Induction of inflammatory cytokine release from human umbilical vein endothelial cells by agonists of proteinase-activated receptor-2

Increased protease activated receptors in the colon of patients with Hirschsprung's disease

PURPOSE

The pathophysiology of Hirschsprung's associated enterocolitis (HAEC) is not understood. Abnormal intestinal motility and altered intestinal epithelial barrier function have been suggested to play a key role in the causation of HAEC. Protease-activated receptors (PARs) 1 and 2, have been implicated in inflammatory reactions, intestinal permeability and modulation of motility in the gut.

METHODS

We investigated PAR-1 and PAR-2 protein expression in aganglionic and ganglionic regions of patients with Hirschsprung's Disease (HSCR) (n = 10) versus normal control colon (n = 10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression were quantified using quantitative real-time polymerase chain reaction (qPCR), western blot analysis, and densitometry.

RESULTS

qPCR and Western blot analysis revealed that PAR-1 and PAR-2 expression was significantly increased in ganglionic and aganglionic bowel in HSCR compared to controls (p < 0.003). Confocal microscopy revealed strong PAR-1 and PAR-2 expression in smooth muscles, interstitial cells of Cajal (ICCs), platelet-derived growth factor-alpha receptor-positive (PDGFRα⁺) cells, enteric neurons and epithelium in the ganglionic and aganglionic bowel compared to controls.

CONCLUSION

Increased PAR-1 and PAR-2 expression in the colon of patients with HSCR suggests that excessive local release of PAR activating proteases may trigger inflammatory responses leading to HAEC.

Clarithromycin suppresses induction of monocyte chemoattractant protein-1 and matrix metalloproteinase-9 and improves pathological changes in the lungs and heart of mice infected with influenza A virus

The influenza A virus (IAV)-cytokine-trypsin/matrix metalloproteinase-9 (MMP-9) cycle is one of the important mechanisms of multiple organ failure in severe influenza. Clarithromycin, a macrolide antibiotic, has immune modulatory and anti-inflammatory effects. We analyzed the effects of clarithromycin on the induction of chemokines, cytokines, MMP-9, trypsin, vascular hyper-permeability and inflammatory aggravation in mice with IAV infection. IAV/Puerto Rico/8/34(H1N1) infection increased the levels of monocyte chemoattractant protein-1 (MCP-1) and cytokines in serum, and MMP-9 and trypsin in serum and/or the lungs and heart. Clarithromycin significantly suppressed the induction of serum MCP-1 and MMP-9 and vascular hyperpermeability in these organs in the early phase of infection, but did not suppress the induction of trypsin, IL-6 or IFN-γ. Histopathological examination showed that clarithromycin tended to reduce inflammatory cell accumulation in the lungs and heart. These results suggest that clarithromycin suppresses infection-related inflammation and reduces vascular hyperpermeability by suppressing the induction of MCP-1 and MMP-9.

IL-1β is a key cytokine that induces trypsin upregulation in the influenza virus-cytokine-trypsin cycle

Severe influenza is characterized by a cytokine storm, and the influenza virus-cytokine-trypsin cycle is one of the important mechanisms of viral multiplication and multiple organ failure. The aim of this study was to define the key cytokine(s) responsible for trypsin upregulation. Mice were infected with influenza virus strain A/Puerto Rico/8/34 (H1N1) or treated individually or with a combination of interleukin-1β, interleukin-6, and tumor necrosis factor α. The levels of these cytokines and trypsin in the lungs were monitored. The neutralizing effects of anti-IL-1β antibodies on cytokine and trypsin expression in human A549 cells and lung inflammation in the infected mice were examined. Infection induced interleukin-1β, interleukin-6, tumor necrosis factor α, and ectopic trypsin in mouse lungs in a dose- and time-dependent manner. Intraperitoneal administration of interleukin-1β combined with other cytokines tended to upregulate trypsin and cytokine expression in the lungs, but the combination without interleukin-1β did not induce trypsin. In contrast, incubation of A549 cells with interleukin-1β alone induced both cytokines and trypsin, and anti-interleukin-1β antibody treatment abrogated these effects. Administration of the antibody in the infected mice reduced lung inflammation area. These findings suggest that IL-1β plays a key role in trypsin upregulation and has a pathological role in multiple organ failure.

Influenza A virus infection of vascular endothelial cells induces GSK-3β-mediated β-catenin degradation in adherens junctions, with a resultant increase in membrane permeability

Multiorgan failure with vascular hyperpermeability is the final outcome in the progression of seasonal influenza virus pneumonia and influenza-associated encephalopathy, and it is also common in infection with highly pathogenic avian influenza virus. However, the precise molecular mechanism by which influenza virus infection causes vascular endothelial cell hyperpermeability remains poorly defined. We investigated the mechanisms of hyperpermeability of human umbilical vein endothelial cells infected with influenza A virus (IAV)/Puerto Rico/8/34 (PR8) (H1N1). The levels of β-catenin, a key regulatory component of the vascular endothelial-cadherin cell adhesion complex, were markedly decreased during infection for 28 h, with increments of vascular hyperpermeability measured by transendothelial electrical resistance. Lactacystin (at 2 μM), a proteasome inhibitor, inhibited the decrease in β-catenin levels. Since the N-terminal phosphorylation of β-catenin by glycogen synthase kinase (GSK)-3β is the initiation step of proteasome-dependent degradation, we examined the effects of GSK-3β suppression by RNA interference in endothelial cells. IAV-infection-induced β-catenin degradation was significantly inhibited in GSK-3β-knockdown cells, and transfection of cells with recombinant β-catenin significantly suppressed IAV-induced hyperpermeability. These findings suggest that IAV infection induces GSK-3β-mediated β-catenin degradation in the adherens junctional complexes and induces vascular hyperpermeability. The in vitro findings of β-catenin degradation and activation of GSK-3β after IAV infection were confirmed in lungs of mice infected with IAV PR8 during the course of infection from day 0 to day 6. These results suggest that GSK-3β-mediated β-catenin degradation in adherens junctions is one of the key mechanisms of vascular hyperpermeability in severe influenza.

Ectopic trypsin in the myocardium promotes dilated cardiomyopathy after influenza A virus infection

We have previously reported that ectopic trypsin in the myocardium triggers acute myocarditis after influenza A virus (IAV) infection. As myocarditis is a common precursor to dilated cardiomyopathy (DCM), the aim of the present study was to investigate the influence of trypsin on the progression of DCM after IAV infection. IAV-infected mice treated with saline or trypsin inhibitor were euthanized on days 0, 9, 20, 40 and 60 postinfection. Trypsin expression colocalized with myocardial inflammatory loci and IAV-induced myocarditis peaked on day 9 postinfection and alleviated by day 20 but persisted until day 60 postinfection, even though replication of IAV was not detected from day 20 postinfection. Similar time courses were observed for the activation of pro-matrix metalloproteinase (pro-MMP)-9 and expression of the proinflammatory cytokines IL-6, IL-1β, and TNF-α. Degradation of collagen type I, proliferation of ventricular interstitial collagen, and expression of collagen type I and III mRNA increased significantly during acute and chronic phases; collagen type III mRNA increased more significantly than collagen type I mRNA. Cardiac function progressively deteriorated with progressive left ventricular dilation. The trypsin inhibitor aprotinin suppressed pro-MMP-9 activation and cytokine release, alleviated myocardial inflammation, and restored collagen metabolism during acute and chronic phases of myocarditis. This effectively prevented ventricular dilation and improved cardiac function. These results suggest that ectopic trypsin in the myocardium promoted DCM through chronic activation of pro-MMP-9, persistent induction of cytokines, and mediation of collagen remodeling. Pharmacological inhibition of trypsin activity might be a promising approach for the prevention of viral cardiomyopathy.

Butyrate impairs atherogenesis by reducing plaque inflammation and vulnerability and decreasing NFκB activation

BACKGROUND & AIMS

Butyrate is a four-carbon fatty acid that presents anti-inflammatory, anti-oxidative and apoptotic properties in colon and several cell lines. Because atherosclerosis has important oxidative and inflammatory components, butyrate could reduce oxidation and inflammation, impairing atherogenesis. We evaluated the effects of butyrate supplementation of butyrate on atherosclerosis and its mechanisms of action.

METHODS AND RESULTS

ApoE knockout mice were fed on chow diet or 1% butyrate-supplemented chow diet (Butyrate) for 10 weeks to assess atherosclerosis lesions area and inflammatory status. Macrophage and endothelial cells were also pretreated with butyrate (0.5 mM) for 2 h before oxLDL stimulation to study oxLDL uptake and pro and anti-inflammatory cytokine production. Butyrate reduced atherosclerosis in the aorta by 50%. In the aortic valve, butyrate reduced CCL2, VCAM1 and MMP2 productions in the lesion site, resulting in a lower migration of macrophage and increased collagen depositions in the lesion and plaque stability. When EA.hy926 cells were pretreated with butyrate, oxLDL uptake, CD36, VCAM1, CCL2 TNF, IL1β and IL6 productions were reduced, whereas IL10 production was increased. These effects were accompanied by a lower activation of NFκB due to a lower nuclear translocation of the p65 subunit.

CONCLUSION

Oral butyrate is able to slow the progression of atherosclerosis by reducing adhesion and migration of macrophages and increasing plaque stability. These actions are linked to the reduction of CD36 in macrophages and endothelial cells, decreased pro-inflammatory cytokines and lower activation of NFκB all of these data support a possible role for butyrate as an atheroprotective agent.

Evaluation on potential contributions of protease activated receptors related mediators in allergic inflammation

Protease activated receptors (PARs) have been recognized as a distinctive four-member family of seven transmembrane G protein-coupled receptors (GPCRs) that can be cleaved by certain serine proteases. In recent years, there has been considerable interest in the role of PARs in allergic inflammation, the fundamental pathologic changes of allergy, but the potential roles of PARs in allergy remain obscure. Since many of these proteases are produced and actively involved in the pathologic process of inflammation including exudation of plasma components, inflammatory cell infiltration, and tissue damage and repair, PARs appear to make important contribution to allergy. The aim of the present review is to summarize the expression of PARs in inflammatory and structural cells, the influence of agonists or antagonists of PARs on cell behavior, and the involvement of PARs in allergic disorders, which will help us to better understand the roles of serine proteases and PARs in allergy.

MASP-1 induces a unique cytokine pattern in endothelial cells: a novel link between complement system and neutrophil granulocytes

Microbial infection urges prompt intervention by the immune system. The complement cascade and neutrophil granulocytes are the predominant contributors to this immediate anti-microbial action. We have previously shown that mannan-binding lectin-associated serine protease-1 (MASP-1), the most abundant enzyme of the complement lectin pathway, can induce p38-MAPK activation, NFkappaB signaling, and Ca²⁺-mobilization in endothelial cells. Since neutrophil chemotaxis and transmigration depends on endothelial cell activation, we aimed to explore whether recombinant MASP-1 (rMASP-1) is able to induce cytokine production and subsequent neutrophil chemotaxis in human umbilical vein endothelial cells (HUVEC). We found that HUVECs activated by rMASP-1 secreted IL-6 and IL-8, but not IL-1alpha, IL-1ra, TNFalpha and MCP-1. rMASP-1 induced dose-dependent IL-6 and IL-8 production with different kinetics. rMASP-1 triggered IL-6 and IL-8 production was regulated predominantly by the p38-MAPK pathway. Moreover, the supernatant of rMASP-1-stimulated HUVECs activated the chemotaxis of neutrophil granulocytes as an integrated effect of cytokine production. Our results implicate that besides initializing the complement lectin pathway, MASP-1 may activate neutrophils indirectly, via the endothelial cells, which link these effective antimicrobial host defense mechanisms.

Endothelial cell adhesiveness is a function of environmental lighting and melatonin level

The endothelial layer regulates the traffic of cells and substances between the blood and tissues and plays a central role in the mounting of an inflammatory response. We have recently shown that inhibition of the nocturnal melatonin surge during the mounting of an inflammatory response primes endothelial cells to a highly reactive state, increasing the expression of adhesion molecules and inducible nitric oxide synthase (iNOS) as well as the in vitro adherence of leukocytes. Here, we investigated whether physiological variations in the plasma melatonin levels owing to the light/dark environmental cycle could also prime the reactive state of endothelial cells. Cultured endothelial cells (16-20 days) obtained from rats killed during the daytime adhere more neutrophils, expressed more adhesion molecules and iNOS, and had a higher content of the transcription factor nuclear factor kappa B (NF-kB) translocated to the nuclei. We also evaluated the expression of 84 genes (using real-time PCR array) related to the innate inflammatory response and observed a higher expression of 19 genes in cultures obtained during the daytime. In addition, the only gene that was highly expressed in cells obtained from rats killed during nighttime was one that encodes a protein that negatively modulates inflammatory response. In conclusion, the daily rhythm of melatonin also primes the ability of endothelial cells to adhere to neutrophils. This new approach for evaluating the influence of the donor on cells maintained in culture should have applications for the standardization of cell banks.

The brominated compound aeroplysinin-1 inhibits proliferation and the expression of key pro- inflammatory molecules in human endothelial and monocyte cells

Aeroplysinin-1 is a brominated antibiotic used by some sponges for defense against bacterial pathogen invasion. Aeroplysinin-1 has a wide spectrum of anti-tumoral action and behaves as a potent anti-angiogenic compound for bovine aortic endothelial cells. In this study, we demonstrate anti-angiogenic effects of aeroplysinin-1 on human endothelial cells. Furthermore, the response of angiogenesis related genes to aeroplysinin-1 treatment was studied in human endothelial cells by using gene arrays. The major changes were observed in thrombospondin 1 (TSP-1) and monocyte chemoattractant protein-1 (MCP-1), both of which were down-regulated. These inhibitory effects of aeroplysinin-1 were confirmed by using independent experimental approaches. To have a deeper insight on the anti-inflammatory effects of aeroplysinin-1 in endothelial cells, cytokine arrays were also used. This experimental approach confirmed effects on MCP-1 and TSP-1 and showed down-regulation of several other cytokines. Western blotting experiments confirmed down-regulation of ELTD1 (EGF, latrophilin and seven transmembrane domain-containing protein 1), interleukin 1α and matrix metalloproteinase 1 (MMP-1). These results along with our observation of a dramatic inhibitory effect of aeroplysinin-1 on cyclooxygenase-2 protein expression levels in endothelial cells and a human monocyte cell line suggest that aeroplysinin-1 could be a novel anti-inflammatory compound with potential pharmacological interest.

Modulating human proteinase activated receptor 2 with a novel antagonist (GB88) and agonist (GB110)

BACKGROUND AND PURPOSE

Many cells express proteinase activated receptor 2 (PAR2) on their plasma membrane. PAR2 is activated by proteolytic enzymes, such as trypsin and tryptase that cleave the receptor N-terminus, inititating signalling to intracellular G proteins. Studies on PAR2 have relied heavily upon activating effects of proteases and peptide agonists that lack stability and bioavailability in vivo.

EXPERIMENTAL APPROACH

A novel small molecule agonist GB110 and an antagonist GB88 were characterized in vitro against trypsin, peptide agonists, PAR2 antibody, PAR1 agonists and flow cytometry,in seven cell lines using intracellular Ca(2+) mobilization and examined in vivo against PAR2- and PAR1-induced rat paw oedema.

KEY RESULTS

GB110 is a potent non-peptidic agonist activating PAR2-mediated Ca(2+) release in HT29 cells (EC(50) ∼200 nM) and six other human cell lines, inducing PAR2 internalization. GB88 is a unique PAR2 antagonist, inhibiting PAR2 activated Ca(2+) release (IC(50) ∼2 µM) induced by native (trypsin) or synthetic peptide and non-peptide agonists. GB88 was a competitive and surmountable antagonist of agonist 2f-LIGRLO-NH(2), a competitive but insurmountable antagonist of agonist GB110, and a non-competitive insurmountable antagonist of trypsin. GB88 was orally active and anti-inflammatory in vivo, inhibiting acute rat paw oedema elicited by agonist GB110 and proteolytic or peptide agonists of PAR2 but not by corresponding agonists of PAR1 or PAR4.

CONCLUSIONS AND IMPLICATIONS

The novel PAR2 agonist and antagonist modulate intracellular Ca(2+) and rat paw oedema, providing novel molecular tools for examining PAR2-mediated diseases.

Effects of inhibitors of Toll-like receptors, protease-activated receptor-2 signalings and trypsin on influenza A virus replication and upregulation of cellular factors in cardiomyocytes

Severe influenza sometimes causes myocarditis. We recently found that influenza A virus (IAV) infection induces various cellular factors, such as proinflammatory cytokines IL-6, IL-1β and TNF-α, matrix metalloproteinases (MMPs) and ectopic trypsin in mice hearts and in H9c2 cardiomyocytes. The induction of these cellular factors in turn promotes viral replication, myocardial inflammation and cellular damage through their intracellular signal transductions in cooperation with the IAV-induced Toll-like receptors (TLRs) and proteinase-activated receptor-2 (PAR-2) signalings, although the precise nature of these interactions remain obscure. By using specific inhibitors of TLRs and PAR-2 signalings and trypsin inhibitor aprotinin, we analyzed the role of TLR signaling and PAR-2 signaling in the IAV-induced pathological changes in cardiomyocytes. Inhibitors of TLR7/8-Myeloid Differentiation factor 88-nuclear factor-κB signaling and aprotinin effectively suppressed IAV-induced upregulation of proinflammatory cytokines, MMPs, trypsinogen and viral replication. Inhibitor of TLR3-Toll/interleukin-1 receptor domain-containing adaptor inducing interferons-dependent signaling predominantly suppressed the upregulation of interferon-β, a key intracellular host immune response factor. In contrast to the suppressive effect of trypsin inhibitor aprotinin on IAV replication, PAR-2 inhibitor FSY-NH(2), induced marginal upregulation of trypsinogen and subsequent stimulation of IAV replication.

Structure, function and pathophysiology of protease activated receptors

Discovered in the 1990s, protease activated receptors(1) (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Up-regulation of ectopic trypsins in the myocardium by influenza A virus infection triggers acute myocarditis

AIMS

Influenza A virus (IAV) infection markedly up-regulates ectopic trypsins in various organs, viral envelope glycoprotein processing proteases, which are pre-requisites for virus entry and multiplication. We investigated the pathological roles of trypsin up-regulation in the progression of IAV-induced myocarditis, cytokine induction, and viral replication in the hearts, and also investigated the protective effects of trypsin inhibitor on cardiac dysfunction in vivo and selective knockdown of trypsin on IAV-induced cellular damage in cardiomyoblasts.

METHODS AND RESULTS

The relationship of the expression among IAV RNA, trypsins, matrix metalloproteinase (MMP)-9, MMP-2, pro-inflammatory cytokines interleukin (IL)-6, IL-1β, and tumour necrosis factor-α was analysed in mice hearts and cardiomyoblasts after IAV infection. The severity of myocarditis was most noticeable during Day 6-9 post-infection, along with peak expression of viral RNA, trypsins, particularly trypsin₂, MMPs, and cytokines. Cardiac ATP levels were the lowest at Day 9. Up-regulated trypsins, viral protein, and tissue-injured loci in the myocardium were closely localized. Trypsin inhibitor aprotinin treatment in vivo and selective trypsin₁- and trypsin₂-knockdown, particularly the latter, in H9c2 cardiomyoblasts significantly suppressed viral replication, up-regulation of MMPs, and production of active MMP-9 and cytokines, resulting in marked protection against cellular damage, ATP depletion, and apoptosis. IAV infection-induced cardiac dysfunction monitored by echocardiography was improved significantly by aprotinin treatment.

CONCLUSIONS

IAV-induced trypsins, particularly trypsin₂, in the myocardium trigger acute viral myocarditis through stimulation of IAV replication, proMMP-9 activation, and cytokine induction. These results suggest that up-regulation of trypsins is one of the key host pathological findings in IAV-induced myocarditis.

Protease-activated receptor 2 deficiency reduces cardiac ischemia/reperfusion injury

OBJECTIVE

To investigate the effect of protease-activated receptor (PAR) 2 deficiency on ischemia/reperfusion (I/R) injury-induced infarct size, inflammation, heart remodeling, and cardiac function.

METHODS AND RESULTS

PAR-2 signaling enhances inflammation in different diseases. The effect of PAR-2 deficiency in cardiac I/R injury is unknown. PAR-2(-/-) mice and wild-type littermates were subjected to 30 minutes of ischemia and up to 4 weeks of reperfusion. Infarct size, oxidative/nitrative stress, phosphorylation of mitogen-activated protein kinases, and inflammatory gene expression were assessed 2 hours after reperfusion. Changes in heart size and function were measured by echocardiography up to 4 weeks after reperfusion. Infarct size was significantly reduced in hearts of PAR-2(-/-) mice compared with wild-type littermates. In addition, oxidative/nitrative stress, phosphorylation of mitogen-activated protein kinase, and expression of proinflammatory genes were significantly attenuated in injured hearts of PAR-2(-/-) mice. Finally, PAR-2(-/-) mice were protected from postinfarction remodeling and showed less impairment in heart function compared with wild-type littermates up to 4 weeks after I/R injury.

CONCLUSIONS

PAR-2 deficiency reduces myocardial infarction and heart remodeling after I/R injury.

Common pathways for activation of proinflammatory gene expression by G protein-coupled receptors in primary lung epithelial and endothelial cells

Acute lung injury is associated with an inflammatory response resulting from the action of multiple mediators. Many proinflammatory mediators released during lung injury exert effects by binding to G protein-coupled receptors (GPCRs). The authors' earlier studies showed that substance P (SP), a ligand for the tachykinin 1 receptor, induced nuclear factor (NF)-kappa B activation and interleukin (IL)-8 up-regulation through a G(q)-dependent pathway. Here the authors extend these findings by examining effects of multiple ligands for G(q)-coupled GPCRs in primary human small airway epithelial cells (SAECs) and rat lung microvessel endothelial cells (RLMVECs). SP, bradykinin, protease activated receptor 2 agonist, and platelet-activating factor (PAF) stimulated IL-8 production in SAECs, whereas only SP and PAF up-regulated CINC-1 (a rat IL-8 homolog) in RLMVECs. Using signaling inhibitors, the authors investigated PAF-induced IL-8 expression and SP-induced CINC-1 expression in primary cells. Signaling cascades were similar in SAECs and RLMVECs and involved phospholipase C/calcium/protein kinase C (PKC) and Ras/Raf/Erk pathways. In addition, the tyrosine kinase inhibitor AG 17 and the proteasome inhibitor MG132 significantly reduced IL-8 and CINC-1 expression induced by GPCR ligands. The results demonstrate a common signaling pathway in primary lung epithelial and endothelial cells, suggesting a generalized mechanism for the induction of proinflammatory gene expression by G(q)-coupled GPCRs following lung injury.

The recovery time course of the endothelial cell glycocalyx in vivo and its implications in vitro

Compelling evidence continues to emerge suggesting that the glycocalyx surface layer on vascular endothelial cells plays a determining role in numerous physiological processes including inflammation, microvascular permeability, and endothelial mechanotransduction. Previous research has shown that enzymes degrade the glycocalyx, whereas inflammation causes shedding of the layer. To track the endogenous recovery of the glycocalyx in vivo, we used fluorescent microparticle image velocimetry (micro-PIV) in mouse cremaster muscle venules to estimate the hydrodynamically relevant glycocalyx thickness 1, 3, 5, and 7 days after enzymatic or cytokine-mediated degradation of the layer. Results indicate that after acute degradation of the glycocalyx, 5 to 7 days are required for the layer to endogenously restore itself to its native hydrodynamically relevant thickness in vivo. In light of these findings, and because demonstrable evidence has emerged that standard cell culture conditions are not conducive to providing the environment and/or cellular conditions necessary to produce and maintain a physiologically relevant cell surface glycocalyx in vitro, we sought to determine whether merely the passage of time would be sufficient to promote the production of a hydrodynamically relevant glycocalyx on a confluent monolayer of human umbilical vein endothelial cells (HUVECs). Using micro-PIV, we found that the hydrodynamically relevant glycocalyx was substantially absent 7 days postconfluence on HUVEC-lined cylindrical collagen microchannels maintained under standard culture conditions. Thus, it remains to be determined how a hydrodynamically relevant glycocalyx surface layer can be synthesized and maintained in culture before the endothelial cell culture model can be used to elucidate glycocalyx-mediated mechanisms of endothelial cell function.

Expression of proteinase-activated receptor-2 in the intervertebral disc

STUDY DESIGN

Immunohistochemical and biochemical analyses of proteinase-activated receptor-2 (PAR-2) in rat and human intervertebral discs (IVDs).

OBJECTIVES

To examine the expression and function of PAR-2 in rat IVD cells, and to determine if PAR-2 is expressed in human IVDs.

SUMMARY OF BACKGROUND DATA

PAR-2 is a G protein-coupled receptor that contributes to the regulation of inflammatory reactions and the pathophysiology of inflammatory diseases, including arthritis. The expression of PAR-2 in the IVD has not been determined.

METHODS

PAR-2 expression by rat IVD cells and tissues was examined using immunohistochemistry and western blot. Rat anulus fibrosus cells in monolayer culture were used to examine the biologic role of PAR-2 in vitro. The effect of PAR-2-activating peptide (PAR-2AP) on the catabolic cascade was assessed by western blot and real-time PCR. The expression of PAR-2 by human IVD tissues at different stages of degeneration was determined by immunohistochemical analyses.

RESULTS

PAR-2 was expressed by rat IVD cells and in both anulus fibrosus and nucleus pulposus tissues, PAR-2 expression was up-regulated by interleukin-1beta (IL-1beta). PAR-2AP significantly increased the release of IL-1beta into the medium. Although PAR-2AP had no direct effect on matrix metalloproteinase-3 (MMP-3) and MMP-13 mRNA levels, treatment with PAR-2AP significantly up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4. The simultaneous administration of PAR-2AP and IL-1beta synergistically up-regulated the mRNA levels of a disintegrin and metalloproteinase with thrombospondin motif-4, MMP-3, and MMP-13. The expression of PAR-2 was identified in human IVD tissues. The number of PAR-2-expressing cells was significantly elevated in advanced stages of IVD degeneration compared with those in early stages of degeneration.

CONCLUSION

Our results demonstrate for the first time that IVD cells express PAR-2. The expression of PAR-2 is regulated by IL-1beta stimulation. PAR-2 activation accelerates the expression of matrix-degrading enzymes. PAR-2 may play an important role in the cytokine-mediated catabolic cascade and consequently may be involved in IVD degeneration.