Histamine H1-receptor-mediated keratan sulfate production in rabbit chondrocytes: involvement of protein kinase C

Orai1-Orai2 complex is involved in store-operated calcium entry in chondrocyte cell lines

Ca(2+) influx via store-operated Ca(2+) entry (SOCE) plays critical roles in many essential cellular functions. The Ca(2+) release-activated Ca(2+) (CRAC) channel complex, consisting of Orai and STIM, is one of the major components of store-operated Ca(2+) (SOC) channels. Our previous study demonstrated that histamine can cause sustained Ca(2+) entry through SOC channels in OUMS-27 cells derived from human chondrosarcoma. This SOCE was increased by low- and decreased by high-concentrations of 2-aminoethoxydiphenyl borate. Quantitative reverse transcription PCR and Western blot analyses revealed abundant expressions of Orai1, Orai2 and STIM1. Introduction of dominant negative mutant of Orai1, or siOrai1 knockdown significantly attenuated SOCE. Following histamine application, single molecule imaging using total internal reflection fluorescence (TIRF) microscopy demonstrated punctate Orai1-STIM1 complex formation in plasma membrane. In contrast, knockdown or over-expression of Orai2 resulted in an increase or a decrease in SOCE, respectively. Finally, TIRF imaging revealed direct coupling between Orai1 and Orai2, and suggested that Orai2 reduces Orai1 function by formation of a hetero-tetramer. These results provide substantial evidence that Orai1, Orai2 and STIM1 form functional CRAC channels in OUMS-27 cells and that these complexes are responsible for sustained Ca(2+) entry in response to agonist stimulation.

Accelerated Ca2+ entry by membrane hyperpolarization due to Ca2+-activated K+ channel activation in response to histamine in chondrocytes

In articular cartilage inflammation, histamine release from mast cells is a key event. It can enhance cytokine production and matrix synthesis and also promote cell proliferation by stimulating chondrocytes. In this study, the functional impact of Ca2+-activated K+ (KCa) channels in the regulation of intracellular Ca2+ concentration ([Ca2+]i) in chondrocytes in response to histamine was examined using OUMS-27 cells, as a model of chondrocytes derived from human chondrosarcoma. Application of histamine induced a significant [Ca2+]i rise and also membrane hyperpolarization, and both effects were mediated by the stimulation of H1 receptors. The histamine-induced membrane hyperpolarization was attenuated to ∼50% by large-conductance KCa (BK) channel blockers, and further reduced by intermediate (IK) and small conductance KCa (SK) channel blockers. The tonic component of histamine-induced [Ca2+]i rise strongly depended on the presence of extracellular Ca2+ ([Ca2+]o) and was markedly reduced by La3+ or Gd3+ but not by nifedipine. It was significantly attenuated by BK channel blockers, and further blocked by the cocktail of BK, IK, and SK channel blockers. The KCa blocker cocktail also significantly reduced the store-operated Ca2+ entry (SOCE), which was induced by Ca2+ addition after store-depletion by thapsigargin in [Ca2+]o free solution. Our results demonstrate that the histamine-induced membrane hyperpolarization in chondrocytes due to KCa channel activation contributes to sustained Ca2+ entry mainly through SOCE channels in OUMS-27 cells. Thus, KCa channels appear to play an important role in the positive feedback mechanism of [Ca2+]i regulation in chondrocytes in the presence of articular cartilage inflammation.

Cyclic tensile stretch loaded on bovine chondrocytes causes depolymerization of hyaluronan: involvement of reactive oxygen species

OBJECTIVE

We have previously demonstrated that reactive oxygen species (ROS) are involved in cartilage degradation. Decreased size of hyaluronan (HA), the major macromolecule in synovial fluid, to which it imparts viscosity, is reported in patients with arthritis. The purpose of this study was to determine the alteration in the molecular weight range of HA as a result of mechanical deformation loaded on the chondrocytes, as well as the involvement of ROS in this action.

METHODS

ROS were generated via the oxidation of hypoxanthine by xanthine oxidase. Cyclic tensile stretch was loaded using a vacuum-operated instrument. Levels of HA were measured using a sandwich enzyme-binding assay. Superoxide dismutase (SOD) activity and ROS were measured using water-soluble tetrazolium and a chemiluminescent probe, respectively.

RESULTS

ROS depolymerized HA molecules. Cyclic tensile stretch depolymerized HA and induced ROS. SOD inhibited not only ROS induction but also HA depolymerization caused by the mechanical stress.

CONCLUSION

ROS play an important role in mechanical stress-induced HA depolymerization.

Reactive oxygen species depolymerize hyaluronan: involvement of the hydroxyl radical

We have previously demonstrated that reactive oxygen species (ROS) are involved in cartilage degradation. A decrease in the size of hyaluronan (HA), which is the major macromolecule in synovial fluid and is responsible for imparting viscosity to it, is reported in arthritis patients. The purpose of this study is to determine the ROS that depolymerize HA. The luminol derivative, L-012, was used to determine the generation of ROS. To generate hydroxyl radicals, a mixture of hydrogen peroxide (H(2)O(2)) and ferrous ions (Fe(2+)) was added to HA. The antioxidants and the depolymerization of HA were studied in this system. The hydroxyl radical is one of the ROS, causing the depolymerization of HA, which reacts with L-01. These data suggest that hydroxyl radicals play an important role at the site of inflammation.

Activation of histamine H1 receptor results in enhanced proteoglycan synthesis by human articular chondrocyte: involvement of protein kinase C and intracellular Ca(2+)

In earlier work, we obtained evidence for the presence of histamine H1 and H2 receptors on chondrocytes. Activation of the H1 receptor enhanced keratan sulfate synthesis, and protein kinase C (PKC) inhibitors antagonized histamine-stimulated keratan sulfate (KS) synthesis. These data do indicate the involvement of PKC in activation of H1 receptor, but precise mechanisms remained to be clarified. Human articular chondrocytes were treated with different concentrations of histamine and its antagonist. Intracellular Ca(2+) and proteoglycan synthesis was measured, using the fluorescent indicator dye Fura-2 AM and [35S]-sulfate incorporation, respectively. Activation of the H1 receptor led to stimulation of proteoglycan synthesis and evoked increases in levels of intracellular Ca(2+). Activity of PKC was also enhanced with activation of the H1 receptor. Intracellular Ca(2+) and activation of PKC are involved in the signal transduction pathway of H1 receptor-mediated stimulation of proteoglycan synthesis.

Interleukin-4 reversed the Interleukin-1-inhibited proteoglycan synthesis through the inhibition of NO release: a possible involvement of intracellular calcium ion

Interleukin-1 (IL-1) causes cartilage degradation through nitric oxide (NO) synthesis. Although Interleukin-4 (IL-4) antagonizes the IL-1-mediated cartilage degradation, the precise mechanisms are not clear. We examined the effect of IL-4 on NO synthesis in parallel with intracellular Ca levels ([Ca(2+)]i) and proteoglycan (PG) synthesis. IL-4-inhibited IL-1-enhanced NO release in a dose-dependent manner. IL-1-enhanced [Ca(2+)]i in the chondrocytes, and IL-4 attenuated this increase. IL-4 reversed IL-1-inhibited PG synthesis. Accordingly, IL-4 reversed the IL-1-inhibited PG synthesis through the inhibition of NO release. An increase in [Ca(2+)]i with IL-1 is possibly involved in this action.

Calphostin C induces AP1 synthesis and AP1-dependent c-jun transactivation in normal human chondrocytes independent of protein kinase C-alpha inhibition: possible role for c-jun N-terminal kinase

Activator protein-1 (AP1) regulates the promoter activity of a large number of genes associated with developmental, proliferative, inflammatory, and homeostatic processes in human connective tissue cells. Some of these genes (e.g., cyclooxygenase-2) are regulated by the protein kinase C (PKC) inhibitor, calphostin C (CalC). We examined whether CalC could indeed induce AP1 and AP1 gene transactivation (c-jun) in human chondrocytes. Exploratory studies confirmed the anti-PKC effects of CalC, as equal molar concentrations of CalC blocked the PMA-induced translocation of PKC-alpha from the cytosolic to the membrane fraction. CalC induction of AP1, as judged by gel-shift analysis, using a consensus AP1 oligonucleotide, was biphasic with an initial increase (maximum 4 h), followed by a decline, reaching its nadir after 16 h, and finally a major upregulation phase at 24 h. Maximum induction of AP-1 was reached at a concentration of 250 nmol/L of CalC. CalC did not block PMA-induced AP1 synthesis. Gel-shift analysis in the presence of specific antibodies to c-Jun, JunB, JunD, c-Fos, and CREB/ATF showed that the AP1 complexes were probably c-Jun/c-Jun, c-Fos/c-Jun, c-Fos/JunB, or c-Jun/JunB dimers. Northern blot analysis confirmed that c-jun, junB, and c-Fos were the principal proto-oncogenes induced by CalC. To confirm that c-jun induction occurs at the transcriptional level and to examine the role of the AP1 site present in the c-jun promoter in the induction of c-jun by CalC, we performed transient transfections of c-jun promoter-CAT constructs harboring either wild-type (WT) AP1 regulatory element sites or mutant AP1 sites. CalC (250 nmol/L) induced a marked increase in CAT activity (i.e., promoter activation) with WT AP1 c-jun promoter-CAT plasmids, but the response was completely abrogated when using constructs where the AP1 site was mutated. PMA produced similar results, but the induction of the WT AP1 c-jun promoter-CAT plasmid was smaller. CalC (250 nmol/L) inhibited MAPK (p42/44) activity while stimulating c-Jun N-terminal kinase activity in a time-frame coincident with the activation of AP1. We conclude that CalC induces signaling pathways that activate AP1 and transactivate genes harboring AP1 enhancer sites independent of PKC-alpha.

Factors related to degradation of articular cartilage in osteoarthritis: a review

OBJECTIVES

Osteoarthritis (OA) is a common joint deterioration initiated by multiple factors. To better understand related factors in the development of this disease, we focused on the mechanical stress loaded on articular cartilage.

MATERIALS AND METHODS

The anterior cruciate ligaments of rabbit knee joints were transected, and expression of protein kinase C (PKC) examined immunohistochemically. The PKC activator 12-o-tetradecanoyl-phorbol-13-acetate (TPA) was then administered intraarticularly. To determine the involvement of gas mediators, a cartilage defect was made on the medical femoral condyle of rabbit knee joints. Hydrostatic pressure was loaded on the cartilage taken from the surrounding defects, and levels of superoxide anion and nitric oxide (NO) were measured. Bovine chondrocytes were subjected to cyclic mechanical stretch using a Flexercell Strain Instrument. Proteoglycan synthesis and PKC activity were measured. Expression of matrix metalloproteinase (MMP)-3 and tissue inhibitor of metalloproteinase (TIMP)-1 in articular cartilages obtained from OA patients were examined using Northern blots.

RESULTS

Chondrocytes from experimentally induced OA were stained positively with anti-alpha-PKC antibody. Intraarticular administration of TPA prevented the development of OA changes. Cyclic tensile stretch loaded on chondrocytes decreased proteoglycan synthesis and PKC activity. Thus, PKC is involved in the stress-mediated degradation of articular cartilage. Cartilage defects led to degradation of surrounding cartilage and to enhanced superoxide anion and NO synthesis. We also noted increased and decreased expressions of MMP-3 and TIMP-1 mRNA in human OA cartilage, respectively.

CONCLUSION

PKC, gas mediators (superoxide anion, NO), and proteinases are all involved in OA.

Cyclic tensile stretch on bovine articular chondrocytes inhibits protein kinase C activity

Osteoarthrosis, a common pathway of joint deterioration, is caused by mechanical stress loaded on articular cartilage. We previously demonstrated the involvement of protein kinase C (PKC) in the development of osteoarthritis in vitro. In this study, we examined the effect of mechanical stress on chondrocyte metabolism and the activity of PKC in vitro. Low frequency and magnitude of cyclic tensile stretch loaded on chondrocytes increased proteoglycan synthesis. However, high frequency and magnitude of stress decreased its synthesis. In this condition, activity of PKC was reduced. These results suggest an involvement of PKC in the stress-mediated inhibition of proteoglycan synthesis.

A role for histamine receptors in rheumatoid arthritis

Although neurotransmitters and various chemical mediators play an important role in the pathogenesis of rheumatoid arthritis (RA), precise underlying mechanisms have yet to be determined. Histamine is a classical mediator of inflammation and three types of receptors are known. We investigated the presence and functions of histamine receptors of lymphocytes, bone marrow cells, synovial fibroblasts, and chondrocytes in experimentally-induced arthritis and human RA. The function of H2 receptors in peripheral blood lymphocytes and bone marrow cells were down regulated as measured by increments of intracellular cAMP and IL-6 production. Synovial fibroblasts from RA patients did not respond to H2 agonist to synthesize hyaluronic acid. It is evident that H2 receptors are down-regulated in lymphocytes, bone marrow cells, and synovial fibroblasts. The reduced function of H2 receptors in collagen-induced arthritis was normalized by transfer of the receptor-bearing lymphocytes and bone marrow cells. These data suggest that histamine is involved in the pathogenesis of RA.

Histamine-induced cytosolic calcium increase in porcine articular chondrocytes

Chondrocytes have been shown to possess two types of histamine receptors, H1 and H2. The application of histamine to isolated porcine chondrocytes was found to significantly increase intracellular calcium and this increase was partially dependent upon the presence of extracellular calcium. This, therefore, implies that there is some role for a plasma membrane calcium transport system in the increase of cytosolic calcium in response to histamine. The increase in intracellular calcium in response to the application of histamine was found to be reduced by both H1 and H2 receptor antagonists.

Protein kinase C activator inhibits progression of osteoarthritis induced in rabbit knee joints

To study the role of protein kinase C (PKC) in cartilage tissue in osteoarthritis, experimental osteoarthritis was induced in the knee joints of rabbits by resection of the anterior cruciate ligament (ACL). At 4 weeks after the operation, osteoarthritic changes varying from surface irregularities and cleft formation to loss of the tangential layer were observed, and cloning or hypocellularity of the chondrocytes was observed mainly in the transitional and radial layers. The PKC activator 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or non-PKC-activating phorbol ester 4 alpha-phorbol-12,13-didecanate (PDD) was administered intraarticularly once a week from the day of the operation for 3 weeks. Histologic evaluation with a rating scale was carried out. In the TPA-administered group, cartilage structures were preserved almost completely, and score of the cartilage lesion was significantly less than that in animals administered PDD or in nonadministered controls. A chondroprotective role of PKC under mechanical stress was suggested.

Zonal differences in nitric oxide synthesis by bovine chondrocytes exposed to interleukin-1

To determine the role of nitric oxide (NO) in the inhibition of aggrecan synthesis, we measured levels of NO produced by bovine chondrocytes from different layers of articular cartilage in the presence of interleukin-1 (IL-1). Chondrocytes from the superficial layer showed a large increase in NO synthesis in response to IL-1. Although chondrocytes from the deep layer also produced NO in response to IL-1, the amount was less than that from the superficial layer. Enhanced NO production evoked by IL-1 was accompanied by a significant inhibition of aggrecan synthesis. These data suggest that chondrocytes in both superficial and deep layer of articular cartilage inhibit aggrecan synthesis with IL-1 via NO production. In addition, superficial layer cells respond to lower amounts of IL-1 with respect to NO-production and inhibition of proteoglycan synthesis.

Interleukin-1 inhibits keratan sulfate production by rabbit chondrocytes: possible role of prostaglandin E2

We investigated the importance of prostaglandin E2 (PGE2) release in interleukin-1 (IL-1)-induced inhibition of aggrecan synthesis by chondrocytes. Keratan sulfate (KS) production was measured in parallel with PGE2 release in chondrocytes. IL-1 inhibited KS production and stimulated PGE2 release. In the presence of PGE2, there was a dose-dependent decrease in baseline KS production. Indomethacin and dexamethasone partially blocked the IL-1-induced PGE2 release while KS production recovered. Our results suggest that IL-1 inhibits KS production, in part, by stimulating the release of PGE2.

Keratan sulfate inhibits its release in rabbit chondrocyte

Keratan sulfate (KS) is one of the major glycosaminoglycans in cartilage matrix proteoglycan. We find that exogenously added KS totally blocks keratanase sensitive glycosaminoglycan release measured by radiolabeled ligand. We also find that KS release is potentially inhibited by its own presence as measured by ELISA. When KS is digested with keratanase before its addition to the medium, its inhibitory effect on KS secretion is partially blocked. Exogenously added KS promotes the accumulation of the KS epitope in the cell layer. These data suggest that KS negatively regulates its own secretion.