John Morser

RAGE mediates a novel proinflammatory axis: a central cell surface receptor for S100/calgranulin polypeptides.

S100/calgranulin polypeptides are present at sites of inflammation, likely released by inflammatory cells targeted to such loci by a range of environmental cues. We report here that receptor for AGE (RAGE) is a central cell surface receptor for EN-RAGE (extracellular newly identified RAGE-binding protein) and related members of the S100/calgranulin superfamily. Interaction of EN-RAGEs with cellular RAGE on endothelium, mononuclear phagocytes, and lymphocytes triggers cellular activation, with generation of key proinflammatory mediators. Blockade of EN-RAGE/RAGE quenches delayed-type hypersensitivity and inflammatory colitis in murine models by arresting activation of central signaling pathways and expression of inflammatory gene mediators. These data highlight a novel paradigm in inflammation and identify roles for EN-RAGEs and RAGE in chronic cellular activation and tissue injury.

The Receptor for Advanced Glycation End Products (RAGE) Is a Cellular Binding Site for Amphoterin MEDIATION OF NEURITE OUTGROWTH AND CO-EXPRESSION OF RAGE AND AMPHOTERIN IN THE DEVELOPING NERVOUS SYSTEM

The receptor for advanced glycation end products (RAGE), a newly-identified member of the immunoglobulin superfamily, mediates interactions of advanced glycation end product (AGE)-modified proteins with endothelium and other cell types. Survey of normal tissues demonstrated RAGE expression in situations in which accumulation of AGEs would be unexpected, leading to the hypothesis that under physiologic circumstances, RAGE might mediate interaction with ligands distinct from AGEs. Sequential chromatography of bovine lung extract identified polypeptides with Mr values of ≈12,000 (p12) and ≈23,000 (p23) which bound RAGE. NH-terminal and internal protein sequence data for p23 matched that reported previously for amphoterin. Amphoterin purified from rat brain or recombinant rat amphoterin bound to purified sRAGE in a saturable and dose-dependent manner, blocked by anti-RAGE IgG or a soluble form of RAGE (sRAGE). Cultured embryonic rat neurons, which express RAGE, displayed dose-dependent binding of I-amphoterin which was prevented by blockade of RAGE using antibody to the receptor or excess soluble receptor (sRAGE). A functional correlate of RAGE-amphoterin interaction was inhibition by anti-RAGE F(ab′) and sRAGE of neurite formation by cortical neurons specifically on amphoterin-coated substrates. Consistent with a potential role for RAGE-amphoterin interaction in development, amphoterin and RAGE mRNA/antigen were co-localized in developing rat brain. These data indicate that RAGE has physiologically relevant ligands distinct from AGEs which are likely, via their interaction with the receptor, to participate in physiologic processes outside of the context of diabetes and accumulation of AGEs.

TAFI, or Plasma Procarboxypeptidase B, Couples the Coagulation and Fibrinolytic Cascades through the Thrombin-Thrombomodulin Complex

TAFI (thrombin-activatable fibrinolysis inhibitor) is a recently discovered plasma protein that can be activated by thrombin-catalyzed proteolysis to a carboxypeptidase B-like enzyme that inhibits fibrinolysis. This work shows that the thrombin-thrombomodulin complex, rather than free thrombin, is the most likely physiologic activator. Thrombomodulin increases the catalytic efficiency of the reaction by a factor of 1250, an effect expressed almost exclusively through an increase in kcat. The kinetics of the reaction conform to a model whereby thrombin can interact with either TAFI (Km = 1.0 μM) or thrombomodulin (Kd = 8.6 nM), and either binary complex so formed can then interact with the third component to form the ternary thrombin-thrombomodulin-TAFI complex from which activated TAFI is produced with kcat = 1.2 s−1. This work also shows that activated TAFI down-regulates tPA-induced fibrinolysis half-maximally at a concentration of 1.0 nM in a system of purified components. This concentration of TAFI is about 2% of the level of the zymogen in plasma, which indicates that ample activated TAFI could be generated to very significantly modulate fibrinolysis in vivo. Therefore, TAFI in vitro and possibly in vivo defines an explicit molecular connection between the coagulation and fibrinolytic cascades, such that expression of activity in the former down-regulates the activity of the latter.

The pattern recognition receptor (RAGE) is a counterreceptor for leukocyte integrins: a novel pathway for inflammatory cell recruitment.

The pattern recognition receptor, RAGE (receptor for advanced glycation endproducts), propagates cellular dysfunction in several inflammatory disorders and diabetes. Here we show that RAGE functions as an endothelial adhesion receptor promoting leukocyte recruitment. In an animal model of thioglycollate-induced acute peritonitis, leukocyte recruitment was significantly impaired in RAGE-deficient mice as opposed to wild-type mice. In diabetic wild-type mice we observed enhanced leukocyte recruitment to the inflamed peritoneum as compared with nondiabetic wild-type mice; this phenomenon was attributed to RAGE as it was abrogated in the presence of soluble RAGE and was absent in diabetic RAGE-deficient mice. In vitro, RAGE-dependent leukocyte adhesion to endothelial cells was mediated by a direct interaction of RAGE with the β2-integrin Mac-1 and, to a lower extent, with p150,95 but not with LFA-1 or with β1-integrins. The RAGE–Mac-1 interaction was augmented by the proinflammatory RAGE-ligand, S100-protein. These results were corroborated by analysis of cells transfected with different heterodimeric β2-integrins, by using RAGE-transfected cells, and by using purified proteins. The RAGE–Mac-1 interaction defines a novel pathway of leukocyte recruitment relevant in inflammatory disorders associated with increased RAGE expression, such as in diabetes, and could provide the basis for the development of novel therapeutic applications.

Increased local expression of coagulation factor X contributes to the fibrotic response in human and murine lung injury

Uncontrolled activation of the coagulation cascade contributes to the pathophysiology of several conditions, including acute and chronic lung diseases. Coagulation zymogens are considered to be largely derived from the circulation and locally activated in response to tissue injury and microvascular leak. Here we report that expression of coagulation factor X (FX) is locally increased in human and murine fibrotic lung tissue, with marked immunostaining associated with bronchial and alveolar epithelia. FXa was a potent inducer of the myofibroblast differentiation program in cultured primary human adult lung fibroblasts via TGF-beta activation that was mediated by proteinase-activated receptor-1 (PAR1) and integrin alphavbeta5. PAR1, alphavbeta5, and alpha-SMA colocalized to fibrotic foci in lung biopsy specimens from individuals with idiopathic pulmonary fibrosis. Moreover, we demonstrated a causal link between FXa and fibrosis development by showing that a direct FXa inhibitor attenuated bleomycin-induced pulmonary fibrosis in mice. These data support what we believe to be a novel pathogenetic mechanism by which FXa, a central proteinase of the coagulation cascade, is locally expressed and drives the fibrotic response to lung injury. These findings herald a shift in our understanding of the origins of excessive procoagulant activity and place PAR1 central to the cross-talk between local procoagulant signaling and tissue remodeling.

Corin, a Mosaic Transmembrane Serine Protease Encoded by a Novel cDNA from Human Heart

A novel cDNA has been identified from human heart that encodes an unusual mosaic serine protease, designated corin. Corin has a predicted structure of a type II transmembrane protein and contains two frizzled-like cysteine-rich motifs, seven low density lipoprotein receptor repeats, a macrophage scavenger receptor-like domain, and a trypsin-like protease domain in the extracellular region. Northern analysis showed that corin mRNA was highly expressed in the human heart. In mice, corin mRNA was detected by in situ hybridization in the cardiac myocytes of the embryonic heart as early as embryonic day (E) 9.5. By E11.5–13.5, corin mRNA was most abundant in the primary atrial septum and the trabecular ventricular compartment. Expression in the heart was maintained through the adult. In addition, mouse corin mRNA was also detected in the prehypertrophic chrondrocytes in developing bones. By fluorescentin situ hybridization analysis, the human corin gene was mapped to 4p12–13 where a congenital heart disease locus, total anomalous pulmonary venous return, had been previously localized. The unique domain structure and specific embryonic expression pattern suggest that corin may have a function in cell differentiation during development. The chromosomal localization of the human corin gene makes it an attractive candidate gene for total anomalous pulmonary venous return.

Thrombin activatable fibrinolysis inhibitor, a potential regulator of vascular inflammation.

The latent plasma carboxypeptidase thrombin-activable fibrinolysis inhibitor (TAFI) is activated by thrombin/thrombomodulin on the endothelial cell surface, and functions in dampening fibrinolysis. In this study, we examined the effect of activated TAFI (TAFIa) in modulating the proinflammatory functions of bradykinin, complement C5a, and thrombin-cleaved osteopontin. Hydrolysis of bradykinin and C5a and thrombin-cleaved osteopontin peptides by TAFIa was as efficient as that of plasmin-cleaved fibrin peptides, indicating that these are also good substrates for TAFIa. Plasma carboxypeptidase N, generally regarded as the physiological regulator of kinins, was much less efficient than TAFIa. TAFIa abrogated C5a-induced neutrophil activation in vitro. Jurkat cell adhesion to osteopontin was markedly enhanced by thrombin cleavage of osteopontin. This was abolished by TAFIa treatment due to the removal of the C-terminal Arg168 by TAFIa from the exposed SVVYGLR α4β1 integrin-binding site in thrombin-cleaved osteopontin. Thus, thrombin cleavage of osteopontin followed by TAFIa treatment may sequentially up- and down-modulate the pro-inflammatory properties of osteopontin. An engineered anticoagulant thrombin, E229K, was able to activate endogenous plasma TAFI in mice, and E229K thrombin infusion effectively blocked bradykinin-induced hypotension in wild-type, but not in TAFI-deficient, mice in vivo. Our data suggest that TAFIa may have a broad anti-inflammatory role, and its function is not restricted to fibrinolysis.

Oxidation of a specific methionine in thrombomodulin by activated neutrophil products blocks cofactor activity. A potential rapid mechanism for modulation of coagulation.

Endothelial thrombomodulin (TM) plays a critical role in hemostasis as a cofactor for thrombin-dependent formation of activated protein C, a potent anticoagulant. Chloramine T, H2O2, or hypochlorous acid generated from H2O2 by myeloperoxidase rapidly destroy 75-90% of TM cofactor activity. Activated PMN, the primary in vivo source of biological oxidants, also rapidly inactivate TM. Oxidation of TM by PMN is inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase. Both Met291 and Met388 in the six epidermal growth factor-like repeat domain are oxidized; however, only substitutions of Met388 lead to TM analogues that resist oxidative inactivation. We suggest that in inflamed tissues activated PMN may inactivate TM and demonstrate further evidence of the interaction between the inflammatory process and induction of thrombotic potential.

Efficacy of 23-valent pneumococcal vaccine in preventing pneumonia and improving survival in nursing home residents: double blind, randomised and placebo controlled trial

Objective To determine the efficacy of a 23-valent pneumococcal polysaccharide vaccine in people at high risk of pneumococcal pneumonia. Design Prospective, randomised, placebo controlled double blind study. Setting Nursing homes in Japan. Participants 1006 nursing home residents. Interventions Participants were randomly allocated to either 23-valent pneumococcal polysaccharide vaccine (n=502) or placebo (n=504). Main outcome measures The primary end points were the incidence of all cause pneumonia and pneumococcal pneumonia. Secondary end points were deaths from pneumococcal pneumonia, all cause pneumonia, and other causes. Results Pneumonia occurred in 63 (12.5%) participants in the vaccine group and 104 (20.6%) in the placebo group. Pneumococcal pneumonia was diagnosed in 14 (2.8%) participants in the vaccine group and 37 (7.3%) in the placebo group (P<0.001). All cause pneumonia and pneumococcal pneumonia were significantly more frequent in the placebo group than in the vaccine group: incidence per 1000 person years 55 v 91 (P<0.0006) and 12 v 32 (P<0.001), respectively. Death from pneumococcal pneumonia was significantly higher in the placebo group than in the vaccine group (35.1% (13/37) v 0% (0/14), P<0.01). The death rate from all cause pneumonia (vaccine group 20.6% (13/63) v placebo group 25.0% (26/104), P=0.5) and from other causes (vaccine group 17.7% (89/502) v placebo group (80/504) 15.9%, P=0.4) did not differ between the two study groups. Conclusion The 23-valent pneumococcal polysaccharide vaccine prevented pneumococcal pneumonia and reduced mortality from pneumococcal pneumonia in nursing home residents. Trial registration Japan Medical Association Center for Clinical Trials JMA-IIA00024.

Processing of Pro-atrial Natriuretic Peptide by Corin in Cardiac Myocytes

Corin is a type II transmembrane serine protease abundantly expressed in the heart. In a previous study using transfected 293 cells, we showed that corin converted pro-atrial natriuretic peptide (pro-ANP) to atrial natriuretic peptide (ANP), suggesting that corin is likely the pro-ANP convertase. Because other serine proteases such as thrombin and kallikrein had previously also been shown to cleave pro-ANP in vitro, it remained to demonstrate that corin is indeed the endogenous pro-ANP convertase in cardiomyocytes. In this study, we examined pro-ANP processing in a murine cardiac muscle cell line, HL-5. Northern analysis showed that corin mRNA was present in HL-5 cells. In HL-5 cells transfected with a plasmid expressing pro-ANP, recombinant pro-ANP was converted to mature ANP as determined by Western analysis, indicating the presence of the endogenous pro-ANP convertase in these cells. The processed recombinant ANP was shown to be active in an enzyme-linked immunosorbent assay-based cGMP assay in baby hamster kidney cells. The processing of recombinant pro-ANP in HL-5 cells was highly sequence-specific, because mutation R98A, but not mutations R101A and R102A, in pro-ANP prevented the conversion of pro-ANP to ANP. Expression of recombinant wild-type corin enhanced the processing of pro-ANP in HL-5 cells. In contrast, overexpression of active site mutant corin S985A or transfection of oligonucleotide small interfering RNA duplexes directed against the mouse corin gene completely inhibited the processing of recombinant pro-ANP in HL-5 cells. These results indicate that corin is the physiological pro-ANP convertase in cardiac myocytes.