John A. Di Battista

Reduced progression of experimental osteoarthritis in vivo by selective inhibition of inducible nitric oxide synthase

OBJECTIVE To evaluate the in vivo therapeutic efficacy of N-iminoethyl-L-lysine (L-NIL), a selective inhibitor of inducible nitric oxide synthase (iNOS), on the progression of lesions in an experimental osteoarthritis (OA) dog model. The effect of L-NIL on metalloprotease activity, levels of interleukin-1beta (IL-1beta), prostaglandin E2 (PGE2), and nitrite/nitrate in synovial fluid was determined. METHODS The OA model was created by sectioning the anterior cruciate ligament of the right stifle joint of mongrel dogs by a stab wound. Dogs were separated into experimental groups: Group 1 was made up of unoperated dogs that received no treatment, group 2 were operated dogs with no treatment, and group 3 were operated dogs that received oral L-NIL (10 mg/kg/twice daily) starting immediately after surgery. The OA dogs were killed at 10 weeks after surgery. RESULTS Experiments showed that dog OA cartilage explants in culture produced an increased amount of NO (nitrite). Immunohistochemical study demonstrated that this was due to an increased level of iNOS in chondrocytes. OA dogs treated with L-NIL showed a reduction in the incidence of osteophytes compared with the untreated OA dogs (58% versus 92%) as well as in their size (mean +/- SEM 1.92 +/- 0.58 mm versus 5.08 +/- 0.66 mm). Macroscopically, L-NIL decreased the size of the cartilage lesions by approximately 50% both on condyles and plateaus. The histologic severity of both the cartilage lesions and synovial inflammation was significantly decreased in the L-NIL-treated dogs. Treatment with L-NIL also significantly decreased both collagenase and general metalloprotease activity in the cartilage and the levels of IL-1beta, PGE2, and nitrite/nitrate in synovial fluid. CONCLUSION This study demonstrated the effectiveness of a selective inhibitor of iNOS, L-NIL, in attenuating the progression of experimental OA. The data suggest that L-NIL may act by reducing the activity of metalloproteases in cartilage and the production of IL-1beta by synovium, both of which are known to play a major role in the pathophysiology of OA structural changes.

Peroxisome proliferator–activated receptor γ activators inhibit interleukin‐1β–induced nitric oxide and matrix metalloproteinase 13 production in human chondrocytes

OBJECTIVE To determine the effects of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists on interleukin-1 (IL-1) induction of nitric oxide (NO) and matrix metalloproteinase 13 (MMP-13) in human chondrocytes. METHODS PPARgamma expression and synthesis in human chondrocytes were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Chondrocytes were cultured with IL-1beta, tumor necrosis factor alpha (TNFalpha), and IL-17 in the presence or absence of PPARgamma agonists, and NO and MMP-13 synthesis and expression levels were measured. Transient transfection experiments were performed with the 7-kb inducible NO synthase (iNOS) and 1.6-kb MMP-13 human promoters, as well as with the PPARgamma expression vector and the activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB) reporter constructs. RESULTS RT-PCR and immunohistochemical analysis revealed that human chondrocytes expressed and produced PPARgamma. Treatment of chondrocytes with PPARgamma ligands BRL 49653 and 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2), but not with PPARalpha ligand Wy 14643, decreased IL-1beta-induced NO and MMP-13 production in a dose-dependent manner. In addition, both iNOS and MMP-13 messenger RNA were inhibited in the presence of 15d-PGJ2. The inhibitory effect of PPARgamma activation was not restricted to IL-1beta, since TNFalpha- and IL-17-induced NO and MMP-13 production were also inhibited by 15d-PGJ2. In transient transfection experiments, we showed that a constitutively active form of mitogen-activated protein kinase kinase kinase 1 (AMEKK-1) induced the MMP-13 and iNOS human promoter activity. This process was reduced by 15d-PGJ2 and further inhibited by cotransfection with a PPARgamma expression vector. Similarly, in a PPARgamma-dependent manner, 15d-PGJ2 inhibited deltaMEKK-1-induced AP-1- and NF-kappaB-luciferase reporter plasmid activation. CONCLUSION The findings of this study demonstrate that PPARgamma agonists inhibit IL-1beta induction of both NO and MMP-13 in human chondrocytes. The inhibition occurs at least at the transcriptional level through a PPARgamma-dependent pathway, probably by interfering with the activation of AP-1 and NF-kappaB.

Mitogen-activated protein kinase and nuclear factor κB together regulate interleukin-17–induced nitric oxide production in human osteoarthritic chondrocytes: Possible role of transactivating factor mitogen–activated protein kinase–activated protein kinase (MAPKAPK)

OBJECTIVE To explore the signaling pathways by which the proinflammatory cytokine interleukin-17 (IL-17) may contribute to cartilage catabolism in osteoarthritis (OA) by inducing inducible nitric oxide synthase (iNOS) expression in chondrocytes. METHODS We examined the IL-17-induced NO production in human OA chondrocytes, in combination with the proinflammatory cytokines IL-1beta, tumor necrosis factor alpha (TNF alpha), and leukemia inhibitory factor (LIF); the antiinflammatory cytokines IL-4, IL-10, and IL-13; and IL-1 receptor antagonist (IL-1Ra). Further, we explored the major intracellular signaling pathways through which IL-17 induced iNOS expression and NO production. RESULTS Treatment with IL-17 induced a dose-dependent increase in the level of NO. When IL-17 was combined with the above factors, it resulted in a synergistic effect with TNF alpha, an additive effect with LIF, and no further effect than when used alone with IL-1beta. IL-4, IL-10, IL-13, and IL-1Ra had no true effect on IL-17-induced NO production. The cAMP mimetics, 3-isobutyl-1-methyl xanthine plus forskolin, completely blocked IL-17-induced NO production. KT-5720, genistein, and Calphostin C, inhibitors of protein kinase A (PKA), tyrosine kinase, and protein kinase C, respectively, reduced the IL-17-induced NO production by 72%, 56%, and 42%, respectively. Within minutes, IL-17 induced the phosphorylation of mitogen-activated protein kinase kinase-1/2 (MEK-1/2), -3/6 (MKK-3/6), p44/42, p38, and inhibitor of nuclear factor kappaB (I kappaB)-alpha, as well as the activation of mitogen-activated protein kinase-activated protein kinase-1 and -2 (MAPKAPK-1 and -2). Interestingly, IL-17 induced phosphorylation of the stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) (p54/46) only when PKA was inhibited. Specific protein kinase inhibitors for MEK-1/2 (PD98059), p38 (SB202190), and nuclear factor kappaB (NF-kappaB) (pyrrolidine dithiocarbamate) each markedly decreased the IL-17-increased iNOS level and NO production. Inhibiting MAPK, including MEK-1/2 and p38, had no effect on the IL-17-induced activation of IkappaB-alpha, but reversed the IL-17 activation of MAPKAPK-1 and -2, respectively. CONCLUSION These findings show that the stimulation of NO production by IL-17 is mediated mainly by a complex activation of kinases, especially PKA, NF-kappaB, and MAPK. NF-kappaB appears to require MAPK activation, with downstream activation of MAPKAPK probably acting as a transactivating factor, to induce iNOS expression.

Inhibition of tumor necrosis factor α–induced prostaglandin E2 production by the antiinflammatory cytokines interleukin‐4, interleukin‐10, and interleukin‐13 in osteoarthritic synovial fibroblasts: Distinct targeting in the signaling pathways

OBJECTIVE To investigate the effects of the antiinflammatory cytokines interleukin-4 (IL-4), IL-10, and IL-13 on tumor necrosis factor alpha (TNFalpha)-induced prostaglandin E2 (PGE2) release in the cellular signaling cascade on human osteoarthritis (OA) synovial fibroblasts. METHODS Human OA synovial fibroblasts were cultured to explore the impact of IL-4, IL-10, and IL-13 on TNFalpha binding to TNF receptors (TNFR), soluble TNFR (sTNFR), cytoplasmic phospholipase A2 (cPLA2), and cyclooxygenase-2 (COX-2) production, and on the binding activity of the transcription factors nuclear factor kappaB (NF-kappaB), CCAAT-enhancer binding protein (C/EBP), activator protein 2 (AP-2), and cyclic AMP response element-binding protein (CREB). RESULTS IL-4, IL-10, and IL-13 at 5 ng/ml dramatically reduced TNFalpha-induced PGE2 release by approximately 90% (P < 0.0001). IL-4 up-regulated the level of TNFalpha-induced TNFR by 47% (P < 0.06), while IL-10 down-regulated it by 71% (P < 0.02); IL-13 had no effect. Although statistical significance was not reached, all 3 cytokines up-regulated the basal level of sTNFR-55. IL-4 and IL-10, while not altering the basal level of sTNFR-75, significantly increased the TNFalpha-stimulated release of sTNFR-75. IL-4, IL-10, and IL-13 reduced the TNFalpha-induced COX-2 level, and IL-4 and IL-10 reduced the cPLA2 level. IL-4 had no effect on TNFalpha up-regulation of NF-kappaB, and a slight decrease was noted with IL-10 and IL-13 at the highest concentration used (5 ng/ml). IL-4 and IL-13 decreased the TNFa-induced C/EBP accumulation in a dose-dependent manner, while IL-10 up-regulated its basal level. AP-2 and CREB were not induced by TNFalpha. CONCLUSION The results indicate that these antiinflammatory cytokines reversed the TNFalpha-induced release of PGE2 by OA synovial fibroblasts, by acting at various levels of the TNFa-dependent signaling cascade. These data shed new light on the mechanisms by which these cytokines reduce inflammatory processes.

Transcriptional induction of cyclooxygenase-2 gene by okadaic acid inhibition of phosphatase activity in human chondrocytes: Co-stimulation of AP-1 and CRE nuclear binding proteins

The involvement of serine/threonine protein phosphatases in signaling pathways that control the expression of the cyclooxygenase‐2 (COX‐2) gene in human chondrocytes was examined. Okadaic acid (OKA), an inhibitor of protein phosphatases 1 (PP‐1) and 2A (PP‐2A), induced a delayed, time‐dependent increase in the rate of COX‐2 gene transcription (runoff assay) resulting in increased steady‐state mRNA levels and enzyme synthesis. The latter response was dose dependent over a narrow range of 1–30 nmol/L with declining expression and synthesis of COX‐2 at higher concentrations due to cell toxicity. The delayed increase in COX‐2 mRNA expression was accompanied by the induction of the proto‐oncogenes c‐jun, junB, junD, and c‐fos (but not FosB or Fra‐1). Increased phosphorylation of CREB‐1/ATF‐1 transcription factors was observed beginning at 4 h and reached a zenith at 8 h. Gel‐shift analysis confirmed the up‐regulation of AP‐1 and CRE nuclear binding proteins, though there was little or no OKA‐induced nuclear protein binding to SP‐1, AP‐2, NF‐κB or NF‐IL‐6 regulatory elements. OKA‐induced nuclear protein binding to 32P‐CRE oligonucleotides was abrogated by a pharmacological inhibitor of protein kinase A (PKA), KT‐5720; the latter compound also inhibited OKA‐induced COX‐2 enzyme synthesis. Calphostin C (CalC), an inhibitor of PKC isoenzymes, had little effect in this regard. Inhibition of 32P‐CRE binding was also observed in the presence of an antibody to CREB‐binding protein (265‐kDa CBP), an integrator and coactivator of cAMP‐responsive genes. The binding to 32P‐CRE was unaffected in the presence of excess radioinert AP‐1 and COX‐2 NF‐IL‐6 oligonucleotides, although a COX‐2 CRE‐oligo competed very efficiently. 32P‐AP‐1 consensus sequence binding was unaffected by incubation of chondrocytes with KT‐5720 or CalC, but was dramatically diminished by excess radioinert AP‐1 and CRE‐COX‐2 oligos. Supershift analysis in the presence of antibodies to c‐Jun, c‐Fos, JunD, and JunB suggested that AP‐1 complexes were composed of c‐Fos, JunB, and possibly c‐Jun. OKA has no effect on total cellular PKC activity but caused a delayed time‐dependent increase in total PKA activity and synthesis. OKA suppressed the activity of the MAP kinases, ERK1/2 in a time‐dependent fashion, suggesting that the Raf‐1/MEKK1/MEK1/ERK1,2 cascade was compromised by OKA treatment. By contrast, OKA caused a dramatic increase in SAPK/JNK expression and activity, indicative of an activation of MEKK1/JNKK/SAPK/JNK pathway. OKA stimulated a dose‐dependent activation of CAT activity using transfected promoter‐CAT constructs harboring the regulatory elements AP‐1 (c‐jun promoter) and CRE (CRE‐tkCAT). We conclude that in primary phenotypically stable human chondrocytes, COX‐2 gene expression may be controlled by critical phosphatases that interact with phosphorylation dependent (e.g., MAP kinases:AP‐1, PKA:CREB/ATF) signaling pathways. AP‐1 and CREB/ATF families of transcription factors may be important substrates for PP‐1/PP‐2A in human chondrocytes. J. Cell. Biochem. 69:392–413, 1998.

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 (PGE2) production. In contrast, HNE had no effect on basal iNOS expression or nitric oxide (NO) release. However, HNE strongly inhibited IL‐1β‐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‐1β‐induced iNOS expression and promoter activity mainly through NF‐κB site (−5,817/−5,808) possibly via suppression of IKKα‐induced IκBα phosphorylation and NF‐κB/p65 nuclear translocation. Upon examination of upstream signaling components, we found that IKKα was inactivated through HNE/IKKα 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 IKKα inactivation. J. Cell. Biochem. 100: 1217–1231, 2007.

Prostaglandin PGE2 at very low concentrations suppresses collagen cleavage in cultured human osteoarthritic articular cartilage: this involves a decrease in expression of proinflammatory genes, collagenases and COL10A1, a gene linked to chondrocyte hypertrophy

Suppression of type II collagen (COL2A1) cleavage by transforming growth factor (TGF)-β2 in cultured human osteoarthritic cartilage has been shown to be associated with decreased expression of collagenases, cytokines, genes associated with chondrocyte hypertrophy, and upregulation of prostaglandin (PG)E2 production. This results in a normalization of chondrocyte phenotypic expression. Here we tested the hypothesis that PGE2 is associated with the suppressive effects of TGF-β2 in osteoarthritic (OA) cartilage and is itself capable of downregulating collagen cleavage and hypertrophy in human OA articular cartilage. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with a wide range of concentrations of exogenous PGE2 (1 pg/ml to 10 ng/ml). COL2A1 cleavage was measured by ELISA. Proteoglycan content was determined by a colorimetric assay. Gene expression studies were performed with real-time PCR. In explants from patients with OA, collagenase-mediated COL2A1 cleavage was frequently downregulated at 10 pg/ml (in the range 1 pg/ml to 10 ng/ml) by PGE2 as well as by 5 ng/ml TGF-β2. In control OA cultures (no additions) there was an inverse relationship between PGE2 concentration (range 0 to 70 pg/ml) and collagen cleavage. None of these concentrations of added PGE2 inhibited the degradation of proteoglycan (aggrecan). Real-time PCR analysis of articular cartilage from five patients with OA revealed that PGE2 at 10 pg/ml suppressed the expression of matrix metalloproteinase (MMP)-13 and to a smaller extent MMP-1, as well as the proinflammatory cytokines IL-1β and TNF-α and type X collagen (COL10A1), the last of these being a marker of chondrocyte hypertrophy. These studies show that PGE2 at concentrations much lower than those generated in inflammation is often chondroprotective in that it is frequently capable of selectively suppressing the excessive collagenase-mediated COL2A1 cleavage found in OA cartilage. The results also show that chondrocyte hypertrophy in OA articular cartilage is functionally linked to this increased cleavage and is often suppressed by these low concentrations of added PGE2. Together these initial observations reveal the importance of very low concentrations of PGE2 in maintaining a more normal chondrocyte phenotype.

Alterations of metabolic activity in human osteoarthritic osteoblasts by lipid peroxidation end product 4-hydroxynonenal

Abstract4-Hydroxynonenal (HNE), a lipid peroxidation end product, is produced abundantly in osteoarthritic (OA) articular tissues, but its role in bone metabolism is ill-defined. In this study, we tested the hypothesis that alterations in OA osteoblast metabolism are attributed, in part, to increased levels of HNE. Our data showed that HNE/protein adduct levels were higher in OA osteoblasts compared to normal and when OA osteoblasts were treated with H2O2. Investigating osteoblast markers, we found that HNE increased osteocalcin and type I collagen synthesis but inhibited alkaline phosphatase activity. We next examined the effects of HNE on the signaling pathways controlling cyclooxygenase-2 (COX-2) and interleukin-6 (IL-6) expression in view of their putative role in OA pathophysiology. HNE dose-dependently decreased basal and tumour necrosis factor-α (TNF-α)-induced IL-6 expression while inducing COX-2 expression and prostaglandin E2 (PGE2) release. In a similar pattern, HNE induces changes in osteoblast markers as well as PGE2 and IL-6 release in normal osteoblasts. Upon examination of signaling pathways involved in PGE2 and IL-6 production, we found that HNE-induced PGE2 release was abrogated by SB202190, a p38 mitogen-activated protein kinase (MAPK) inhibitor. Overexpression of p38 MAPK enhanced HNE-induced PGE2 release. In this connection, HNE markedly increased the phosphorylation of p38 MAPK, JNK2, and transcription factors (CREB-1, ATF-2) with a concomitant increase in the DNA-binding activity of CRE/ATF. Transfection experiments with a human COX-2 promoter construct revealed that the CRE element (-58/-53 bp) was essential for HNE-induced COX-2 promoter activity. However, HNE inhibited the phosphorylation of IκBα and subsequently the DNA-binding activity of nuclear factor-κB. Overexpression of IKKα increased TNF-α-induced IL-6 production. This induction was inhibited when TNF-α was combined with HNE. These findings suggest that HNE may exert multiple effects on human OA osteoblasts by selective activation of signal transduction pathways and alteration of osteoblastic phenotype expression and pro-inflammatory mediator production.

Leukotriene B4 BLT Receptor Signaling Regulates the Level and Stability of Cyclooxygenase-2 (COX-2) mRNA through Restricted Activation of Ras/Raf/ERK/p42 AUF1 Pathway

Recent studies suggest that active resolution of the inflammatory response in animal models of arthritis may involve leukotriene B4 (LTB4)-dependent stimulation of “intermediate” prostaglandin production, which in turn favors the synthesis of “downstream” anti-inflammatory and pro-resolving lipoxins, resolvins, and protectins. We explored a putative mechanism involving LTB4-dependent control of cyclooxygenase-2 (COX-2) expression, the rate-limiting step in inflammatory prostaglandin biosynthesis. Indeed, LTB4 potently up-regulated/stabilized interleukin-1β-induced COX-2 mRNA and protein expression under conditions of COX-2 inhibitor-dependent blockade of PGE2 release in human synovial fibroblasts (EC50 = 16.5 ± 1.7 nm for mRNA; 19 ± 2.4 nm for protein, n = 4). The latter response was pertussis toxin-sensitive, and semi-quantitative reverse transcription-PCR confirmed the quantitative predominance of the BLT2 receptor. Transfection experiments, using human COX-2 promoter plasmids and chimeric luciferase-COX-2 mRNA 3′-untranslated region (3′-UTR) reporter constructs, revealed that LTB4 exerted its stabilizing effect at the post-transcriptional level through a 116-bp adenylate/uridylate-rich sequence in the proximal region of the COX-2 3′-UTR. Using luciferase-COX-2 mRNA 3′-UTR reporter constructs and Ras/c-Raf expression and mutant constructs, we showed that the Ras/c-Raf/MEK1/2/ERK1/2 signaling pathway mediated LTB4-dependent COX-2 mRNA stabilization. Knockdown experiments with specific short hairpin RNAs confirmed that LTB4 stabilization of COX-2 mRNA was apparently mediated through the RNA-binding protein, p42 AUF1. The nuclear export of p42 AUF1 was driven by c-Raf/MEK1/2/ERK1/2 signaling and sensitive to leptomycin B treatment, suggesting a CRM1-dependent mechanism. We conclude that LTB4 may support the resolution phase of the inflammatory response by stabilizing COX-2, ensuring a reservoir of ambient pro-resolution lipid mediators.

Prostaglandin E2 Stimulates p53 Transactivational Activity through Specific Serine 15 Phosphorylation in Human Synovial Fibroblasts ROLE IN SUPPRESSION OF c/EBP/NF-κB-MEDIATED MEKK1-INDUCED MMP-1 EXPRESSION

Cyclooxygenase-2 (COX-2) overexpression has been linked to cell survival, transformation, and hyperproliferation. We examined the regulation of the tumor suppressor gene p53 and p53 target genes by prostaglandin E2 (PGE2) in human synovial fibroblasts (HSF). PGE2 induced a time-dependent increase in p53 Ser15 phosphorylation, with no discernible change in overall p53 levels. PGE2-dependent Ser15 phosphorylation was apparently mediated by activated p38 MAP kinase as SB202190, a p38 kinase inhibitor, blocked the response. Overexpression of a MKK3 construct, but not MKK1, stimulated SB202190-sensitive p53 Ser15 phosphorylation. PGE2-stimulated [phospho-Ser15]p53 transactivated a p53 response element (GADD45)-luciferase reporter in transiently transfected HSF (SN7); the effect was compromised by overexpression of a dominant-negative mutant (dnm) of p53 or excess p53S15A expression plasmid but mimicked by a constitutively active p53S15E expression construct. PGE2, wtp53 expression in the presence of PGE2, and p53S15E suppressed steady-state levels of MEKK1-induced MMP-1 mRNA, effects nullified with co-transfection of p53 dnm or p53S15A. MEKK1-induced MMP-1 promoter-driven luciferase activity was largely dependent on a c/EBPβ-NF-κB-like enhancer site at –2008 to –1972 bp, as judged by deletion and point mutation analyses. PGE2, overexpression of p53wt with PGE2, or p53S15E abolished the MEKK1-induced MMP-1 promoter luciferase activity. Gel-shift/super gel-shift analyses identified c/EBPβ dimers and c/EBPβ/NF-κB p65 heterodimers as binding species at the apparent site of MEKK1-dependent transactivation. PGE2-stimulated [phospho-Ser15]p53 abrogated the DNA binding of c/EBPβ dimers and c/EBPβ/NF-κB p65 heterodimers. Our data suggest that COX-2 prostaglandins may be implicated in p53 function and p53 target gene expression.