The accumulation of neutrophils and proinflammatory mediators, such as leukotriene B4 (LTB4), is a classic marker of inflammatory disease. The clearance of apoptotic neutrophils, inhibition of proinflammatory signaling, and production of proresolving lipids (including lipoxins, such as lipoxin A4 [LXA4]) are imperative for resolving inflammation. Tulathromycin (TUL), a macrolide used to treat bovine respiratory disease, confers immunomodulatory benefits via mechanisms that remain unclear. We recently reported the anti-inflammatory properties of TUL in bovine phagocytes in vitro and in Mannheimia haemolytica-challenged calves. The findings demonstrated that this system offers a powerful model for investigating novel mechanisms of pharmacological immunomodulation. In the present study, we examined the effects of TUL in a nonbacterial model of pulmonary inflammation in vivo and characterized its effects on lipid signaling. In bronchoalveolar lavage (BAL) fluid samples from calves challenged with zymosan particles (50 mg), treatment with TUL (2.5 mg/kg of body weight) significantly reduced pulmonary levels of LTB4 and prostaglandin E2 (PGE2). In calcium ionophore (A23187)-stimulated bovine neutrophils, TUL inhibited phospholipase D (PLD), cytosolic phospholipase A2 (PLA2) activity, and the release of LTB4. In contrast, TUL promoted the secretion of LXA4 in resting and A23187-stimulated neutrophils, while levels of its precursor, 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], were significantly lower. These findings indicate that TUL directly modulates lipid signaling by inhibiting the production of proinflammatory eicosanoids and promoting the production of proresolving lipoxins.
Activation of the complement system is primarily initiated by pathogen- and damage-associated molecular surface patterns on cellular surfaces. However, there is increasing evidence for direct activation of individual complement components by extrinsic proteinases as part of an intricate crosstalk between physiological effector systems. We hypothesized that kallikrein-related peptidases (KLKs), previously known to regulate inflammation via proteinase-activated receptors, can also play a substantial role in innate immune responses via complement. Indeed, KLKs exemplified by KLK14 were efficiently able to cleave C3, the point of convergence of the complement cascade, indicating a potential modulation of C3-mediated functions. By using in vitro fragmentation assays, mass spectrometric analysis, and cell signaling responses, we pinpointed the generation of the C3a fragment of C3 as a product with potential biological activity released by the proteolytic action of KLK14. Using mice with various complement deficiencies, we demonstrated that the intraplantar administration of KLK14 results in C3-associated paw edema. The edema response was dependent on the presence of the receptor for C3a but was not associated with the receptor for the downstream complement effector C5a. Our findings point to C3 as one of the potential substrates of KLKs during inflammation. Given the wide distribution of the KLKs in tissues and biological fluids where complement components may also be expressed, we suggest that via C3 processing, tissue-localized KLKs can play an extrinsic complement-related role during activation of the innate immune response.
anaphylatoxin; C3a receptor; complement; inflammation; kallikrein-related peptidases; paw edema; trypsin
Background. Nonbacterial prostatitis has no established etiology. We hypothesized that proteinase-activated receptor-1 (PAR1) can play a role in prostatitis. We therefore investigated the effects of PAR1 stimulation in the context of a new model of murine nonbacterial prostatitis. Methods. Using a hapten (ethanol-dinitrobenzene sulfonic acid- (DNBS-)) induced prostatitis model with both wild-type and PAR1-null mice, we examined (1) the location of PAR1 in the mouse prostate and (2) the impact of a PAR1-activating peptide (TFLLR-NH2: PAR1-TF) on ethanol-DNBS-induced inflammation. Results. Ethanol-DNBS-induced inflammation was maximal at 2 days. In the tissue, PAR1 was expressed predominantly along the apical acini of prostatic epithelium. Although PAR1-TF on its own did not cause inflammation, its coadministration with ethanol-DNBS reduced all indices of acute prostatitis. Further, PAR1-TF administration doubled the prostatic production of interleukin-10 (IL-10) compared with ethanol-DNBS treatment alone. This enhanced IL-10 was not observed in PAR1-null mice and was not caused by the reverse-sequence receptor-inactive peptide, RLLFT-NH2. Surprisingly, PAR1-TF, also diminished ethanol-DNBS-induced inflammation in PAR1-null mice. Conclusions. PAR1 is expressed in the mouse prostate and its activation by PAR1-TF elicits immunomodulatory effects during ethanol-DNBS-induced prostatitis. However, PAR1-TF also diminishes ethanol-DNBS-induced inflammation via a non-PAR1 mechanism by activating an as-yet unknown receptor.
Proteinase-activated receptors (PARs) are a subfamily of G protein-coupled receptors (GPCRs) with four members, PAR1, PAR2, PAR3 and PAR4, playing critical functions in hemostasis, thrombosis, embryonic development, wound healing, inflammation and cancer progression. PARs are characterized by a unique activation mechanism involving receptor cleavage by different proteinases at specific sites within the extracellular amino-terminus and the exposure of amino-terminal “tethered ligand“ domains that bind to and activate the cleaved receptors. After activation, the PAR family members are able to stimulate complex intracellular signalling networks via classical G protein-mediated pathways and beta-arrestin signalling. In addition, different receptor crosstalk mechanisms critically contribute to a high diversity of PAR signal transduction and receptor-trafficking processes that result in multiple physiological effects.
In this review, we summarize current information about PAR-initiated physical and functional receptor interactions and their physiological and pathological roles. We focus especially on PAR homo- and heterodimerization, transactivation of receptor tyrosine kinases (RTKs) and receptor serine/threonine kinases (RSTKs), communication with other GPCRs, toll-like receptors and NOD-like receptors, ion channel receptors, and on PAR association with cargo receptors. In addition, we discuss the suitability of these receptor interaction mechanisms as targets for modulating PAR signalling in disease.
From the individual perspective of the two authors who were long-time colleagues of Karl Lederis at the University of Calgary, the events and personal interactions are described, that are relevant to the discovery of Urotensin I (UI) in the Lederis laboratory, along with the concurrent discovery of Urotensin II (UII) in the Bern laboratory and corticotropin-releasing factor (CRF/CRH) in the Vale laboratory. The fortuitous sabbatical experiences that put Professors Lederis and Bern on the track of the Urotensins, along with the essential isolation paradigm that resulted in the complete sequencing and synthesis of UI and UII are summarized. The chance interaction between Drs. Vale and Lederis who, prior to the publications of the sequences of UI and CRF, realized the sequence commonalities of these peptides with the vasoactive frog peptide, sauvagine, is outlined. Further, the relationship between the pharmacological studies done with UI in the Calgary laboratory and the more recent understanding of the biology and receptor pharmacology for the entire Urotensin I–CRF–Urocortin peptide family is dealt with. The value of a comparative endocrinology approach to understanding hormone action is emphasized, along with a projection to the future, based on new hypotheses that can be generated by unexplained data already in the literature. Based on the previously described pharmacology of the UI–CRF–Urocortin peptides in a number of target tissues, it is suggested that the use of current molecular approaches can be integrated with a ‘classical’ pharmacological approach to generate new insights about the UI–CRF–Urocortin hormone family.
PMID: 19409389 CAMSID: cams2629
Corticotropin-releasing factor (CRF); CRF1; CRF2; Oxytocin; Urocortin; Urophysis; Urotensin; Vasopressin; Fish; Teleosts
Distal sensory polyneuropathy is a frequent complication of lentivirus infections of the peripheral nervous system including both human immunodeficiency virus and feline immunodeficiency virus. Proteinase-activated receptors are G protein-coupled receptors implicated in the pathogenesis of neuroinflammation and neurodegeneration. Proteinase-activated receptor-1 is expressed on different cell types within the nervous system including neurons and glia, but little is known about its role in the pathogenesis of inflammatory peripheral nerve diseases, particularly lentivirus-related distal sensory polyneuropathy. Herein, the expression and functions of proteinase-activated receptor-1 in the peripheral nervous system during human immunodeficiency virus and feline immunodeficiency virus infections were investigated. Proteinase-activated receptor-1 expression was most evident in autopsied dorsal root ganglion neurons from subjects infected with human immunodeficiency virus, compared with the dorsal root ganglia of uninfected subjects. Human immunodeficiency virus or feline immunodeficiency virus infection of cultured human or feline dorsal root ganglia caused upregulation of interleukin-1β and proteinase-activated receptor-1 expression. In the human immunodeficiency virus- or feline immunodeficiency virus-infected dorsal root ganglia, interleukin-1β activation was principally detected in macrophages, while neurons showed induction of proteinase-activated receptor-1. Binding of proteinase-activated receptor-1 by the selective proteinase-activated receptor-1-activating peptide resulted in neurite retraction and soma atrophy in conjunction with cytosolic calcium activation in human dorsal root ganglion neurons. Interleukin-1β exposure to feline or human dorsal root ganglia caused upregulation of proteinase-activated receptor-1 in neurons. Exposure of feline immunodeficiency virus-infected dorsal root ganglia to the interleukin-1 receptor antagonist prevented proteinase-activated receptor-1 induction and neurite retraction. In vivo feline immunodeficiency virus infection was associated with increased proteinase-activated receptor-1 expression on neurons and interleukin-1β induction in macrophages. Moreover, feline immunodeficiency virus infection caused hyposensitivity to mechanical stimulation. These data indicated that activation and upregulation of proteinase-activated receptor-1 by interleukin-1β contributed to dorsal root ganglion neuronal damage during lentivirus infections leading to the development of distal sensory polyneuropathy and might also provide new targets for future therapeutic interventions.
PAR1; HIV; FIV; dorsal root ganglion; IL-1β
TNF-α activates multiple mitogen-activated protein kinase (MAPK) cascades in intestinal epithelial cells (IECs) leading to the secretion of interleukin 8 (IL-8), a neutrophil chemoattractant and an angiogenic factor with tumor promoting properties. As the epidermal growth factor receptor (EGFR) is a known transducer of proliferative signals and a potent activator of MAPKs, we hypothesized that the EGFR participates in TNF-dependent MAPK activation and IL-8 secretion by intestinal epithelial cells (IECs).
We show that the EGFR is tyrosine-phosphorylated following treatment of IECs (HT-29 and IEC-6) with TNF-α. This requires EGFR autophosphorylation as it was blocked by the EGFR kinase inhibitor AG1478. Autophosphorylation was also inhibited by both a Src-kinase inhibitor and the metalloproteinase inhibitor batimastat. TNF treatment of IECs resulted in the accumulation of soluble TGF-α; treatment of IECs with batimastat suppressed TGF-α release and immunoneutralization of TGF-α resulted in decreased EGFR and ERK phosphorylations. TNF-α treatment of IECs resulted in an association between EGFR and HER2 and inhibition of HER2 using a specific inhibitor AG879 in combination with AG1478-suppressed TNF-α-dependent ERK phosphorylation and IL-8 release. Downregulation of HER2 via siRNA resulted in a significant decrease in ERK phosphorylation and a 50% reduction in IL-8 secretion.
Implantation S1 family serine proteinases (ISPs) are tryptases involved in embryo hatching and uterine implantation in the mouse. The two different ISP proteins (ISP1 and ISP2) have been detected in both pre- and post-implantation embryo tissue. To date, native ISP obtained from uterus and blastocyst tissues has been isolated only as an active hetero-dimer that exhibits trypsin-like substrate specificity. We hypothesised that in isolation, ISP1 might have a unique substrate specificity that could relate to its role when expressed alone in individual tissues. Thus, we isolated recombinant ISP1 expressed in Pichia pastoris and evaluated its substrate specificity. Using several chromogenic substrates and serine proteinase inhibitors, we demonstrate that ISP1 exhibits trypsin-like substrate specificity, having a preference for lysine over arginine at the P1 position. Phage display peptide mimetics revealed an expanded but mixed substrate specificity of ISP1, including chymotryptic and elastase activity. Based upon targets observed using phage display, we hypothesised that ISP1 might signal to cells by cleaving and activating proteinase-activated receptors (PARs) and therefore assessed PARs 1, 2 and 4 as potential ISP1 targets. We observed that ISP1 silenced enzyme-triggered PAR signaling by receptor-disarming. This PAR-disarming action of ISP1 may be important for embryo development and implantation.
Protease-activated receptor-2 (PAR2) is highly expressed throughout the gut and regulates inflammatory, mitogenic, fibroproliferative, and nociceptive responses to injury. PAR2 is strikingly upregulated and exhibits increased activation in response to intestinal irradiation. We examined the mechanistic significance of in radiation enteropathy development by assessing the effect of exogenous PAR2 activation.
Methods and Materials
Rat small bowel was exposed to localized single-dose radiation (16.5 Gy). The PAR2 agonist (2-furoyl-LIGRLO-NH2) or vehicle was injected intraperitoneally daily for 3 days before irradiation (“before”), for 7 days after irradiation (“after”), or both 3 days before and 7 days after irradiation (“before-after”). Early and delayed radiation enteropathy was assessed 2 and 26 weeks after irradiation by quantitative histology, morphometry, and immuno-histochemical analysis.
The PAR2 agonist did not elicit changes in unirradiated (shielded) intestine. In contrast, in irradiated intestine procured 2 weeks after irradiation, administration of PAR2 agonist was associated with more sever mucosal injury and increased intestinal wall thickness in all 3 treatment groups (p < 0.05) compared to vehicle-treated controls. The PAR2 agonist also exacerbated radiation injury score, serosal thickening, and mucosal inflammation (p < 0.05) in the before and the before-after groups. Short term exogenous activation of PAR2 did not impact radiation-induced intestinal injury at 26 weeks.
This study supports a role for PAR2 activation in the pathogenesis of early radiation-induced intestinal injury. Pharmacological PAR2 antagonists may have the potential to reduce intestinal side effects of radiation therapy and/or as countermeasures in radiological accidents or terrorism scenarios.
Intestines; Radiation injury; PAR2 activating peptide; PAR2 agonist
Apoptosis of distal lung epithelial cells plays a pivotal role in the pathogenesis of acute lung injury. In this context, proteinases, either circulating or leukocyte-derived, may contribute to epithelial apoptosis and lung injury. We hypothesized that apoptosis of lung epithelial cells induced by leukocyte elastase is mediated via the proteinase activated receptor (PAR)-1. Leukocyte elastase, thrombin, and PAR-1–activating peptide, but not the control peptide, induced apoptosis in human airway and alveolar epithelial cells as assessed by increases in cytoplasmic histone-associated DNA fragments and TUNEL staining. These effects were largely prevented by a specific PAR-1 antagonist and by short interfering RNA directed against PAR-1. To ascertain the mechanism of epithelial apoptosis, we determined that PAR-1AP, thrombin, and leukocyte elastase dissipated mitochondrial membrane potential, induced translocation of cytochrome c to the cytosol, enhanced cleavage of caspase-9 and caspase-3, and led to JNK activation and Akt inhibition. In concert, these observations provide strong evidence that leukocyte elastase mediates apoptosis of human lung epithelial cells through PAR-1–dependent modulation of the intrinsic apoptotic pathway via alterations in mitochondrial permeability and by modulation of JNK and Akt.
acute lung injury; proteinases; inflammation; signal transduction
The proteinase-activated receptors (PARs) are widely recognized for their modulatory properties of inflammation and neurodegeneration. We investigated the role of PAR2 in the pathogenesis of multiple sclerosis (MS) in humans and experimental autoimmune encephalomyelitis (EAE) in mice. PAR2 expression was increased on astrocytes and infiltrating macrophages in human MS and murine EAE central nervous system (CNS) white matter (P < 0.05). Macrophages and astrocytes from PAR2 wild-type (WT) and knockout (KO) mice exhibited differential immune gene expression with PAR2 KO macrophages showing significantly higher interleukin 10 production after lipopolysaccharide stimulation (P < 0.001). PAR2 activation in macrophages resulted in the release of soluble oligodendrocyte cytotoxins (P < 0.01). Myelin oligodendrocyte glycoprotein–induced EAE caused more severe inflammatory gene expression in the CNS of PAR2 WT animals (P < 0.05), together with enhanced T cell proliferation and interferon γ production (P < 0.05), compared with KO littermates. Indeed, PAR2 WT animals showed markedly greater microglial activation and T lymphocyte infiltration accompanied by worsened demyelination and axonal injury in the CNS compared with their PAR2 KO littermates. Enhanced neuropathological changes were associated with a more severe progressive relapsing disease phenotype (P < 0.001) in WT animals. These findings reveal previously unreported pathogenic interactions between CNS PAR2 expression and neuroinflammation with ensuing demyelination and axonal injury.
Proteinase-activated receptor–1 (PAR1), a G protein–coupled receptor activated by thrombin, is highly expressed in different cell types of the gastrointestinal tract. The activity of thrombin and of other proteinases is significantly increased in the colon of inflammatory bowel disease (IBD) patients. Since PAR1 activation in tissues other than the gut provoked inflammation, we hypothesized that PAR1 activation in the colon is involved in the pathogenesis of IBD. Here, we demonstrate that PAR1 is overexpressed in the colon of IBD patients. In mice, intracolonic administration of PAR1 agonists led to an inflammatory reaction characterized by edema and granulocyte infiltration. This PAR1 activation–induced inflammation was dependent on B and T lymphocytes. Moreover, PAR1 activation exacerbated and prolonged inflammation in a mouse model of IBD induced by the intracolonic administration of trinitrobenzene sulfonic acid (TNBS), while PAR1 antagonism significantly decreased the mortality and severity of colonic inflammation induced by TNBS and dextran sodium sulfate. In these 2 models, colitis development was strongly attenuated by PAR1 deficiency. Taken together, these results imply an important role for PAR1 in the pathogenesis of experimental colitis, supporting the notion that PAR1 inhibition may be beneficial in the context of IBD and possibly in other chronic intestinal inflammatory disorders.
Mast cell (MC)-derived serine proteases have been implicated in a variety of inflammatory processes. We have previously shown that rat peritoneal MC (PMC) express mRNA for protease activated receptor 2 (PAR-2), a G-coupled receptor activated by trypsin-like proteases. Recent evidence also suggests that MC-induced inflammation can be mediated through PAR. Therefore, we hypothesized that specific PAR-2 agonist peptides (PAR-2ap) induce protease release from PMC.
Western blot analysis of PMC supernatants revealed that a PAR-2ap, tc-LIGRLO (10 μM), stimulated the release of rat MC protease (RMCP)-1, RMCP-5 and carboxypeptidase-A. The release was evident by 20 min but further increased up to 8 h. To study the biological effects of protease release we tested supernatants from tc-LIGRLO, tc-OLRGIL (inactive control peptide) and antigen-activated PMC for proteolytic activity by seeding with TNF (150 pg/ml), incubating for 8 h at 37°C, and measuring TNF remaining in the supernatants. Supernatants from tc-LIGRLO-stimulated PMC degraded 44 % of seeded TNF (n = 5). Moreover, this TNF proteolysis was dependent on the concentration of tc-LIGRLO used to stimulate PMC, and was significantly inhibited (94 %) by soybean trypsin inhibitor. Antigen and tc-OLRGIL induced no significant release of such proteolytic activity.
These data indicate that a PAR-2ap induces the release of proteases from mast cells, which may degrade extracellular cytokines and other substrates thus modulating the inflammatory response.
The use of adenovirus vectors for human gene therapy is limited by potent inflammatory responses that result in significant morbidity. In kidney-derived epithelial cells (REC), activation of extracellular signal-regulated kinase 1/2 (ERK) and p38 kinase (p38) pathways occurred within 20 min of transduction with the serotype 5 adenovirus vector AdCMVβgal. Inhibition of ERK and p38 with U0126 and SB203580, respectively, reduced the expression of IP-10 mRNA following transduction with AdCMVβgal. To determine the role of the coxsackievirus-adenovirus receptor (CAR) or αv integrins in the activation of ERK and p38 and the expression of IP-10, REC cells were transduced with the fiber-modified and RGD-deleted adenovirus vectors AdL.F(RAEK-HA) and AdL.PB(HA), respectively. Compared with the wild-type capsid vector Ad5Luc, transduction with AdL.F(RAEK-HA) and AdL.PB(HA) resulted in reduced ERK-p38 activation and less IP-10 mRNA expression. The decreased IP-10 expression induced by the tropism-modified vectors was due to diminished transduction, since increasing multiplicity of infection resulted in increased IP-10 expression. Inhibition of adenovirus penetration with bafilomycin A1 or ammonium chloride attenuated the activation of ERK-p38 and IP-10 mRNA expression following infection, suggesting that endosomal escape was required to trigger these pathways. In vivo, direct inhibition of ERK and p38 signaling pathways inhibited adenovirus vector-induced IP-10 expression in mouse liver 1 h following transduction. These results demonstrate the importance of signaling via ERK and p38 in the early host response to adenovirus vectors and will permit the development of novel strategies to improve the safety and efficacy of these agents in human gene therapy.