Development of the synovial membrane in the rat temporomandibular joint as demonstrated by immunocytochemistry for heat shock protein 25

Sarcomas of synovial origin in dogs: An updated review

The purpose of this review is to clarify the terminology, possible cells of origin, and expected behavior of the most common synovial tumors in dogs. The synovial lining consists of 2 cell types, type A and type B. Type A synoviocytes are histiocytes of bone marrow origin that are immunoreactive with antibodies against typical markers of histiocyte origin, such as CD18, Iba-1, and CD204. Certain breeds and dogs with previous injury to a joint, especially cranial cruciate ligament rupture, are predisposed to synovial histiocytic sarcoma. Type B synoviocytes are mesenchymal cells that produce synovial fluid. There are no specific markers of type B synoviocytes, but based on their gross and microscopic appearance, synovial myxosarcomas (previously considered synovial myxomas) are presumed to be of type B synoviocyte origin. These can infiltrate into surrounding tissues, but are slow-growing and rarely metastasize, and then only to regional lymph nodes. Synovial histiocytic sarcomas and myxosarcomas can cause lysis in multiple bones surrounding the joint, but they have different prognoses and require histopathology and sometimes immunohistochemistry to diagnose them. Synovial sarcoma and synovial cell sarcoma are terms used in the human medical literature for a tumor that is not of synovial origin; these terms should not be used in veterinary medicine.

Development of synovial membrane in the temporomandibular joint of the human fetus

The development of the synovial membrane was analyzed in serial sections of 21 temporomandibular joints of human fetuses at 9 to 13 weeks of gestation. Sections of two fetuses at 12 weeks of development were used to perform immunohistochemical expression of the markers CD68 and Hsp27 on the synovial lining. Macrophage-like type A and fibroblast-like type B cells, which express CD68 and Hsp27, respectively, were observed at the twelfth week of development. Our results suggest that the development of the synovial membrane is related to the vascularization of the joint and the formation of the articular cavities.

Analysis by Light, Scanning, and Transmission Microscopy of the Intima Synovial of the Temporomandibular Joint of Human Fetuses during the Development

Objective. To characterize morphologically and ultrastructurally using light microscopy, the scanning electron microscopy and transmission electron microscopy the intima synovial of the temporomandibular joint (TMJ) of human fetuses between the 10th and the 38th week of development. Materials and Methods. The TMJ was dissected bilaterally in 37 human fetuses belonging to the Institute of Embryology of the University Complutense of Madrid and of the Federal University of São Paulo. Results. The outcome by light microscopy showed the morphology of the TMJ and that the formation of inferior joint cavity precedes the superior joint cavity and the presence of blood vessels in the synovial. Conclusion. By scanning and transmission electron microscopy we observed the presence of two well-defined cell types in the intima layer of synovial of the TMJ of human fetuses, macrophage-like type A cell and fibroblast-like type B cell, and the presence of the a third cell type, defined by the name of intermediate lining cell in the intima layer of the synovial.

Synovial cysts of the temporomandibular joint: an immunohistochemical characterization and literature review

Synovial cysts of the temporomandibular joint (TMJ) are very rare, and to date, only 12 cases of a synovial cyst in the TMJ region have been reported in the literature. In this paper, we present the clinicopathological and immunohistochemical characteristics of one such lesion affecting a 48-year-old woman, presented with a mass in the left preauricular region. We describe the usefulness of immunohistochemical analysis for recognizing the synovial lining, which allowed for clear differentiation between ganglion and synovial cysts. Immunohistochemical analyses can be used to diagnose synovial cysts with certainty; however, using at least two markers is advisable to distinguish the two existing synovial cell subtypes. Our findings indicate that synovial cysts of TMJ possess an internal lining dominated by type B (fibroblast-like) synoviocytes.

Qualitative study of young, adult, and aged Wistar rats temporomandibular synovial membrane employing light, scanning, and transmission electron microscopy

The aim of this study was to analyze the rat temporomandibular joint (TMJ) synovial membrane at different ages using light, scanning, and transmission electron microscopy. Under light microscopic analysis, the TMJ structures were observed such as condyle, capsule, disk, the synovial membrane collagen type, and cells distribution. In the scanning electron microscopy, the synovial membrane surface exhibited a smooth aspect in young animals and there was an increase with ageing in the number of folds. The transmission electron microscopic analysis showed more synoviocytes in the synovial layer in the young group and still a great number of vesicles and cisterns dilation of rough endoplasmic reticulum in the aged group. In the three groups, a dense layer of collagen fibers in the synovial layer and cytoplasmic extensions were clearly seen. It was possible to conclude that synovial membrane structures in aged group showed alterations contributing to the decrease in joint lubrication and in the sliding between disk and joint surfaces. These characteristic will reflect in biomechanics of chewing, and may cause the TMJ disorders, currently observed in clinical processes.

An in situ hybridization study of the insulin-like growth factor system in developing condylar cartilage of the fetal mouse mandible

The objective of this study was to investigate the involvement of the insulin-like growth factor (IGF) system in the developing mandibular condylar cartilage and temporomandibular joint (TMJ). Fetal mice at embryonic day (E) 13.0-18.5 were used for in situ hybridization studies using [35S]-labeled RNA probes for IGF-I, IGF-II, IGF-I receptor (-IR), and IGF binding proteins (-BPs). At E13.0, IGF-I and IGF-II mRNA were expressed in the mesenchyme around the mandibular bone, but IGF-IR mRNA was not expressed within the bone. At E14.0, IGF-I and IGF-II mRNA were expressed in the outer layer of the condylar anlage, and IGF-IR mRNA was first detected within the condylar anlage, suggesting that the presence of IGF-IR mRNA in an IGF-rich environment triggers the initial formation of the condylar cartilage. IGFBP-4 mRNA was expressed in the anlagen of the articular disc and lower joint cavity from E15.0 to 18.5. When the upper joint cavity was formed at E18.5, IGFBP-4 mRNA expression was reduced in the fibrous mesenchymal tissue facing the upper joint cavity. Enhanced IGFBP-2 mRNA expression was first recognized in the anlagen of both the articular disc and lower joint cavity at E16.0 and continued expression in these tissues as well as in the fibrous mesenchymal tissue facing the upper joint cavity was observed at E18.5. IGFBP-5 mRNA was continuously expressed in the outer layer of the perichondrium/fibrous cell layer in the developing mandibular condyle. These findings suggest that the IGF system is involved in the formation of the condylar cartilage as well as in the TMJ.

Canine Synovial Myxoma

This report describes the signalment, clinical findings, gross appearance, histological and immunohistochemical characteristics, and behavior of 39 cases of canine synovial myxoma. Large-breed middle-aged dogs—especially, Doberman Pinschers and Labrador Retrievers—were most commonly affected. The stifle and digit were the most common sites. Grossly, the tumors were composed of gelatinous nodules that often filled the joint cavity and exuded viscous fluid on cut section. In 12 cases (31%), radiographic bony lysis or grossly invasive growth was noted clinically. Histologically, the nodules were sparsely cellular and composed of stellate to spindle cells suspended in an abundant myxomatous matrix. By immunohistochemistry, the cells were positive for vimentin, heat shock protein 25, and cadherin 11 and negative for cytokeratin and S100 protein; some cells (20–40%) were positive for CD18. Affected dogs had long survival times (average, 2.5 years), even with incomplete excision of the tumor. Three cases had local recurrence, but none metastasized or directly resulted in death. Canine synovial myxoma is a histologically distinctive tumor with a good prognosis.

Characterization of normal canine anterior cruciate ligament-associated synoviocytes

This study was designed to identify and quantify synoviocyte phenotypes enveloping the canine anterior cruciate ligament (ACL) to test the hypothesis that there are at least two synoviocyte phenotypes, each with distinct quantities and topographical distributions. CD18 and HSP25 epitopes were colocalized in the synovium of 10 normal canine ACLs. Sagittal sections were prepared from medial, central, and lateral aspects of each ACL and phenotypes were quantified in the proximal, middle, and distal aspects of each section. Distinct synoviocyte populations stained positive for CD18 (CD18+) or HSP25 (HSP25+), and a small population of cells stained for both epitopes (DS+). The proportion (mean +/- SEM) of HSP25+ synoviocytes (57% +/- 7.5%) was significantly greater than the proportion of CD18+ synoviocytes (27% +/- 8.2%), which was significantly greater than the proportion of DS+ synoviocytes (16% +/- 3.5%). Reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analysis, and immunoelectron microscopy confirmed the presence of CD18 and HSP25 epitopes in the canine ACL. Identification and quantification of ACL synoviocytes may serve as the foundation for future studies involving ACL disease or reconstruction.

Expression of caveolin-3 in the fibroblast-like type B synoviocytes in the rat temporomandibular joint

The present study revealed that the fibroblast-like type B synoviocytes (covering the surface of the synovial membrane in the rat temporomandibular joint) had muscle-specific caveolin-3 protein in their caveolae. The existence of two kinds of type B synoviocytes (with and without caveolin-3-immunoreactions even in the synovial lining layer) might reflect the functional difference between them.

The relationship between the termination of cell proliferation and expression of heat-shock protein-25 in the rat developing tooth germ

Odontoblast- and ameloblast-lineage cells acquire heat-shock protein (HSP)-25 immunoreactivity after they complete cell division during postnatal odontogenesis in rat molars. However, there are no data available concerning the relationship between the termination of cell proliferation and HSP-25 immunoreactivity during tooth morphogenesis. We compared the expression of HSP-25 in tooth germs with their proliferative activity in the rat prenatal to perinatal molar and postnatal incisor to clarify the functional significance of HSP-25 during tooth morphogenesis by immunohistochemistry using anti-HSP-25 and anti-Ki67/5-bromo-2'-deoxyuridine (BrdU). Numerous proliferating cells in developing molars were distributed throughout the tooth germ and HSP-25 immunoreactivity was recognizable in the dental epithelial and mesenchymal cells after they completed cell division. However, both cell proliferation and immunoreaction for HSP-25 are absent in the enamel knots. The distribution pattern of the proliferating cells in the incisors was basically identical to that in the prenatal molars except for the lack of non-proliferating secondary enamel knots and the sparse distribution of proliferating cells in the apical bud. Thus, HSP-25 protein is suggested to act as a switch between cell proliferation and terminal cyto-differentiation during odontogenesis.

An immunohistochemical study of the expression of heat-shock protein-25 and cell proliferation in the dental pulp and enamel organ during odontogenesis in rat molars

OBJECTIVES

The aim of this study is to clarify the functional significance of heat-shock protein (HSP)-25 during tooth development.

DESIGN

We compared the expression of HSP-25 in the dental epithelial and mesenchymal cells with their proliferative activity during odontogenesis in rat molars on postnatal days 1-100 by immunohistochemistry using anti-HSP-25 and anti-5-bromo-2'-deoxyuridine (BrdU) for cell proliferation assay.

RESULTS

On day 1, BrdU-immunoreactive cells were densely located in the inner enamel epithelium in the cervical loop and intercusped areas and the dental pulp adjacent to them, whereas HSP-25-immunoractivity (IR) was restricted to the cusped area where odontoblasts and ameloblasts had already differentiated. Subsequently, BrdU-IR shifted in the apical direction to be localized around Hertwig's epithelial root sheath during days 5-30, never overlapping with concomitantly apically-shifted HSP-25-IR. On days 60-100, BrdU-immunoreactive cells were hardly recognizable in the dental pulp, where HSP-25-IR was exclusively localized in the odontoblast layer. Furthermore, the odontoblast- and ameloblast-lineage cells exhibited two steps in the expression of HSP-25 throughout the postnatal stages: first, dental epithelial and pulpal mesenchymal cells showed a weak IR for HSP-25 after the cessation of their proliferative activity, and subsequently odontoblasts and ameloblasts consistently expressed an intense HSP-25-IR.

CONCLUSION

Odontoblast- and ameloblast-lineage cells acquire HSP-25-IR after they complete their cell division, suggesting that this protein acts as a switch between cell proliferation and differentiation during tooth development. The consistent expression of HSP-25-IR in the formative cells may be involved in the maintenance of their functional integrity.

Expression of caveolin-1 in the rat temporomandibular joint

This immunocytochemical study revealed the expression of caveolin-1, a major protein of caveolae, in the rat temporomandibular joint. In the synovial lining layer, immunoreactive products for caveolin-1 were detected on the cell membrane of the fibroblast-like type B cells, as confirmed by immunocytochemistry for heat shock protein 25. The cells in the articular disk, the articular layer, and zone of proliferation of the mandibular condyle also showed intense immunoreactions for caveolin-1.

Development of the articular cavity in the rat temporomandibular joint with special reference to the behavior of endothelial cells and macrophages

Previous developmental studies on the temporomandibular joint (TMJ) have proposed several hypotheses on the formation of its articular cavity. However, detailed information is meager. The present study examined the formation process of the articular cavity in the rat TMJ by immunocytochemistry for CD31, RECA-1, and ED1, which are useful cellular markers for endothelial cells and monocyte/macrophage lineages, respectively. The upper articular cavity formation had begun by embryonic day 21 (E21) and was completed at postnatal day 1 (P1) in advance of the lower cavitation; the latter took place from P1 to P3. The occurrence and distribution pattern of the CD31-, RECA-1-, and ED1-positive cells differed between the upper and lower articular cavity-forming areas: the ED1-positive cells exclusively occurred in the area of the prospective upper articular cavity prior to its formation, while no ED1-positive cell appeared in the lower cavity-forming area. In contrast, the CD31- and RECA-1-positive endothelial cells were restricted to the lower cavity-forming area (never the prospective upper cavity) at E19 and diminished thereafter. Throughout the cavity formation, we failed to find any apoptotic cells in the cavity formation area, indicating no involvement of apoptosis in the cavity formation in TMJ. The present findings on the behaviors of endothelial cells and ED1-positive cells show a possibility of different mechanism in the cavity formation between the upper and lower articular cavities in the rat TMJ. The appearance of ED1-reactive cells and temporal vascularization may play crucial roles in the upper and lower articular cavity formation, respectively.