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

Pathophysiology of psoriasis: recent advances on IL-23 and Th17 cytokines

T helper (Th) 17 cells, a novel T-cell subset, have been implicated in the pathogenesis of psoriasis and other autoimmune inflammatory diseases. Interleukin (IL)-23 stimulates survival and proliferation of Th17 cells, and thus serves as a key master cytokine regulator for these diseases. In psoriasis, IL-23 is overproduced by dendritic cells and keratinocytes, and this cytokine stimulates Th17 cells within dermis to make IL-17A and IL-22. IL-22, in particular, drives keratinocyte hyperproliferation in psoriasis. Future targeting of these key cytokines is likely to lead to dramatic clinical improvement in patients with psoriasis. This review focuses on the numerous recent studies on the roles of IL-23 and Th17 cells in the pathogenesis of psoriasis.

Th17 cells: effector T cells with inflammatory properties

Upon activation, naïve CD4(+) T cells differentiate into effector T cells with specific effector functions and cytokine profiles. The Th1/Th2 paradigm has recently been reevaluated to include a third population of T helper cells, producing IL-17 and designated Th17. The differentiation of Th17 cells requires the coordinate and specific action of the proinflammatory cytokine IL-6 and the immunosuppressive cytokine TGF-beta. In addition, the IL-12 family member IL-23 is involved in the maintenance of these cells. Analogous to other T helper cell subsets, Th17 commitment is initiated by sequential involvement of STAT molecules, i.e. STAT3 downstream of cytokine receptors, and specific transcription factors, i.e. ROR-gammat. Recent data also support the existence of a complex network of cytokines regulating Th17 cells. Clearly, the specific effector functions of Th17 cells expand beyond previously described effects of Th1 and Th2 immunity, with specific roles in host defense against certain pathogens and in organ-specific autoimmunity. The potential dynamics of Th17 cell populations and their interplay with other inflammatory cells in the induction of tissue inflammation in host defense and organ-specific autoimmunity are discussed.

IL-17 enhances chemokine gene expression through mRNA stabilization

IL-17 plays an important role in host defense and autoimmunity via the induction of proinflammatory gene expression, particularly in combination with TNF-alpha. The molecular mechanisms by which IL-17 regulates such expression are not well understood. Using the mouse chemokine CXCL1 (KC) gene as a model, we have examined the effects of IL-17 alone or in combination with TNF-alpha on transcriptional and posttranscriptional events. Although treatment of mouse embryonic fibroblasts with IL-17 alone only modestly increased KC expression, the combination of IL-17 with TNF-alpha induced a synergistic response. IL-17 treatment exerted a strong posttranscriptional effect by extending the t1/2 of the highly unstable, TNF-alpha-induced KC mRNA. Using a tetracycline-regulated transgene in HeLa cells, we determined that IL-17 treatment alone promoted stabilization of KC mRNA in the absence of TNF-alpha. IL-17 treatment exerted little effect on KC transcription or NF-kappaB activation, suggesting that it primarily acts posttranscriptionally. We identified a number of other mRNAs whose t1/2 are prolonged in response to IL-17, suggesting that this is a common mechanism by which IL-17 promotes enhanced gene expression. Finally, activator of NF-kappaB1 protein (Act1), an adaptor protein recently implicated in IL-17 signaling, was necessary for IL-17-induced stabilization, and overexpression of Act1 resulted in stabilization of KC mRNA, indicating that events downstream of Act1 are sufficient to initiate this process. Thus, the synergy between TNF-alpha and IL-17 reflects their independent actions on KC gene expression; TNF-alpha serves as a stimulus to initiate transcription through activation of NF-kappaB, whereas IL-17 drives mRNA stabilization through an Act1-dependent pathway.

A novel heterodimeric cytokine consisting of IL-17 and IL-17F regulates inflammatory responses

CD4+ helper T (TH) cells play crucial roles in immune responses. Recently a novel subset of TH cells, termed TH(IL-17), TH17 or inflammatory TH (THi), has been identified as critical mediators of tissue inflammation. These cells produce IL-17 (also called IL-17A) and IL-17F, two most homologous cytokines sharing similar regulations. Here we report that when overexpressed in 293T cells, IL-17 and IL-17F form not only homodimers but also heterodimers, which we name as IL-17A/F. Fully differentiated mouse THi cells also naturally secrete IL-17A/F as well as IL-17 and IL-17F homodimeric cytokines. Recombinant IL-17A/F protein exhibits intermediate levels of potency in inducing IL-6 and KC (CXCL1) as compared to homodimeric cytokines. IL-17A/F regulation of IL-6 and KC expression is dependent on IL-17RA and TRAF6. Thus, IL-17A/F cytokine represents another mechanism whereby T cells regulate inflammatory responses and may serve as a novel target for treating various immune-mediated diseases.

A role for the cytoplasmic adaptor protein Act1 in mediating IL-17 signaling

Interleukin (IL)-17 (also known as IL-17A) plays an important role in host defense and inflammatory disorders, in part by linking the activation of a subset of T lymphocytes to the mobilization of neutrophils and macrophages. IL-17 exerts its effects both directly and indirectly; the latter by stimulating the production of various chemokines, IL-6, and growth factors from resident cells in the affected tissue. As a result, IL-17 coordinates the innate immune response to extracellular bacteria, which is interesting because IL-17 is produced by several types of T cells that are traditionally regarded as key players in adaptive immunity. Studies have uncovered the function and relevance of a unique subset of CD4(+) T helper (Th) cells that produce IL-17 (Th17 cells), but our understanding of the function of IL-17 receptors (IL-17Rs) and their downstream signaling pathways remains poor. This Review discusses studies that suggest that the cytoplasmic adaptor protein Act1 [nuclear factor-kappaB (NF-kappaB) activator 1] is essential for linking stimulation of IL-17Rs to downstream signaling pathways, and, therefore, that Act1 might play a role in local inflammatory responses. Act1 mediates activation of NF-kappaB and the subsequent production of IL-6 and chemokines that are chemotactic for neutrophils and macrophages. These findings have increased our understanding of host defense against bacteria and indicated a role for Act1 in mediating in chronic inflammatory disease. Future studies on Act1 and IL-17 signaling should contribute to the identification and improved understanding of the mechanisms behind aberrant innate immune responses in chronic inflammatory disease.

IL-17A versus IL-17F induced intracellular signal transduction pathways and modulation by IL-17RA and IL-17RC RNA interference in AGS gastric adenocarcinoma cells

Inflammatory processes are implicated in gastric cancer development. In contrast, the role of inflammation and proinflammatory cytokines in established cancer remains to be clarified. We investigated the contribution of IL-17A versus IL-17F-mediated intracellular signalling pathways in human gastric adenocarcinoma AGS cells. IL-8 secretion was evaluated by ELISA, mitogen-activated protein kinase (MAPK)(4) by Western blotting, and activator protein 1(AP-1) and nuclear factor kappa B (NFkappaB) by TransAM transcription factor assay or qRT-PCR. IL-17RA and IL-17RC inhibition were achieved by small interfering RNA (siRNA). IL-17A significantly induced activation of all three MAPK (ERK, p38 and JNK) and downstream transcription factors AP-1 and p65 NFkappaB. IL-17F was less potent but induced a significant activation of p65 NFkappaB. Consistently, IL-17A was more potent to induce IL-8 secretion than IL-17F. Inhibition of either IL-17RA or IL-17RC expression via siRNA led to near complete abrogation of IL-17A-mediated c-Jun and p65 activation. These data suggest that in gastric cancer, absence of either IL-17RA or IL-17RC can inhibit IL-17 responsiveness. Conversely, downstream of IL-17R binding, IL-17A and IL-17F induce key signal transduction pathways implicated in inflammation and carcinogenesis. IL-17A, and possibly IL-17F, may contribute to amplification and persistence of inflammatory processes implicated in inflammation-associated cancer.

Ultrasound induces cyclooxygenase-2 expression through integrin, integrin-linked kinase, Akt, NF-kappaB and p300 pathway in human chondrocytes

It has been shown that ultrasound (US) stimulation accelerates fracture healing in the animal models and in clinical studies. However, the precise molecular events generated by US in chondrocytes have not been clarified well. Here we found that US stimulation transiently increased the surface expression of alpha2, alpha5, beta1 or beta3 but not alpha3 or alpha4 integrins in human chondrocytes, as shown by flow cytometric analysis. US stimulation increased prostaglandin E(2) formation as well as the protein and mRNA levels of cyclooxygenase-2 (COX-2). At the mechanistic level, anti-integrin beta1 and beta3 antibodies or beta1 and beta3 integrin small interference RNA attenuated the US-induced COX-2 expression. Integrin-linked kinase (ILK) inhibitor (KP-392), Akt inhibitor, NF-kappaB inhibitor (PDTC) or IkappaB protease inhibitor (TPCK) also inhibited the potentiating action of US. US stimulation promotes kinase activity of ILK, phosphorylation of Akt. In addition, US stimulation also induces IKKalpha/beta phosphorylation, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation at Ser(276), p65 and p50 translocation from the cytosol to the nucleus, and kappaB-luciferase activity. The binding of p65 to the NF-kappaB element, as well as the recruitment of p300 and the enhancement of p50 acetylation on the COX-2 promoter was enhanced by US. Taken together, our results provide evidence that US stimulation increases COX-2 expression in chondrocytes via the integrin/ILK/Akt/NF-kappaB and p300 signaling pathway.

Induction of a distinct CD8 Tnc17 subset by transforming growth factor-beta and interleukin-6

Cross-talk between TGF-beta and IL-6 has been shown to direct the differentiation of CD4(+) cells into special IL-17-secreting cells, which are termed Th17 cells. In this study, we demonstrated that TGF-beta and IL-6 could stimulate CD8(+) cells to differentiate into noncytotoxic, IL-17-producing cells in MLC. These IL-17-producing CD8(+) cells exhibit a unique granzyme B(-)IFN-gamma(-)IL-10(-) phenotype. The mRNA level of Th2/T cytotoxic 2 (Tc2) transcription factors GATA3 and Th1/Tc1 transcription factors T-box expressed in T cell (T-bet) as well as its target H2.O-like homeobox (Hlx) is decreased in CD8(+) cells from TGF-beta- and IL-6-treated MLC. In addition, these CD8(+) cells display a marked up-regulation of retinoic acid-related orphan receptor-gammat, a key IL-17 transcription factor. These results demonstrate that the existence of an IL-17-producing CD8(+) subset belongs to neither the Tc1 nor the Tc2 subset and can be categorized as a T noncytotoxic 17 (Tnc17) subset.

Nitric oxide synthase and cyclooxygenase interactions in cartilage and meniscus: relationships to joint physiology, arthritis, and tissue repair

Rheumatoid arthritis and osteoarthritis are painful and debilitating diseases with complex pathophysiology. There is growing evidence that pro-inflammatory cytokines (e.g., interleukin-1 and tumor necrosis factor alpha) and mediators (e.g., prostaglandins, leukotrienes, and nitric oxide) play critical roles in the development and perpetuation of tissue inflammation and damage in joint tissues such as articular cartilage and meniscus. While earlier studies have generally focused on cells of the synovium (especially macrophages), there is increasing evidence that chondrocytes and meniscal cells actively contribute to inflammatory processes. In particular, it is now apparent that mechanical forces engendered by joint loading are transduced to biological signals at the cellular level and that these signals modulate gene expression and biochemical processes. Here we give an overview of the interplay of cytokines and mechanical stress in the production of cyclooxygenases and prostaglandins; lipoxygenases and leukotrienes; and nitric oxide synthases and nitric oxide in arthritis, with particular focus on the interactions of these pathways in articular cartilage and meniscus.

Cells of the synovium in rheumatoid arthritis. T lymphocytes

Recent findings have substantiated the importance of T lymphocytes to the pathogenesis of rheumatoid arthritis (RA). Here, we review emerging data regarding genetic predisposition, spontaneous animal models of arthritis, and cell-cell interactions that implicate T cells as driving synovial inflammation and joint destruction. Information regarding the proinflammatory role of interleukin-17-producing T cells and the functional state of regulatory T cells both in animal models and in patients with RA is also discussed. In light of the overwhelming evidence that disrupted T-cell homeostasis greatly contributes to joint pathology in RA, the therapeutic potential of targeting activators of pro-inflammatory T cells or their products is compelling.

Role of interleukin-17 and interleukin-17-induced cytokines interleukin-6 and interleukin-8 in unstable coronary artery disease

BACKGROUND

Atherosclerosis is a chronic inflammatory disease and interleukins are considered to play a key role in the chronic vascular inflammatory response that is typical of atherosclerosis. The serum levels of several of these cytokines have been found to positively correlate with coronary arterial disease and its sequelae.

AIM

The aim of our study was to evaluate the levels of a comparatively new cytokine IL-17, in patients with stable and unstable coronary artery disease in order to assess whether unstable coronary artery disease patients had higher IL-17 levels.

MATERIALS AND METHODS

We analyzed the concentrations of IL-17, IL-6, IL-8 and IL-10 using enzyme-linked immunosorbent assay and heat-sensitive C-reactive protein using latex particle-enhanced immunoturbidimetry in 58 consecutive unselected patients divided into three groups: stable angina (n=14), unstable angina (n=24) and acute myocardial infarction (n=20). We further compared them with 20 healthy controls. These 58 patients were also angiographically studied and divided into two groups: simple lesion (n=22) and complex lesion (n=36), on the basis of the coronary plaque morphology.

RESULTS

Our results show increased concentrations of the proinflammatory cytokines IL-17, IL-6, IL-8 and heat-sensitive C-reactive protein, and decreased concentration of IL-10 in plasma of unstable angina and acute myocardial infarction patients. Plasma concentration of IL-17 was also positively correlated with plasma concentrations of IL-6 and heat-sensitive C-reactive protein. Our findings further showed that IL-17 values were higher in patients having angiographically visible complex types of lesions but no difference was observed between complex and simple lesion morphology patients.

CONCLUSION

In conclusion, these findings point towards a role of inflammation in the form of increased activity of IL-17, IL-6 and IL-8 in patients of unstable angina and acute myocardial infarction and thus suggest that IL-17-driven inflammation may play a role in the promotion of clinical instability in patients with coronary artery disease.

Changes in gene expression profiles in response to selenium supplementation among individuals with arsenic-induced pre-malignant skin lesions

The molecular basis and downstream targets of oral selenium supplementation in individuals with elevated risk of cancer due to chronic exposure from environmental carcinogens has been largely unexplored. In this study, we investigated genome-wide differential gene expression in peripheral blood mononuclear cells (PBMC) from individuals with pre-malignant arsenic (As)-induced skin lesions before and after 6 months daily oral supplementation of 200 microg L-selenomethionine. The Affymetrix GeneChip Human 133A 2.0 array, containing probes for 22,277 gene transcripts, was used to assess gene expression. Three different normalization methods, RMA (robust multi-chip analysis), GC-RMA and PLIER (Probe logarithmic intensity error), were applied to explore differentially expressed genes. We identified a list of 28 biologically meaningful, significantly differentially expressed genes. Genes up-regulated by selenium supplementation included TNF, IL1B, IL8, SOD2, CXCL2 and several other immunological and oxidative stress-related genes. When mapped to a biological association network, many of the differentially expressed genes were found to regulate functional classes such as fibroblast growth factor, collagenase, matrix metalloproteinase and stromelysin-1, and thus, considered to affect cellular processes like apoptosis, proliferation and others. Many of the significantly up-regulated genes following selenium-supplementation were previously found by us to be down-regulated in a different set of individuals with As-induced skin lesions compared to those without. In conclusion, findings from this study may elucidate the biological effect of selenium supplementation in humans. Additionally, this study suggests that long-term selenium supplementation may revert some of the gene expression changes presumably induced by chronic As exposure in individuals with pre-malignant skin lesions.

Role of mesothelial cell-derived granulocyte colony-stimulating factor in interleukin-17-induced neutrophil accumulation in the peritoneum

Recent studies suggest that peritoneal CD4(+) T lymphocytes may control recruitment of polymorphonuclear leukocytes (PMN) during peritonitis by an interleukin-17 (IL-17)-dependent mechanism. IL-17 and granulocyte colony-stimulating factor (G-CSF) have been proposed to form an axis that regulates PMN transmigration. Here we report on the role of G-CSF released by human peritoneal mesothelial cells (HPMCs) in IL-17A-mediated peritoneal PMN accumulation. In vitro exposure of HPMCs to IL-17A resulted in a time- and dose-dependent release of G-CSF. This effect was related to the induction of G-CSF mRNA and mediated through the nuclear factor-kappaB (NF-kappaB) pathway. The novel observation was that IL-17A-stimulated NF-kappaB activation in HPMCs followed a biphasic profile, with an early induction (45 min), followed by the return to basal levels (90 min), and a delayed induction (3 h). Tumor necrosis factor alpha synergistically amplified IL-17A-induced G-CSF production by enhanced NF-kappaB activation and through stabilization of G-CSF mRNA. Intraperitoneal (i.p.) administration of IL-17A in Balb/c mice resulted in increased local levels of G-CSF and selective PMN accumulation. Administration of anti-G-CSF blocking antibody before IL-17A injection significantly reduced the IL-17A-triggered PMN infiltration. This effect occurred despite increased i.p. levels of PMN-specific chemokines KC and macrophage inflammatory protein-2 seen in animals treated with anti-G-CSF antibody. These data demonstrate that the mesothelium-derived G-CSF plays an important role in IL-17A-induced PMN recruitment into the peritoneum.

Differential regulation of cyclooxygenase-2 and inducible nitric oxide synthase by 4-hydroxynonenal in human osteoarthritic chondrocytes through ATF-2/CREB-1 transactivation and concomitant inhibition of NF-κB signaling cascade

4-hydroxynonenal (HNE), a lipid peroxidation end product, is produced abundantly in osteoarthritic (OA) articular tissues and was recently identified as a potent catabolic factor in OA cartilage. In this study, we provide additional evidence that HNE acts as an inflammatory mediator by elucidating the signaling cascades targeted in OA chondrocytes leading to cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) gene expression. HNE induced COX-2 protein and mRNA levels with accompanying increases in prostaglandin E2 (PGE(2)) production. In contrast, HNE had no effect on basal iNOS expression or nitric oxide (NO) release. However, HNE strongly inhibited IL-1beta-induced iNOS or NO production. Transient transfection experiments revealed that the ATF/CRE site (-58/-53) is essential for HNE-induced COX-2 promoter activation and indeed HNE induced ATF-2 and CREB-1 phosphorylation as well as ATF/CRE binding activity. Overexpression of p38 MAPK enhanced the HNE-induced ATF/CRE luciferase reporter plasmid activation, COX-2 synthesis and promoter activity. HNE abrogated IL-1beta-induced iNOS expression and promoter activity mainly through NF-kappaB site (-5,817/-5,808) possibly via suppression of IKKalpha-induced IkappaBalpha phosphorylation and NF-kappaB/p65 nuclear translocation. Upon examination of upstream signaling components, we found that IKKalpha was inactivated through HNE/IKKalpha adduct formation. Taken together, these findings illustrate the central role played by HNE in the regulation of COX-2 and iNOS in OA. The aldehyde induced selectively COX-2 expression via ATF/CRE activation and inhibited iNOS via IKKalpha inactivation.

The IL-17 cytokine family

IL-17A and its receptor are the founding members of a recently described cytokine family, with unique sequences and functions in the immune system and elsewhere. Consisting of six ligands (IL-17A-F) and five receptors (IL-17RA-IL-17RE) in mammals, these molecules have distinct primary amino acid structures with only minimal homology to other cytokine families. By far the best studied of these cytokines to date are IL-17A and its receptor, IL-17RA. IL-17A is produced primarily by T cells, and is the hallmark cytokine of a newly defined T helper cell subset that appears to be involved in generation of autoimmunity. Despite its production by the adaptive immune system, IL-17A exhibits proinflammatory activities similar to innate immune cytokines such as IL-1beta and TNF-alpha and appears to play important and nonredundant roles in regulating granulocytes in vivo. As a result, IL-17A also plays key roles in host defense. In contrast to the restricted expression of IL-17A, the IL-17RA receptor is ubiquitously expressed, and thus most cells are potential physiological targets of IL-17A. This chapter describes the major molecular properties, biological activities, and known signaling pathways of the IL-17 family, with an emphasis on IL-17A and IL-17RA.

IL-17A induces eotaxin-1/CC chemokine ligand 11 expression in human airway smooth muscle cells: role of MAPK (Erk1/2, JNK, and p38) pathways

Recently, IL-17A has been shown to be expressed in higher levels in respiratory secretions from asthmatics and correlated with airway hyperresponsiveness. Although these studies raise the possibility that IL-17A may influence allergic disease, the mechanisms remain unknown. In this study, we investigated the molecular mechanisms involved in IL-17A-mediated CC chemokine (eotaxin-1/CCL11) production from human airway smooth muscle (ASM) cells. We found that incubation of human ASM cells with rIL-17A resulted in a significant increase of eotaxin-1/CCL11 release from ASM cells that was reduced by neutralizing anti-IL-17A mAb. Moreover, IL-17A significantly induced eotaxin-1/CCL11 release and mRNA expression, an effect that was abrogated with cycloheximide and actinomycin D treatment. Furthermore, transfection studies using a luciferase-driven reporter construct containing eotaxin-1/CCL11 proximal promoter showed that IL-17A induced eotaxin-1/CCL11 at the transcriptional level. IL-17A also enhanced significantly IL-1beta-mediated eotaxin-1/CCL11 mRNA, protein release, and promoter activity in ASM cells. Primary human ASM cells pretreated with inhibitors of MAPK p38, p42/p44 ERK, JNK, or JAK but not PI3K, showed a significant decrease in eotaxin-1/CCL11 release upon IL-17A treatment. In addition, IL-17A mediated rapid phosphorylation of MAPK (p38, JNK, and p42/44 ERK) and STAT-3 but not STAT-6 or STAT-5 in ASM cells. Taken together, our data provide the first evidence of IL-17A-induced eotaxin-1/CCL11 expression in ASM cells via MAPK (p38, p42/p44 ERK, JNK) signaling pathways. Our results raise the possibility that IL-17A may play a role in allergic asthma by inducing eotaxin-1/CCL11 production.

Act1 adaptor protein is an immediate and essential signaling component of interleukin-17 receptor

Interleukin (IL)-17, the founding member of the IL-17 cytokine family, is the hallmark of a novel subset of CD4+ T cells that is regulated by TGFbeta, IL-6, and IL-23. IL-17 plays an important role in promoting tissue inflammation in host defense against infection and in autoimmune diseases. Although IL-17 has been reported to regulate the expression of proinflammatory cytokines, chemokines, and matrix metalloproteinases, the signaling mechanism of IL-17 receptor has not been understood. An earlier study found that IL-17 activates NF-kappaB and MAPK pathways and requires TRAF6 to induce IL-6. However, it is unknown what molecule(s) directly associates with IL-17 receptor to initiate the signaling. We demonstrate here that IL-17 receptor family shares sequence homology in their intracellular region with Toll-IL-1 receptor (TIR) domains and with Act1, a novel adaptor previously reported as an NF-kappaB activator. MyD88 and IRAK4, downstream signaling components of TIR, are not required for IL-17 signaling. On the other hand, Act1 and IL-17 receptor directly associate likely via homotypic interaction. Deficiency of Act1 in fibroblast abrogates IL-17-induced cytokine and chemokine expression, as well as the induction of C/EBPbeta, C/EBPdelta, and IkappaBzeta. Also, absence of Act1 results in a selective defect in IL-17-induced activation of NF-kappaB pathway. These results thus indicate Act1 as a membrane-proximal adaptor of IL-17 receptor with an essential role in induction of inflammatory genes. Our study not only for the first time reveals an immediate signaling mechanism downstream of an IL-17 family receptor but also has implications in therapeutic treatment of various immune diseases.

Corticosteroid and doxycycline suppress MMP-9 and inflammatory cytokine expression, MAPK activation in the corneal epithelium in experimental dry eye

We investigated the effects of corticosteroid and doxycycline on expression of matrix metalloproteinase (MMP)-9 and inflammatory cytokines and activation of mitogen-activated protein kinase (MAPK) signaling pathways, c-jun N-terminal kinases (JNK), extracellular-regulated kinases (ERK) and p38, in experimental murine dry eye. Experimental dry eye (EDE) was created in C57BL6 mice, with or without or topical treatment consisting of 1% methylprednisolone, 0.025% doxycycline or balanced salt solution four times per day. MMP-9 expression in the cornea epithelia was evaluated by laser scanning confocal microscopy. Gelatinase activity in the cornea was evaluated by in situ zymography and MMP-9 activity in tear washings was evaluated by gelatin zymography. Total and phosphorylated MAPKs (JNK1/2, ERK1/2, p38) were detected by Luminex immunobead assay. Levels of MMP-9, interleukin (IL)-1alpha, IL-1beta and tumor necrosis factor (TNF)-alpha RNA transcripts were evaluated by real-time PCR. MMP-9 immunoreactivity was localized to the apical corneal epithelial cell membranes in normal control eyes. Desiccating stress significantly increased production of MMP-9 by the corneal epithelium and increased its activity in the corneal epithelium and tear fluid. Dryness also increased expression of IL-1alpha, IL-1beta and TNF-alpha mRNA and stimulated phosphorylation of JNK1/2, ERK1/2 and p38 MAPKs in the corneal epithelium. Both methylprednisolone and doxycycline reduced expression and activity of MMP-9, decreased levels of inflammatory cytokines transcripts and reduced activation of MAPKs in the corneal epithelium in response to EDE. Desiccating stress stimulates expression of MMP-9, IL-1alpha, IL-1beta and TNF-alpha mRNA , as well as activates MAPK signaling pathways in the corneal epithelium. Both corticosteroid and doxycycline suppressed this molecular stress response.

IL-17A promotes the growth of airway epithelial cells through ERK-dependent signaling pathway

The effects of IL-17A on mucin production and growth of airway epithelial cells were examined. Histological and immunohistochemical analyses revealed that IL-17A increased the mucin production and number of tracheal epithelial cells in air-liquid interface cultures. The biological property of IL-17A to stimulate the mucin production by tracheal epithelial cells was determined using an ELISA. The mitogenic effect of IL-17A on tracheal epithelial cells was confirmed with Calcein-AM assay. The growth-stimulatory effect of IL-17A was dose-dependent and mediated via the ERK MAP kinase pathway. Inhibitors of MEK abrogated the mitogenic effect of IL-17A, whereas an inhibitor of p38 or JNK displayed no significant inhibitory effect. Moreover, relatively lower doses of IL-13 also significantly increased the growth of tracheal epithelial cells through a distinct signaling pathway from that of IL-17A. These findings provide the first evidence that IL-17A stimulates the growth of airway epithelial cells through the ERK MAP kinase pathway.

Gene therapy for cartilage defects

Focal defects of articular cartilage are an unsolved problem in clinical orthopaedics. These lesions do not heal spontaneously and no treatment leads to complete and durable cartilage regeneration. Although the concept of gene therapy for cartilage damage appears elegant and straightforward, current research indicates that an adaptation of gene transfer techniques to the problem of a circumscribed cartilage defect is required in order to successfully implement this approach. In particular, the localised delivery into the defect of therapeutic gene constructs is desirable. Current strategies aim at inducing chondrogenic pathways in the repair tissue that fills such defects. These include the stimulation of chondrocyte proliferation, maturation, and matrix synthesis via direct or cell transplantation-mediated approaches. Among the most studied candidates, polypeptide growth factors have shown promise to enhance the structural quality of the repair tissue. A better understanding of the basic scientific aspects of cartilage defect repair, together with the identification of additional molecular targets and the development of improved gene-delivery techniques, may allow a clinical translation of gene therapy for cartilage defects. The first experimental steps provide reason for cautious optimism.

Interleukin-17 acts independently of TNF-alpha under arthritic conditions

The proinflammatory T cell cytokine IL-17 is a potent inducer of other cytokines such as IL-1 and TNF-alpha. The contribution of TNF in IL-17-induced joint inflammation is unclear. In this work we demonstrate using TNF-alpha-deficient mice that TNF-alpha is required in IL-17-induced joint pathology under naive conditions in vivo. However, overexpression of IL-17 aggravated K/BxN serum transfer arthritis to a similar degree in TNF-alpha-deficient mice and their wild-type counterparts, indicating that the TNF dependency of IL-17-induced pathology is lost under arthritic conditions. Also, during the course of the streptococcal cell wall-induced arthritis model, IL-17 was able to enhance inflammation and cartilage damage in the absence of TNF. Additional blocking of IL-1 during IL-17-enhanced streptococcal cell wall-induced arthritis did not reduce joint pathology in TNF-deficient mice, indicating that IL-1 is not responsible for this loss of TNF dependency. These data provide further understanding of the cytokine interplay during inflammation and demonstrate that, despite a strong TNF dependency under naive conditions, IL-17 acts independently of TNF under arthritic conditions.

Identification of IRF-8 and IRF-1 target genes in activated macrophages

Interferon regulatory factor 1 (IRF-1) and IRF-8, also known as interferon consensus sequence binding protein (ICSBP), are important regulators of macrophage differentiation and function. These factors exert their activities through the formation of heterocomplexes. As such, they are coactivators of various interferon-inducible genes in macrophages. To gain better insights into the involvement of these two transcription factors in the onset of the innate immune response and to identify their regulatory network in activated macrophages, DNA microarray was employed. Changes in the expression profile were analyzed in peritoneal macrophages from wild type mice and compared to IRF-1 and IRF-8 null mice, before and following 4 h exposure to IFN-gamma and LPS. The expression pattern of 265 genes was significantly changed (up/down) in peritoneal macrophages extracted from wild type mice following treatment with IFN-gamma and LPS, while no changes in the expression levels of these genes were observed in samples of the same cell-type from both IRF-1 and IRF-8 null mice. Among these putative target genes, numerous genes are involved in macrophage activity during inflammation. The expression profile of 10 of them was further examined by quantitative RT-PCR. In addition, the promoter regions of three of the identified genes were analyzed by reporter gene assay for the ability to respond to IRF-1 and IRF-8. Together, our results suggest that both IRF-1 and IRF-8 are involved in the transcriptional regulation of these genes. We therefore suggest a broader role for IRF-1 and IRF-8 in macrophages differentiation and maturation, being important inflammatory mediators.

Innervation, inflammation, and hypermobility may characterize pathologic disc degeneration: review of animal model data

Animal models provide important clues to the pathomechanisms of human intervertebral disc degeneration. Previous reviews on this topic have highlighted the fact that loss of nuclear volume (and, consequently, pressure) is a common trigger for tissue-remodeling and anatomic change consistent with degeneration in humans. Unfortunately, a large gap still exists in the medical knowledge base that serves to distinguish symptomatic from asymptomatic degeneration. Because disc degeneration per se is not a basis for clinical intervention, identification of specific features underlying discogenic pain is of the utmost importance to advance the current level of care and identify novel therapeutic targets. This article presents animal-model evidence that pathologic, or painful, degeneration is characterized by ineffective injury-healing of peripheral tissue. Because the disc is only vascularized at the vertebral end plate and the outer part of the anulus, these are the likely sites for focal damage, inflammation, neoinnervation, and nociceptor sensitization. Consequently, while nuclear insufficiency is likely the root of degenerative change, the end plate and peripheral part of the anulus are more likely the source of patient discomfort.

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.

Involvement of TNF Receptor-Associated Factor 6 in IL-25 Receptor Signaling

IL-25 (IL-17E) induces IL-4, IL-5, and IL-13 production from an unidentified non-T/non-B cell population and subsequently induces Th2-type immune responses such as IgE production and eosinophilic airway inflammation. IL-25R is a single transmembrane protein with homology to IL-17R, but the IL-25R signaling pathways have not been fully understood. In this study, we investigated the signaling pathway under IL-25R, especially the possible involvement of TNFR-associated factor (TRAF)6 in this pathway. We found that IL-25R cross-linking induced NF-kappaB activation as well as ERK, JNK, and p38 activation. We also found that IL-25R-mediated NF-kappaB activation was inhibited by the expression of dominant negative TRAF6 but not of dominant negative TRAF2. Furthermore, IL-25R-mediated NF-kappaB activation, but not MAPK activation, was diminished in TRAF6-deficient murine embryonic fibroblast. In addition, coimmunoprecipitation assay revealed that TRAF6, but not TRAF2, associated with IL-25R even in the absence of ligand binding. Finally, we found that IL-25R-mediated gene expression of IL-6, TGF-beta, G-CSF, and thymus and activation-regulated chemokine was diminished in TRAF6-deficient murine embryonic fibroblast. Taken together, these results indicate that TRAF6 plays a critical role in IL-25R-mediated NF-kappaB activation and gene expression.

Up-regulation of CC chemokine ligand 20 expression in human airway epithelium by IL-17 through a JAK-independent but MEK/NF-kappaB-dependent signaling pathway

CCL20, like human beta-defensin (hBD)-2, is a potent chemoattractant for CCR6-positive immature dendritic cells and T cells in addition to recently found antimicrobial activities. We previously demonstrated that IL-17 is the most potent cytokine to induce an apical secretion and expression of hBD-2 by human airway epithelial cells, and the induction is JAK/NF-kappaB-dependent. Similar to hBD-2, IL-17 also induced CCL20 expression, but the nature of the induction has not been elucidated. Compared with a panel of cytokines (IL-1alpha, 1beta, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 18, IFN-gamma, GM-CSF, and TNF-alpha), IL-17 was as potent as IL-1alpha, 1beta, and TNF-alpha, with a time- and dose-dependent phenomenon in stimulating CCL20 expression in both well-differentiated primary human and mouse airway epithelial cell culture systems. The stimulation was largely dependent on the treatment of polarized epithelial cultures from the basolateral side with IL-17, achieving an estimated 4- to 10-fold stimulation at both message and protein levels. More than 90% of induced CCL20 secretion was toward the basolateral compartment (23.02 +/- 1.11 ng/chamber/day/basolateral vs 1.82 +/- 0.82 ng/chamber/day/apical). Actinomycin D experiments revealed that enhanced expression did not occur at mRNA stability. Inhibitor studies showed that enhanced expression was insensitive to inhibitors of JAK/STAT, p38, JNK, and PI3K signaling pathways, but sensitive to inhibitors of MEK1/2 and NF-kappaB activation, suggesting a MEK/NF-kappaB-based mechanism. These results suggest that IL-17 can coordinately up-regulate both hBD-2 and CCL20 expressions in airways through differentially JAK-dependent and -independent activations of NF-kappaB-based transcriptional mechanisms, respectively.

Intra-Articular Injections for Joint Disease in Horses

Lameness remains an important source of reduced performance in many types of horses. Pain referable to joints is among the most common causes, and intra-articular injections remain a common and important means of addressing lameness referable to joints in horses.

Regulation of B7.1 costimulatory molecule is mediated by the IFN regulatory factor-7 through the activation of JNK in lipopolysaccharide-stimulated human monocytic cells

The engagement of CD28 or CTLA-4 with B7.1 provides the essential second costimulatory signal that regulates the development of immune responses, including T cell activation, differentiation, and induction of peripheral tolerance. The signaling molecules and the transcription factors involved in B7.1 regulation are poorly understood. In this study we investigated the role of MAPKs in the regulation of LPS-induced B7.1 expression in human monocytes and the promonocytic THP-1 cells. Our results show that LPS-induced B7.1 expression in monocytic cells did not involve the activation of either p38 or ERKs. Using the JNK-specific inhibitor SP600125, small interfering RNAs specific for JNK1 and JNK2, and agents such as dexamethasone that inhibit JNK activation, we determined that LPS-induced B7.1 expression was regulated by JNK MAPK in both monocytes and THP-1 cells. In addition, we identified a distinct B7.1-responsive element corresponding to the IFN regulatory factor-7 (IRF-7) binding site in the B7.1 promoter responsible for the regulation of LPS-induced B7.1 transcription. Furthermore, SP600125 and dexamethasone inhibited LPS-induced IRF-7 activity. Taken together, these results suggest that LPS-induced B7.1 transcription in human monocytic cells may be regulated by JNK-mediated activation of the IRF-7 transcription factor.

Requirement of IL-17 receptor signaling in radiation-resistant cells in the joint for full progression of destructive synovitis

IL-17 is a proinflammatory cytokine suspected to be involved in inflammatory and autoimmune diseases such as rheumatoid arthritis. In the present study, we report that IL-17R signaling is required in radiation-resistant cells in the joint for full progression of chronic synovitis and bone erosion. Repeated injections of Gram-positive bacterial cell wall fragments (streptococcal cell wall) directly into the knee joint of naive IL-17R-deficient (IL-17R-/-) mice had no effect on the acute phase of arthritis but prevented progression to chronic destructive synovitis as was noted in wild-type (wt) mice. Microarray analysis revealed significant down-regulation of leukocyte-specific chemokines, selectins, cytokines, and collagenase-3 in the synovium of IL-17R-/- mice. Bone marrow (BM) chimeric mice revealed the need for IL-17R expression on radiation-resistant joint cells for destructive inflammation. Chimeric mice of host wt and donor IL-17R-/- BM cells developed destructive synovitis in this chronic reactivated streptococcal cell wall arthritis model similar to wt-->wt chimeras. In contrast, chimeric mice of host IL-17R-/- and donor wt BM cells were protected from chronic destructive arthritis similar as IL-17R-/- -->IL-17R-/- chimeras. These data strongly indicate that IL-17R signaling in radiation-resistant cells in the joint is required for turning an acute macrophage-mediated inflammation into a chronic destructive synovitis.

Carbon monoxide inhibits IL-17-induced IL-6 production through the MAPK pathway in human pulmonary epithelial cells

Interleukin (IL)-17 is a proinflammatory cytokine that is produced by activated memory CD4 T cells, which regulates pulmonary neutrophil emigration by the induction of CXC chemokines and cytokines. IL-17 constitutes a potential target for pharmacotherapy against exaggerated neutrophil recruitment in airway diseases. As a cytoprotective and anti-inflammatory gaseous molecule, carbon monoxide (CO) may also regulate IL-17-induced inflammatory responses in pulmonary cells. Herein, we examine the production of cytokine IL-6 induced by IL-17 and the effect of CO on IL-17-induced IL-6 production in human pulmonary epithelial cell A549. We first show that IL-17 can induce A549 cells to release IL-6 and that CO can markedly inhibit IL-17-induced IL-6 production. IL-17 activated the ERK1/2 MAPK pathway but did not affect p38 and JNK MAPK pathways. CO exposure selectively attenuated IL-17-induced ERK1/ERK2 MAPK activation without significantly affecting either JNK or p38 MAPK activation. Furthermore, in the presence of U0126 and PD-98059, selective inhibitors of MEK1/2, IL-17-induced IL-6 production was significantly attenuated. We conclude that CO inhibits IL-17-stimulated inflammatory response via the ERK1/2-dependent pathway.

Pathophysiological roles for IL-18 in inflammatory arthritis

IL-18 is a unique cytokine with prominently wide spectrum biological actions. Among these, its IFN-gamma/TNF-alpha-inducing activity primarily contributes to the development of various inflammatory diseases including inflammatory arthritis. IL-18 levels correlate with the disease activity of rheumatoid arthritis (RA) and osteoarthritis (OA). IL-18 is spontaneously released from RA synovial cells and OA chondrocytes and seems to participate in the development of the inflammatory and destructive alterations of joints via induction of TNF-alpha, a potent effector molecule. TNF-alpha, in turn, increases IL-18 expression in RA synovial cells. Recent clinical trials have revealed the efficacy of TNF-alpha in RA with a reduction in circulatory IL-18 levels. These may implicate the positive circuit between IL-18 and TNF-alpha for development of RA. As IL-18-deficient mice evade collagen-induced arthritis in a mouse RA model, therapeutics targeting IL-18 may be beneficial against RA/OA. Here, the authors review the possible roles of IL-18 in inflammatory arthritis.

Activation and signaling of the p38 MAP kinase pathway

The family members of the mitogen-activated protein (MAP) kinases mediate a wide variety of cellular behaviors in response to extracellular stimuli. One of the four main sub-groups, the p38 group of MAP kinases, serve as a nexus for signal transduction and play a vital role in numerous biological processes. In this review, we highlight the known characteristics and components of the p38 pathway along with the mechanism and consequences of p38 activation. We focus on the role of p38 as a signal transduction mediator and examine the evidence linking p38 to inflammation, cell cycle, cell death, development, cell differentiation, senescence and tumorigenesis in specific cell types. Upstream and downstream components of p38 are described and questions remaining to be answered are posed. Finally, we propose several directions for future research on p38.

Development of comprehensive functional genomic screens to identify novel mediators of osteoarthritis

OBJECTIVE

The aim of this study was to develop high-throughput assays for the analysis of major chondrocyte functions that are important in osteoarthritis (OA) pathogenesis and methods for high-level gene expression and analysis in primary human chondrocytes.

METHODS

In the first approach, complementary DNA (cDNA) libraries were constructed from OA cartilage RNA and full-length clones were selected. These cDNAs were transferred into a retroviral vector using Gateway Technology. Full-length clones were over-expressed in human articular chondrocytes (HAC) by retroviral-mediated gene transfer. The induction of OA-associated markers, including aggrecanase-1 (Agg-1), matrix metalloproteinase-13 (MMP-13), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), collagen IIA and collagen X was measured by quantitative real-time polymerase chain reaction (QPCR). Induction of a marker gene was verified by independent isolation of 2-3 clones per gene, re-transfection followed by QPCR as well as nucleotide sequencing. In the second approach, whole cDNA libraries were transduced into chondrocytes and screened for chondrocyte cluster formation in three-dimensional agarose cultures.

RESULTS

Using green fluorescent protein (eGFP) as a marker gene, it was shown that the retroviral method has a transduction efficiency of >90%. A total of 40 verified hits were identified in the QPCR screen. The first set of 19 hits coordinately induced iNOS, COX-2, Agg-1 and MMP-13. The most potent of these genes were the tyrosine kinases Axl and Tyro-3, receptor interacting kinase-2 (RIPK2), tumor necrosis factor receptor 1A (TNFR1A), fibroblast growth factor (FGF) and its receptor FGFR, MUS81 endonuclease and Sentrin/SUMO-specific protease 3. The second set of seven hits induced both Agg-1 and MMP-13 but none of the other markers. Five of these seven genes regulate the phosphoinositide-3-kinase pathway. The most potently induced OA marker was iNOS. This marker was induced 20-500 fold by seven genes. Collagen IIA was also induced by seven genes, the most potent being transforming growth factor beta (TGFbeta)-stimulated protein TSC22, vascular endothelial growth factor (VEGF) and splicing factor 3a. This screening assay did not identify inducers of collagen X. The second chondrocyte cluster formation screen identified 14 verified hits. Most of the genes inducing cluster formation were kinases. Additional genes had not been previously known to regulate chondrocyte cluster formation or any other chondrocyte function.

CONCLUSIONS

The methods developed in this study can be applied to screen for genes capable of inducing an OA-like phenotype in chondrocytes on a genome-wide scale and identify novel mediators of OA pathogenesis. Thus, coordinated functional genomic approaches can be used to delineate key genes and pathways activated in complex human diseases such as OA.

Retinoid signaling regulates CTGF expression in hypertrophic chondrocytes with differential involvement of MAP kinases

Retinoids are important for growth plate chondrocyte maturation, but their downstream effectors remain unclear. Recently, CTGF (CCN2) was found to regulate chondrocyte function, particularly in the hypertrophic zone. The goal of the study was to determine whether CTGF is a retinoid signaling effector molecule, how it is regulated, and how it acts.

INTRODUCTION

Using a combination of in vivo and in vitro approaches, we carried out a series of studies at the cellular, biochemical, and molecular level to determine whether and how retinoid signaling is related to expression and function of connective tissue growth factor (CTGF) in chondrocyte maturation and endochondral ossification.

MATERIALS AND METHODS

Limbs of chick embryos in ovo were implanted with retinoic pan-antagonist RO 41-5253-filled beads, and phenotypic changes were assessed by in situ hybridization. CTGF gene expression and roles were tested in primary cultures of immature and hypertrophic chondrocytes. Cross-talk between retinoid signaling and other pathways was tested by determining endogenous levels of active ERK1/2 and p38 MAP kinases and phenotypic modulations exerted by specific antagonists of mitogen-activated protein (MAP) kinases and BMP signaling (Noggin).

RESULTS

Interference with retinoid signaling blocked expression of CTGF and other posthypertrophic markers in long bone anlagen in vivo and hypertrophic chondrocyte cultures, whereas all-trans-retinoic acid (RA) boosted CTGF expression and even induced it in immature proliferating cultures. Exogenous recombinant CTGF stimulated chondrocyte maturation, but failed to do so in presence of retinoid antagonists. Immunoblots showed that hypertrophic chondrocytes contained sizable levels of phosphorylated ERK1/2 and p38 MAP kinases that were dose- and time-dependently increased by RA treatment. Experimental ERK1/2 inhibition led to a severe drop in baseline and RA-stimulated CTGF expression, whereas p38 inhibition increased it markedly. These responses were gene-specific, because the opposite was seen with other hypertrophic chondrocyte genes such as collagen X and RA receptor gamma (RARgamma). Tests with Noggin showed that RA induction of CTGF expression was negatively influenced by BMP signaling, whereas induction of collagen X expression was BMP-dependent.

CONCLUSIONS

Retinoids appear to have a preeminent role in controlling expression and function of CTGF in hypertrophic and posthypertrophic chondrocytes and do so with differential cooperation and intervention of MAP kinases and BMP signaling.

Mithramycin downregulates proinflammatory cytokine-induced matrix metalloproteinase gene expression in articular chondrocytes

Interleukin-1 (IL-1), IL-17 and tumor necrosis factor alpha (TNF-α) are the main proinflammatory cytokines implicated in cartilage breakdown by matrix metalloproteinase (MMPs) in arthritic joints. We studied the impact of an anti-neoplastic antibiotic, mithramycin, on the induction of MMPs in chondrocytes. MMP-3 and MMP-13 gene expression induced by IL-1β, TNF-α and IL-17 was downregulated by mithramycin in human chondrosarcoma SW1353 cells and in primary human and bovine femoral head chondrocytes. Constitutive and IL-1-stimulated MMP-13 levels in bovine and human cartilage explants were also suppressed. Mithramycin did not significantly affect the phosphorylation of the mitogen-activated protein kinases, extracellular signal-regulated kinase, p38 and c-Jun N-terminal kinase. Despite effective inhibition of MMP expression by mithramycin and its potential to reduce cartilage degeneration, the agent might work through multiple unidentified mechanisms.

Interleukin (IL)-17 enhances tumor necrosis factor-alpha-stimulated IL-6 synthesis via p38 mitogen-activated protein kinase in osteoblasts

Inflammatory cytokines are well known to play crucial roles in the pathogenesis of rheumatoid arthritis. Among them, interleukin (IL)-17 is a cytokine that is mainly synthesized by activated T cells and its receptors are present in osteoblasts. The synthesis of IL-6, known to stimulate osteoclastic bone resorption, is reportedly responded to bone resorptive agents such as tumor necrosis factor-alpha (TNF-alpha) in osteoblasts. It has been reported that IL-17 enhances TNF-alpha-stimulated IL-6 synthesis in osteoblast-like MC3T3-E1 cells. We previously showed that sphingosine 1-phosphate (S1-P) mediates TNF-alpha-stimulated IL-6 synthesis in these cells. In the present study, we investigated the mechanism of IL-17 underlying enhancement of IL-6 synthesis in MC3T3-E1 cells. IL-17 induced phosphorylation of p38 mitogen-activated protein (MAP) kinase. SB203580 and PD169316, specific inhibitors of p38 MAP kinase, significantly reduced the enhancement by IL-17 of TNF-alpha-stimulated IL-6 synthesis. IL-17 also amplified S1-P-stimulated IL-6 synthesis, and the amplification by IL-17 was suppressed by SB203580. Anisomycin, an activator of p38 MAP kinase, which alone had no effect on IL-6 level, enhanced the IL-6 synthesis stimulated by TNF-alpha. SB203580 and PD169316 inhibited the amplification by anisomycin of the TNF-alpha-induced IL-6 synthesis. Taken together, our results strongly suggest that IL-17 enhances TNF-alpha-stimulated IL-6 synthesis via p38 MAP kinase activation in osteoblasts.

Triptolide suppresses proinflammatory cytokine-induced matrix metalloproteinase and aggrecanase-1 gene expression in chondrocytes

A hallmark of rheumatoid- and osteoarthritis (OA) is proinflammatory cytokine-induced degeneration of cartilage collagen and aggrecan by matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS). Effects of the Chinese herb, Tripterygium wilfordii Hook F (TWHF), on cartilage and its anti-arthritic mechanisms are poorly understood. This study investigated the impact of a purified derivative of TWHF, PG490 (triptolide), on cytokine-stimulated expression of the major cartilage damaging proteases, MMP-3, MMP-13, and ADAMTS4. PG490 inhibited cytokine-induced MMP-3, MMP-13 gene expression in primary human OA chondrocytes, bovine chondrocytes, SW1353 cells, and human synovial fibroblasts. Triptolide was effective at low doses and blocked the induction of MMP-13 by IL-1 in human and bovine cartilage explants. TWHF extract and PG490 also suppressed IL-1-, IL-17-, and TNF-alpha-induced expression of ADAMTS-4 in bovine chondrocytes. Thus, PG490 could protect cartilage from MMP- and aggrecanase-driven breakdown. The immunosuppressive, cartilage protective, and anti-inflammatory properties could make PG490 potentially a new therapeutic agent for arthritis.

Cytokines link osteoblasts and inflammation: microarray analysis of interleukin-17- and TNF-alpha-induced genes in bone cells

The novel cytokine interleukin (IL)-17 has been implicated in many infectious and autoimmune settings, especially rheumatoid arthritis. Consistent with its proinflammatory effects on bone, osteoblast cells are highly responsive to IL-17, particularly in combination with other inflammatory cytokines. To better understand the spectrum of activities controlled by IL-17, we globally profiled genes regulated by IL-17 and tumor necrosis factor alpha (TNF-alpha) in the preosteoblast cell line MC3T3-E1. Using Affymetrix microarrays, 80-90 genes were up-regulated, and 19-50 genes were down-regulated with IL-17 and TNF-alpha as compared with TNF-alpha alone. These included proinflammatory chemokines and cytokines, inflammatory genes, transcriptional regulators, bone-remodeling genes, signal transducers, cytoskeletal genes, genes involved in apoptosis, and several unknown or unclassified genes. The CXC family chemokines were most dramatically induced by IL-17 and TNF-alpha, confirming the role of IL-17 as a potent mediator of inflammation and neutrophil recruitment. Several transcription factor-related genes involved in inflammatory gene expression were also enhanced, including molecule possessing ankyrin repeats induced by lipopolysaccharide/inhibitor of kappaBzeta (MAIL/kappaBzeta), CCAAT/enhancer-binding protein delta (C/EBPdelta), and C/EBPbeta. We also identified the acute-phase gene lipocalin-2 (LCN2/24p3) as a novel IL-17 target, which is regulated synergistically by TNF-alpha and IL-17 at the level of its promoter. A similar but not identical pattern of genes was induced by IL-17 and TNF-alpha in ST2 bone marrow stromal cells and murine embryonic fibroblasts. This study provides a profile of genes regulated by IL-17 and TNF-alpha in osteoblasts and suggests that in bone, the major function of IL-17 is to cooperate and/or synergize with other cytokines to amplify inflammation.

The role of T-cell interleukin-17 in conducting destructive arthritis: lessons from animal models

Interleukin-17 (IL-17) is a T cell cytokine spontaneously produced by cultures of rheumatoid arthritis (RA) synovial membranes. High levels have been detected in the synovial fluid of patients with RA. The trigger for IL-17 is not fully identified; however, IL-23 promotes the production of IL-17 and a strong correlation between IL-15 and IL-17 levels in synovial fluid has been observed. IL-17 is a potent inducer of various cytokines such as tumor necrosis factor (TNF)-alpha, IL-1, and receptor activator of NF-kappaB ligand (RANKL). Additive or even synergistic effects with IL-1 and TNF-alpha in inducing cytokine expression and joint damage have been shown in vitro and in vivo. This review describes the role of IL-17 in the pathogenesis of destructive arthritis with a major focus on studies in vivo in arthritis models. From these studies in vivo it can be concluded that IL-17 becomes significant when T cells are a major element of the arthritis process. Moreover, IL-17 has the capacity to induce joint destruction in an IL-1-independent manner and can bypass TNF-dependent arthritis. Anti-IL-17 cytokine therapy is of interest as an additional new anti-rheumatic strategy for RA, in particular in situations in which elevated IL-17 might attenuate the response to anti-TNF/anti-IL-1 therapy.

Interleukin-17: the missing link between T-cell accumulation and effector cell actions in rheumatoid arthritis?

The prominence of T cells and monocyte/macrophages in rheumatoid synovium suggests T cells may localize and amplify the effector functions of monocyte/macrophages in rheumatoid disease. However, while T cells are abundant in rheumatoid joints, classic T-cell derived cytokines are scarce, especially when compared to the levels of monokines IL-1 beta and TNF-alpha. For this reason, it has been speculated that monocyte/macrophages may act independently of T cells in rheumatoid disease and that the role of T cells may be more or less irrelevant to core disease mechanisms. The question of T-cell influence requires re-evaluation in light of the characterization of IL-17, a T-cell derived cytokine that is abundant in rheumatoid synovium and synovial fluid. IL-17 has a number of pro-inflammatory effects, both directly and through amplification of the effects of IL-1 beta and TNF-alpha. IL-17 is able to induce expression of pro-inflammatory cytokines and stimulate release of eicosanoids by monocytes and synoviocytes. Furthermore, IL-17 has been implicated in the pathogenesis of inflammatory bone and joint damage through induction of matrix metalloproteinases and osteoclasts, as well as inhibition of proteoglycan synthesis. In animal models of arthritis, intra-articular injection of IL-17 results in joint inflammation and damage. The recognition of IL-17 as a pro-inflammatory T cell derived cytokine, and its abundance within rheumatoid joints, provides the strongest candidate mechanism to date through which T cells can capture and localize macrophage effector functions in rheumatoid arthritis. As such, IL-17 warrants consideration for its potential as a therapeutic target in rheumatoid arthritis.

Protein kinases in chondrocyte signaling and osteoarthritis

Protein kinases, particularly mitogen-activated protein kinases and receptor-tyrosine kinases play crucial roles in mammalian cellular metabolism by regulating intracellular signaling pathways that control proliferation, differentiation, cytokine gene induction and cytokine responsiveness, matrix metalloproteinase gene expression, mechanical transduction, as well as programmed cell death (apoptosis). Many of these pathways are also important components of cartilage homeostasis because alterations in intracellular signaling pathways appear to play a prominent role in chondrocyte dysfunction that is part of osteoarthritis pathogenesis and disease progression. Several mitogen-activated protein kinases and receptor-tyrosine kinases have been characterized as participating in chondrocyte signaling pathways. They are c-Jun-amino-terminal protein kinase, p38 kinase, extracellular signal-regulated protein kinase, and Ror2. Janus kinases and signal transducers and activators of transcription factors (Janus kinase/signal transducers and activators of transcription pathway) are also implicated in modulating the chondrogenic phenotype. Mitogen-activated protein kinase activation is required for their role as phosphorylating enzymes. Activation results from mitogen-activated protein kinase phosphorylation carried out by at least seven upstream kinases known as mitogen-activated protein kinase kinases. Additional upstream kinases (for example, MKKKKs and MKKKs) often require low molecular weight GTP-binding proteins to mediate the mitogen-activated protein-kinase kinases cascade. Identifying the functions of mitogen-activated protein kinases in normal and aging cartilage and the extent to which mitogen-activated protein kinases may be altered in osteoarthritis cartilage and synovium will be critical for developing novel therapies for osteoarthritis management.

The role of cytokines in cartilage matrix degeneration in osteoarthritis

Chondrocytes are the single cellular component of hyaline cartilage. Under physiologic conditions, they show steady-state equilibrium between anabolic and catabolic activities that maintains the structural and functional integrity of the cartilage extracellular matrix. Implicit in the loss of cartilage matrix that is associated with osteoarthritis is that there is a disturbance in the regulation of synthetic (anabolic) and resorptive (catabolic) activities of the resident chondrocytes that results in a net loss of cartilage matrix components and deterioration in the structural and functional properties of the cartilage. Multiple mechanisms likely are involved in the disturbance of chondrocyte remodeling activities in OA. They include the development of acquired or age-related alterations in chondrocyte function, the effects of excessive mechanical loading, and the presence of dysregulated cytokine activities. Cytokines are soluble or cell-surface molecules that play an essential role in mediating cell-cell interactions. It is possible to classify the cytokines that regulate cartilage remodeling as catabolic, acting on target cells to increase products that enhance matrix degradation; as anticatabolic, tending to inhibit or antagonize the activity of the catabolic cytokines; and as anabolic, acting on chondrocytes to increase synthetic activity. This review will focus on the role of proinflammatory cytokines and their roles in mediating the increased matrix degradation that characterizes the osteoarthritic cartilage lesion.

Extracellular signal-regulated protein kinase mediates interleukin 17 (IL-17)-induced IL-8 secretion in Helicobacter pylori-infected human gastric epithelial cells

Helicobacter pylori-induced mucosal inflammation results in high production of interleukin 17 (IL-17), a potent inducer of IL-8 in gastric epithelial cells. The aim of this study was to investigate signaling pathways by which IL-17 regulates IL-8 production in human gastric epithelial cells. Activation of mitogen-activated protein (MAP) kinases in both IL-17-stimulated MKN28 cells and epithelial cells isolated from H. pylori-colonized gastric mucosa was assessed by Western blotting. In IL-17-stimulated MKN28 cells the activation of activatior protein 1 (AP-1), nuclear factor (NF)-IL-6, and NF-kappaB was also assessed by electrophoretic mobility shift assay. IL-8 production was evaluated by reverse transcription-PCR and enzyme-linked immunosorbent assay (ELISA) both for IL-17-stimulated MKN28 cells treated with specific MAP kinase inhibitors and gastric biopsy cultures treated with a neutralizing IL-17 antibody. Serum from H. pylori-infected patients was tested for immunoglobulin G response to CagA by ELISA. Treatment of MKN28 cells with IL-17 caused activation of extracellular signal-regulated protein kinase 1/2 (ERK 1/2) but not other MAP kinases and had the downstream effects of AP-1 and NF-kappaB activation and IL-8 synthesis. Blocking ERK 1/2 activity inhibited AP-1-mediated, but not NF-kappaB-mediated, IL-8 induction. Enhanced activation of ERK 1/2 was seen in gastric epithelial cells isolated from H. pylori-infected patients in comparison to uninfected controls, and this was associated with high IL-8. These effects were even more pronounced in patients seropositive for CagA than in seronegative ones. In gastric biopsy cultures, the addition of a neutralizing IL-17 antibody decreased ERK 1/2 activation, thus resulting in a significant inhibition of IL-8. In H. pylori-colonized gastric epithelial cells, IL-17-induced IL-8 synthesis is associated with and depends at least in part on the activation of ERK 1/2 MAP kinase.

IL-17 markedly up-regulates beta-defensin-2 expression in human airway epithelium via JAK and NF-kappaB signaling pathways

Using microarray gene expression analysis, we first observed a profound elevation of human beta-defensin-2 (hBD-2) message in IL-17-treated primary human airway epithelial cells. Further comparison of this stimulation with a panel of cytokines (IL-1alpha, 1beta, 2-13, and 15-18; IFN-gamma; GM-CSF; and TNF-alpha) demonstrated that IL-17 was the most potent cytokine to induce hBD-2 message (>75-fold). IL-17-induced stimulation of hBD-2 was time and dose dependent, and this stimulation also occurred at the protein level. Further studies demonstrated that hBD-2 stimulation was attenuated by IL-17R-specific Ab, but not by IL-1R antagonist or the neutralizing anti-IL-6 Ab. This suggests an IL-17R-mediated signaling pathway rather than an IL-17-induced IL-1alphabeta and/or IL-6 autocrine/paracrine loop. hBD-2 stimulation was sensitive to the inhibition of the JAK pathway, and to the inhibitors that affect NF-kappaB translocation and the DNA-binding activity of its p65 NF-kappaB subunit. Transient transfection of airway epithelial cells with an hBD-2 promoter-luciferase reporter gene expression construct demonstrated that IL-17 stimulated promoter-reporter gene activity, suggesting a transcriptional mechanism for hBD-2 induction. These results support an IL-17R-mediated signaling pathway involving JAK and NF-kappaB in the transcriptional stimulation of hBD-2 gene expression in airway epithelium. Because IL-17 has been identified in a number of airway diseases, especially diseases related to microbial infection, these findings provide a new insight into how IL-17 may play an important link between innate and adaptive immunity, thereby combating infection locally within the airway epithelium.

Induction of granulocyte-macrophage colony-stimulating factor by a new cytokine, ML-1 (IL-17F), via Raf I-MEK-ERK pathway

BACKGROUND

ML-1 (IL-17F) is a recently discovered cytokine, and its function remains elusive. GM-CSF is a crucial cytokine for the maturation of various cell types and regulates allergic airway inflammation.

OBJECTIVE

The functional effect of ML-1 in the expression of GM-CSF was investigated.

METHODS

The levels of gene and protein expression in normal human bronchial epithelial cells (NHBEs) in the presence or absence of various kinase inhibitors or, in some cases, of a Raf1 dominant-negative mutant were determined by RT-PCR and ELISA, respectively. Western blotting was performed to investigate kinase activation.

RESULTS

The results showed first that ML-1 induces, in a time-dependent and dose-dependent manner, the gene and protein expression for GM-CSF NHBEs, which are associated with activation of Raf1 and MAP kinase kinase (MEK) kinases. Selective MEK inhibitors, PD98059 and U0126, and Raf1 kinase inhibitor I significantly inhibited ML-1-induced GM-CSF production. Furthermore, overexpression of Raf1 dominant-negative mutants inhibited IL-17F-induced GMCSF expression. The combination of PD98059 and Raf1 kinase inhibitor I completely blocked GM-CSF production, whereas 2 protein kinase C inhibitors, Ro-31-7549 and GF109203X, and a phosphatidylinositol 3-kinase inhibitor, LY294002, showed no inhibitory effect.

CONCLUSION

These findings suggest that ML-1 induces GM-CSF expression through the activation of the Raf1-MEK-extracellular signal-regulated kinase 1/2 pathway.