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Introduction: Aging, an inevitable physiological process, leads to morphological and histological degenerative changes in the mandibular condylar cartilage (MCC); however, the molecular mechanism has not yet been elucidated, and little information is available on age-related factors. Therefore, this study was designed to identify age-related factors by investigating the age-related differentially expressed genes (DEGs) and localization of their translated protein expression in the mandibular condyle., Methods: Mandibular condyles were collected from 10- and 50-week-old mice. Total RNA was extracted from the samples and then analyzed using cap analysis of gene expression (CAGE) to identify age-related DEGs. Gene ontology (GO) enrichment analysis was performed to determine which biological processes were most affected by aging in terms of gene expression using Metascape. The mandibular condyle samples were processed for histology to investigate morphological changes caused by aging and for immunohistochemistry to localize the protein expression encoded by age-related genes identified with CAGE. Semi-quantitative immunohistochemistry was performed to assess age-related extracellular matrix (ECM) protein levels in the MCC. The histological sections were also used for Alcian blue histochemistry to detect glycosaminoglycans (GAGs)., Results: GO enrichment analysis revealed that the genes related to "extracellular matrix organization," including Acan, Col1a1, Col1a2, Col2a1, Mmp3, Mmp9, and Mmp13, were most differentially expressed in the aged mandibular condyle. Among these seven genes, Mmp3 was upregulated, and the others were downregulated with aging. Histological examination showed the age-related morphological and histological changes in the MCC. Immunohistochemical investigation showed the localization of matrix metalloproteinases (MMPs)-3, -9, and -13 and their substrate proteins, aggrecan, type I collagen, and type II collagen, in the mandibular condyle at 10 and 50 weeks, indicating different localizations between the young and the aged. In the aged MCC, semi-quantitative immunohistochemistry showed a significant decrease in the aggrecan protein level, and Alcian blue histochemistry showed a decrease in GAGs., Conclusion: MMP-3, MMP-9, and MMP-13 contribute to the remodeling of the ECM of the MCC and subchondral bone during aging by degrading ECM proteins at specific times and sites under the regulation of their production and secretion., (© 2023 The Author(s). Published by S. Karger AG, Basel.)

Objectives: The mandibular condylar cartilage is a heterogeneous tissue containing cells at various stages of chondrocyte maturation organized into 4 zones: superficial, polymorphic, flattened, and hypertrophic. The goal of this study was to use transgenic mice containing chondrocyte maturation markers fused to fluorescent protein transgenes to isolate and characterize homogenous cell populations of the mandibular condylar cartilage., Methods: Fluorescent reporter expression in the mandibular condylar cartilage of transgenic mice containing the 3.6-kb fragment of the rat collagen type 1 promoter fused to a topaz-fluorescent protein (Col3.6-tpz), collagen type 2 promoter fused to a cyan-fluorescent protein (Col2-cyan), and/or collagen type 10 promoter fused to cherry-fluorescent protein (Col10-cherry) was examined. Mandibular condylar cartilage cells were analyzed by fluorescence-activated cell sorting (FACS) and either used for gene expression analysis or plated in cell cultures and exposed to adipogenic, osteogenic, or chondrogenic conditions. To determine cell fate, transgenic mice containing the Col3.6-cre recombinase were bred with cre reporter mice., Results: Localization and analysis of gene expression revealed that Col3.6-tpz-positive cells corresponded to the polymorphic/flattened zones and Col2-cyan-positive cells corresponded to the flattened/hypertrophic zones of the mandibular condylar cartilage. Mandibular condylar cartilage FACS-sorted Col3.6-tpz-positive cells have the potential to differentiate into bone, cartilage, and fat. Cell fate mapping revealed that Col3.6 cells are precursors of some of the hypertrophic chondrocytes in the mandibular condylar cartilage., Conclusion: Col3.6-tpz cells represent an earlier stage of the mandibular condylar cartilage maturation pathway., (Copyright © 2011 S. Karger AG, Basel.)

Osteoarthritic lesions appear in the articular cartilage of the temporomandibular joint of mice aged 7 months and older. Reduced rate of proteoglycan (PG) synthesis leading to destruction of the articular cartilage was observed in this joint. The purpose of the present study was to test the ability of transforming growth factor-beta1 (TGF-beta1), insulin-like growth factor-1 (IGF-1) and growth hormone (GH) to induce PG synthesis in joint cartilage of aged animals and to compare it with the effect of interleukin-1alpha (IL-1alpha). Mandibular condyle explants from 18-month-old mice were cultured up to 72 h in serum-free medium, supplemented with IL-1alpha (TGF-beta1 (0.1-5.0 ng/ml), TGF-beta1 (1.0 ng/ml) + IGF-1 (2 ng/ml) or GH (10 ng/ml). The incorporation of (35)S-SO(4) into sulfated PG was tested. Cartilage samples were processed for histomorphometry using sections stained with 0.1% toluidine blue (TB), pH 1.8. Results indicated that in cultures supplemented (48 h) with either TGF-beta, TGF-beta + IGF-1 or with GH, an increased height and area of TB-positive staining as well as increased incorporation of (35)S-SO(4) into sulfated PG were observed. In contrast, the cytokine IL-1alpha exerted an inhibitory effect on TB staining and on (35)S-SO(4) incorporation. The present study demonstrated that in vitro supplementation of IL-1alpha to mandibular condyle cartilage reduced the height and area of TB staining and incorporation of (35)S-SO(4), whereas TGF-beta1, TGF-beta1 + IGF-1 or GH increased the height and area of TB staining and increased incorporation of (35)S-SO(4). The two parameters used to identify increased PG synthesis were shown to reveal similar results and were useful for studying the dynamic events taking place in cartilage destruction and repair in osteoarthritis., (Copyright 2000 S. Karger AG, Basel)

In this study we compared the compositions of extracellular matrices of condylar, costal and nasal cartilages to characterize differences in growth patterns in relation to matrix composition. Condylar, costal and nasal cartilages of 25- and 35-day-old rabbits were extracted and subjected to bio- and histochemical analysis to determine total amounts of collagen and amounts and aggregating properties of proteoglycans. We found that proteoglycan content and aggregate formation were greatest in nasal cartilage, and lower in costal and markedly lower in condylar cartilage. The amount of proteoglycans increased by varying amounts in all samples with age. Collagen content was highest in costal cartilage. In 25-day-old rabbits the quantity of collagen in condylar cartilage exceeded that in nasal cartilage. In 35-day-old rabbits the quantities were nearly the same. It is suggested that collagen does not only provide tensile strength, but counteracts forces responsible for interstitial growth such as osmotic pressure. Based on the results, it seems that the amount of proteoglycans is greater in cartilages, which have greater independent growth potential. Variations in increase in amount of proteoglycans with age could reflect differences in the timing of growth of such cartilages.

Condylar growth was studied after an operation simulating functional orthodontic appliances. Twenty-five rabbits underwent a surgical operation for the induction of premature synostosis to displace the glenoid fossa posteriorly during growth. Twenty-five control rabbits underwent sham operations. At the age of 15 days, 10 experimental and 10 control animals and, at the age of 20 days, 5 experimental and 5 control animals were killed. Their mandibular condyles were organ-cultured for 3 h in the presence of radiolabelled sulphur. The condyles were used for autoradiographic purposes. Digital image analysis of autoradiograms of histological sections showed synthesis of glycosaminoglycans to have increased from the anterior to the posterior direction. This increase was more marked in experimental animals than in the condyles of control animals. Ten experimental and 10 control animals were killed at the age of 15 days, and mandibular condyles were organ-cultured for 1, 4 and 7 days. Differentiation of proliferating prechondroblasts into hypertrophied chondrocytes continued under organ culture conditions. A marked decrease in the proliferating cell layer was noticed, especially in control condyles. Hypertrophy was faster and came closer to the surface of the condyle in the anterior region of the condyle. This was most marked in the condyles of experimental animals. The results indicate that a procedure carried out on the glenoid fossa with the same effect as functional appliances increases the synthesis of extracellular matrix in the posterosuperior region of the mandibular condyle.

Mandibular condylar cartilage (MCC) of growing mammals contains four layers of cells which display a series of increasingly differentiated phenotypes and which culminate in a terminally differentiated cell that produces a calcified matrix. In this study, MCC cells were placed into culture in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum and 50 micrograms/ml ascorbic acid. After 12 h in culture, transmission electron microscopy revealed the presence of multiple cell types that underwent differentiation with additional time in culture. By 7 days, fusiform-shaped cells were seen that contained numerous actin-like cytofilaments and micropinocytotic vesicles characteristic of myofibroblasts. Chondroblast-like cells were also observed. By 10 days, without addition of beta-glycerophosphate or dexamethasone, these cellular events culminated in the formation of mineralized nodules containing matrix vesicles. The nodular surface at day 13 consisted of two or more layers of myofibroblast-like cells, while the deeper zones of the nodule contained cells displaying a morphology typical of calcified hypertrophic chondroblasts. These ultrastructural observations are consistent with the hypothesis that cells from the MCC are capable of recapitulating in culture the maturational events seen in vivo. This cell culture model may be useful for investigating cell-mediated cartilage calcification without the addition of exogenous phosphate or other regulatory factors.

In the mandibular condyle of the newborn mouse the chondroprogenitor (CP) zone is the only layer that incorporates 3H-thymidine thus serving the source for cells of the cartilage lineage. Ultrastructurally these cells have a mesenchymal appearance surrounded by collagen fibrils as well as by additional filaments that become apparent following fixation with ferrocyanide-reduced OsO4. In addition, electron-dense particles indicative of proteoglycans are scattered throughout the matrix in the CP zone as well as in the chondroblastic and hypertrophic zones. Following labeling with 35S-sulfate the CP zone as well as the other compartments revealed a substantial number of grains following processing for autoradiography. The number of grains per cell was highest in the hypertrophic zone. Indirect immunofluorescence indicated the presence of fibronectin in the articular surface, CP zone and in the hypertrophic zone. The immunogold method localized fibronectin intracellularly in CP cells and extracellularly in the hypertrophic zone. Therefore, in the mandibular condyle the CP cells which are capable for DNA synthesis are also involved in the synthesis of macromolecules of which some are specific for the cartilage phenotype, while others are associated with other functions of connective tissue cells.

The response of the condylar cartilage to alterations in compressive joint reaction forces in vivo has been little studied. In an attempt to reduce or eliminate the occlusal forces resulting from mastication or incision, male weanling rats were fed a soft diet requiring little chewing and/or had their incisors clipped every other day. Incorporation (dpm/micrograms DNA) of [3H]-thymidine and [35S]-sulfate was significantly decreased relative to controls in the incisor-clipped group, but not in the soft-diet group. Animals having both treatments also exhibited significantly lower incorporation values than controls, suggesting the importance of incision for loading at the mandibular joint. These data corroborate in vitro studies which suggest that compressive forces can affect mitotic activity and synthesis of proteoglycans in the condylar cartilage. However, additional factors, both hormonal and biomechanical in nature, may be important in the in vivo environment.

(1) 6-week-old ICR mice were injected daily with pharmacologic doses of triamcinolone diacetate (1.5 mg/kg body weight) for 8 consecutive weeks. (2) The temporomandibular joint served as a model for histological and histochemical examinations concerning the effect of glucocorticoid hormone upon bone and cartilage. (3) Histochemical reactions indicated a large number of lipid droplets within the peripheral vasculature. (4) Histological examinations revealed pathologic features, indicative of primary osteoarthrosis.

Histological and histochemical qualitative and quantitative determinations are provided concerning the skeletal changes taking place in the growth center of the mandibular condyle in the neonatal ICR mouse. This study followed the changes in both the major matrical components (collagen, acidic glycosaminoglycans and glycolipids) as well as in the various cartilage cells throughout the maturational period of the neonatal condyle. It was found that the transformation of neonatal condylar cartilage to its mature form involved a significant decrease in its acid glycosaminoglycan content concomitant with a rapid increase in its collagen content. In addition, significant quantitative changes were found within the zone of hypertrophic chondrocytes. The period of highest growth activity along the mandibular posterior vertical dimension (ramus) was between birth and weanling 3rd postnatal week). At this time interval, the adaptive abilities of the growing condyle appeared maximal. A high degree of correlation was noted between the overall reduction in the height of the condylar cartilage and that of its hypertrophic zone. Further, the increase in the ramal height was highly correlated with the structural changes characteristic of the neonatal condyle.