The effects of IL-1 on mitogen-activated protein kinases in rabbit articular chondrocytes

Global chondrocyte gene expression after a single anabolic loading period: Time evolution and re-inducibility of mechano-responses

Aim of this study was a genome-wide identification of mechano-regulated genes and candidate pathways in human chondrocytes subjected to a single anabolic loading episode and characterization of time evolution and re-inducibility of the response. Osteochondral constructs consisting of a chondrocyte-seeded collagen-scaffold connected to β-tricalcium-phosphate were pre-cultured for 35 days and subjected to dynamic compression (25% strain, 1 Hz, 9 × 10 min over 3 hr) before microarray-profiling was performed. Proteoglycan synthesis was determined by ³⁵ S-sulfate-incorporation over 24 hr. Cell viability and hardness of constructs were unaltered by dynamic compression while proteoglycan synthesis was significantly stimulated (1.45-fold, p = 0.016). Among 115 significantly regulated genes, 114 were up-regulated, 48 of them ≥ twofold. AP-1-relevant transcription factors FOSB and FOS strongly increased in line with elevated ERK1/2-phosphorylation and rising MAP3K4 expression. Expression of proteoglycan-synthesizing enzymes CHSY1 and GALNT4 was load-responsive as were factors associated with the MAPK-, TGF-β-, calcium-, retinoic-acid-, Wnt-, and Notch-signaling pathway which were significantly upregulated SOX9, and BMP6 levels rose significantly also after multiple loading episodes at daily intervals even at the 14th cycle with no indication for desensitation. Canonical pSmad2/3 and pSmad1/5/9-signaling showed no consistent regulation. This study associates novel genes with mechanoregulation in chondrocytes, raising SOX9 protein levels with anabolic loading and suggests that more pathways than so far anticipated apparently work together in a complex network of stimulators and feedback-regulators. Upregulation of mechanosensitive indicators extending differentially into the resting time provides crucial knowledge to maximize cartilage matrix deposition for the generation of high-level cartilage replacement tissue.

Evaluation of the anti-inflammatory, anti-catabolic and pro-anabolic effects of E-caryophyllene, myrcene and limonene in a cell model of osteoarthritis

Osteoarthritis is a progressive joint disease and a major cause of disability for which no curative therapies are yet available. To identify compounds with potential anti-osteoarthritic properties, in this study, we screened one sesquiterpene, E-caryophyllene, and two monoterpenes, myrcene and limonene, hydrocarbon compounds for anti-inflammatory, anti-catabolic and pro-anabolic activities in human chondrocytes. At non-cytotoxic concentrations, myrcene and limonene inhibited IL-1β-induced nitric oxide production (IC50=37.3μg/ml and 85.3µg/ml, respectively), but E-caryophyllene was inactive. Myrcene, and limonene to a lesser extent, also decreased IL-1β-induced NF-κB, JNK and p38 activation and the expression of inflammatory (iNOS) and catabolic (MMP-1 and MMP-13) genes, while increasing the expression of anti-catabolic genes (TIMP-1 and -3 by myrcene and TIMP-1 by limonene). Limonene increased ERK1/2 activation by 30%, while myrcene decreased it by 26%, relative to IL-1β-treated cells. None of the compounds tested was able to increase the expression of cartilage matrix-specific genes (collagen II and aggrecan), but both compounds prevented the increased expression of the non-cartilage specific, collagen I, induced by IL-1β. These data show that myrcene has significant anti-inflammatory and anti-catabolic effects in human chondrocytes and, thus, its ability to halt or, at least, slow down cartilage destruction and osteoarthritis progression warrants further investigation.

Regulation of chondrogenesis by protein kinase C: Emerging new roles in calcium signalling

During chondrogenesis, complex intracellular signalling pathways regulate an intricate series of events including condensation of chondroprogenitor cells and nodule formation followed by chondrogenic differentiation. Reversible phosphorylation of key target proteins is of particular importance during this process. Among protein kinases known to be involved in these pathways, protein kinase C (PKC) subtypes play pivotal roles. However, the precise function of PKC isoenzymes during chondrogenesis and in mature articular chondrocytes is still largely unclear. In this review, we provide a historical overview of how the concept of PKC-mediated chondrogenesis has evolved, starting from the first discoveries of PKC isoform expression and activity. Signalling components upstream and downstream of PKC, leading to the stimulation of chondrogenic differentiation, are also discussed. Although it is evident that we are only at the beginning to understand what roles are assigned to PKC subtypes during chondrogenesis and how they are regulated, there are many yet unexplored aspects in this area. There is evidence that calcium signalling is a central regulator in differentiating chondroprogenitors; still, clear links between intracellular calcium signalling and prototypical calcium-dependent PKC subtypes such as PKCalpha have not been established. Exploiting putative connections and shedding more light on how exactly PKC signalling pathways influence cartilage formation should open new perspectives for a better understanding of healthy as well as pathological differentiation processes of chondrocytes, and may also lead to the development of novel therapeutic approaches.

Calcium input potentiates the transforming growth factor (TGF)-beta1-dependent signaling to promote the export of inorganic pyrophosphate by articular chondrocyte

Transforming growth factor (TGF)-β1 stimulates extracellular PP(i) (ePP(i)) generation and promotes chondrocalcinosis, which also occurs secondary to hyperparathyroidism-induced hypercalcemia. We previously demonstrated that ANK was up-regulated by TGF-β1 activation of ERK1/2 and Ca(2+)-dependent protein kinase C (PKCα). Thus, we investigated mechanisms by which calcium could affect ePP(i) metabolism, especially its main regulating proteins ANK and PC-1 (plasma cell membrane glycoprotein-1). We stimulated articular chondrocytes with TGF-β1 under extracellular (eCa(2+)) or cytosolic Ca(2+) (cCa(2+)) modulations. We studied ANK, PC-1 expression (quantitative RT-PCR, Western blotting), ePP(i) levels (radiometric assay), and cCa(2+) input (fluorescent probe). Voltage-operated Ca(2+)-channels (VOC) and signaling pathways involved were investigated with selective inhibitors. Finally, Ank promoter activity was evaluated (gene reporter). TGF-β1 elevated cCa(2+) and ePP(i) levels (by up-regulating Ank and PC-1 mRNA/proteins) in an eCa(2+) dose-dependent manner. TGF-β1 effects were suppressed by cCa(2+) chelation or L- and T-VOC blockade while being mostly reproduced by ionomycin. In the same experimental conditions, the activation of Ras, the phosphorylation of ERK1/2 and PKCα, and the stimulation of Ank promoter activity were affected similarly. Activation of SP1 (specific protein 1) and ELK-1 (Ets-like protein-1) transcription factors supported the regulatory role of Ca(2+). SP1 or ELK-1 overexpression or blockade experiments demonstrated a major contribution of ELK-1, which acted synergistically with SP1 to activate Ank promoter in response to TGF-β1. TGF-β1 promotes input of eCa(2+) through opening of L- and T-VOCs, to potentiate ERK1/2 and PKCα signaling cascades, resulting in an enhanced activation of Ank promoter and ePP(i) production in chondrocyte.

Muscone protects vertebral end-plate degeneration by antiinflammatory property

Most chronic neck pain is the result of degeneration of the cervical spine. IL-1beta may play an important role in intervertebral disc degeneration. This being the case, inhibiting IL-1beta could provide a therapeutic approach for reducing or preventing disc degeneration. Muscone reportedly relieves pain and suppresses inflammation. Therefore, we asked whether muscone, a potent antiinflammatory agent, could reduce proinflammatory cytokines in vitro (end-plate cartilage cultures) and end-plate degeneration in vivo (a rat model that induces intervertebral disc degeneration). In vitro, muscone reversed IL-1beta-induced upregulation of IL-1beta, tumor necrosis factor alpha, cyclooxygenase 2, inducible nitric oxide synthase, matrix metalloproteinase 13, aggrecanase 2, and nitric oxide and downregulation of Col2alpha1 and aggrecan. Pretreatment with muscone (6.25, 12.5, 25 mumol/L) inhibited the IL-1beta-induced phosphorylation of extracellular signal-regulated kinases 1/2 and c-Jun N-terminal kinase in a dose-dependent manner. In vivo, muscone inhibited the expression of prostaglandin E2, 6-keto-prostaglandin F1alpha, IL-1beta, and tumor necrosis factor alpha and recovered the structural distortion of the degenerative disc. Our findings suggest muscone is a promising agent for treating intervertebral disc degeneration through its antiinflammatory effects.

Cytokine-dependent balance of mitogenic effects in primary human lung fibroblasts related to cyclic AMP signaling and phosphodiesterase 4 inhibition

Interleukin-1beta (IL-1beta) and basic fibroblast growth factor (bFGF) are important regulators of proliferation, and their expression is increased in lungs of patients with asthma, idiopathic pulmonary fibrosis (IPF), or chronic obstructive pulmonary disease (COPD). We investigated the effect of IL-1beta and bFGF on proliferation of human lung fibroblasts and the role of COX-2, PGE(2), and cAMP in this process. Furthermore, the effect of phosphodiesterase (PDE) 3 and 4 inhibition was analyzed. In primary human lung fibroblasts low concentrations of IL-1beta (<10 pg/ml) potentiated the bFGF-induced DNA synthesis, whereas higher concentrations revealed antiproliferative effects. Higher concentrations of IL-1beta-induced COX-2 mRNA and protein associated with an increase in PGE(2) and cAMP, and all of these parameters were potentiated by bFGF. The PDE4 inhibitor piclamilast concentration-dependently reduced proliferation by a partial G1 arrest. The PDE3 inhibitor motapizone was inactive by itself but enhanced the effect of the PDE4 inhibitor. This study demonstrates that bFGF and IL-1beta act in concert to fine-tune lung fibroblast proliferation resulting in amplification or reduction. The antiproliferative effect of IL-1beta is likely attributed to the induction of COX-2, which is further potentiated by bFGF, and the subsequent generation of PGE(2) and cAMP. Inhibition of PDE4 inhibition (rather than PDE3) may diminish proliferation of human lung fibroblasts and therefore could be useful in the therapy of pathological remodeling in lung diseases.

Dynamic compression alters NFkappaB activation and IkappaB-alpha expression in IL-1beta-stimulated chondrocyte/agarose constructs

OBJECTIVE AND DESIGN

Determine the effect of IL-1beta and dynamic compression on NFkappaB activation and IkappaB-alpha gene expression in chondrocyte/agarose constructs.

METHODS

Constructs were cultured under free-swelling conditions or subjected to dynamic compression for up to 360 min with IL-1beta and/or PDTC (inhibits NFkappaB activation). Nuclear translocation of NFkappaB-p65 was analysed by immunofluoresence microscopy. Gene expression of IkappaB-alpha, iNOS, IL-1beta and IL-4 was assessed by real-time qPCR.

RESULTS

Nuclear translocation of NFkappaB-p65 was concomitant with an increase in nuclear fluorescence intensity which reached maximum values at 60 min with IL-1beta (p < 0.001). Dynamic compression or PDTC reduced nuclear fluorescence and NFkappaB nuclear translocation in cytokine-treated constructs (p < 0.001 and p < 0.01 respectively). IL-1beta increased IkappaB-alpha expression (p < 0.001) at 60 min and either induced iNOS (p < 0.001) and IL-1beta (p < 0.01) or inhibited IL-4 (p < 0.05) expression at 360 min. These time-dependent events were partially reversed by dynamic compression or PDTC (p < 0.01) with IL-1beta. Co-stimulation by dynamic compression and PDTC favoured suppression (IkappaB-alpha, iNOS, IL-1beta) or induction (IL-4) of gene expression.

CONCLUSIONS

NFkappaB is one of the key players in the mechanical and inflammatory pathways, and its inhibition by a biophysical/therapeutic approach could be a strategy for attenuating the catabolic response in osteoarthritis.

Dynamic compression counteracts IL-1beta induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.

Methods

Chondrocyte/agarose constructs were cultured under free-swelling conditions with or without IL-1β and/or SB203580 (inhibitor of p38 MAPK) for up to 48 hours. Using a fully characterized bioreactor system, constructs were subjected to dynamic compression for 6, 12 and 48 hours under similar treatments. The activation or inhibition of p38 MAPK by IL-1β and/or SB203580 was analyzed by western blotting. iNOS, COX-2, aggrecan and collagen type II signals were assessed utilizing real-time quantitative PCR coupled with molecular beacons. Release of nitrite and PGE₂ was quantified using biochemical assays. Two-way analysis of variance and the post hoc Bonferroni-corrected t-test were used to examine data.

Results

IL-1β activated the phosphorylation of p38 MAPK and this effect was abolished by SB203580. IL-1β induced a transient increase in iNOS expression and stimulated the production of nitrite release. Stimulation by either dynamic compression or SB203580 in isolation reduced the IL-1β induced iNOS expression and nitrite production. However, co-stimulation with both dynamic compression and SB203580 inhibited the expression levels of iNOS and production of nitrite induced by the cytokine. IL-1β induced a transient increase in COX-2 expression and stimulated the cumulative production of PGE₂ release. These effects were inhibited by dynamic compression or SB203580. Co-stimulation with both dynamic compression and SB203580 restored cytokine-induced inhibition of aggrecan expression. This is in contrast to collagen type II, in which we observed no response with the cytokine and/or SB203580.

Conclusion

These data suggest that dynamic compression directly influences the expression levels of iNOS and COX-2. These molecules are current targets for pharmacological intervention, raising the possibility for integrated pharmacological and biophysical therapies for the treatment of cartilage joint disorders.

Chondrocyte signaling and artificial matrices for articular cartilage engineering

Chondrocytes depend on their environment to aid in their expression of appropriate proteins. It has been found that the interaction of integrin receptors with chondrocytes effects the production of extracellular molecules such as type II collagen and aggrecan. Additionally, the presence of growth factors such as IGF-1, TGF-beta1 and BMP-7 induce various signaling pathways that also aid in transducing phenotypic expressions by chondrocytes. Natural and synthetic polymers have been used to act as a scaffold for chondrocytes. The production of extracellular matrix proteins by chondrocytes has been studied. As tissue engineers, it is advantageous to explore the possibility of how altering biomaterial properties affect the signaling cascades by activation of receptors and transduction through the cytoplasm. This vital information will be able to aid in the future of engineering an appropriate biomaterial that can incorporate chondrocytes to act as a scaffold for articular cartilage.

Interleukin-1beta impairment of transforming growth factor beta1 signaling by down-regulation of transforming growth factor beta receptor type II and up-regulation of Smad7 in human articular chondrocytes

OBJECTIVE

Extracellular matrix deposition is tightly controlled by a network of regulatory cytokines. Among them, interleukin-1beta (IL-1beta) and transforming growth factor beta1 (TGFbeta1) have been shown to play antagonistic roles in tissue homeostasis. The purpose of this study was to determine the influence of IL-1beta on TGFbeta receptor type II (TGFbetaRII) regulation and TGFbeta1 responsiveness in human articular chondrocytes.

METHODS

TGFbeta1-induced gene expression was analyzed through plasminogen activator inhibitor 1 and p3TP-Lux induction. Receptor-activated Smad (R-Smad) phosphorylation, TGFbeta receptors, and Smad expression were determined by Western blotting and real-time reverse transcription-polymerase chain reaction techniques. Signaling pathways were investigated using specific inhibitors, messenger RNA (mRNA) silencing, and expression vectors.

RESULTS

IL-1beta down-regulated TGFbetaRII expression at both the protein and mRNA levels and led to inhibition of the TGFbeta1-induced gene expression and Smad2/3 phosphorylation. Moreover, IL-1beta strongly stimulated the expression of inhibitory Smad7. TGFbetaRII overexpression abolished the loss of TGFbeta1 responsiveness induced by IL-1beta. The decrease in TGFbetaRII required de novo protein synthesis and involved both the NF-kappaB and JNK pathways.

CONCLUSION

We demonstrate that IL-1beta impairs TGFbeta1 signaling through down-regulation of TGFbetaRII, which is mediated by the p65/NF-kappaB and activator protein 1/JNK pathways, and secondarily through the up-regulation of Smad7. These findings show that there is cross-talk in the signaling of 2 regulatory cytokines involved in inflammation.

Beta-endorphin regulation of MAPKs in cultured human articular chondrocytes: MAPK inhibitors prevent the increase of IL-1 beta protein levels during beta-endorphin stimulation

We investigated the effect of beta-endorphin on the activities of mitogen-activated protein kinases in cultured human articular chondrocytes in order to elucidate its effect on cartilage. Monolayer cultures of chondrocytes obtained from patients undergoing total knee arthroplasty were treated with 60, 600, or 6000 ng/ml beta-endorphin, or 100 ng/ml naltrexone combined with 600 ng/ml beta-endorphin. The regulation of three major mitogen-activated protein kinases phosphorylation, ERKp44/p42, p38, and JNK, was determined by Western blotting. We also examined the influence of specific mitogen-activated protein kinase inhibitors on IL-1 beta protein levels during beta-endorphin stimulation. The results demonstrate that beta-endorphin, dependent on concentration and duration of stimulation, significantly affected the activation of the three mitogen-activated protein kinases in cultured human articular chondrocytes. Naltrexone in some cases significantly regulated the mitogen-activated protein kinases in different ways when added to beta-endorphin 600 ng/ml. Furthermore, specific mitogen-activated protein kinase inhibitors hindered the increase of IL-1 beta during beta-endorphin incubation. The effect of beta-endorphin seen in this study is considered critical for the production of several mediators of cartilage damage in an arthritic joint.

Hyperosmotic stress-induced apoptotic signaling pathways in chondrocytes

Articular chondrocytes have a well-developed osmoregulatory system that enables cells to survive in a constantly changing osmotic environment. However, osmotic loading exceeding that occurring under physiological conditions severely compromises chondrocyte function and leads to degenerative changes. The aim of the present study was to investigate the form of cell death and changes in apoptotic signaling pathways under hyperosmotic stress using a primary chondrocyte culture. Cell viability and apoptosis assays performed with annexin V and propidium iodide staining showed that a highly hyperosmotic medium (600 mOsm) severely reduced chondrocyte viability and led mainly to apoptotic cell death, while elevating osmotic pressure within the physiological range caused no changes compared to isosmotic conditions. Western blot analysis revealed that a 600 mOsm hyperosmotic environment induced the activation of proapoptotic members of the mitogen-activated protein kinase family such as c-Jun N-terminal kinase (JNK) and p38, and led to an increased level of extracellular signal regulated kinase (ERK1/2). Hyperosmotic stress also induced the activation of caspase-3. In summary, our results show that hyperosmotic stress leads to mainly apoptotic cell death via the involvement of proapoptotic signaling pathways in a primary chondrocyte culture.

Toll-like receptors and chondrocytes: The lipopolysaccharide-induced decrease in cartilage matrix synthesis is dependent on the presence of toll-like receptor 4 and antagonized by bone morphogenetic protein 7

OBJECTIVE

To assess the presence of Toll-like receptors (TLRs) 1-9 in human articular cartilage, and to investigate the effects of lipopolysaccharide (LPS)-induced activation of TLR-4 on biosynthetic activity and matrix production by human articular chondrocytes.

METHODS

TLRs 1-9 were assessed in human articular cartilage by reverse transcription-polymerase chain reaction (RT-PCR); TLR-4 was also analyzed by Western blotting and immunohistochemistry. Articular chondrocytes were isolated from human donors and from wild-type or TLR-4(-/-) mice. Chondrocyte monolayer cultures were incubated with interleukin-1beta (IL-1beta) and LPS in the absence or presence of bone morphogenetic protein 7 (BMP-7) and IL-1 receptor antagonist (IL-1Ra). Neosynthesis of sulfated glycosaminoglycans (sGAG) was measured by (35)S-sulfate incorporation. Endogenous gene expression of cartilage markers as well as IL-1beta was examined using RT-PCR. The involvement of p38 kinase or p44/42 kinase (ERK-1/2) in LPS-mediated TLR-4 signaling was investigated by immunoblotting, RT-PCR, and sGAG synthesis.

RESULTS

TLRs 1-9 were found on the messenger RNA (mRNA) level in human articular chondrocytes. The presence of TLR-4 was also observed on the protein level. In murine and human articular chondrocytes, but not in chondrocytes derived from TLR-4(-/-) mice, stimulation with LPS resulted in a decrease in total proteoglycan synthesis. IL-1beta mRNA expression was increased by TLR-4 activation, whereas expression of aggrecan and type II collagen was significantly decreased. The presence of BMP-7 and IL-1Ra antagonized the anti-anabolic effects of LPS. Blocking of p38, but not ERK-1/2, resulted in inhibition of both LPS-mediated IL-1beta gene expression and the negative effects of LPS on matrix biosynthesis.

CONCLUSION

These data demonstrate the presence of TLRs in human articular cartilage. The suppressive effects of LPS on cartilage biosynthetic activity are dependent on the presence of TLR-4, are governed, at least in part, by an up-regulation of IL-1beta, and are mediated by p38 kinase. These in vitro data indicate an anti-anabolic effect of TLR-4 in articular chondrocytes that may hamper cartilage repair in various joint diseases.

Goldring M, Moilanen E. Inhibitors of mitogen-activated protein kinases downregulate COX-2 expression in human chondrocytes

Inducible prostaglandin synthase (cyclooxygenase-2, COX-2) is expressed in rheumatoid and osteoarthritic cartilage and produces high amounts of proinflammatory prostanoids in the joint. In the present study we investigated the effects of the inhibitors of mitogen-activated protein kinase (MAPK) pathways Erk1/2, p38, and JNK on COX-2 expression and prostaglandin E2 (PGE2) production in human chondrocytes. Proinflammatory cytokine IL-1beta caused a transient activation of Erk1/2, p38, and JNK in immortalized human T/C28a2 chondrocytes and that was followed by enhanced COX-2 expression and PGE2 production. PD98059 (an inhibitor of Erk1/2 pathway) suppressed IL-1-induced COX-2 expression and PGE2 production in a dose-dependent manner, and seemed to have an inhibitory effect on COX-2 activity. SB203580 (an inhibitor of p38 pathway) but not its negative control compound SB202474 inhibited COX-2 protein and mRNA expression and subsequent PGE2 synthesis at micromolar drug concentrations. SP600125 (a recently developed JNK inhibitor) but not its negative control compound N1-methyl-1,9-pyrazolanthrone downregulated COX-2 expression and PGE2 formation in a dose-dependent manner. SP600125 did not downregulate IL-1-induced COX-2 mRNA expression when measured 2 h after addition of IL-1beta but suppressed mRNA levels in the later time points suggesting post-transcriptional regulation. Our results suggest that activation of Erk1/2, p38, and JNK pathways belongs to the signaling cascades that mediate the upregulation of COX-2 expression and PGE2 production in human chondrocytes exposed to proinflammatory cytokine IL-1beta.

Effects of glucosamine and chondroitin sulfate on mediators of osteoarthritis in cultured equine chondrocytes stimulated by use of recombinant equine interleukin-1beta

OBJECTIVE

To determine whether glucosamine and chondroitin sulfate (CS) at concentrations approximating those achieved in plasma by oral administration would influence gene expression of selected mediators of osteoarthritis in cytokine-stimulated equine articular chondrocytes.

SAMPLE POPULATION

Samples of grossly normal articular cartilage obtained from the metacarpophalangeal joint of 13 horses.

PROCEDURE

Equine chondrocytes in pellet culture were stimulated with a subsaturating dose of recombinant equine interleukin (reIL)-1beta. Effects of prior incubation with glucosamine (2.5 to 10.0 microg/mL) and CS (5.0 to 50.0 microg/mL) on gene expression of matrix metalloproteinase (MMP)-1, -2, -3, -9, and -13; aggrecanase 1 and 2; inducible nitric oxide synthase (iNOS); cyclooxygenase (COX)-2; nuclear factor kappaB; and c-Jun-N-terminal kinase (JNK) were assessed by use of a quantitative real-time polymerase chain reaction assay.

RESULTS

Glucosamine at a concentration of 10 microg/mL significantly reduced reIL-1beta-induced mRNA expression of MMP-13, aggrecanase 1, and JNK. Reductions in cytokine-induced expression were also observed for iNOS and COX-2. Chondroitin sulfate had no effect on gene expression at the concentrations tested.

CONCLUSIONS AND CLINICAL RELEVANCE

Concentrations of glucosamine similar to those achieved in plasma after oral administration in horses exerted pretranslational regulation of some mediators of osteoarthritis, an effect that may contribute to the cartilage-sparing properties of this aminomonosaccharide. Analysis of results of this study indicated that the influence of CS on pretranslational regulation of these selected genes is limited or lacking.

The regulation of chondrocyte function by proinflammatory mediators: prostaglandins and nitric oxide

Within the mature articular cartilage matrix, which has no blood or nerve supply, chondrocytes show little metabolic activity with low turnover of matrix components. Under conditions of stress because of biomechanical factors, however, chondrocytes are capable of producing mediators that are associated with inflammation, including cytokines such as interleukin-1 and tumor necrosis factor-alpha, which in turn stimulate the production of prostaglandins and nitric oxide. Chondrocytes also express receptors for these mediators, which accumulate at high local concentrations and can act in an autocrine-paracrine fashion to feedback-regulate chondrocyte responses. Prostaglandin E2 can exert catabolic or anabolic effects depending on the microenvironment. Nitric oxide can promote cellular injury and increase chondrocyte susceptibility to cytokine-induced apoptosis. Because cross-talk between these mediators produces complex modulation of catabolic and anabolic pathways, further studies in vitro and in vivo are required to elucidate their precise roles in osteoarthritis.

Cytokines as therapeutic targets for osteoarthritis

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with the aging process. With the exception of anti-inflammatory corticosteroids and nonsteroidal anti-inflammatory drugs which inhibit cyclo-oxygenase-2, the enzyme responsible for prostaglandin biosynthesis in inflammation, no specific therapy based on fundamental intracellular pathways of chondrocytes and synoviocytes exists for the medical management of OA. At the molecular level, OA is characterized by an imbalance between chondrocyte anabolism and catabolism. Disruption of chondrocyte homeostasis primarily affects the cartilage extracellular matrix (ECM), which is responsible for the biomechanical properties of the tissue. Recent evidence has implicated cytokines, among which interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-17 seem most involved in the OA process of cartilage destruction. The primary role of these cytokines is to modulate the expression of matrix metalloproteinases and cartilage ECM proteins. Cartilage repair that could restore the functional integrity of the joint is also impaired because chondrocytes in OA cartilage appear unable to respond to insulin-like growth factor-1 or respond abnormally to transforming growth factor-beta. As these growth factors also modulate cytokine expression, they may prove useful in designing strategies for suppressing 'chondrocyte activation'. Although cytokines and growth factors provide a potential therapeutic target for OA, it will be necessary to elucidate the fundamental mechanisms that cytokines employ to cause chondrocyte and synoviocyte dysfunction before 'anti-cytokine' therapy can be employed in the medical management of the disease.

Inhibition of MEK/ERK 1/2 pathway reduces pro-inflammatory cytokine interleukin-1 expression in focal cerebral ischemia

It has been proposed that mitogen-activated protein kinase (MAPK) pathways may play a role in the regulation of pro-inflammatory cytokines, such as interlukine-1, during cerebral ischemia. Our previous study showed that extracellular-signal-regulated kinases 1 and 2 (ERK 1/2) were activated during focal cerebral ischemia in mice [J. Cereb. Blood Flow Metab. 20 (2000) 1320]. However, the effect of ERK 1/2 activation in focal cerebral ischemia is still unclear. In this study we reported that in vivo phospho-ERK 1/2 expression increased following 30 min of middle cerebral artery occlusion (MCAO) in the mouse brain in both the ischemic core and perifocal regions. Western blot analysis and immunohistochemistry demonstrated that pro-treatment with 1,4-diamino-2,3-dicyano-1,4-bis butadiene (U0126) [J. Biol. Chem. 273 (1998) 18623] could significantly inhibit mouse brain phospho-MEK 1/2 and phospho-ERK 1/2 expression after 1-2 h of MCAO (p<0.05). Compared to the control group of mice, brain infarct volume was significantly decreased after 24 h of MCAO in the U0126-treated mice (27+/-6 vs. 46+/-9 mm(2), p<0.05). Inhibition of the MEK/ERK 1/2 pathway also prevented downstream kinase Elk-1 phosphorylation, and further reduced cytokine IL-1beta mRNA, but not TNFalpha, IL-1alpha, or chemokine MIP-1alpha mRNA expression. Our data demonstrates that in vivo the close linking of MEK 1/2, ERK 1/2, Elk-1, and IL-1 mRNA expression in the cerebral ischemia animals suggests that ERK 1/2 pathway activation is important in pro-inflammatory cytokine IL-1beta signaling, which induces an inflammatory response and exacerbates ischemic brain injury. Inhibiting the ERK 1/2 pathway may therefore provide a novel approach for the reduction of ischemia-induced IL-1beta overexpression.

Mechanical regulation of mitogen-activated protein kinase signaling in articular cartilage

Articular chondrocytes respond to mechanical forces by alterations in gene expression, proliferative status, and metabolic functions. Little is known concerning the cell signaling systems that receive, transduce, and convey mechanical information to the chondrocyte interior. Here, we show that ex vivo cartilage compression stimulates the phosphorylation of ERK1/2, p38 MAPK, and SAPK/ERK kinase-1 (SEK1) of the JNK pathway. Mechanical compression induced a phased phosphorylation of ERK consisting of a rapid induction of ERK1/2 phosphorylation at 10 min, a rapid decay, and a sustained level of ERK2 phosphorylation that persisted for at least 24 h. Mechanical compression also induced the phosphorylation of p38 MAPK in strictly a transient fashion, with maximal phosphorylation occurring at 10 min. Mechanical compression stimulated SEK1 phosphorylation, with a maximum at the relatively delayed time point of 1 h and with a higher amplitude than ERK1/2 and p38 MAPK phosphorylation. These data demonstrate that mechanical compression alone activates MAPK signaling in intact cartilage. In addition, these data demonstrate distinct temporal patterns of MAPK signaling in response to mechanical loading and to the anabolic insulin-like growth factor-I. Finally, the data indicate that compression coactivates distinct signaling pathways that may help define the nature of mechanotransduction in cartilage.

Chondrocyte response to growth factors is modulated by p38 mitogen-activated protein kinase inhibition

Inhibitors of p38 mitogen-activated protein kinase (MAPK) diminish inflammatory arthritis in experimental animals. This may be effected by diminishing the production of inflammatory mediators, but this kinase is also part of the IL-1 signal pathway in articular chondrocytes. We determined the effect of p38 MAPK inhibition on proliferative and synthetic responses of lapine chondrocytes, cartilage, and synovial fibroblasts under basal and IL-1-activated conditions.

Basal and growth factor-stimulated proliferation and proteoglycan synthesis were determined in primary cultures of rabbit articular chondrocytes, first-passage synovial fibroblasts, and cartilage organ cultures. Studies were performed with or without p38 MAPK inhibitors, in IL-1-activated and control cultures. Media nitric oxide and prostaglandin E₂ were assayed.

p38 MAPK inhibitors blunt chondrocyte and cartilage proteoglycan synthesis in response to transforming growth factor beta; responses to insulin-like growth factor 1 (IGF-1) and fetal calf serum (FCS) are unaffected. p38 MAPK inhibitors significantly reverse inhibition of cartilage organ culture proteoglycan synthesis by IL-1. p38 MAPK inhibition potentiated basal, IGF-1-stimulated and FCS-stimulated chondrocyte proliferation, and reversed IL-1 inhibition of IGF-1-stimulated and FCS-stimulated DNA synthesis. Decreases in nitric oxide but not prostaglandin E₂ synthesis in IL-1-activated chondrocytes treated with p38 MAPK inhibitors are partly responsible for this restoration of response. Synovial fibroblast proliferation is minimally affected by p38 MAPK inhibition.

p38 MAPK activity modulates chondrocyte proliferation under basal and IL-1-activated conditions. Inhibition of p38 MAPK enhances the ability of growth factors to overcome the inhibitory actions of IL-1 on proliferation, and thus could facilitate restoration and repair of diseased and damaged cartilage.

Glutathione mediates LPS-stimulated COX-2 expression via early transient p42/44 MAPK activation

This study examines whether endotoxin (LPS)-stimulated COX-2 is modulated by an interaction between mitogen activated protein kinases (MAPK) and intracellular glutathione. Bovine pulmonary artery endothelial cells (BPAEC) were pretreated for 30 min with the following prior to addition of 0.1 microg/ml endotoxin in 2% FBS in medium 199: 5 mM N-acetylcysteine (NAC) or 5 mM glutathione ethyl ester (GSE) (modulators of intracellular glutathione); 10 microM SB203580 or 25 microM PD98059 (inhibitors of p38 and p42/44 MAPKs, respectively). End-points included assessment of COX-1 and COX-2 gene expression by reverse transcription polymerase chain reaction (RT-PCR); COX-1, COX-2, p38, and p42/44 protein by Western analysis; and measurement of PGE2 and 6-keto-PGF1alpha releases by GC/MS. Both GSE and NAC resulted in significant exacerbation of the LPS-stimulated increase in COX-2 gene and protein expression and prostaglandin release, and suppressed the LPS-induced decrease in COX-1. LPS caused a biphasic activation of p42/44 MAPKs, an early increase peaking at 30 min and a second sustained phase, lasting up to 24 h; LPS also caused an early and sustained increase p38 MAPK activity. Pretreatment of cells with either GSE or NAC increased the early LPS-stimulated activation of p42/44 but had little effect on the sustained phase. Inhibition of either p38 or p42/44 MAPKs suppressed LPS-stimulated COX-2 gene and protein expression, and prostaglandin release (P<0.05) but had little effect on COX-1. We conclude that intracellular glutathione modulates LPS-stimulated COX-2 gene expression and prostaglandin synthesis in BPAEC via early activation of p42/44 MAPKs.

Microenvironment regulation of extracellular signal-regulated kinase activity in chondrocytes: effects of culture configuration, interleukin-1, and compressive stress

OBJECTIVE

To compare extracellular signal-regulated kinase (ERK) activity in response to interleukin-1 (IL-1) in chondrocytes under various culture configurations designed for the study of cartilage biology and repair, and also in response to dynamic load for chondrocytes in cartilage.

METHODS

Isolated bovine articular chondrocytes were maintained in serum-supplemented medium under 4 culture configurations: high-density monolayer, attached to a cut surface of cartilage, within tissue-engineered constructs, or within intact cartilage explants. Samples were subjected to a change of medium with or without IL-1. Cartilage explants were also subjected to dynamic compression.

RESULTS

In chondrocyte monolayers, both basal and IL-1-stimulated ERK activities were similarly elevated at 0.5 hours after medium change, diminishing by 74% after 16 hours. In contrast, chondrocytes in other culture configurations exhibited lower basal levels of ERK activity and a moderate activation of ERK in response to IL-1 that was sustained over the 16-hour treatment time. The dynamic component of loading of cartilage explants led to a 5-fold activation of ERK, compared with free-swelling controls, that was indistinguishable from the effects of IL-1.

CONCLUSION

ERK signaling in response to IL-1 in chondrocyte monolayers exhibited a pattern that was distinct from that in other culture systems, suggesting that the extracellular matrix plays an important regulatory role in modulating the response to extracellular stimuli. Since IL-1 and dynamic loading have distinct effects on chondrocyte biosynthesis, signaling pathways other than ERK participate in the chondrocyte responses to these stimuli.

Basic FGF mediates an immediate response of articular cartilage to mechanical injury

The extracellularly regulated kinase (ERK), one of the three types of mitogen-activated kinases, was rapidly activated after cutting porcine articular cartilage either when maintained as explants or in situ. Cutting released a soluble ERK-activating factor from the cartilage, which was purified and identified by MS as basic fibroblast growth factor (bFGF). Experiments with neutralizing Abs to bFGF and an FGFR1 tyrosine kinase inhibitor showed that this growth factor was the major ERK-activating factor released after injury. Treating cartilage with the heparin-degrading enzyme heparitinase also caused release of bFGF, suggesting the presence of an extracellular store that is sequestered in the matrix and released upon damage. Basic FGF induced the synthesis of a number of chondrocyte proteins including matrix metalloproteinases 1 and 3, tissue inhibitor of metalloproteinases-1, and glycoprotein 38, which were identified by MS. The strong induction of matrix metalloproteinases and tissue inhibitor of metalloproteinases-1 suggests that bFGF could have a role in remodeling damaged tissue.

Inhibition of interleukin-1-stimulated MAP kinases, activating protein-1 (AP-1) and nuclear factor kappa B (NF-kappa B) transcription factors down-regulates matrix metalloproteinase gene expression in articular chondrocytes

Interleukin-1 (IL-1), the main cytokine instigator of cartilage degeneration in arthritis, induces matrix metalloproteinase-3 (MMP-3) and MMP-13 RNA and protein in chondrocytes. The molecular mechanisms of this induction were investigated with specific inhibitors of mitogen-activated protein kinase (MAPK) signaling pathways and activating protein (AP-1) and nuclear factor kappa B (NF-kappa B) transcription factors. IL-1 rapidly induced the activation of extracellular-signal regulated kinase (ERK), protein 38 (p38) and c-Jun N-terminal kinase (JNK) MAPKs in the first-passage human femoral head OA chondrocytes. The ERK-MAPK pathway inhibitor, PD98059, attained 46-53% (MMP-3) and 59-66% (MMP-13) inhibition of RNA induction in human OA and 47-52% (MMP-3) and 69-73% (MMP-13) inhibition in bovine chondrocytes. U0126 conferred 37-77% (MMP-3) and 43-73% (MMP-13) suppression in human and 77-100% (MMP-3) and 96-100% (MMP-13) in bovine chondrocytes. P38 and JNK inhibitor, SB203580 caused 35-37% reduction of MMP-3 and MMP-13 RNA in human and 36-46% (MMP-3) and 60-88% (MMP-13) in bovine chondrocytes. Inhibitor of JNK, AP-1 and NF-kappa B, curcumin, achieved 48-99% suppression of MMP-3 and 45-97% of MMP-13 in human and 8-100% (MMP-3) and 32-100% (MMP-13) in bovine chondrocytes. NF-kappaB inhibitor, pyrrolidine dithiocarbamate yielded 83-84% reduction of MMP-3 and 38-55% for MMP-13 in human chondrocytes. In bovine chondrocytes, the induction decreased by 54-64% for MMP-3 and 74-93% for MMP-13 RNA. These results suggest the involvement of MAPKs, AP-1 and NF-kappa B transcription factors in the IL-1 induction of MMPs in chondrocytes. Inhibition of IL-1 signal transduction by these agents could be useful for reducing cartilage resorption by MMPs in arthritis.

Differentiation regulates interleukin-1beta-induced cyclo-oxygenase-2 in human articular chondrocytes: role of p38 mitogen-activated protein kinase

Chondrocyte dedifferentiation has been noted in osteoarthritic cartilage, but the contribution of this phenomenon is poorly understood. Interleukin (IL)-1beta, the major pro-inflammatory cytokine found in osteoarthritic synovial fluid, induces the dedifferentiation of cultured articular chondrocytes, whereas E-series prostaglandins (PGE) are capable of inducing cell differentiation. Since PGE(2) synthesis is up-regulated by IL-1beta, we addressed the question of whether the state of chondrocyte differentiation may influence the production of IL-1-induced PGE(2) by modulating cyclooxygenase (COX)-2 expression. Immortalized human articular chondrocytes, (tsT/AC62) cultured in monolayer after passage through alginate matrix (alg+) produced 5-fold greater amounts of PGE(2) than continuous monolayer cultures (alg-) after stimulation with IL-1beta. Moreover, IL-1beta induced COX-2 expression at 0.01 ng/ml in (alg+) cells, whereas a 100-fold higher dose of cytokine was necessary for stimulation in (alg-) cells. SB203580, a selective p38 mitogen-activated protein kinase (MAPK) inhibitor, completely abolished the IL-1beta-induced COX-2 mRNA. Overexpression of p38 MAPK induces a COX-2 reporter, whereas overexpression of dominant negative p38 MAPK represses IL-1beta-induced promoter expression. Interestingly, IL-1beta-induced p38 MAPK activity was greatly enhanced in (alg+) compared with (alg-) cells. Our results suggest that differentiated articular chondrocytes are highly responsive to IL-1beta and that p38 MAPK mediates this response by inducing COX-2 gene expression.

Role of mitogen-activated protein kinases and tyrosine kinases on IL-1-Induced NF-kappaB activation and iNOS expression in bovine articular chondrocytes

Nitric oxide (NO), produced by the inducible isoform of the NO synthase (iNOS), plays an important role in the pathophysiology of arthritic diseases. This work aimed at elucidating the role of the mitogen-activated protein kinases (MAPK), p38MAPK and p42/44MAPK, and of protein tyrosine kinases (PTK) on interleukin-1beta (IL-1)-induced iNOS expression in bovine articular chondrocytes. The specific inhibitor of the p38MAPK, SB 203580, effectively inhibited IL-1-induced iNOS mRNA and protein synthesis, as well as NO production, while the specific inhibitor of the p42/44MAPK, PD 98059, had no effect. These responses to IL-1 were also inhibited by treatment of the cells with the tyrosine kinase inhibitors, genistein and tyrphostin B42, which also prevented IL-1-induced NF-kappaB activation. The p38MAPK inhibitor, SB 203580, had no effect on IL-1-induced NF-kappaB activation. Finally, the p42/44MAPK inhibitor, PD 98059, prevented IL-1-induced AP-1 activation in a concentration that did not inhibit iNOS expression. In conclusion, this study shows that (1) PTK are part of the signaling pathway that leads to IL-1-induced NF-kappaB activation and iNOS expression; (2) the p38MAPK cascade is required for IL-1-induced iNOS expression; (3) the p42/44MAPK and AP-1 are not involved in IL-1-induced iNOS expression; and (4) NF-kappaB and the p38MAPK lie on two distinct pathways that seem to be independently required for IL-1-induced iNOS expression. Hence, inhibition of any of these two signaling cascades is sufficient to prevent iNOS expression and the subsequent production of NO in articular chondrocytes.

Differential involvement of p38 mitogen-activated protein kinase and phosphatidyl inositol 3-kinase in the IL-1-mediated NF-κB and AP-1 activation

Interleukin-1 (IL-1) is a central regulator of the immune and inflammatory responses by which various inflammatory genes are induced. Although IL-1 signaling is known to involve PI3-kinase, p38 mitogen-activated protein (MAP) kinase and extracellular signal-regulated kinase (ERK), the crosstalk of these kinases on the IL-1-mediated signal transduction is not clear. We used two specific inhibitors, SB203580 which selectively inhibits p38 MAP kinase and LY294002 which inhibits PI3-kinase, respectively, to explore the involvement of these kinases in the IL-1-induced NF-kappa B activation, using a human glioblastoma cell line, T98G. Two kinase inhibitors decreased IL-1-induced IL-8 mRNA and protein levels markedly. IL-1 caused phosphorylation of p38 MAP kinase with concomitant recruitment of PI3-kinase to IL-1 receptor I (IL-1RI) and its activation. In this context, pretreatment of LY294002, but not SB203580, inhibited IL-1-induced NF-kappa B activation significantly. While IL-1 induced-AP-1 activation was moderate, both LY294002 and SB203580 suppressed IL-1-induced AP-1 activation. These observations were prominent particularly in the TRAF6 transfection system, in which overexpression of wild type TRAF6 augmented the IL-1 mediated NF-kappa B and AP-1 activation, while dominant negative TRAF6 construct (delta TRAF6) suppressed these activation. Namely, LY294002 inhibited TRAF6-mediated IL-1-induced NF-kappa B and AP-1 activation markedly, while SB203580 inhibited TRAF6-induced AP-1 activation but not NF-kappa B activation. Above results indicated that both PI3-kinase and p38 MAP kinase are differentially involved in IL-1-induced NF-kappa B and AP-1 activation.

Expression of extracellular matrix genes: transforming growth factor (TGF)-beta1 and ras in tibial fracture healing of lathyritic rats

Experimental osteolathyrism, induced by dietary aminoacetonitrile (AAN), was used to study the effect of altered extracellular matrix on the expression of connective tissue components in long bone healing. AAN inhibits lysyl oxidase, which is needed for the formation of collagen cross-link precursors, and is also shown to act as a regulator of Ras. Fractured tibias in lathyritic rats develop excessive amounts of mechanically weak callus tissue with irregular cartilage and reduced glycosaminoglycan accumulation. Cartilage-specific proteins (collagen types II, IX, and X and aggrecan) were expressed temporally much wider in lathyritic calluses than in the controls, and active transcription was observed even during the fibrous and ossifying stages. Soft connective tissue was still present in 2- and 3-week-old lathyritic calluses and could explain the elevated type III collagen, biglycan, and decorin mRNA levels. Both transforming growth factor (TGF)-beta1 and c-Ha-ras, which control cell growth and differentiation, were upregulated during the cartilaginous stage. The maximal expression of TGF-beta1 preceded that of ras in osteolathyrism.

Inhibition of MAP kinase kinase (MEK) results in an anti-inflammatory response in vivo

The MAP kinase pathway has been well-characterized as a cascade of sequential protein phosphorylation events leading to the upregulation of a variety of genes in response to growth factors and mitogens. We are interested in the role of these kinases in inflammation and have thus examined their activity in vivo using TPA-induced ear edema in the mouse as a model of inflammation. We show that the activities of both ERK-1 and ERK-2 are upregulated in this model in response to TPA. Increased levels of ERK phosphorylation are measurable as early as 15 min poststimulation and reach a level 8-fold over controls at 4 h. In contrast, minimal activation of JNK or p38 is observed. Topical treatment of ears with the MEK inhibitor, U0126, prevents ERK phosphorylation and ear swelling in a dose-dependent manner in this model. These results suggest that the MEK/ERK pathway is important during an inflammatory response in vivo.

Interleukin-1beta regulates the human brain natriuretic peptide promoter via Ca(2+)-dependent protein kinase pathways

We have shown that interleukin-1beta (IL-1beta) activates the human brain natriuretic peptide (hBNP) promoter via a transcriptional mechanism. Others have reported that changes in intracellular calcium (Ca(2+)) mediate the action of IL-1beta. We questioned whether Ca(2+) and Ca(2+)-dependent pathways mediate IL-1beta regulation of the hBNP promoter in cardiac myocytes. The hBNP promoter (-1818 to +100) coupled to a luciferase cDNA reporter gene was transferred into neonatal cardiac myocytes. Cells were then treated with agents that modify Ca(2+) levels or inhibit Ca(2+)-dependent kinases, and luciferase activity was measured as an index of hBNP promoter activity. The Ca(2+) ionophore A23187 increased hBNP promoter activity; however, neither EGTA nor nifedipine reduced IL-1beta-stimulated promoter activity. Long-term treatment with thapsigargin, which depletes intracellular Ca(2+) stores, decreased basal promoter activity and blocked the effect of IL-1beta. Inhibition of protein kinase C completely blocked IL-1beta-stimulated hBNP promoter activity, whereas inhibition of Ca(2+)/calmodulin-dependent kinase II decreased promoter activity by 40%. In contrast, inhibition of the Ca(2+)-regulated phosphatase calcineurin by cyclosporin A had no effect. These data suggest that (1) Ca(2+) activates the hBNP promoter; (2) release of Ca(2+) from intracellular stores is important to IL-1beta regulation of the hBNP promoter, but transport via voltage-sensitive Ca(2+) channels is not; (3) protein kinase C and Ca(2+)/calmodulin-dependent kinase II mediate the action of IL-1beta; and (4) the phosphatase calcineurin is not involved in IL-1beta regulation of the hBNP promoter. Thus, Ca(2+) and Ca(2+)-dependent pathways are critical to IL-1beta regulation of the hBNP promoter.

Mitogen-activated protein (MAP) kinases are involved in interleukin-1 (IL-1)-induced IL-6 synthesis in osteoblasts: modulation not of p38 MAP kinase, but of p42/p44 MAP kinase by IL-1-activated protein kinase C

We previously reported that interleukin-1alpha (IL-1alpha)-induced activation of protein kinase C (PKC) via phosphatidylcholine-specific phospholipase C (PC-PLC) limits IL-6 synthesis induced by IL-1alpha itself in osteoblast-like MC3T3-E1 cells. In the present study, we further investigated the mechanism behind IL-1alpha-induced IL-6 synthesis in MC3T3-E1 cells. IL-1alpha time-dependently stimulated the phosphorylation of both p42/p44 mitogen-activated protein (MAP) kinase and p38 MAP kinase. PD98059, a specific inhibitor of the upstream kinase that activates p42/p44 MAP kinase, inhibited the IL-1alpha-induced IL-6 synthesis as well as the phosphorylation of p42/p44 MAP kinase induced by IL-1alpha. SB203580, a specific inhibitor of p38 MAP kinase, also reduced both the phosphorylation of p38 MAP kinase and the IL-6 synthesis. 1-Oleoyl-2-acetylglycerol, an activator of PKC, suppressed the IL-1alpha-induced IL-6 synthesis. Calphostin C, a specific inhibitor of PKC, or D-609, a specific inhibitor of PC-PLC, significantly enhanced the IL-1alpha-induced phosphorylation of p42/p44 MAP kinase without affecting the phosphorylation of p38 MAP kinase. The phosphorylation of p42/p44 MAP kinase by IL-1alpha was markedly increased in PKC-down-regulated MC3T3-E1 cells. Neither 12-O-tetradecanoylphorbol-13-acetate, known to be an activator of PKC, nor 1-oleoyl-2-acetylglycerol affected the phosphorylation of p38 MAP kinase induced by IL-1alpha. These results strongly suggest that IL-1alpha-induced IL-6 synthesis is mediated via activations of both p42/p44 MAP kinase and p38 MAP kinase in osteoblasts, and that PKC activated by IL-1alpha itself negatively regulates IL-6 synthesis at a point upstream from p42/p44 MAP kinase.

The interleukin-1 type I receptor is expressed in human hypothalamus

Several lines of evidence suggest that interleukin-1 (IL-1) acts directly on the central nervous system, probably within the hypothalamus, causing effects such as fever, activation of the immune response and sickness behaviour. IL-1 has also been shown to be involved in the aetiology of several neuronal diseases, including neurodegeneration, stroke and Alzheimer's disease. However, the question as to whether the full-length type I IL-1 receptor (IL-1RI) is expressed in the human hypothalamus has yet to be addressed. Using the polymerase chain reaction, we cloned a full-length cDNA encoding the human hypothalamic IL-1RI from human hypothalamic cDNA. The DNA sequence of the human hypothalamic receptor was identical to that of the human fibroblast IL-1RI. The IL-1RI receptor protein was detected in astrocytes of normal human hypothalamic brain sections using immunocytochemical techniques. To ascertain that the cloned receptor was functional, Chinese hamster ovary (CHO) cells were transfected with a plasmid vector containing the IL-1RI coding region. IL-1RI-mediated-signal transduction was assessed by microphysiometry and activation of p38 MAP (mitogen-activated protein) kinase. We report the first demonstration that both the type I IL-1 transcript and the protein are expressed in the human hypothalamus. The receptor was expressed in a stable CHO cell line, providing a tool with which to embark on a thorough analysis of the signalling mechanisms mediated by IL-1 via this receptor.

Redox-sensitive protein phosphatase activity regulates the phosphorylation state of p38 protein kinase in primary astrocyte culture

Reactive oxygen species (ROS) have been implicated as second messengers that activate protein kinase cascades, although the means by which ROS regulate signal transduction remains unclear. In the present study, we show that interleukin 1beta (IL1beta), H2O2, and sorbitol-induced hyperosmolarity mediate a 5- to 10-fold increase in phosphorylation (activation) of the p38 protein kinase in rat primary glial cells as measured by analyses of Western blots using an antibody directed against the dually phosphorylated (active) p38. Additionally, IL1beta was found to elicit H2O2 synthesis in these cells. Concurrent with p38 phosphorylation, all three stimulation paradigms caused an inhibition of protein phosphatase activity. Phenyl-tert-butyl nitrone (PBN), a nitrone-based free radical trap and N-acetyl-cysteine (NAC), a thiol reducing agent, were examined for their effects on the phosphorylation of p38 as well as phosphatase activity. Pretreatment of cells with either PBN or NAC at 1.0 mM suppressed IL1beta H2O2, and sorbitol-mediated activation of p38 and significantly increased phosphatase activity. These data suggest that ROS, particularly H2O2, are used as second messenger substances that activate p38 in part via the transient inactivation of regulatory protein phosphatases.

Interleukin-1beta regulation of the human brain natriuretic peptide promoter involves Ras-, Rac-, and p38 kinase-dependent pathways in cardiac myocytes

Because both the brain natriuretic peptide (BNP) gene and the cytokine interleukin-1beta (IL-1beta) are induced in the infarcted myocardium, localized production of IL-1beta may regulate the BNP gene. We tested whether (1) IL-1beta regulates the human BNP promoter, (2) cis elements in the proximal promoter respond to IL-1beta, and (3) mitogen-activated protein kinase (MAPK) signaling pathways [p42/44, c-jun (JNK) and p38 kinase] are involved. We transferred the hBNP promoter coupled to a luciferase reporter gene or constructs with mutations in the proximal promoter GATA and M-CAT elements into neonatal rat ventricular myocytes and treated the cells with IL-1beta for 24 hours. IL-1beta-stimulated hBNP luciferase activity was eliminated by pretreatment with the transcription inhibitor actinomycin D. Both the p38 kinase inhibitor SB205380 (SB) and cotransfection of a dominant-negative mutant of p38 kinase reduced IL-1beta stimulation of the hBNP promoter. Dominant-negative mutants of Ras and Rac inhibited IL-1beta-stimulated hBNP luciferase activity by 64% and 90%, respectively. Constitutively active forms of Rac and MKK6, the immediate upstream activator of p38, were stimulatory; however, only the effect of MKK6 was inhibited by SB. Neither the p42/44 nor the JNK pathway was involved in the action of IL-1beta. Both IL-1beta and MKK6 activation of the hBNP promoter were partially reduced when the promoter contained a mutated M-CAT element. In summary, (1) IL-1beta is a transcriptional activator of the hBNP promoter; (2) IL-1beta acts through a Ras-dependent pathway not coupled to activation of p42/44 MAPK or JNK; (3) IL-1beta acts through a Rac-dependent pathway, but the downstream effector is not known; and (4) IL-1beta activation of p38 kinase is partially involved in regulation of the hBNP promoter, targeting the proximal M-CAT element.

Interleukin-17-induced gene expression in articular chondrocytes is associated with activation of mitogen-activated protein kinases and NF-kappaB

This study examines intracellular signaling events associated with the activation of chondrocytes by the cytokine interleukin-17 (IL-17). Stimulation of normal human articular chondrocytes with IL-17 induced nitric oxide (NO) production, concomitant with an increase in transcripts and de novo translation products of the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) genes. Several other genes associated with inflammation and cartilage degradation, such as IL-1beta, IL-6, and stromelysin, were also up-regulated in IL-17-treated chondrocytes. Among signaling events displaying early response to IL-17 in chondrocytes were the mitogen-activated protein (MAP) kinases ERK1, ERK2, JNK, and p38. DNA binding activity of NF-kappaB was also significantly induced. IL-17 effects on NO release, as well as iNOS, COX-2, and IL-6 protein expression, were inhibited by the anti-inflammatory drug dexamethasone. Importantly, dexamethasone blunted IL-17-dependent activation of MAP kinases, suggesting a mechanistic relationship between these activities and the aforementioned gene expression responses. Similar effects of a lesser extent were observed with the p38-specific inhibitor SB203580. These results suggest that IL-17 activation of chondrocytes is associated with and depends at least in part on the activation of MAP kinases and NF-kappaB.

SB 203580 Inhibits p38 Mitogen-Activated Protein Kinase, Nitric Oxide Production, and Inducible Nitric Oxide Synthase in Bovine Cartilage-Derived Chondrocytes

Nitric oxide (NO) is implicated in a number of inflammatory processes and is an important mediator in animal models of rheumatoid arthritis and in in vitro models of cartilage degradation. The pyridinyl imidazole SB 203580 inhibits p38 mitogen-activated protein (MAP) kinase in vitro, blocks proinflammatory cytokine production in vitro and in vivo, and is effective in animal models of arthritis. The purpose of this study was to determine whether SB 203580 could inhibit p38 MAP kinase activity, NO production, and inducible NO synthase (iNOS) in IL-1 stimulated bovine articular cartilage/chondrocyte cultures. The results indicated that SB 203580 inhibited both IL-1 stimulated p38 MAP kinase activity in isolated chondrocytes and NO production in bovine chondrocytes and cartilage explants with an IC50 value of approximately 1 μM. To inhibit NO production, SB 203580 had to be present in cartilage explant cultures during the first 8 h of IL-1 stimulation, and activity was lost when it was added 24 h following IL-1. SB 203580 did not inhibit iNOS activity, as measured by the conversion of arginine to citrulline, when added directly to cultures where the enzyme had already been induced, but had to be present during the induction period. Using a 372-bp probe for bovine iNOS we demonstrated inhibition of IL-1-induced mRNA by SB 203580 at both 4 and 24 h following IL-1 treatment. The iNOS mRNA levels were consistent with NO levels in 24-h cell culture supernatants of the IL-1-stimulated bovine chondrocytes used to obtain the RNA.