Immunocytochemical demonstration of the synovial membrane in experimentally induced arthritis of the rat temporomandibular joint

Low-Intensity Pulsed Ultrasound Suppresses Synovial Macrophage Infiltration and Inflammation in Injured Knees in Rats

This study was designed to investigate how low-intensity pulsed ultrasound (LIPUS) suppresses traumatic joint inflammation and thereafter affects the progression of posttraumatic osteoarthritis. Intra-articular fracture (IAF) was created in the right knee of rats. LIPUS was applied to the knees with IAFs for 20 min/d for 2 wk-LIPUS(+) group. The study controls included rats that underwent sham surgery but no LIPUS treatment (control group) or underwent IAF surgery without LIPUS treatment-LIPUS(-) group. By histology, at 4 wk, leukocyte infiltration in the synovium was reduced in the LIPUS(+) group. Furthermore, LIPUS treatment reduced CD68⁺ macrophages in the synovium and limited their distribution mostly in the subintimal synovium. Measured with enzyme-linked immunosorbent assay, interleukin-1β (IL-1β) in the joint fluid of the LIPUS(+) group was reduced to about one-third that in the LIPUS(-) group. By reducing synovial macrophages and lowering IL-1β in the joint fluid, LIPUS is potentially therapeutic for posttraumatic osteoarthritis.

Contribution of synovial lining cells to synovial vascularization of the rat temporomandibular joint

The lining layer of the synovial membrane in the temporomandibular joint (TMJ) contains two types of lining cells: macrophage-like type A and fibroblast-like type B cells. The type B cells are particularly heterogeneous in their morphology and immunoreactivity, so that details of their functions remain unclear. Some of the type B cells exhibit certain resemblances in their ultrastructure to those of an activated capillary pericyte at the initial stage of the angiogenesis. The articular surface, composed of cartilage and the disc in the TMJ, has few vasculatures, whereas the synovial lining layer is richly equipped with blood capillaries to produce the constituent of synovial fluid. The present study investigated at both the light and electron microscopic levels the immunocytochemical characteristics of the synovial lining cells in the adult rat TMJ, focusing on their contribution to the synovial vascularization. It also employed an intravascular perfusion with Lycopersicon esculentum (tomato) lectin to identify functional vessels in vivo. Results showed that several type B cells expressed desmin, a muscle-specific intermediate filament which is known as the earliest protein to appear during myogenesis as well as being a marker for the immature capillary pericyte. These desmin-positive type B cells showed immunoreactions for vimentin and pericyte markers (neuron-glial 2; NG2 and PDGFRβ) but not for the other markers of myogenic cells (MyoD and myogenin) or a contractile apparatus (αSMA and caldesmon). Immunoreactivity for RECA-1, an endothelial marker, was observed in the macrophage-like type A cells. The arterioles and venules inside the synovial folds extended numerous capillaries with RECA-1-positive endothelial cells and desmin-positive pericytes to distribute densely in the lining layer. The distal portion of these capillaries showing RECA-1-immunoreactivity lacked lectin-staining, indicating a loss of blood-circulation due to sprouting or termination in the lining layer. The desmin-positive type B and RECA-1-positive type A cells attached to this portion of the capillaries. Some capillaries in the lining layer also expressed ninein, a marker for sprouting endothelial cells, called tip cells. Since an activated pericyte, macrophage and tip cell are known to act together at the forefront of the vessel sprout during angiogenesis, the desmin-positive type B cell and RECA-1-positive type A cell might serve as these angiogenic cells in the synovial lining layer. Tomato lectin perfusion following decalcification would be a highly useful tool for research on the vasculature of the mineralized tissue. Use of this technique combined with immunohistochemistry should permit future extensive investigations on the presence of the physiological angiogenesis and on the function of the lining cells in the synovial membrane.

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.

Effect of simvastatin injections on temporomandibular joint inflammation in growing rats

PURPOSE

Juvenile idiopathic arthritis often affects the temporomandibular joint (TMJ), resulting in facial deformities, and intra-articular injections of anti-inflammatory steroids used in treatment may inhibit bone growth in the developing condyle. The purpose of this pilot study was to evaluate the anti-inflammatory properties of simvastatin (SIM), a bone anabolic drug, compared with the common steroid triamcinolone hexacetonide (TH) in experimental TMJ arthritis of growing rats.

METHODS

Joint inflammation was induced by injecting complete Freund's adjuvant (CFA) into the TMJs of 32 growing (4-week-old) Sprague-Dawley rats while simultaneously receiving 1) ethanol drug carrier, 2) 0.1 mg of SIM, 3) 0.5 mg of SIM, or 4) 0.15 mg of TH. Six rats had no treatment to the TMJ. Animals were euthanized 28 days later, and TMJs were decalcified and stained with hematoxylin-eosin.

RESULTS

Histopathologic TMJ results showed that CFA injection along with drug carrier induced increased thickness of the articular layer on the head of the condyle and inflammation of the retrodiscal area (CFA and ethanol). Although both TH and SIM reduced the articular layer thickness, 0.5 mg of SIM was more effective at reducing subsynovial inflammation.

CONCLUSIONS

Intra-articular simvastatin showed anti-inflammatory properties in this TMJ model, prompting its further study in the growing TMJ, where bone anabolic properties would be important.

Amelioration of pain and histopathologic joint abnormalities in the Col1-IL-1beta(XAT) mouse model of arthritis by intraarticular induction of mu-opioid receptor into the temporomandibular joint

OBJECTIVE

To evaluate opioid receptor function as a basis for novel antinociceptive therapy in arthritis.

METHODS

We induced human mu-opioid receptor (HuMOR) expression in arthritic joints of mice, using the feline immunodeficiency virus (FIV) vector, which is capable of stably transducing dividing, growth-arrested, and terminally differentiated cells. Male and female Col1-IL-1beta(XAT)-transgenic mice developed on a C57BL/6J background and wild-type littermates were studied.

RESULTS

A single injection of FIV(HuMOR) into the temporomandibular joints of Col1-IL-1beta(XAT)-transgenic mice 1 week prior to induction of arthritis prevented the development of orofacial pain and joint dysfunction, and reduced the degree of histopathologic abnormality in the joint. In addition, FIV(HuMOR) prevented the attendant sensitization of trigeminal sensory neurons and activation of astroglia in brainstem trigeminal sensory nuclei. These effects were mediated by the transduction of primary sensory neurons via transport of FIV vectors from peripheral nerve endings to sensory ganglia, as evidenced by HuMOR expression in neuronal cell bodies located in the trigeminal ganglia, as well as in their proximal and distal nerve branches located in the main sensory and subnucleus caudalis of the brainstem and joints, respectively. The presence of MOR ligands predominantly in the descending trigeminal nucleus suggested that the observed antinociception occurred at the subnucleus caudalis. Articular chondrocytes and meniscal tissue were also infected by FIV(HuMOR), which presumably exerted an antiinflammatory effect on cartilage.

CONCLUSION

Our results indicate that prophylactic therapy with MOR overexpression in joints can successfully prevent the development of pain, dysfunction, and histopathologic abnormalities in the joints in arthritis. These findings may provide a basis for the future development of spatiotemporally controlled antinociceptive and antiinflammatory therapy for arthritis.

Localization of CD44 and hyaluronan in the synovial membrane of the rat temporomandibular joint

Previous studies have pointed out a lack of adhesion structures in the synovial lining layer of the rat temporomandibular joint (TMJ) despite showing an epithelial arrangement. CD44, a major cell adhesion molecule, plays crucial roles as an anchor between cells and extracellular matrices by binding hyaluronan (HA) for the development of organs or the metastasis of tumors. The present study examined the localization of CD44 in the synovial membrane of the rat TMJ by immunocytochemistry for OX50, ED1, and Hsp25, which are markers for the rat CD44, macrophage-like type A, and fibroblast-like type B synoviocytes, respectively. Histochemistry for HA-binding protein (HABP) was also employed for the detection of HA. OX50 immunoreactions were found along the cell surface and, in particular, accumulated along the surface of the articular cavity. Observations by a double immunostaining and immunoelectron microscopy revealed that all the OX50-immunopositive cells were categorized as fibroblastic type B cells, which had many caveolae and a few vesicles reactive to intense OX50. However, the macrophage-like type A cells did not have any OX50 immunoreaction in the synovial lining layer. A strong HABP reaction was discernable in the extracellular matrix surrounding both OX50-positive and -negative cells in the synovial lining layers, exhibiting a meshwork distribution, but weak in its sublining layer. This localization pattern of CD44 and HABP might be involved in the formation of the epithelial arrangement of the synovial lining layer. Furthermore, OX50 immunonegativity in the type A cells suggests their low phagocytotic activity in the rat TMJ under normal conditions.

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.

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

The synovial lining layer of the temporomandibular joint (TMJ) consists of macrophage-like type A cells and fibroblast-like type B cells. Until now, little information has been available on the development of the synovial membrane in TMJ. In the present study we examined the development of the synovial lining layer in the rat TMJ by light- and electron-microscopic immunocytochemistry for heat shock protein (Hsp) 25, which is a useful marker for type B cells. At embryonic day 19 (E19), a few Hsp25-positive cells first appeared in the upper portion of the developing condyle. During the formation of the upper articular cavity (E21 to postnatal day 1 (P1)), a few positive cells were arranged on its surface. Immunoelectron microscopy demonstrated that these cells had ultrastructural features of fibroblast-like type B cells. In addition, some Hsp25-positive cells moved to the deep portion by extending their cytoplasmic processes toward the articular cavity at P3. At that time, the presence of typical macrophage-like type A cells in the lining layer was confirmed by immunoelectron microscopy. The slender processes of Hsp25-positive cells showed a continuous covering with the synovial surface at P7, followed by a drastic increase in the Hsp25-positive cells at P15 and later, when active jaw movement occurred. These findings suggested that the arrangement and morphological maturation of type B cells are closely related to the formation of the articular cavity in the embryonic period and the commencement of active jaw movement after birth, respectively.

Synovial membrane in the temporomandibular joint--its morphology, function and development

This paper reviews recent findings of the synovial membrane, in particular the morphology, function and development of synovial lining cells, in the temporomandibular joint (TMJ). Electron microscopic studies have confirmed the synovial membrane in TMJ consists of macrophage-like type A cells and fibroblast-like type B cells identical to those in other systematic joints. The macrophage-like type A cells react with anti-macrophage and macrophage-derived substances including the major histocompatibility class II molecule, and show a drastic increase in their number in the inflamed synovial membrane. In addition, they have the ability to produce substances involved in the progression of TMJ inflammation such as nitric oxide and inducible nitric oxide synthase. Observation of osteopetrotic mice revealed that macrophage-like type A cells in TMJ are derived from monocyte lineage. Immunocytochemistry for 25kDa heat shock protein was able to depict the entire shape of fibroblast-like type B cells including their unique processes. The expression of an estrogen receptor alpha-immunoreaction in the fibroblast-like type B cells may explain the etiology of temporomandibular disorders at a higher frequency in females than in males, suggesting that TMJ is a target tissue for estrogen. Furthermore, fibroblast-like type B cells are equipped with a basement membrane to serve as an adhesion molecule for the fibroblast-like type B cells to keep their epithelial arrangement. A clear understanding of the morphology of the intact synovial membrane will serve to clarify the etiology and development of temporomandibular disorders.

Nerve terminals extend into the temporomandibular joint of adjuvant arthritic rats

The innervation of the temporomandibular joint (TMJ) has attracted particular interest because of the close association with complex mandibular movement. Although the pathological changes of disk innervation may have a crucial role in the development of TMJ pain, the innervation of the TMJ disk by experimentally induced arthritis has rarely been examined in detail. Arthritic rats were induced by injection with 0.1ml solution of Complete Freund's adjuvant (CFA). We investigated three-dimensional distribution of nerve fibers in the TMJ disk using immunohistochemistry for protein gene product-9.5 (PGP-9.5) and calcitonin gene-related peptide (CGRP) in naive and arthritic rats. To clarify the possible role of nerve growth factor (NGF) and its receptor on changes in peripheral innervation of the TMJ, the expressions of trkA and p75 receptor in trigeminal ganglia were examined. Although PGP-9.5 and CGRP immunoreactive (ir) fibers were seen in the peripheral part of the TMJ disk, they were not seen in its central part. The total length and the length density of PGP-9.5 ir and CGRP ir nerve fibers increased in arthritic rats. The innervation area of fibers proliferating in the rostro-medial part merged with that of fibers in the rostro-lateral part in the arthritic rats. In addition, the ratio of trkA- and p75-positive small- and medium-sized cells increased in trigeminal ganglia. It is assumed that increasing innervation of the TMJ disk may be important for the pathophysiology of TMJ pain. NGF and its receptors are likely involved in pathological changes of the TMJ disk.

Sleep alterations in an experimental orofacial pain model in rats

This study sought to assess sleep patterns in rats injected with Freund's adjuvant (FA) in the temporomandibular joint (TMJ) as a potential experimental orofacial pain model. Pain response to indomethacin was also assessed. Rats were implanted with electrodes to record electrocorticogram and eletromyogram signals. After a baseline (B) recording, they were injected with Freund's adjuvant (orofacial pain group, n=8) or saline (sham group, n=8) in the temporomandibular joint, and their sleep was monitored over two 12-h light periods. In the second phase of the study, after injecting Freund's adjuvant, indomethacin was administered (1 mg/kg p.o.) at 12- intervals, and sleep patterns were recorded for two additional light periods. The orofacial pain group showed a reduction in sleep efficiency during the two light periods compared with the baseline recording and with the sham group (p<0.001). Increases in sleep and paradoxical sleep (PS) latencies of approximately 200% and 420%, respectively, were observed, as well as an increase in the number of awakenings during both periods (p<0.001). Treatment with indomethacin increased sleep efficiency (p<0.001) and paradoxical sleep time (p<0.001). The number of awakenings (p<0.001) and sleep (p<0.001) and paradoxical sleep latencies (p<0.001) were reduced reestablishing the normal sleep pattern. The results showed the reliability and usefulness of the temporomandibular joint pain model to characterize sleep disturbances related to pain and its response to indomethacin.

PPAR gamma ligands inhibit nitrotyrosine formation and inflammatory mediator expressions in adjuvant-induced rheumatoid arthritis mice

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor, whose activation has been linked to several physiologic pathways including those related to the regulation of insulin sensitivity. Here, we investigate effects of PPARgamma specific ligands, rosiglitazone and pioglitazone, on formation of nitrotyrosine and increased expression of inflammatory mediators such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 and intercellular adhesion molecule-1 (ICAM-1) in adjuvant-induced murine arthritis. Administration of rosiglitazone or pioglitazone (30 mg/kg, p.o.) significantly inhibited the adjuvant-induced increase in formation of nitrotyrosine and expression of iNOS on both ankle and temporomandibular joints. Rosiglitazone also inhibited the adjuvant-induced expression of M30 positive cells, as a marker of apoptosis, in the joint tissues. In addition, treatment with rosiglitazone or pioglitazone (30 microM) inhibited lipopolysaccharide plus tumor necrosis factor (TNF)-alpha-induced protein expression of iNOS, cyclooxygenase-2, ICAM-1 and nitrotyrosine formation in RAW 264 cells, a murine macrophage-like cell line. Rosiglitazone or pioglitazone inhibited increase in phosphorylated I-kappaB (pI-kappaB) expression, as an index of activation of nuclear factor (NF)-kappaB, in both joint tissues and RAW264 cells. Furthermore, in PPARgamma-transfected HEK293 cells, rosiglitazone inhibited the TNF-alpha-stimulated response using NF-kappaB-mediated transcription reporter assay. These results indicate that PPARgamma ligands may possess anti-inflammatory activity against adjuvant-induced arthritis via the inhibition of NF-kappaB pathway.

Evaluation of opioid receptors in synovial membranes of horses

OBJECTIVE

To evaluate mu-opioid receptors in synovial membranes of horses and determine whether these receptors are up-regulated in nerve endings during inflammation.

SAMPLE POPULATION

Synovial tissue obtained from 39 client-owned horses during arthroscopy and 14 research horses during necropsy; brain and synovial tissues were obtained during necropsy from 1 horse, and control tissues were obtained from a mouse.

PROCEDURE

Horses were classified into 7 groups on the basis of histologically determined degree of inflammation. Binding of primary rabbit antibody developed against mu-opioid receptors in equine synovial tissue was studied, using western blot analysis. Synovial membranes were tested for mu-opioid receptors by immunohistochemical staining, using a diaminobenzidine-cobalt chloride chromogen. Homogenates of synovial membranes were evaluated by use of radioligand binding.

RESULTS

Examination of western blots of equine thalamus revealed that rabbit antibody developed against mu-opioid receptors yielded a band (molecular weight, 55 kd) that corresponded with that of other opioid receptors. Use of immunohistochemical staining of synovial tissue revealed considerable staining in the proliferative lining layer and in regions surrounding vascular structures. Specific radioligand binding of tissue homogenates was found in all groups. We did not detect significant differences in binding between horses with inflammation and horses without inflammation.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of immunohistochemical analysis and radioligand binding of tissue homogenates suggest that there are opioid receptors in synovial membranes of horses. Our results support the practice of intra-articular administration of opioids to relieve pain after arthroscopic surgery in horses.

Calcitonin gene-related peptide and substance P immunoreactivity in rat trigeminal ganglia and brainstem following adjuvant-induced inflammation of the temporomandibular joint

The immunoreactivity of two inflammatory mediators, calcitonin gene-related peptide (CGRP) and substance P, was measured in the trigeminal ganglia and brainstem to characterize an adjuvant-induced inflammation within the rat temporomandibular joint at various acute (6, 24 and 48 h) and intermediate (10 day) time intervals. Concentrations of adjuvant-related neuropeptides were compared to those in both contralateral vehicle-related tissues and non-injected controls. By 6 h, CGRP immunoreactivity in the trigeminal ganglia was significantly above that in contralateral vehicle-injected tissue. The CGRP had decreased at each of the following time-points, but remained significantly elevated at 10 days. Substance P in the ganglion on the injected side was significantly increased for all four time periods. In brainstem subnucleus caudalis, CGRP was significantly increased for all four time periods. Substance P immunoreactivity in the subnucleus caudalis was significantly increased for the initial three time periods, but by day 10 had been reduced to that of the control. These data show that the pattern of changes in neuropeptides following the induction of inflammation is different between substance P and CGRP. Moreover, the pattern of change varies between the brainstem and the trigeminal ganglion. This suggests that the two neuropeptides may have different roles in the inflammatory process, and that this process may be modulated by different mechanisms at the brainstem and ganglion.

Morphology and functional roles of synoviocytes in the joint

The joint capsule exhibits a unique cellular lining in the luminal surface of the synovial membrane. The synovial intimal cells, termed synoviocytes, are believed to be responsible for the production of synovial fluid components, for absorption from the joint cavity, and for blood/synovial fluid exchanges, but their detailed structure and function as well as pathological changes remain unclear. Two types of synoviocytes, macrophagic cells (type A cells) and fibroblast-like cells (type B cells) have been identified. Type A synoviocytes are non-fixed cells that can phagocytose actively cell debris and wastes in the joint cavity, and possess an antigen-presenting ability. These type A cells, derived from blood-borne mononuclear cells, can be considered resident macrophages (tissue macrophages) like hepatic Kupffer cells. Type B synoviocytes are characterized by the rich existence of rough endoplasmic reticulum, and dendritic processes which form a regular network in the luminal surface of the synovial membrane. Their complex three-dimensional architecture was first revealed by our recent scanning electron microscopy of macerated samples. The type B cells, which are proper synoviocytes, are involved in production of specialized matrix constituents including hyaluronan, collagens and fibronectin for the intimal interstitium and synovial fluid. The proliferative potentials of type B cells in loco are much higher than type A cells, although the transformation of subintimal fibroblasts into type B cells can not be excluded. In some mammals, type B cells show features suggesting endocrine and sensory functions, but these are not recognized in other species. The synoviocytes, which form a discontinuous cell layer, develop both fragmented basement membranes around the cells and junctional apparatus such as desmosomes and gap junctions. For an exact understanding of the mechanism of arthritis, we need to establish the morphological background of synoviocytes as well as their functions under normal conditions.

Immunocytochemical demonstration of laminin in the synovial lining layer of the rat temporomandibular joint

This immunocytochemical study describes the distribution of laminin in the synovial lining of the rat temporomandibular joint. Laminin immunostaining was present around some synovial lining cells and blood vessels. Ultrastructurally, immunoreactive products for laminin were deposited around cells with a well-developed rough endoplasmic reticulum and secretory granules, suggesting that they were type B synovial lining cells. The localization of laminin immunoreactivity was not uniform around the cell membrane, the most intense immunoreaction being present on the basal aspect membrane as is seen in the basement membrane of epithelia. In contrast, macrophage-like synovial lining type A cells did not show laminin immunoreactivity. This different immunostaining pattern suggests that laminin acts as an adhesion molecule for the type B cells in their epithelial-like arrangement.