a role for it in the maintenance of TMJ homeostasis. Further studies are needed to elucidate expression patterns of aquaporins in diseased TMJ discs.