Bradykinin induces a rapid cyclooxygenase-2 mRNA expression via Ca2+mobilization in human gingival fibroblasts primed with interleukin-1 β

Regulation of smooth muscle contractility by the epithelium in rat tracheas: role of prostaglandin E2 induced by the neurotransmitter acetylcholine

Background

Previous studies have suggested the involvement of epithelium in modulating the contractility of neighboring smooth muscle cells. However, the mechanism underlying epithelium-derived relaxation in airways remains largely unclear. This study aimed to investigate the mechanism underlying epithelium-dependent smooth muscle relaxation mediated by neurotransmitters.

Methods

The contractile tension of Sprague-Dawley (SD) rat tracheal rings were measured using a mechanical recording system. Intracellular Ca²⁺ level was measured using a Ca²⁺ fluorescent probe Fluo-3 AM, and the fluorescence signal was recorded by a laser scanning confocal imaging system. The prostaglandin E₂ (PGE₂) content was measured using an enzyme-linked immunosorbent assay kit.

Results

We observed that the neurotransmitter acetylcholine (ACh) restrained the electric field stimulation (EFS)-induced contraction in the intact but not epithelium-denuded rat tracheal rings. After inhibiting the muscarinic ACh receptor (mAChR) or cyclooxygenase (COX), a critical enzyme in prostaglandin synthesis, the relaxant effect of ACh was attenuated. Exogenous PGE₂ showed a similar inhibitory effect on the EFS-evoked contraction of tracheal rings. Moreover, ACh triggered phospholipase C (PLC)-coupled Ca²⁺ release from intracellular Ca²⁺ stores and stimulated COX-dependent PGE₂ production in primary cultured rat tracheal epithelial cells.

Conclusions

Collectively, this study demonstrated that ACh induced rat tracheal smooth muscle relaxation by promoting PGE₂ release from tracheal epithelium, which might provide valuable insights into the cross-talk among neurons, epithelial cells and neighboring smooth muscle cells in airways.

Protein kinase Cε regulates nuclear translocation of extracellular signal-regulated kinase, which contributes to bradykinin-induced cyclooxygenase-2 expression

The proinflammatory mediator bradykinin stimulated cyclooxygenase-2 (COX-2) expression and subsequently prostaglandin E₂ synthesis in dermal fibroblasts. The involvement of B2 receptors and Gαq in the role of bradykinin was suggested by using pharmacological inhibitors. The PKC activator PMA stimulated COX-2 mRNA expression. Bradykinin failed to induce COX-2 mRNA expression in the presence of PKC inhibitors, whereas the effect of bradykinin was observed in the absence of extracellular Ca²⁺. Bradykinin-induced COX-2 mRNA expression was inhibited in cells transfected with PKCε siRNA. These observations suggest that the novel PKCε is concerned with bradykinin-induced COX-2 expression. Bradykinin-induced PKCε phosphorylation and COX-2 mRNA expression were inhibited by an inhibitor of 3-phosphoinositide-dependent protein kinase-1 (PDK-1), and bradykinin-induced PDK-1 phosphorylation was inhibited by phospholipase D (PLD) inhibitors, suggesting that PLD/PDK-1 pathway contributes to bradykinin-induced PKCε activation. Pharmacological and knockdown studies suggest that the extracellular signal-regulated kinase 1 (ERK1) MAPK signaling is involved in bradykinin-induced COX-2 expression. Bradykinin-induced ERK phosphorylation was attenuated in the cells pretreated with PKC inhibitors or transfected with PKCε siRNA. We observed the interaction between PKCε and ERK by co-immunoprecipitation experiments. These observations suggest that PKCε activation contributes to the regulation of ERK1 activation. Bradykinin stimulated the accumulation of phosphorylated ERK in the nuclear fraction, that was inhibited in the cells treated with PKC inhibitors or transfected with PKCε siRNA. Consequently, we concluded that bradykinin activates PKCε via the PLD/PDK-1 pathway, which subsequently induces activation and translocation of ERK1 into the nucleus, and contributes to COX-2 expression for prostaglandin E₂ synthesis in dermal fibroblasts.

Human salivary gland cells express bradykinin receptors that modulate the expression of proinflammatory cytokines

Bradykinin is an important peptide modulator that affects the function of neurons and immune cells. However, there is no evidence of the bradykinin receptors and their functions in human salivary glands. Here we have identified and characterized bradykinin receptors on human submandibular gland cells. Both bradykinin B1 and B2 receptors are expressed on human submandibular gland cells, A253 cells, and HSG cells. Bradykinin increased the intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) in a concentration-dependent manner. Interestingly, a specific agonist of the B1 receptor did not have any effect on [Ca²⁺ ]_i in HSG cells, whereas specific agonists of the B2 receptor had a Ca²⁺ mobilizing effect. Furthermore, application of the B1 receptor antagonist, R715, did not alter the bradykinin-mediated increase in cytosolic Ca²⁺ , whereas the B2 receptor antagonist, HOE140, showed a strong inhibitory effect, which implies that bradykinin B2 receptors are functional in modulating the concentration of cytosolic Ca²⁺ . Bradykinin did not affect a carbachol-induced rise of [Ca²⁺ ]_i and did not modulate translocation of aquaporin-5. However, bradykinin did promote the expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), implying the role of bradykinin in salivary gland inflammation. These data suggest that bradykinin receptors are involved in Ca²⁺ signaling in human submandibular gland cells and serve a unique role, which is separate from that of other salivary gland G protein-coupled receptors.

Regulation of myofibroblast differentiation by cardiac glycosides

Myofibroblast differentiation is a key process in pathogenesis of fibrotic diseases. Cardiac glycosides (ouabain, digoxin) inhibit Na(+)-K(+)-ATPase, resulting in increased intracellular [Na(+)]-to-[K(+)] ratio in cells. Microarray analysis suggested that increased intracellular [Na(+)]/[K(+)] ratio may promote the expression of cyclooxygenase-2 (COX-2), a critical enzyme in the synthesis of prostaglandins. Given antifibrotic effects of prostaglandins through activation of protein kinase A (PKA), we examined if cardiac glycosides stimulate COX-2 expression in human lung fibroblasts and how they affect myofibroblast differentiation. Ouabain stimulated a profound COX-2 expression and a sustained PKA activation, which was blocked by COX-2 inhibitor or by COX-2 knockdown. Ouabain-induced COX-2 expression and PKA activation were abolished by the inhibitor of the Na(+)/Ca(2+) exchanger, KB-R4943. Ouabain inhibited transforming growth factor-β (TGF-β)-induced Rho activation, stress fiber formation, serum response factor activation, and the expression of smooth muscle α-actin, collagen-1, and fibronectin. These effects were recapitulated by an increase in intracellular [Na(+)]/[K(+)] ratio through the treatment of cells with K(+)-free medium or with digoxin. Although inhibition of COX-2 or of the Na(+)/Ca(2+) exchanger blocked ouabain-induced PKA activation, this failed to reverse the inhibition of TGF-β-induced Rho activation or myofibroblast differentiation by ouabain. Together, these data demonstrate that ouabain, through the increase in intracellular [Na(+)]/[K(+)] ratio, drives the induction of COX-2 expression and PKA activation, which is accompanied by a decreased Rho activation and myofibroblast differentiation in response to TGF-β. However, COX-2 expression and PKA activation are not sufficient for inhibition of the fibrotic effects of TGF-β by ouabain, suggesting that additional mechanisms must exist.

IL-4 and IL-13 inhibit IL-1β and TNF-α induced kinin B1 and B2 receptors through a STAT6-dependent mechanism

BACKGROUND AND PURPOSE

Bone resorption induced by interleukin-1β (IL-1β) and tumour necrosis factor (TNF-α) is synergistically potentiated by kinins, partially due to enhanced kinin receptor expression. Inflammation-induced bone resorption can be impaired by IL-4 and IL-13. The aim was to investigate if expression of B1 and B2 kinin receptors can be affected by IL-4 and IL-13.

EXPERIMENTAL APPROACH

We examined effects in a human osteoblastic cell line (MG-63), primary human gingival fibroblasts and mouse bones by IL-4 and IL-13 on mRNA and protein expression of the B1 and B2 kinin receptors. We also examined the role of STAT6 by RNA interference and using Stat6(-/-) mice.

KEY RESULTS

IL-4 and IL-13 decreased the mRNA expression of B1 and B2 kinin receptors induced by either IL-1β or TNF-α in MG-63 cells, intact mouse calvarial bones or primary human gingival fibroblasts. The burst of intracellular calcium induced by either bradykinin (B2 agonist) or des-Arg(10) -Lys-bradykinin (B1 agonist) in gingival fibroblasts pretreated with IL-1β was impaired by IL-4. Similarly, the increased binding of B1 and B2 ligands induced by IL-1β was decreased by IL-4. In calvarial bones from Stat6-deficient mice, and in fibroblasts in which STAT6 was knocked down by siRNA, the effect of IL-4 was decreased.

CONCLUSIONS AND IMPLICATIONS

These data show, for the first time, that IL-4 and IL-13 decrease kinin receptors in a STAT6-dependent mechanism, which can be one important mechanism by which these cytokines exert their anti-inflammatory effects and impair bone resorption.

Involvement of protein kinase C in IL-1beta-induced expression of cyclooxygenase-2 in human gingival fibroblasts

Interleukin-1beta (IL-1beta) stimulates expression of the highly inducible enzyme cyclooxygenase-2 (COX-2) via activation of nuclear factor kappaB (NFkappaB), and consequently provokes prostaglandin E(2) (PGE(2)) synthesis, which induces inflammatory responses. In this study, the contribution of protein kinase C (PKC) to IL-1beta-induced PGE(2) synthesis in human gingival fibroblasts was investigated. The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated PGE(2) release and COX-2 mRNA expression, as shown in human gingival fibroblasts stimulated by IL-1beta. However, PMA showed only a weak effect on the formation of COX-2-NFkappaB DNA-protein complex, whereas IL-1beta had a clearly stimulatory effect. In cells in which PMA-dependent PKC was down-regulated, PMA failed to induce the formation of NFkappaB DNA-protein complex and reduced the release of PMA-induced PGE(2), whereas IL-1beta stimulated the formation of COX-2-NFkappaB DNA-protein complex and PGE(2) release. The atypical PKC (aPKC) inhibitor Gö6983 clearly suppressed the formation of COX-2-NFkappaB DNA-protein complex and PGE(2) release stimulated by IL-1beta but not the inhibitor of conventional PKC (cPKC) and the novel PKC (nPKC) inhibitor Gö6976. These observations suggest that aPKC is involved in IL-1beta-induced PGE(2) synthesis, which is controlled by transcription of the COX-2 gene via the NFkappaB-dependent pathway in human gingival fibroblasts.

Characterization of Arecoline-Induced Effects on Cytotoxicity in Normal Human Gingival Fibroblasts by Global Gene Expression Profiling

Areca nut is the most widely used psychoactive substance and an important environmental risk factor for development of oral premalignant lesions and cancer. Arecoline, the major alkaloid of areca nut, has been known to cause cytotoxicity and genotoxicity in mammalian cells in vivo and in vitro and even contributes to carcinogenicity. However, the susceptible genes accounting for arecoline-induced damage in normal human oral cells are still lacking, which possibly involves in initial molecular damage via alternation of gene expression level on biological pathways. The present study was undertaken to characterize the toxic effects of arecoline in gene expression profiling on normal human gingival fibroblasts (HGF) using cDNA microarray and quantitative real-time reverse transcription PCR. The cytotoxicity of arecoline on HGF-1 cell line was elevated in a dose-dependent manner (p < 0.05) accompanied with distinct morphological change and formation of intracellular vacuoles were observed. At optimum concentration of arecoline determined from dose-response curve of the cytotoxicity, a large number of genes were significantly repressed than induced by arecoline in global gene expression profiling. Five induced- and seven repressed genes including glutathione synthetase were further validated, and their gene expression changes were increased in a dose-dependent manner in a concentration range of 50-150 microg/ml. In conclusion, we proposed a tentative model to explain arecoline-induced effects on contribution of oral pathogenesis. The findings identified that 12 susceptible genes can potentially serve as biomarkers of arecoline-induced damage in betel chewers.

Expression of COX-1 and COX-2 in a clinical model of acute inflammation

Cyclooxygenase (COX) plays an important role in the induction of pain and inflammation as well as the analgesic actions of NSAIDs and coxibs. This study evaluates the expression of the two isoforms COX-1 and COX-2 in a clinical model in which the surgical removal of impacted third molars is used to evaluate the analgesic activity of anti-inflammatory drugs. A 3-mm punch biopsy was performed on the oral mucosa overlying 1 impacted third molar immediately before extraction of 2 impacted lower third molars. After the second tooth was extracted, a second biopsy was performed adjacent to the surgical site either immediately after surgery or 30, 60, or 120 minutes after surgery. RNA was extracted from the biopsy specimens, and RT-PCR was performed to assess mRNA levels of COX-1, COX-2, and glyceraldehyde-3-phosphate dehydrogenase (G3PDH). The RT-PCR products in the biopsy specimens were normalized to G3PDH and compared with baseline. COX-2 mRNA was progressively increased at 30, 60, and 120 minutes after surgery (P<.05); COX-1 mRNA was transiently decreased at 60 minutes during the postsurgical period (P<.05). The results demonstrate peripheral elevation of COX-2 after tissue injury, which may contribute to increased prostaglandin E(2) at the site of injury, pain onset, and the analgesic activity of both nonselective NSAIDs and selective COX-2 inhibitors.

PERSPECTIVE

This clinical study uses a physiologically relevant model to determine the time course of expression of COX-1 and COX-2 in acute inflammation of the human oral mucosa. This study furthers our understanding of the contribution of the COX isoforms to acute pain.

Platelet-derived growth factor-induced arachidonic acid release for enhancement of prostaglandin E(2) synthesis in human gingival fibroblasts pretreated with interleukin-1beta

Platelet-derived growth factor (PDGF) is a biological mediator for connective tissue cells and plays a critical role in a wide variety of physiological and pathological processes. We here investigated the effect of PDGF on arachidonic acid release and prostaglandin E(2) (PGE(2)) synthesis in human gingival fibroblasts (HGF). PDGF induced arachidonic acid release in a time- and dose-dependent manner, and simultaneously induced a transient increase in intracellular Ca(2+) concentration ([Ca(2+)](i)), but less provoked PGE(2) release and cyclooxygenase-2 (COX-2) mRNA expression. When [Ca(2+)](i) was increased by Ca(2+)-mobilizing reagents, arachidonic acid release was increased. The PDGF-induced arachidonic acid release and increase in [Ca(2+)](i) were prevented by a tyrosine kinase inhibitor. On the other hand, in the HGF pre-stimulated with interleukin-1beta (IL-1beta), PDGF clearly increased PGE(2) release. The PDGF-induced PGE(2) release was inhibited by a tyrosine kinase inhibitor. In the HGF pretreated with IL-1beta, arachidonic acid strongly enhanced PGE(2) release and COX-2 mRNA expression. These results suggest that PDGF stimulates arachidonic acid release by the increase in [Ca(2+)](i) via tyrosine kinase activation, and which contributes to PGE(2) production via COX-2 expression in HGF primed with IL-1beta.

Bradykinin regulates cyclooxygenase-2 in rat renal thick ascending limb cells

Cyclooxygenase-2 (COX-2) is constitutively expressed in a subset of thick ascending limb cells in the cortex and medulla and increases when the renin-angiotensin and kallikrein-kinin systems are activated. Although the contribution of angiotensin II to the regulation of COX-2 is known, the effects of bradykinin on COX-2 expression have not been determined in this nephron segment. We evaluated expression of B2 bradykinin receptors in thick ascending limb cells containing COX-2 and the effect of bradykinin on COX-2 expression in primary cultured medullary thick ascending cells. The presence of B2 receptors was studied in renal sections by immunohistochemistry with antibodies against B2, COX-2, and Tamm-Horsfall glycoprotein. B2 receptors were detected on the apical and basolateral portion of the thick ascending cells. These cells also contained COX-2, suggesting that COX-2 expression may be regulated via B2 receptor. Incubation of cultured medullary thick ascending cells with bradykinin (10(-7) to 10(-5) mol/L) induced a significant increase on COX-2 protein expression. Maximal expression of COX-2 was observed 4 hours after exposure to bradykinin (10(-7) mol/L), effect abolished by a B2 receptor antagonist (HOE-140; 10(-6) mol/L). Prostaglandin E2 production increased when these cells were challenged with bradykinin for 4 hours, indicating that COX-2 was enzymatically active. We have demonstrated (1) the presence of B2 receptors in thick ascending limb cells expressing COX-2 and (2) the stimulatory effect of bradykinin on COX-2 protein expression, via B2 receptors, in cultured medullary thick ascending cells. We suggest that bradykinin can affect ion transport in the thick ascending limb via a COX-2-mediated mechanism.

The Bradykinin B2 receptor is required for full expression of renal COX-2 and renin

Angiotensin converting enzyme (ACE) inhibition leads to increased levels of bradykinin, cyclooxygenase-2 (COX-2), and renin. Since bradykinin stimulates prostaglandin release, renin synthesis may be regulated through a kinin-COX-2 pathway. To test this hypothesis, we examined the impact of bradykinin B2 receptor (B2R) gene disruption in mice on kidney COX-2 and renin gene expression. Kidney COX-2 mRNA and protein levels were significantly lower in B2R-/- mice by 40-50%. On the other hand, renal COX-1 levels were similar in B2R-/- and +/+ mice. Renal renin protein was 61% lower in B2R-/- compared to B2R+/+ mice. This was accompanied by a significant reduction in renin mRNA levels in B2R-/- mice. Likewise, intrarenal angiotensin I levels were significantly lower in B2R-/- mice compared to B2R+/+ mice. In contrast, kidney angiotensin II levels were not different and averaged 261+/-16 and 266+/-15fmol/g in B2R+/+ and B2R-/- mice, respectively. Kidney angiotensinogen, AT1 receptor and ACE activity were not different between B2R+/+ and B2R-/- mice. The results of these studies demonstrate suppression of renal renin synthesis in mice lacking the bradykinin B2R and support the notion that B2R regulation of COX-2 participates in the steady-state control of renin gene expression.

Angiotensin II induces prostaglandin E(2) release in human gingival fibroblasts

We investigated the effect of angiotensin II on prostaglandin E(2) release in human gingival fibroblasts. Stimulation of human gingival fibroblasts with angiotensin II elicited prostaglandin E(2) release in a concentration- and time-dependent manner. Angiotensin III also induced prostaglandin E(2) release, but the effect was weaker than that of angiotensin II. Angiotensin II- and angiotensin III-induced prostaglandin E(2) release was inhibited by AT(1) receptor antagonist FR-130,739, but not AT(2) receptor antagonist PD-123,319. Angiotensin II evoked an increase in intracellular Ca(2+) in fura-2-loaded human gingival fibroblasts. These results suggest that angiotensin II functions as a physiological mediator via Ca(2+)-mobilizing AT(1) receptor activation in human gingival fibroblasts.

Tumor necrosis factor alpha (TNF-alpha)-induced prostaglandin E2 release is mediated by the activation of cyclooxygenase-2 (COX-2) transcription via NFkappaB in human gingival fibroblasts

Nuclear factor kappaB (NFkappaB) is a transcription factor and plays a key role in the expression of several genes involved in the inflammatory process. Cyclooxygenase (COX) is the key regulatory enzyme of the prostaglandin/eicosanoid synthetic pathway. COX-2 is a highly inducible enzyme by proinflammatory cytokines, of which gene expression is regulated by NFkappaB. TNF-alpha is a pro-inflammatory cytokine. In this paper, we investigated the involvement of NFkappaB on TNF-alpha-mediated prostaglandin E2 (PGE2) release and COX-2 gene expression in human gingival fibroblasts (HGF). TNF-alpha-induced PGE2 release and COX-2 mRNA accumulation in a time- and concentration-dependent manner in HGF. The results of transient transfection assays using a chimeric construct of the human COX-2 promoter (nts -1432 approximately +59) ligated to a luciferase reporter gene indicated that TNF-a stimulated the transcriptional activity approximately 1.4-fold. Gel mobility shift assays with a radiolabelled COX-2-NFkappaB oligonucleotide (nts -223 to -214) revealed an increase in the binding of nuclear proteins from TNF-alpha-stimulated HGF. The COX-2-NFKB DNA-protein complex disappeared after treatment with pyrrolidine dithiocarbamate (PDTC; an antioxidant) or herbimycin A (a tyrosine kinase inhibitor). PDTC and herbimycin A attenuated TNF-alpha-stimulated PGE2 release. These results suggest that NFkappaB transcription factor is a key regulator of COX-2 expression in TNF-alpha-induced PGE2 production, which is mediated through a tyrosine kinase pathway in HGF.

4-Bromophenacyl bromide induces Ca2+ influx in human gingival fibroblasts

4-Bromophenacyl bromide (BPB) is generally used as a phospholipase A(2) (PLA2) inhibitor. In the present study, we demonstrate that BPB induces Ca2+ influx in human gingival fibroblasts. In fura-2-loaded human gingival fibroblasts, BPB evoked a transient increase in intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner. The BPB-induced Ca2+ mobilization was also shown in a single fluo-3-loaded-fibroblast. The BPB-induced increase in [Ca2+]i was completely abolished by the elimination of the external Ca2+. Ca2+ influx induced by the Ca2+-mobilizing agonist histamine was markedly enhanced in the presence of BPB. These suggest that the BPB-induced Ca2+ mobilization is due to the influx of extracellular Ca2+. However, it is unlikely that the effect of BPB is dependent on the inhibition of PLA2 activity, because other PLA2 inhibitors, such as AACOCF3, quinacrine dihydrochloride and manoalide, failed to induce Ca2+ mobilization. Chemical compounds similar to BPB, but which have no -CH2-Br at position 1 in the benzene ring failed to evoke Ca2+ mobilization, indicating that the position of -CH2--Br in BPB is important for causing the Ca2+ influx.