Characterisation of chondrocyte activation in response to cytokines synthesised by a synovial cell line

Synovial Membrane Microarthroscopy of the Equine Midcarpal Joint

OBJECTIVE

To evaluate the value of microarthroscopy in the equine midcarpal joint using the vital stains methylene blue, trypan blue, neutral red, and Janus green B to observe components of the synovial lamina propria, vascular architecture, and synoviocytes.

STUDY DESIGN

Experimental.

ANIMALS

Ten horses.

METHODS

Microarthroscopy of left and right midcarpal joints was performed with and without vital staining of the synovium. Four vital stains (methylene blue, trypan blue, neutral red, and Janus green B) were evaluated, with each stain used in 5 joints. Synovial biopsy specimens were collected from the dorsomedial and dorsolateral aspects of the joint.

RESULTS

All dyes were biocompatible. At x 60 without vital staining, synovial surface topography, vascular network, and translucency were observed. Intra-articular vital dyes improved evaluation of synovial surface topography. At x 150 with vital staining, individual synoviocytes were clearly identified with all dyes, except neutral red. Although methylene blue provided the best in vivo microscopic differentiation of the structure of the intima, trypan blue had superior retention in conventionally processed synovial biopsies.

CONCLUSIONS

Methylene blue, trypan blue, neutral red, and Janus green B stains can be used safely for microarthroscopy. Good visualization of cells and vascular network can be obtained by microarthroscopy, and microarthroscopic evaluation of the synovium compares favorably with conventional histologic evaluation of biopsy specimens.

CLINICAL RELEVANCE

Microarthroscopy may be beneficial in both research and clinical diagnosis of equine articular diseases.

In vitro studies of a photo-oxidized bovine articular cartilage

Bovine articular cartilage was photo-oxidized and cultured with native articular bovine cartilage and synovial membrane to study the interaction between these tissues mimicking the physiological situation in the joint. The photo-oxidation was applied as a pretreatment of cartilage for future use in cartilage resurfacing procedures in joints. Properties of the transplant were assessed by testing the production of local mediators, such as nitric oxide (NO) and prostaglandin E2 (PGE2), and neutral metalloproteinase activities under normal conditions and after stimulation with various stimulants representative of inflammatory changes in pathophysiological conditions. Unlike normal cartilage photo-oxidized cartilage did not release significant amounts of NO and PGE2 and showed less gelatinolytic and caseinolytic activity compared to native bovine articular cartilage. Enzyme activity of the combined cultures was at a level intermediate between that of photo-oxidized cartilage and native cartilage cultures alone. In contrast to normal cartilage, living chondrocytes were not visible in photo-oxidized cartilage using live/dead staining. These results indicate, that the photo-oxidized cartilage may have a beneficial effect on adjacent native host cartilage and therefore be a suitable transplant for use in in vivo experiments.

A coculture model of synoviocytes and bone for the evaluation of potential arthritis therapies

OBJECTIVE

To evaluate the symbiotic relationship between musculoskeletal cells in the intact joint utilizing a coculture system and to determine if the model can be utilized to evaluate potential treatments for articular diseases.

METHODS

Two neonatal mouse calvariae were placed on steel supports on a monolayer of rabbit synovial fibroblasts, and net calcium flux, bone cell activity, and undecalcified histology were determined at 6, 24, and 48 h. To determine if the model was predictive of response to known therapies for articular disease, the coculture was incubated in the presence and absence of indomethacin or doxycycline, and the net calcium flux was measured.

RESULTS

The coincubation of calvariae with synoviocytes led to a fivefold increase in net calcium efflux compared to calvariae alone. The concentration in the media of the osteoblastic enzyme alkaline phosphatase increased at 6 h but decreased thereafter, whereas the concentration of osteoclastic enzyme beta-glucuronidase increased with time. Undecalcified bone histology revealed progressive demineralization and an increase in the number of osteoclasts in calvariae incubated with synoviocytes compared to calvariae alone. Both indomethacin and doxycycline inhibited calcium flux from cocultures but the predominant effect of doxycycline was on the synoviocyte whereas the predominant effect of indomethacin was on bone.

CONCLUSION

The coincubation of synoviocytes with calvariae led to an increase in bone mineral dissolution with time. This effect could be partially inhibited by known treatments for rheumatoid arthritis. Thus, the coculture model may simulate certain aspects of the in vivo processes relevant to rheumatoid arthritis. This model should prove useful for the study of potential therapies for inflammatory arthritis and distinguish between effects of these therapies on different cellular components of the joint.

Mechanism of mechanically induced intercellular calcium waves in rabbit articular chondrocytes and in HIG-82 synovial cells

Intercellular communication through gap junctions allows tissue coordination of cell metabolism and sensitivity to extracellular stimuli. Intercellular Ca2+ signaling was investigated with digital fluorescence video imaging in primary cultures of articular chondrocytes and in HIG-82 synovial cells. In both cell types, mechanical stimulation of a single cell induced a wave of increased Ca2+ that was communicated to surrounding cells. Intercellular Ca2+ spreading was inhibited by 18alpha-glycyrrhetinic acid, demonstrating the involvement of gap junctions in signal propagation. In the absence of extracellular Ca2+, mechanical stimulation induced communicated Ca2+ waves similar to controls; however, the number of HIG-82 cells recruited decreased significantly. Mechanical stress induced Ca2+ influx both in the stimulated chondrocyte and HIG-82 cell, but not in the adjacent cells, as assessed by the Mn2+ quenching technique. Treatment of cells with thapsigargin and with the phospholipase C (PLC) inhibitor U73122 blocked mechanically induced signal propagation. These results provide evidence that in chondrocytes and in HIG-82 synovial cells, mechanical stimulation activates PLC, thus leading to an increase of intracellular inositol 1,4,5-trisphosphate. The second messenger, by permeating gap junctions, stimulates intracellular Ca2+ release in neighboring cells. It is concluded that intercellular Ca2+ waves may provide a mechanism to coordinate tissue responses in joint physiology.

Intercellular calcium signalling between chondrocytes and synovial cells in co-culture

Intercellular communication allows the co-ordination of cell metabolism between tissues as well as sensitivity to extracellular stimuli. Paracrine stimulation and cell-to-cell coupling through gap junctions induce the formation of complex cellular networks that favour the intercellular exchange of nutrients and second messengers. Heterologous intercellular communication was studied in co-cultures of articular chondrocytes and HIG-82 synovial cells by measuring mechanically induced cytosolic changes in Ca2+ ion levels by digital fluorescence video imaging. In confluent co-cultures, mechanical stimulation induced intercellular Ca2+ waves that propagated to both cell types with similar kinetics. Intercellular wave spreading was inhibited by 18alpha-glycyrrhetinic acid and by treatments inhibiting the activation of purinoreceptors, suggesting that intercellular signalling between these two cell types occurs both through gap junctions and ATP-mediated paracrine stimulation. In rheumatoid arthritis the formation of the synovial pannus induces structural changes at the chondrosynovial junction, where chondrocyte and synovial cells come into close apposition: these results provide the first evidence for direct intercellular communication between these two cell types.

Transfer of genes to chondrocytic cells of the lumbar spine. Proposal for a treatment strategy of spinal disorders by local gene therapy

STUDY DESIGN

In the current study, chondrocytic cells from bovine intervertebral end plates were cultivated in vitro and modified genetically.

OBJECTIVE

The authors intended to perform isolation and cultivation of cells from bovine end plates of the spine. They also intended to show, in principle, the feasibility of introducing exogenous genes into chondrocytic cells from bovine intervertebral end plates by way of retroviral vectors.

SUMMARY OF BACKGROUND DATA

The involvement of cytokines in the destruction of articular cartilage is established. It appears possible that similar mechanisms may play a role in intervertebral disc degeneration and other spinal disorders. Conventional medication and surgery of intervertebral disc degeneration addresses neither the pathophysiology nor the chronicity of the disease. Therapeutic proteins carry great potential as locally produced drugs after transfer of their cognate genes to the sites of interest.

METHODS

Vertebral end plate tissue was obtained from bovine os coccygis. Chondrocytic cells were isolated and cultured in vitro. The bacterial beta-galactosidase (LacZ) gene and, alternatively, the complementary DNA (DNA copy of the mRNA) of the human interleukin-1 receptor antagonist were introduced into the isolated cells by retrovirus mediated gene transfer. beta-galactosidase activity was determined by staining, and interleukin-1 receptor antagonist protein was quantitated by enzyme-linked immunosorbent assay.

RESULTS

Isolation and cultivation of chondrocytic end plate cells is possible. Native cells continue to grow in culture for more than 2 months. Transfer of the beta-galactosidase gene to cultured cells resulted in approximately 1% beta-galactosidase positive cells. Transfer of the interleukin-1 receptor antagonist complementary DNA resulted in the production of 24 ng/ml/10(6) cells interleukin-1 receptor antagonist protein in 48 hours.

CONCLUSIONS

The introduction of exogenous therapeutic genes into cells from the intervertebral end plate opens the possibility for a local gene-based treatment of intervertebral disc degeneration. This approach avoids some of the shortcomings of conventional drug- and surgery-based treatments and has the potential to be specific, effective, and appropriate to the chronicity of the disease.

Role of protein kinase A in collagenase-1 gene regulation by prostaglandin E1: studies in a rabbit synoviocyte cell line, HIG-82

Gene expression of the matrix-degrading enzyme collagenase-1 in rabbit synoviocytes and human fibroblasts is down-regulated by prostaglandin E1 (PGE1) through a cyclic adenosine monophosphate (cAMP)-dependent pathway. In the current study, we examined the role of protein kinase A (PKA) in the PGE1-mediated effect on collagenase-1 gene expression. Collagenase-1 gene expression was rapidly induced several-fold above control both by a phorbol ester, 12-o-tetradecanoyl phorbol 13 acetate, and interleukin-1 beta (IL-1 beta) in HIG-82 synoviocytes. Treatment with PGE1 and forskolin increased PKA activity in the HIG-82 cells within 15 minutes of adding the stimulating agents. Two inhibitors of PKA, the isoquinoline-sulfonamide derivative, H-89 and a cAMP analog, RpcAMP, blocked the ability of PGE1 to down-regulate collagenase-1 gene expression. However, if PGE1 was added from 6 h to 30 minutes before the PKA inhibitor H-89, collagenase-1 gene expression was inhibited. Constitutive PKA activity was increased in HIG-82 synoviocytes stably transfected with an expression vector pCMV.C alpha that caused the HIG-82 cells to overexpress an active catalytic subunit of PKA. Cells stably transfected with an inactive, mutated C-alpha-variant showed no change in PKA activity. Collagenase-1 mRNA levels in TPA-stimulated cells were reduced to baseline levels in the pCMV.C alpha but not in the mutated C-alpha-transfected cells. These data show the importance of PKA in regulating collagenase-1 gene expression in a synoviocyte cell line.

Neurotoxicity in rat cortical cells caused by N-methyl-D-aspartate (NMDA) and gp120 of HIV-1: induction and pharmacological intervention

Incubation of highly enriched neurons from rat cerebral cortex with the human immunodeficiency virus type 1 (HIV-1) coat protein gp120 for 18 h results in fragmentation of DNA at internucleosomal linkers, a feature of apoptosis. We report that neurons respond to exposure to gp120 with an increased release of arachidonic acid via activation of phospholipase A2. This process is not inhibited by antagonists of the N-methyl-D-aspartate (NMDA) receptor channels. To investigate the influence of arachidonic acid on the sensitivity of NMDA receptor towards its against, low concentrations of NMDA were coadministered with arachidonic acid. Under these conditions the NMDA-mediated cytotoxicity was enhanced. We conclude that gp120 causes an activation of phospholipase A2, resulting in an increased release of arachidonic acid which in turn sensitizes the NMDA receptor. Two compounds were found to act cytoprotectively against the deleterious effect caused by gp120 on neurons: Memantine [1-amino-3,5-dimethyladamantane] and Flupirtine [2-amino-3-ethoxycarbonylamino-6-(4-fluoro-benzyl-amino)-pyridine maleate]. Both compounds have been found to display a potent cytoprotective effect on neurons treated with the excitatory amino acid NMDA or with the human immunodeficiency virus type 1 (HIV-1) coat protein gp120. The NMDA antagonist Memantine, a drug currently used in the therapy of spasticity and Parkinson's disease, prevented the effects of gp120 at micromolar concentrations. Flupirtine was previously found to be a centrally acting, nonopiate analgesic agent which additionally possesses anticonvulsant and muscle-relaxant activity at doses similar to those producing analgesia. The cytoprotective effect of Flupirtine in vitro was significant (above 10 microM). Considering the fact that both Memantine and Flupirtine display almost no clinical side effects, these drugs may prove useful both in preventing primary infection of brain cells with the HIV virus, as well as in treating the neurological disorders often associated with the immunodeficiency syndrome such as AIDS-related dementia.

Exposure to gp120 of HIV-1 induces an increased release of arachidonic acid in rat primary neuronal cell culture followed by NMDA receptor-mediated neurotoxicity

After incubation of highly enriched neurons from rat cerebral cortex with the HIV-1 coat protein gp120 for 18 h, cells showed fragmentation of DNA at internucleosomal linkers followed by NMDA receptor-mediated neurotoxicity. We report that in response to exposure to gp120 cells react with an increased release of arachidonic acid (AA) via activation of phospholipase A2. This process was not inhibited by NMDA receptor antagonists. To investigate the role of AA on the sensitivity of the NMDA receptor towards its agonist, low concentrations of NMDA were co-administered with AA. This condition enhanced the NMDA-mediated cytotoxicity. Administration of mepacrine reduced cytotoxicity caused by gp120. We conclude that gp120 causes an activation of phospholipase A2, resulting in the increased release of AA, which may in turn sensitize the NMDA receptor.

Intraarticular expression of biologically active interleukin 1-receptor-antagonist protein by ex vivo gene transfer

Gene therapy offers a radical different approach to the treatment of arthritis. Here we have demonstrated that two marker genes (lacZ and neo) and cDNA coding for a potentially therapeutic protein (human interleukin 1-receptor-antagonist protein; IRAP or IL-1ra) can be delivered, by ex vivo techniques, to the synovial lining of joints; intraarticular expression of IRAP inhibited intraarticular responses to interleukin 1. To achieve this, lapine synoviocytes were first transduced in culture by retroviral infection. The genetically modified synovial cells were then transplanted by intraarticular injection into the knee joints of rabbits, where they efficiently colonized the synovium. Assay of joint lavages confirmed the in vivo expression of biologically active human IRAP. With allografted cells, IRAP expression was lost by 12 days after transfer. In contrast, autografted synoviocytes continued to express IRAP for approximately 5 weeks. Knee joints expressing human IRAP were protected from the leukocytosis that otherwise follows the intraarticular injection of recombinant human interleukin 1 beta. Thus, we report the intraarticular expression and activity of a potentially therapeutic protein by gene-transfer technology; these experiments demonstrate the feasibility of treating arthritis and other joint disorders with gene therapy.

Interleukin-1 beta enhances the response of human articular chondrocytes to extracellular ATP

It has been observed that both interleukin-1 (IL-1) and extracellular ATP stimulate the production of prostaglandin E (PGE) by human articular chondrocytes in monolayer culture. The combined effects of recombinant human IL-1 beta and ATP were therefore studied using these cells. IL-1 beta rapidly enhanced the response to a maximally effective concentration of ATP (100 microM). On continuous exposure of the cells to the cytokine, its effect was greatest after approx. 24 h and tended to decline thereafter. The enhancement of the response to 100 microM ATP by IL-1 beta was dose-dependent. Removal of IL-1 beta prior to treating the cells with 100 microM ATP did not affect the degree of enhancement of the response. The effect of the cytokine on the response to suboptimal concentrations of extracellular ATP was also tested. IL-1 beta lowered the minimum concentration of ATP required to elicit an increase in the production of PGE by human articular chondrocytes. These findings are of interest, since they indicate a synergistic interaction between a cytokine and a purinergic agonist. Moreover, since both the sensitivity of the cells to extracellular ATP and the maximum response to this agent were enhanced, it is possible that IL-1 modulates more than one step in the process of P2-purinoceptor-mediated stimulation of PGE production. These observations may be relevant to the pathogenesis of some forms of arthritis.

Synovial protein kinase C and its apparent insensitivity to interleukin-1

Lapine synovial fibroblasts produce prostaglandin E2 (PGE2) and neutral metalloproteinases in response to phorbol 12-myristate 13-acetate (PMA), human recombinant interleukin-1 (hrIL-1) and, in an autocrine fashion, in response to partially purified preparations of their own cytokines known as cell-activating factors (CAF). Here we have examined the possible role of protein kinase C (PKC) in these responses. Whereas the 80-kDa substrate for PKC could not be detected in synovial fibroblasts, these cells contained a 35-kDa protein which fulfilled the criteria for qualifying as a specific substrate of PKC. Translocation assays based upon phosphorylation of the 35-kDa protein and Western blotting techniques allowed the movement of PKC from the cytosolic to the particulate fraction in response to PMA and CAF to be detected but not in response to 4 alpha-PMA or hrIL-1. Inhibitors of PKC suppressed synovial activation by PMA, partially blocked activation by CAF but had no effect on activation by hrIL-1. There thus appear to be PKC-dependent and PKC-independent routes to synovial cell activation. Our data suggest that IL-1 uses the latter, while CAF contains cytokines which utilize both routes.

Collagen stability and collagenolytic activity in the normal and aneurysmal human abdominal aorta

Two issues were addressed in this study. The first was whether a bona fide collagenase exists within the wall of the aorta. The second was whether the activity of this putative collagenase is greater in aneurysmal tissue. No collagenase could be extracted from the wall of the aorta under nondenaturing conditions. However, hydroxyproline was liberated from tissue samples allowed to autolyze at neutral pH under reaction conditions favoring the activity of collagenase. Such an activity was probably enzymic as it occurred in a time- and temperature-dependent fashion and was suppressed by chelators. In normal and stenotic tissue, activity was increased by adding aminophenylmercuric acetate, an activator of latent collagenase. Examination of the blanks revealed that the collagen of aneurysmal aorta was more soluble than normal. Furthermore, its digestion kinetics differed in a way that suggested that aneurysmal aorta possessed a labile component that was absent from normal tissue. Although the activity of the putative aortic collagenase was higher than normal in the aneurysmal tissue, our assays do not distinguish between changes in the amount or activity of the enzyme and alterations in the collagen.

Evidence that responses of articular chondrocytes to interleukin-1 and basic fibroblast growth factor are not mediated by protein kinase C

After exposure to human recombinant interleukin-1 (hrIL-1), chondrocytes increase their synthesis of prostaglandin E2 (PGE2) and neutral metalloproteinases (NMPs). This response, known as chondrocyte activation, is also elicited by partially purified preparations of rabbit synovial IL-1, known as 'chondrocyte activating factors' (CAF). CAF activates chondrocytes more strongly than does hrIL-1, probably because it contains additional growth factors. Basic fibroblast growth factor (bFGF) is one such factor, although CAF also contains others which modulate the activation of chondrocytes. Chondrocyte activation by hrIL-1 is strongly potentiated by bFGF and phorbol myristate acetate (PMA). A series of experiments was conducted to examine the possible role of protein kinase C (PKC) in mediating these effects. Inhibitors of PKC partially blocked the induction of NMPs by CAF and completely suppressed the potentiating effect of PMA. However, induction by 10 units of hrIL-1/ml and potentiation by bFGF were not affected by these inhibitors. Furthermore, cells whose PKC had been down-regulated by prolonged exposure to PMA remained responsive to IL-1. Surprisingly, inhibitors of PKC greatly increased the amounts of NMPs produced in response to a low dose (1 unit/ml) of hrIL-1. These inhibitors also enhanced the synthesis of PGE2 by cells responding to 1 and 10 units of hrIL-1/ml. Phosphorylation of the 80 kDa substrate for PKC was augmented by PMA and CAF, but not by hrIL-1 or bFGF. Moreover, Western-blotting techniques, which confirmed translocation of PKC in response to PMA and CAF, did not detect translocation in cells treated with hrIL-1 or bFGF. Western blotting also demonstrated the presence of PKC isoenzyme type III (alpha), but not types I (gamma) or II (beta). These data argue that PKC does not mediate the effects of hrIL-1 or bFGF in chondrocytes. However, CAF contains additional substances which activate this enzyme and whose effects may in part be mediated by PKC.

Intracellular signal transduction pathways in sponges

Sponges are the lowest multicellular eukaryotic organisms. Due to the relatively low specialization, and concomitantly the high differentiation and dedifferentiation potency of their cells, the sponge cell system has proven to be a useful model to study the mechanism of cell-cell adhesion on molecular levels. Results of detailed biochemical and cell biological studies with the main cell adhesion molecules, the aggregation factor (AF) and the aggregation receptor, led to the formation of the modulation theory of cell adhesion. The events of cell adhesion are contigent on a multiplicity of precisely coordinated intracellular signal transduction pathways. Using the marine sponge Geodia cydonium we showed that during the initial phase of cell-cell contact the AF causes a rapid stimulation of the phosphatidylinositol pathway, resulting in an activation of protein kinase C and a subsequent phosphorylation of DNA topoisomerase II. As one consequence of these processes, the cells undergo a phase of high DNA synthesis. However, at later stages, the AF loses its mitogenic activity; this function is then taken over by the matrix lectin. During this switch, the lectin receptor associates in the plasma membrane with the ras oncogene product. The description of these processes is subject of this review article.

Role of phospholipase A2 in the stimulation of sponge cell proliferation by homologous lectin

Using the Geodia cydonium system, we showed that after incubation of competent sponge cells in the presence of lectin, phospholipase A2 was released from the cells. The substrates for this enzyme, phosphatidylethanolamine and phosphatidylcholine, were identified in the extracellular material of sponge tissue. In addition, the phospholipase A2 inhibitor calelectrin was identified by immunobiochemical techniques; this molecule was associated with the aggregation factor. Reconstitution experiments strongly suggested that phospholipase A2 catalyzed the release of arachidonic acid, which is then taken up by the cells. Intracellularly, arachidonic acid was metabolized primarily to prostaglandin E2. Inhibition studies revealed that prostaglandin E2 is involved in the ultimate increase of DNA synthesis. These findings suggest that the phospholipase A2-arachidonic acid system is involved in the matrix-initiated signal transduction pathway in sponges.

Chondrocyte activation by a putative interleukin-1 derived from lapine polymorphonuclear leukocytes

Polymorphonuclear leukocytes (PMNs) recovered from 4-h lapine peritoneal exudates contained factors which provoked the synthesis of collagenase, gelatinase, caseinase, and prostaglandin E2 by lapine articular chondrocytes. Rapid secretion of these factors occurred after exposing the polymorphs to phorbol myristate acetate or formyl-Met-Leu-Phe. Fractionation of polymorph lysates by HPLC size exclusion chromatography provided a molecular weight of approximately 14,000 for the active principle. Examination of the most active fraction by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by silver staining, confirmed the presence of a single band with this apparent molecular weight. Isoelectric focusing of this fraction revealed the presence of four distinct bands with the pI values 6.90, 7.05, 7.45, and 7.55. This fraction tested positive in a bioassay for interleukin-1. We were unable to activate chondrocytes by exposure to extracts of human PMNs from either peripheral blood or inflammatory synovial fluid.