Regulation of tissue inflammation by thrombin-activatable carboxypeptidase B (or TAFI)

Proximity Elongation Assay and ELISA for the Identification of Serum Diagnostic Biomarkers in Parkinson's Disease and Progressive Supranuclear Palsy

Clinical differentiation of progressive supranuclear palsy (PSP) from Parkinson's disease (PD) is challenging due to overlapping phenotypes and late onset of PSP specific symptoms, highlighting the need for easily assessable biomarkers. We used proximity elongation assay (PEA) to analyze 460 proteins in serum samples from 46 PD, 30 PSP patients, and 24 healthy controls. ANCOVA was used to identify the most promising proteins and machine learning (ML) XGBoost and random forest algorithms to assess their classification performance. Promising proteins were also quantified by ELISA. Moreover, correlations between serum biomarkers and biological and clinical features were investigated. We identified five proteins (TFF3, CPB1, OPG, CNTN1, TIMP4) showing different levels between PSP and PD, which achieved good performance (AUC: 0.892) when combined by ML. On the other hand, when the three most significant biomarkers (TFF3, CPB1 and OPG) were analyzed by ELISA, there was no difference between groups. Serum levels of TFF3 positively correlated with age in all subjects' groups, while for OPG and CPB1 such a correlation occurred in PSP patients only. Moreover, CPB1 positively correlated with disease severity in PD, while no correlations were observed in the PSP group. Overall, we identified CPB1 correlating with PD severity, which may support clinical staging of PD. In addition, our results showing discrepancy between PEA and ELISA technology suggest that caution should be used when translating proteomic findings into clinical practice.

Immunity and Coagulation in COVID-19

Discovered in late 2019, the SARS-CoV-2 coronavirus has caused the largest pandemic of the 21st century, claiming more than seven million lives. In most cases, the COVID-19 disease caused by the SARS-CoV-2 virus is relatively mild and affects only the upper respiratory tract; it most often manifests itself with fever, chills, cough, and sore throat, but also has less-common mild symptoms. In most cases, patients do not require hospitalization, and fully recover. However, in some cases, infection with the SARS-CoV-2 virus leads to the development of a severe form of COVID-19, which is characterized by the development of life-threatening complications affecting not only the lungs, but also other organs and systems. In particular, various forms of thrombotic complications are common among patients with a severe form of COVID-19. The mechanisms for the development of thrombotic complications in COVID-19 remain unclear. Accumulated data indicate that the pathogenesis of severe COVID-19 is based on disruptions in the functioning of various innate immune systems. The key role in the primary response to a viral infection is assigned to two systems. These are the pattern recognition receptors, primarily members of the toll-like receptor (TLR) family, and the complement system. Both systems are the first to engage in the fight against the virus and launch a whole range of mechanisms aimed at its rapid elimination. Normally, their joint activity leads to the destruction of the pathogen and recovery. However, disruptions in the functioning of these innate immune systems in COVID-19 can cause the development of an excessive inflammatory response that is dangerous for the body. In turn, excessive inflammation entails activation of and damage to the vascular endothelium, as well as the development of the hypercoagulable state observed in patients seriously ill with COVID-19. Activation of the endothelium and hypercoagulation lead to the development of thrombosis and, as a result, damage to organs and tissues. Immune-mediated thrombotic complications are termed "immunothrombosis". In this review, we discuss in detail the features of immunothrombosis associated with SARS-CoV-2 infection and its potential underlying mechanisms.

Complement and coagulation crosstalk - Factor H in the spotlight

The immune complement and the coagulation systems are blood-based proteolytic cascades that are activated by pathway-specific triggers, based on protein-protein interactions and enzymatic cleavage reactions. Activation of these systems is finely balanced and controlled through specific regulatory mechanisms. The complement and coagulation systems are generally viewed as distinct, but have common evolutionary origins, and several interactions between these homologous systems have been reported. This complement and coagulation crosstalk can affect activation, amplification and regulatory functions in both systems. In this review, we summarize the literature on coagulation factors contributing to complement alternative pathway activation and regulation and highlight molecular interactions of the complement alternative pathway regulator factor H with several coagulation factors. We propose a mechanism where factor H interactions with coagulation factors may contribute to both complement and coagulation activation and regulation within the haemostatic system and fibrin clot microenvironment and introduce the emerging role of factor H as a modulator of coagulation. Finally, we discuss the potential impact of these protein interactions in diseases associated with factor H dysregulation or deficiency as well as evidence of coagulation dysfunction.

Involvement of complement peptides C3a and C5a in osteoarthritis pathology

Osteoarthritis (OA) affects more than 500 million people worldwide and is among the five diseases in Germany causing the highest suffering of the patients and cost for the society. The quality of life of OA patients is severely compromised, and adequate therapy is lacking owing to a knowledge gap that acts as a major barrier to finding safe and effective solutions. Chronic, low-grade inflammation plays a central role in OA pathogenesis and is associated with both OA pain and disease progression. Innate immune pathways, such as the complement- and pattern-recognition receptor pathways, are pivotal to the inflammation in OA and key components of the innate immune system implicated in OA include DAMP-TLR signaling, the complement system, carboxypeptidase B (CPB), and mononuclear cells. Anaphylatoxins C3a and C5a are small polypeptides (77 and 74 amino acids, respectively) which are released by proteolytic cleavage of the complement components C3 and C5. The alternative complement pathway seems to play a crucial role in OA pathogenesis as these complement components, mostly C3 and its activation peptide C3a, were detected at high levels in osteoarthritic cartilage, synovial membrane, and cultured chondrocytes. Targeting the complement system by using anti-complement drugs as a therapeutic option bears the risk of major side effects such as increasing the risk of infection, interfering with cell regeneration and metabolism, and suppressing the clearance of immune complexes. Despite those adverse effects, several synthetic complement peptide antagonists show promising effects in ameliorating inflammatory cell responses also in joint tissues.

Biomarkers of connective tissue disease-associated interstitial lung disease in bronchoalveolar lavage fluid: A label-free mass spectrometry-based relative quantification study

BACKGROUND

The pathogenesis of connective tissue disease-associated interstitial lung disease (CTD-ILD) is unclear. This study aims to identify differentially expressed proteins (DEPs) in CTD-ILD to determine the potential role of these DEPs that may play in the pathogenesis of CTD-ILD and to offer potential therapeutic targets.

METHODS

Bronchoalveolar lavage fluid (BALF) samples were collected from four patients with CTD-ILD and four patients without CTD-ILD. Label-free mass spectrometry-based relative quantification was used to identify the DEPs. Bioinformatics were used to determine the potential biological processes and signaling pathways associated with these DEPs.

RESULTS

We found 65 upregulated DEPs including SFTPD, CADM1, ACSL4, TSTD1, CD163, LUM, SIGLEC1, CPB2, TGFBI and HGD, and 67 downregulated DEPs including SGSH, WIPF1, SIL1, RAB20, OAS3, GMPR2, PLBD1, DNAJC3, RNASET2 and OAS2. The results of GO functional annotation for the DEPs showed that the DEPS were mainly enriched in the binding, cellular anatomical entity, cellular processes, and biological regulation GO terms. The results of KEGG analyses showed that the pathways most annotated with the DEPs were complement and coagulation cascades, metabolic pathways, pathways in cancer, and PPAR signaling pathway. COG analyses further informed the functions associated with these DEPs, with most focused on signal transduction mechanisms; posttranslational modification, protein turnover, chaperones; intracellular trafficking, secretion, and vesicular transport; amino acid transport and metabolism; and lipid transport and metabolism.

CONCLUSIONS

DEPs identified between patients with vs. without CTD-ILD may play important roles in the development of CTD-ILD and are potential new biomarkers for early diagnosis of CTD-ILD.

Endothelial dysfunction and thromboembolism in children, adolescents, and young adults with acute lymphoblastic leukemia

Endothelial dysfunction has not previously been investigated as a thrombogenic risk factor among patients with acute lymphoblastic leukemia (ALL), known to be at high risk of thromboembolism. We retrospectively explored the association between three circulating biomarkers of endothelial dysfunction (thrombomodulin, syndecan-1, VEGFR-1) measured in prospectively collected blood samples and risk of thromboembolism in 55 cases and 165 time-matched controls, treated according to the NOPHO ALL2008 protocol. In age-, sex-, and risk group-adjusted analysis, increasing levels of thrombomodulin and VEGFR-1 were independently associated with increased odds of developing thromboembolism (OR 1.37 per 1 ng/mL [95% CI 1.20‒1.56, P < 0.0001] and OR 1.21 per 100 pg/mL [95% CI 1.02‒1.21, P = 0.005], respectively). These associations remained significant when including only samples drawn >30 days before thromboembolic diagnosis. Thrombomodulin levels were on average 3.2 ng/mL (95% CI 2.6-8.2 ng/mL) higher in samples with measurable asparaginase activity (P < 0.0001). Among single nucleotide variants located in or neighboring coding genes for the three biomarkers, none were significantly associated with odds of thromboembolism. If results are validated in another cohort, thrombomodulin and VEGFR-1 could serve as predictive biomarkers, identifying patients in need of preemptive antithrombotic prophylaxis.

Longitudinal proteomic analysis of severe COVID-19 reveals survival-associated signatures, tissue-specific cell death, and cell-cell interactions

Mechanisms underlying severe coronavirus disease 2019 (COVID-19) disease remain poorly understood. We analyze several thousand plasma proteins longitudinally in 306 COVID-19 patients and 78 symptomatic controls, uncovering immune and non-immune proteins linked to COVID-19. Deconvolution of our plasma proteome data using published scRNA-seq datasets reveals contributions from circulating immune and tissue cells. Sixteen percent of patients display reduced inflammation yet comparably poor outcomes. Comparison of patients who died to severely ill survivors identifies dynamic immune-cell-derived and tissue-associated proteins associated with survival, including exocrine pancreatic proteases. Using derived tissue-specific and cell-type-specific intracellular death signatures, cellular angiotensin-converting enzyme 2 (ACE2) expression, and our data, we infer whether organ damage resulted from direct or indirect effects of infection. We propose a model in which interactions among myeloid, epithelial, and T cells drive tissue damage. These datasets provide important insights and a rich resource for analysis of mechanisms of severe COVID-19 disease.

Increased Thrombin-Activatable Fibrinolysis Inhibitor in Response to Sublingual Immunotherapy for Allergic Rhinitis

OBJECTIVES/HYPOTHESIS

The objective of this study was to determine the role of thrombin-activatable fibrinolysis inhibitor (TAFI) as a candidate biomarker for therapeutic efficacy of sublingual immunotherapy (SLIT) and to identify the role of TAFI in the pathogenesis of allergic rhinitis (AR).

STUDY DESIGN

Retrospective cohort study and laboratory study.

METHODS

Serum was collected from patients with allergies to Japanese cedar pollen before, during, and after treatment with SLIT. We measured the levels of immunoreactive TAFI, C3a, and C5a in serum by enzyme-linked immunosorbent assay (ELISA) and assessed their relative impact on a combined symptom-medication score. We also examined the impact of TAFI on mast cells and fibroblasts in experiments performed in vitro.

RESULTS

Serum levels of TAFI increased significantly in response to SLIT. By contrast, serum C3a levels decreased significantly over time; we observed a significant negative correlation between serum levels of TAFI versus C3a and symptom-medication score. Mast cell degranulation was inhibited in response to TAFI, as it was the expression of both CCL11 and CCL5 in cultured fibroblasts.

CONCLUSIONS

High serum levels of TAFI may be induced by SLIT. TAFI may play a critical protective role in pathogenesis of AR by inactivating C3a and by inhibiting mast cell degranulation and chemokines expression in fibroblasts.

LEVEL OF EVIDENCE

4 Laryngoscope, 2021.

Plasma proteomics reveals tissue-specific cell death and mediators of cell-cell interactions in severe COVID-19 patients

COVID-19 has caused over 1 million deaths globally, yet the cellular mechanisms underlying severe disease remain poorly understood. By analyzing several thousand plasma proteins in 306 COVID-19 patients and 78 symptomatic controls over serial timepoints using two complementary approaches, we uncover COVID-19 host immune and non-immune proteins not previously linked to this disease. Integration of plasma proteomics with nine published scRNAseq datasets shows that SARS-CoV-2 infection upregulates monocyte/macrophage, plasmablast, and T cell effector proteins. By comparing patients who died to severely ill patients who survived, we identify dynamic immunomodulatory and tissue-associated proteins associated with survival, providing insights into which host responses are beneficial and which are detrimental to survival. We identify intracellular death signatures from specific tissues and cell types, and by associating these with angiotensin converting enzyme 2 (ACE2) expression, we map tissue damage associated with severe disease and propose which damage results from direct viral infection rather than from indirect effects of illness. We find that disease severity in lung tissue is driven by myeloid cell phenotypes and cell-cell interactions with lung epithelial cells and T cells. Based on these results, we propose a model of immune and epithelial cell interactions that drive cell-type specific and tissue-specific damage in severe COVID-19.

Molecular characterization of carboxypeptidase B-like (CPB) in Scylla paramamosain and its role in white spot syndrome virus and Vibrio alginolyticus infection

Carboxypeptidase plays an important physiological role in the tissues and organs of animals. In this study, we cloned an entire 2316 bp carboxypeptidase B-like (CPB) sequence with a 1302 bp open reading frame encoding a 434 amino acid peptide from Scylla paramamosain. The CPB gene was expressed highly in hepatopancreas and decreased in crab hemocytes after challenges with white spot syndrome virus (WSSV) or Vibrio alginolyticus. After CPB gene knockdown using double-stranded RNA (CPB-dsRNA), the expression of JAK, STAT, C-type lectin, crustin antimicrobial peptide, Toll-like receptors, prophenoloxidase, and myosin II essential light chain-like protein were down-regulated in hemocytes at 24 h post dsRNA treatment. CPB knockdown decreases total hemocyte count in crabs indicated that CPB may negatively regulate crab hemocyte proliferation in crabs. CPB showed an inhibitory effect on hemocyte apoptosis in crabs infected with WSSV or V. alginolyticus. The phagocytosis rate of WSSV by hemocytes was increased after CPB-dsRNA treatment. After WSSV challenge, the mortality and WSSV copy number were both decreased but the rate of hemocyte apoptosis was increased in CPB-dsRNA-treated crabs. The results indicate that the antiviral activity of the crabs was enhanced when CPB was knocked down, indicating WSSV may take advantage of CPB to benefit its replication. In contrast, the absence of CPB in crabs increased mortality following the V. alginolyticus challenge. The phagocytosis rate of V. alginolyticus by hemocytes was increased after CPB-dsRNA treatment. It was revealed that CPB may play a positive role in the immune response to V. alginolyticus through increasing the phagocytosis rate of V. alginolyticus. This research further adds to our understanding of the CPB and identifies its potential role in the innate immunity of crabs.

TAFI deficiency causes maladaptive vascular remodeling after hemophilic joint bleeding

Excessive vascular remodeling is characteristic of hemophilic arthropathy (HA) and may contribute to joint bleeding and the progression of HA. Mechanisms for pathological vascular remodeling after hemophilic joint bleeding are unknown. In hemophilia, activation of thrombin-activatable fibrinolysis inhibitor (TAFI) is impaired, which contributes to joint bleeding and may also underlie the aberrant vascular remodeling. Here, hemophilia A (factor VIII-deficient; FVIII-deficient) mice or TAFI-deficient mice with transient (antibody-induced) hemophilia A were used to determine the role of FVIII and TAFI in vascular remodeling after joint bleeding. Excessive vascular remodeling and vessel enlargement persisted in FVIII-deficient and TAFI-deficient mice, but not in transient hemophilia WT mice, after similar joint bleeding. TAFI-overexpression in FVIII-deficient mice prevented abnormal vessel enlargement and vascular leakage. Age-related vascular changes were observed with FVIII or TAFI deficiency and correlated positively with bleeding severity after injury, supporting increased vascularity as a major contributor to joint bleeding. Antibody-mediated inhibition of uPA also prevented abnormal vascular remodeling, suggesting that TAFI's protective effects include inhibition of uPA-mediated plasminogen activation. In conclusion, the functional TAFI deficiency in hemophilia drives maladaptive vascular remodeling in the joints after bleeding. These mechanistic insights allow targeted development of potentially new strategies to normalize vascularity and control rebleeding in HA.

Auxiliary activation of the complement system and its importance for the pathophysiology of clinical conditions

Activation and regulation of the cascade systems of the blood (the complement system, the coagulation/contact activation/kallikrein system, and the fibrinolytic system) occurs via activation of zymogen molecules to specific active proteolytic enzymes. Despite the fact that the generated proteases are all present together in the blood, under physiological conditions, the activity of the generated proteases is controlled by endogenous protease inhibitors. Consequently, there is remarkable little crosstalk between the different systems in the fluid phase. This concept review article aims at identifying and describing conditions where the strict system-related control is circumvented. These include clinical settings where massive amounts of proteolytic enzymes are released from tissues, e.g., during pancreatitis or post-traumatic tissue damage, resulting in consumption of the natural substrates of the specific proteases and the available protease inhibitor. Another example of cascade system dysregulation is disseminated intravascular coagulation, with canonical activation of all cascade systems of the blood, also leading to specific substrate and protease inhibitor elimination. The present review explains basic concepts in protease biochemistry of importance to understand clinical conditions with extensive protease activation.

Sex-specific effect of CPB2 Ala147Thr but not Thr325Ile variants on the risk of venous thrombosis: A comprehensive meta-analysis

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI), encoded by the Carboxypeptidase B2 gene (CPB2), is an inhibitor of fibrinolysis and plays a role in the pathogenesis of venous thrombosis. Experimental findings support a functional role of genetic variants in CPB2, while epidemiological studies have been unable to confirm associations with risk of venous thrombosis. Sex-specific effects could underlie the observed inconsistent associations between CPB2 genetic variants and venous thrombosis.

METHODS

A comprehensive literature search was conducted for associations between Ala147Thr and Thr325Ile variants with venous thrombosis. Authors were contacted to provide sex-specific genotype counts from their studies. Combined and sex-specific random effects meta-analyses were used to estimate a pooled effect estimate for primary and secondary genetic models.

RESULTS

A total of 17 studies met the inclusion criteria. A sex-specific meta-analysis applying a dominant model supported a protective effect of Ala147Thr on venous thrombosis in females (OR = 0.81, 95%CI: 0.68,0.97; p = 0.018), but not in males (OR = 1.06, 95%CI:0.96-1.16; p = 0.263). The Thr325Ile did not show a sex-specific effect but showed variation in allele frequencies by geographic region. A subgroup analysis of studies in European countries showed decreased risk, with a recessive model (OR = 0.83, 95%CI:0.71-0.97, p = 0.021) for venous thrombosis.

CONCLUSIONS

A comprehensive literature review, including unpublished data, provided greater statistical power for the analyses and decreased the likelihood of publication bias influencing the results. Sex-specific analyses explained apparent discrepancies across genetic studies of Ala147Thr and venous thrombosis. While, careful selection of genetic models based on population genetics, evolutionary and biological knowledge can increase power by decreasing the need to adjust for testing multiple models.

Plasma proteins as potential targets of abnormal Savda syndrome in asthma patients treated with unique Uighur prescription

The therapeutic effect of Uighur prescription on abnormal Savda in asthma patients was evaluated using plasma proteomics in order to elucidate the biological mechanism and identify potential therapeutic targets of abnormal Savda. In the present study, 40 asthma patients with abnormal Savda including abnormal Savda Munziq and Savda Mushil were enrolled and treated with Uighur prescription. The effect of Uighur prescription on protein expression and potential targets was investigated by isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics and bioinformatics analysis. Expression of candidate proteins was verified by an enzyme-linked immunosorbent assay. Following treatment with the Uighur prescription, 22 proteins were differentially expressed in the plasma of patients with asthma and abnormal Savda. The majority of these proteins were localized in intermediate filaments and the cytoskeleton and acted as antioxidant enzymes and binding proteins. Furthermore, they participated in the defense and inflammatory response, and the response to oxidative stress and wound healing. Peroxiredoxin 2 and carboxypeptidase B2 expression was significantly upregulated, whereas S100A7 was considerably downregulated in the whole plasma of patients (all P<0.05) in accordance with the iTRAQ proteomics data. Uighur prescription of abnormal Savda may affect the whole regulatory network of protein expression that is altered following the development of abnormal Savda in patients with asthma.

Recombinant Thrombomodulin Modulates Murine Colitis Possibly via High-Mobility Group Box 1 Protein Inhibition

BACKGROUND AND AIM

Thrombomodulin (TM) is an anticoagulant cofactor protein. We hypothesized that its recombinant soluble TM (rhTM) form, widely used to treat disseminated intravascular coagulation, might have anti-inflammatory action in inflammatory bowel disease (IBD), possibly through its inhibition of high-mobility group box 1 protein (HMGB1).

METHODS

We investigated inflammatory effects of HMGB1 and anti-inflammatory effect of rhTM in dextran sulfate sodium (DSS)-treated mice, some cell lines and ulcerative colitis (UC) patients, particularly focusing on changes of vascular endothelial adhesion molecules.

RESULTS

Treatments with rhTM significantly attenuated DSS-treated mice clinically and histologically. The mRNA levels of proinflammatory cytokines and adhesion molecules were decreased by rhTM. Increased inflammatory cells in the colonic mucosa strongly expressed HMGB1 in the cytoplasm in the DSS-treated mice and UC patients' colonic mucosa, which were significantly decreased by rhTM in mice. In in vitro experiments, rhTM significantly decreased the mRNA levels of tumor necrosis factor-alpha (TNF-α) and adhesion molecules increased by endotoxin exposures in RAW 264.7 (macrophage cell line) and bEND.3 cells (endothelial cell line), suggesting the proinflammatory role of HMGB1 in TNF-α production from macrophages.

CONCLUSIONS

These findings suggest that rhTM may be useful for the treatment of IBD by attenuating inflammatory cytokine production and adhesion molecule expression, partly because of its inhibition of HMGB1.

Complement pathway amplifies caspase-11-dependent cell death and endotoxin-induced sepsis severity

Cell death and release of proinflammatory mediators contribute to mortality during sepsis. Specifically, caspase-11-dependent cell death contributes to pathology and decreases in survival time in sepsis models. Priming of the host cell, through TLR4 and interferon receptors, induces caspase-11 expression, and cytosolic LPS directly stimulates caspase-11 activation, promoting the release of proinflammatory cytokines through pyroptosis and caspase-1 activation. Using a CRISPR-Cas9-mediated genome-wide screen, we identified novel mediators of caspase-11-dependent cell death. We found a complement-related peptidase, carboxypeptidase B1 (Cpb1), to be required for caspase-11 gene expression and subsequent caspase-11-dependent cell death. Cpb1 modifies a cleavage product of C3, which binds to and activates C3aR, and then modulates innate immune signaling. We find the Cpb1-C3-C3aR pathway induces caspase-11 expression through amplification of MAPK activity downstream of TLR4 and Ifnar activation, and mediates severity of LPS-induced sepsis (endotoxemia) and disease outcome in mice. We show C3aR is required for up-regulation of caspase-11 orthologues, caspase-4 and -5, in primary human macrophages during inflammation and that c3aR1 and caspase-5 transcripts are highly expressed in patients with severe sepsis; thus, suggesting that these pathways are important in human sepsis. Our results highlight a novel role for complement and the Cpb1-C3-C3aR pathway in proinflammatory signaling, caspase-11 cell death, and sepsis severity.

Low-grade inflammation as a key mediator of the pathogenesis of osteoarthritis

Osteoarthritis (OA) has long been viewed as a degenerative disease of cartilage, but accumulating evidence indicates that inflammation has a critical role in its pathogenesis. Furthermore, we now appreciate that OA pathogenesis involves not only breakdown of cartilage, but also remodelling of the underlying bone, formation of ectopic bone, hypertrophy of the joint capsule, and inflammation of the synovial lining. That is, OA is a disorder of the joint as a whole, with inflammation driving many pathologic changes. The inflammation in OA is distinct from that in rheumatoid arthritis and other autoimmune diseases: it is chronic, comparatively low-grade, and mediated primarily by the innate immune system. Current treatments for OA only control the symptoms, and none has been FDA-approved for the prevention or slowing of disease progression. However, increasing insight into the inflammatory underpinnings of OA holds promise for the development of new, disease-modifying therapies. Indeed, several anti-inflammatory therapies have shown promise in animal models of OA. Further work is needed to identify effective inhibitors of the low-grade inflammation in OA, and to determine whether therapies that target this inflammation can prevent or slow the development and progression of the disease.

Effects of Rituximab and Infliximab Treatment on Carboxypeptidase B and Its Substrates in RA Synovium

Objective.

We evaluated the synovial effects of 2 potent biologic rheumatoid arthritis (RA) therapies, focusing on their effect on the expression level of carboxypeptidase B (CPB) and its substrates.

Methods.

Patients with RA receiving infliximab (IFX; n = 9) or rituximab (RTX; n = 5) had an arthroscopic synovial biopsy at baseline and 16 weeks posttherapy. Expression of CPB, C5a, osteopontin (OPN), CD3, CD20, CD55, and CD68 was assessed by immunohistochemistry and image analysis, and compared with OA synovium. RA disease activity score was assessed at multiple timepoints. Serial serum samples were analyzed for soluble CPB and C5a levels.

Results.

The baseline clinical characteristics of patients receiving IFX and RTX were similar. At the time of the second biopsy, 50% of patients had achieved a European League Against Rheumatism good or moderate response. At baseline, expression of CPB, C5a, and OPN was markedly higher in RA compared with OA synovium and correlated with mononuclear cell infiltration. There was an overall reduction in synovial expression of CPB, C5a, and OPN paralleling a reduction in mononuclear cell infiltration, but these changes were not associated with clinical response. After an early reduction in serum C5a levels, these returned to baseline levels at later timepoints.

Conclusion.

In response to IFX and RTX treatment, RA synovial expression of CPB, C5a, and OPN decrease independently of the clinical response, reflecting the complex proinflammatory and antiinflammatory effects of this pathway.

Potential diagnostic markers for disseminated intravascular coagulation of sepsis

Disseminated intravascular coagulation (DIC) is an acquired thrombo-haemorrhagic disorder which arises in clinical scenarios like sepsis, trauma and malignancies. The clinic-laboratory diagnosis of DIC is made in a patient who develops the combination of laboratory abnormalities in the appropriate clinical scenario. The most common laboratory parameters in this setting have been the clotting profile, platelet count, serum fibrinogen and fibrin degradation markers. These tests had the advantage that they could be performed easily and in most laboratories. However, with the better understanding of the pathophysiology of DIC, in recent years, more specific tests have been suggested to be useful in this setting. The newer tests can also prove to be useful in prognostication in DIC. In addition, they may provide assistance in the selection and monitoring of patients diagnosed with DIC.

Selective modulation of thrombin-activatable fibrinolysis inhibitor (TAFI) activation by thrombin or the thrombin-thrombomodulin complex using TAFI-derived peptides

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a risk factor for coronary heart disease. TAFI is proteolytically activated by thrombin, the thrombin-thrombomodulin complex and plasmin. Once active, it dampens fibrinolysis and inflammation. The aim of this study was to generate TAFI-derived peptides that specifically modulate TAFI activation and activity.

METHODS

Thirty-four overlapping TAFI peptides, and modifications thereof, were synthesized. The effects of these peptides on TAFI activation and TAFIa activity were determined. In addition, the binding of the peptides to thrombin were determined.

RESULTS

Four peptides (peptides 2, 18, 19 and 34) inhibited TAFI activation and two peptides (peptides 14 and 24) inhibited TAFIa activity directly. Peptide 2 (Arg12-Glu28) and peptide 34 (Cys383-Val401) inhibited TAFI activation by the thrombin-thrombomodulin complex with IC50 values of 7.3 ± 1.8 and 6.1 ± 0.9 μm, respectively. However, no inhibition was observed in the absence of thrombomodulin. This suggests that the regions Arg12-Glu28 and Cys383-Val401 in TAFI are involved in thrombomodulin-mediated TAFI activation. Peptide 18 (Gly205-Ser221) and peptide 19 (Arg214-Asp232) inhibited TAFI activation by thrombin and the thrombin-thrombomodulin complex. Furthermore, these peptides bound to thrombin (KD : 1.5 ± 0.4 and 0.52 ± 0.07 μm for peptides 18 and 19, respectively), suggesting that Gly205-Asp232 of TAFI is involved in binding to thrombin. Peptide 14 (His159-His175) inhibited TAFIa activity. The inhibition was TAFIa specific, because no effect on the homologous enzyme carboxypeptidase B was observed.

CONCLUSIONS

Thrombin-activatable fibrinolysis inhibitor-derived peptides show promise as new tools to modulate TAFI activation and TAFIa activity. Furthermore, these peptides revealed potential binding sites on TAFI for thrombin and the thrombin-thrombomodulin complex.

Carboxypeptidase B2 deficiency reveals opposite effects of complement C3a and C5a in a murine polymicrobial sepsis model

BACKGROUND AND OBJECTIVES

Carboxypeptidase B2 (CPB2) is a basic carboxypeptidase with fibrin and complement C3a and C5a as physiological substrates. We hypothesized that in polymicrobial sepsis, CPB2-deficient mice would have sustained C5a activity, leading to disease exacerbation.

METHODS

Polymicrobial sepsis was induced by cecal ligation and puncture (CLP).

RESULTS

Contrary to our hypothesis, Cpb2(-/-) mice had significantly improved survival, with reduced lung edema, less liver and kidney damage, and less disseminated intravascular coagulation. Hepatic pro-CPB2 was induced by CLP, leading to increased pro-CPB2 levels. Thrombomodulin present on mesothelium supported thrombin activation of pro-CPB2. Both wild-type and Cpb2(-/-) animals treated with a C5a receptor antagonist had improved survival, demonstrating that C5a was detrimental in this model. Treatment with a fibrinolysis inhibitor, tranexamic acid, caused a decrease in survival in both genotypes; however, the Cpb2(-/-) animals retained their survival advantage. Administration of a C3a receptor antagonist exacerbated the disease in both wild-type and Cpb2(-/-) mice and eliminated the survival advantage of Cpb2(-/-) mice. C5a receptor is expressed in both peritoneal macrophages and neutrophils; in contrast, C3a receptor expression is restricted to peritoneal macrophages, and C3a induced signaling in macrophages but not neutrophils.

CONCLUSIONS

While C5a exacerbates the peritonitis, resulting in a deleterious generalized inflammatory state, C3a activation of peritoneal macrophages may limit the initial infection following CLP, thereby playing a diametrically opposing protective role in this polymicrobial sepsis model.

Thrombomodulin/activated protein C system in septic disseminated intravascular coagulation

The thrombomodulin (TM)/activated protein C (APC) system plays an important role in maintaining the homeostasis of thrombosis and hemostasis and maintaining vascular integrity in vivo. TM expressed on vascular endothelium binds to thrombin, forming a 1:1 complex and acts as an anticoagulant. In addition, the thrombin-TM complex activates protein C to produce APC, which inactivates factors VIIIa and Va in the presence of protein S, thereby inhibiting further thrombin formation. Intriguingly, APC possesses anti-inflammatory as well as cytoprotective activities. Moreover, the extracellular domain of TM also possesses APC-independent anti-inflammatory and cytoprotective activities. Of note, the TM/APC system is compromised in disseminated intravascular coagulation (DIC) caused by sepsis due to various mechanisms, including cleavage of cell-surface TM by exaggerated cytokines and proteases produced by activated inflammatory cells. Thus, it is reasonable to assume that reconstitution of the TM/APC system by recombinant proteins would alleviate sepsis and DIC. On the basis of the success of the Protein C Worldwide Evaluation in Severe Sepsis (PROWESS) trial, the FDA approved the use of recombinant human APC (rhAPC) for severe sepsis patients in 2002. However, subsequent clinical trials failed to show clinical benefits for rhAPC, and an increased incidence of hemorrhage-related adverse events was noted, which prompted the industry to withdraw rhAPC from the market. On the other hand, recombinant human soluble TM (rTM) has been used for treatment of individuals with DIC since 2008 in Japan, and a phase III clinical trial evaluating the efficacy of rTM in severe sepsis patients with coagulopathy is now ongoing in the USA, South America, Asia, Australia, European Union, and other countries. This review article discusses the molecular mechanisms by which the TM/APC system produces anticoagulant as well as anti-inflammatory and cytoprotective activities in septic DIC patients.

A role for arginine-12 in thrombin-thrombomodulin-mediated activation of thrombin-activatable fibrinolysis inhibitor

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a proenzyme that links coagulation and fibrinolysis. TAFI can be activated by thrombin, the thrombin-thrombomodulin complex and plasmin through cleavage of the first 92 amino acids from the enzyme. In silico analysis of the TAFI sequence revealed a potential thrombin cleavage site at Arg12. The aim of this study was to determine whether TAFI can be cleaved at Arg12 and whether this cleavage plays a role in TAFI activation.

METHODS

A peptide based on the first 18 amino acids of TAFI was used to determine whether thrombin was able to cleave at Arg12. Mass spectrometry was performed to determine whether the Arg12-cleaved peptide was released from full-length TAFI. Furthermore, a TAFI mutant in which Arg12 was replaced by a glutamine (TAFI-R12Q) was constructed and characterized with respect to its activation kinetics.

RESULTS

The peptide and mass spectrometry data showed that thrombin was able to cleave TAFI at Arg12, but with low efficiency in full-length TAFI. Characterization of TAFI-R12Q showed no difference in thrombin-mediated activation from wild-type TAFI. However, there was an approximately 60-fold impairment in activation of TAFI-R12Q by the thrombin-thrombomodulin complex.

CONCLUSIONS

Arg12 of TAFI plays an important role in thrombomodulin-mediated TAFI activation by thrombin. Thrombin is able to cleave TAFI at Arg12, but it remains to be determined whether Arg12 is part of an exosite for thrombomodulin or whether cleavage at Arg12 accelerates thrombomodulin-mediated TAFI activation.

Tissue factor pathway inhibitor and thrombin-activatable carboxypeptidase B for prediction of early atherosclerosis in gouty arthritis

BACKGROUND

Gouty arthritis (GA) is a chronic inflammatory arthritis in which both clinical and subclinical atherosclerosis are more frequent. The dynamic equilibrium between coagulation and fibrinolysis is impaired in inflammatory diseases. We determined TFPI and TAFI antigen levels in GA patients and evaluated their association with subclinical atherosclerosis.

METHODS

We included 45 GA patients (41 males, 4 females; mean age: 51.6years) and 25 asymptomatic hyperuricemic (AHU) subjects (19 males, 6 females; mean age: 48.1years). Cardiovascular risk factors were determined. TAFI and TFPI levels were determined by ELISA. B-mode ultrasonography was used to detect subclinical atherosclerosis.

RESULTS

Cardiovascular risk factors were similar in both groups. The carotid IMT was significantly higher in GA group than in AHU group (0.74±0.23mm vs. 0.61±0.13mm, p=0.009). TFPI level was significantly higher in GA group than in AHU group (86.2±48.9ng/mL vs. 25.8±21.4ng/mL, p<0.001); TAFI antigen was significantly higher in AHU group (22.6±3.6ng/mL vs. 25.7±5.3ng/mL, p=0.006) than in GA patients. Atherosclerotic plaque formation was more frequent in GA group (p=0.041). When GA patients with and without plaques were compared, the first group had significantly higher mean age (p=0.01) and TFPI level (p=0.028). TFPI level correlated with carotid IMT (r=0.302; p=0.028). Logistic regression analysis showed that age (OR: 1.236, 95%CI: 1.059-1.443, p=0.007) and TFPI (OR: 1.031, 95%CI: 1.008-1.054, p=0.008) were independent risk factors for the presence of plaques.

CONCLUSIONS

GA patients had more frequent subclinical atherosclerosis than subjects with AHU. Higher TFPI levels in GA patients -probably associated with enhanced endothelial damage- were related to subclinical atherosclerosis. Lower TAFI levels in GA pointed to impaired fibrinolysis.

Brief report: carboxypeptidase B serves as a protective mediator in osteoarthritis

OBJECTIVE

We previously demonstrated that carboxypeptidase B (CPB) protects against joint erosion in rheumatoid arthritis by inactivating complement component C5a. We also found that levels of CPB are abnormally high in the synovial fluid of individuals with another joint disease, osteoarthritis (OA). We undertook this study to investigate whether CPB plays a role in the pathogenesis of OA.

METHODS

We compared the development of OA in CPB-deficient (Cpb2(-/-) ) mice and wild-type mice by subjecting them to medial meniscectomy and histologically assessing cartilage damage, osteophyte formation, and synovitis in the stifle joints 4 months later. We measured levels of proCPB, proinflammatory cytokines, and complement components in synovial fluid samples from patients with symptomatic and radiographic knee OA. Finally, we used enzyme-linked immunosorbent assay, flow cytometry, and hemolytic assays to assess the effect of CPB on formation of membrane attack complex (MAC)-a complement effector critical to OA pathogenesis.

RESULTS

Cpb2(-/-) mice developed dramatically greater cartilage damage than did wild-type mice (P < 0.01) and had a greater number of osteophytes (P < 0.05) and a greater degree of synovitis (P < 0.05). In synovial fluid samples from OA patients, high levels of proCPB were associated with high levels of proinflammatory cytokines and complement components, and levels of proCPB correlated positively with those of MAC. In in vitro complement activation assays, activated CPB suppressed the formation of MAC as well as MAC-induced hemolysis.

CONCLUSION

Our data suggest that CPB protects against inflammatory destruction of the joints in OA, at least in part by inhibiting complement activation.

C3a, C5a renal expression and their receptors are correlated to severity of IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN) is the most common primary kidney disease, often leading to chronic renal failure. Complement activation products C3a and C5a have broad pro-inflammatory potential through their receptors, C3aR and C5aR, and contribute to the pathogenesis of several inflammatory and autoimmune diseases, but their roles in IgAN are poorly defined.

PURPOSE

This study aimed to establish correlations between renal C3a, C5a, C3aR, C5aR, or serum/urinary C3a, C5a with clinical features and renal histopathology in patients with IgAN.

METHODS

Eighty-three patients with renal biopsy proven IgAN were investigated. Thirty patients fulfilled Haas's II, 30 fulfilled Haas's III and 23 fulfilled Haas's IV criteria. Deposition of C3a and C5a was assessed by immunohistochemistry. C3aR and C5aR mRNAs and proteins in kidney tissue were examined by real-time quantitative PCR (RT-qPCR) and immunohistochemical staining, respectively. C3a and C5a levels were quantified by ELISA in serum and urine samples of 30 IgAN patients, 10 control subjects and 10 septic patients.

RESULTS

Renal C3a and C5a deposition and C3aR and C5aR expression increased with increasing grades of renal pathology in IgAN patients. They positively correlated with proteinuria and serum creatinine (SCr), but not serum C-reactive protein (CRP) or complement 3 (C3). Serum C3a and C5a increased to levels comparable to septic patients but did not differ among IgAN sub-groups. In contrast, urinary C3a and C5a increased significantly and correlated positively with renal pathological grades.

CONCLUSIONS

In patients with IgAN, urinary and renal C3a and C5a and renal expression of C3aR and C5aR are significantly correlated with the activity and severity of renal injury. This observation warrants further study into the roles of C3a, C5a and their receptors in the pathogenesis of IgAN and as potential therapeutic targets.

The role of thrombomodulin lectin-like domain in inflammation

Thrombomodulin (TM) is a cell surface glycoprotein which is widely expressed in a variety of cell types. It is a cofactor for thrombin binding that mediates protein C activation and inhibits thrombin activity. In addition to its anticoagulant activity, recent evidence has revealed that TM, especially its lectin-like domain, has potent anti-inflammatory function through a variety of molecular mechanisms. The lectin-like domain of TM plays an important role in suppressing inflammation independent of the TM anticoagulant activity. This article makes an extensive review of the role of TM in inflammation. The molecular targets of TM lectin-like domain have also been elucidated. Recombinant TM protein, especially the TM lectin-like domain may play a promising role in the management of sepsis, glomerulonephritis and arthritis. These data demonstrated the potential therapeutic role of TM in the treatment of inflammatory diseases.

Complement component 5 contributes to poor disease outcome in humans and mice with pneumococcal meningitis

Pneumococcal meningitis is the most common and severe form of bacterial meningitis. Fatality rates are substantial, and long-term sequelae develop in about half of survivors. Disease outcome has been related to the severity of the proinflammatory response in the subarachnoid space. The complement system, which mediates key inflammatory processes, has been implicated as a modulator of pneumococcal meningitis disease severity in animal studies. Additionally, SNPs in genes encoding complement pathway proteins have been linked to susceptibility to pneumococcal infection, although no associations with disease severity or outcome have been established. Here, we have performed a robust prospective nationwide genetic association study in patients with bacterial meningitis and found that a common nonsynonymous complement component 5 (C5) SNP (rs17611) is associated with unfavorable disease outcome. C5 fragment levels in cerebrospinal fluid (CSF) of patients with bacterial meningitis correlated with several clinical indicators of poor prognosis. Consistent with these human data, C5a receptor-deficient mice with pneumococcal meningitis had lower CSF wbc counts and decreased brain damage compared with WT mice. Adjuvant treatment with C5-specific monoclonal antibodies prevented death in all mice with pneumococcal meningitis. Thus, our results suggest C5-specific monoclonal antibodies could be a promising new antiinflammatory adjuvant therapy for pneumococcal meningitis.

Structural and Functional Analysis of the Complex between Citrate and the Zinc Peptidase Carboxypeptidase A

A high-resolution carboxypeptidase-Zn(2+)-citrate complex was studied by X-ray diffraction and enzyme kinetics for the first time. The citrate molecule acts as a competitive inhibitor of this benchmark zinc-dependent peptidase, chelating the catalytic zinc ion in the active site of the enzyme and inducing a conformational change such that carboxypeptidase adopts the conformation expected to occur by substrate binding. Citrate adopts an extended conformation with half of the molecule facing the zinc ion, while the other half is docked in the S1' hydrophobic specificity pocket of the enzyme, in contrast with the binding mode expected for a substrate like phenylalanine or a peptidomimetic inhibitor like benzylsuccinic acid. Combined structural and enzymatic analysis describes the characteristics of the binding of this ligand that, acting against physiologically relevant zinc-dependent proteases, may serve as a general model in the design of new drug-protecting molecules for the oral delivery of drugs of peptide origin.

Thrombin activatable fibrinolysis inhibitor

Thrombin activatable fibrinolysis inhibitor (TAFI) was discovered two decades ago as a consequence of the identification of an unstable carboxypeptidase (CPU), which was formed upon thrombin activation of the respective pro-enzyme (proCPU). The antifibrinolytic function of the activated form (TAFIa, CPU) is directly linked to its capacity to remove C-terminal lysines from the surface of the fibrin clot. No endogenous inhibitors have been identified, but TAFIa activity is regulated by its intrinsic temperature-dependent instability with a half-life of 8 to 15 min at 37 °C. A variety of studies have demonstrated a role for TAFI/TAFIa in venous and arterial diseases. In addition, a role in inflammation and cell migration has been shown. Since an elevated level of TAFIa it is a potential risk factor for thrombotic disorders, many inhibitors, both at the level of activation or at the level of activity, have been developed and were proven to exhibit a profibrinolytic effect in animal models. Pharmacologically active inhibitors of the TAFI/TAFIa system may open new ways for the prevention of thrombotic diseases or for the establishment of adjunctive treatments during thrombolytic therapy.

Identification of human thrombin-activatable fibrinolysis inhibitor in vascular and inflammatory cells

TAFI (thrombin-activatable fibrinolysis inhibitor) is a carboxypeptidase zymogen originally identified in plasma. The TAFI pathway helps to regulate the balance between the coagulation and fibrinolytic cascades. Activated TAFI (TAFIa) can also inactivate certain pro-inflammatory mediators, suggesting that the TAFI pathway may also regulate communication between coagulation and inflammation. Expression in the liver is considered to be the source of plasma TAFI. TAFI has also been identified in platelets and CPB2 (the gene encoding TAFI) mRNA has been detected in megakaryocytic cell lines as well as in endothelial cells. We have undertaken a quantitative analysis of CPB2 mRNA and TAFI protein in extrahepatic cell types relevant to vascular disease. Using RT-PCR and quantitative RT-PCR, we detected CPB2 mRNA in the human megakaryoblastic cell lines MEG-01 and Dami, the human monocytoid cell line THP-1 as well as THP-1 cells differentiated into a macrophage-like phenotype, and in primary human umbilical vein and coronary artery endothelial cells. CPB2 mRNA abundance in MEG-01, Dami, and THP-1 cells was modulated by the state of differentiation of these cells. Using a recently developed TAFIa assay, we detected TAFI protein in the lysates of the human hepatocellular carcinoma cell line HepG2 as well as in MEG-01 and Dami cells and in the conditioned medium of HepG2 cells, differentiated Dami cells, and THP-1 macrophages. We have obtained clear evidence for extrahepatic expression of TAFI, which has clear implications for the physiological and pathophysiological functions of the TAFI pathway.

High incidence of tumors in diabetic thrombin activatable fibrinolysis inhibitor and apolipoprotein E double-deficient mice

BACKGROUND

Activation of the complement system has been implicated in tumor growth. The antifibrinolytic protein, activated thrombin-activatable fibrinolysis inhibitor (TAFIa), can modulate the activation of the complement system by inactivating the anaphylatoxins C3a and C5a. The apolipoprotein-E (ApoE) genotype has been associated with carcinogenesis.

OBJECTIVE

The aim of this study was to evaluate whether TAFIa can affect the development of cancer in the ApoE-deficient mouse model.

METHODS

TAFI and ApoE double-knockout mice were generated. A group of mice was treated with the diabetogenic and carcinogenic compound streptozotocin (stz). Mice treated with saline, single knockout mice and wild-type (wt) mice served as controls.

RESULTS

Six months after treatment with stz, mice were sacrificed. Hepatic tumors were found in male double-knockout mice treated with stz but none was found in control animals that were not treated with stz or in single knockout of ApoE or wt animals. There was no significant difference in coagulation system activation between the groups of mice. The plasma concentrations of C5a, factor D and transforming growth factor-β1 were increased in TAFI/ApoE double-deficient mice treated with stz compared with the mice of the same genotype treated with saline.

CONCLUSION

Apo-E deficiency alone was not associated with tumors but the lack of TAFI appears to make the mice permissive for tumor formation in ApoE mice.

Interface between hemostasis and adaptive immunity

Stress induced activation or denudation of the endothelium elicits arrest and activation of platelets with attendant triggering of coagulation, culminating in a physical barrier to limit blood loss. Recently, coagulation-activated osteopontin, chemerin, and protease-activated receptor signaling, as well as platelet-derived molecules including platelet factor 4, serotonin, P-selectin, and CD154 (CD40L) have been revealed as new links between hemostasis and adaptive immunity. The initiation of hemostasis establishes a local state of inflammation that serves as an adjuvant system for antigen presentation, consequently influencing the onset and functional characteristics of an evolving adaptive immune response. In this context, the hemostatic system and its associated signaling pathways warrant further study as novel therapeutic targets that may enhance, abrogate, or otherwise selectively direct the adaptive immune response.

Flexibility of the thrombin-activatable fibrinolysis inhibitor pro-domain enables productive binding of protein substrates

We have previously reported that thrombin-activatable fibrinolysis inhibitor (TAFI) exhibits intrinsic proteolytic activity toward large peptides. The structural basis for this observation was clarified by the crystal structures of human and bovine TAFI. These structures evinced a significant rotation of the pro-domain away from the catalytic moiety when compared with other pro-carboxypeptidases, thus enabling access of large peptide substrates to the active site cleft. Here, we further investigated the flexible nature of the pro-domain and demonstrated that TAFI forms productive complexes with protein carboxypeptidase inhibitors from potato, leech, and tick (PCI, LCI, and TCI, respectively). We determined the crystal structure of the bovine TAFI-TCI complex, revealing that the pro-domain was completely displaced from the position observed in the TAFI structure. It protruded into the bulk solvent and was disordered, whereas TCI occupied the position previously held by the pro-domain. The authentic nature of the presently studied TAFI-inhibitor complexes was supported by the trimming of the C-terminal residues from the three inhibitors upon complex formation. This finding suggests that the inhibitors interact with the active site of TAFI in a substrate-like manner. Taken together, these data show for the first time that TAFI is able to form a bona fide complex with protein carboxypeptidase inhibitors. This underlines the unusually flexible nature of the pro-domain and implies a possible mechanism for regulation of TAFI intrinsic proteolytic activity in vivo.

Alterations in gene expression of complement components in chronic rhinosinusitis

BACKGROUND

The complement cascade forms part of the initial innate response to pathogens in the airway. Complement activation is important in the maintenance of host homeostasis, but excessive and uncontrolled activation may lead to inflammation and disease. The role of the complement pathway in the innate response in chronic rhinosinusitis (CRS) is poorly characterized Methods: Sinus mucosa biopsy specimens from the anterior ethmoid or uncinate process of patients with allergic fungal rhinosinusitis (AFRS), CRS without NPs (CRS-NPs), and controls were harvested and gene and protein expression of C3, factor B (fB), C5, and C7 complement proteins were analyzed using quantitative polymerase chain reaction and immunohistochemical techniques.

RESULTS

fB, C3, and C5 gene expression were increased in both AFRS and CRS-NPs compared with controls (p < 0.05). Transcriptional activity for the terminal pathway protein C7 was not significantly increased when compared with controls, with C7 levels actually reduced in AFRS patients when compared with controls. Immunohistochemistry studies showed the presence of C3 and fB on the mucosal surface and in submucosa of both AFRS and CRS-NPs, but not normal controls. Terminal pathway protein C9 was not found in our specimens.

CONCLUSION

Both AFRS and CRS-NPs display up-regulation of the complement pathway, in particular, the alternative pathway (fB) and common pathways (C3 and C5). Enhanced innate responses as shown by alterations in complement components may play a pivotal role in the inflammatory response noted in CRS and provide potential therapeutic targets in the future.

Analysis of a new crystal form of procarboxypeptidase B: further insights into the catalytic mechanism

A new triclinic crystal structure form of porcine pancreatic procarboxypeptidase B (PCPB) was obtained at higher resolution than the previously known tetragonal crystal structure. This new crystal polymorph has allowed for a corrected, accurate assignment of residues along the polypeptide chain based on the currently available gene sequence information and crystallographic data. The present structure shows unbound PCPB in a distinct molecular packing as compared to the previous benzamidine complexed form. Its catalytically important Tyr248 residue is oriented and hydrogen-bonded to solvent water molecules, and locates the furthest away from the catalytic zinc ion as compared to previous structures. A relatively long stretch of residues flanking Tyr248 and guarding the access to the catalytic zinc ion was found to be sequentially unique to the M14 family of peptidases. Predictions from a normal mode analysis indicated that this stretch of residues belongs to a rigid subdomain in the protein structure. The specific presence of a tyrosyl residue at the most exposed position in this region would allow for a delicate balance between extreme hydrophobicity and hydrophilicity, and affect substrate binding and the kinetic efficiency of the enzyme.

Characterization of the substrate specificity of human carboxypeptidase A4 and implications for a role in extracellular peptide processing

CPA4 (carboxypeptidase A4) is a member of the metallocarboxypeptidase family. CPA4 was originally found in a screen of mRNAs up-regulated by sodium butyrate-induced differentiation of cancer cells. Further studies suggested a relation between CPA4 and prostate cancer aggressiveness. In the present study, we determined that CPA4 is secreted from cells as a soluble proenzyme (pro-CPA4) that can be activated by endoproteases, such as trypsin. Three complementary approaches were used to study the substrate specificity of CPA4; kinetic analysis was performed using a new series of chromogenic substrates and some biologically relevant peptides, the cleavage of synthetic peptides was tested individually, and the cleavage of a mixture of >100 mouse brain peptides was examined using a quantitative peptidomics mass spectrometry-based approach. CPA4 was able to cleave hydrophobic C-terminal residues with a preference for Phe, Leu, Ile, Met, Tyr, and Val. However, not all peptides with C-terminal hydrophobic residues were cleaved, indicating the importance of additional residues within the peptide. Aliphatic, aromatic, and basic residues in the P1 position have a positive influence on the cleavage specificity. In contrast, acidic residues, Pro, and Gly have a negative influence in the P1 position. Some of the peptides identified as CPA4 substrates (such as neurotensin, granins, and opioid peptides) have been previously shown to function in cell proliferation and differentiation, potentially explaining the link between CPA4 and cancer aggressiveness. Taken together, these studies suggest that CPA4 functions in neuropeptide processing and regulation in the extracellular environment.

Pulmonary hypertension is ameliorated in mice deficient in thrombin-activatable fibrinolysis inhibitor

BACKGROUND

The fibrinolytic system has been implicated in the pathogenesis of pulmonary hypertension (PH). Thrombin-activatable fibrinolysis inhibitor (TAFI) inhibits fibrinolysis and therefore its absence would be expected to increase fibrinolysis and ameliorate PH.

OBJECTIVE

The objective of the present study was to evaluate the effect of TAFI deficiency on pulmonary hypertension in the mouse.

METHODS AND RESULTS

PH was induced in C57/Bl6 wild-type (WT) or TAFI-deficient (KO) mice by weekly subcutaneous treatment with 600 mg kg(-1) monocrotaline (MCT) for 8 weeks. PH was inferred from right heart hypertrophy measured using the ratio of right ventricle-to-left ventricle-plus-septum weight [RV/(LV+S)]. Pulmonary vascular remodeling was analyzed by morphometry. TAFI-deficient MCT-treated and wild-type MCT-treated mice suffered similar weight loss. TAFI-deficient MCT-treated mice had reduced levels of total protein and tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), transforming growth factor-beta (TGF-beta) and monocyte chemoattractant protein-1 (MCP-1) in bronchial alveolar lavage compared with wild-type MCT-treated mice. The ratio of RV to (LV+S) weight was significantly higher in WT/MCT than in KO/MCT mice. The pulmonary artery wall area and vascular stenosis were both greater in MCT-treated WT mice compared with MCT-treated TAFI-deficient mice.

CONCLUSIONS

TAFI-deficient MCT-treated mice had less pulmonary hypertension, vascular remodeling and reduced levels of cytokines compared with MCT-treated WT animals, possibly as a result of reduced coagulation activation.

Regulation of inflammation by the protein C system

OBJECTIVE

To review new findings about the function of the protein C system during inflammation and coagulation.

MAIN FINDINGS

Coagulation proteases and their cofactors modify the outcome of severe inflammation by engaging signaling-competent cell surface receptors. The central effector protease of the protein C pathway, activated protein C, interacts with the endothelial cell protein C receptor, protease-activated receptors, and other receptors to exert multiple effects on hemostasis and immune cell function. Thrombomodulin controls the complement arm of the innate immune system in a thrombin-dependent manner through activation of the thrombin activatable inhibitor of fibrinolysis, and in a thrombin-independent, constitutive manner via its lectin-like extracellular domain; and inhibits the inflammatory effects of high-mobility box group 1 protein. Protein S not only suppresses coagulation as an enhancing cofactor for the coagulation inhibitors activated protein C and tissue factor pathway inhibitor but also is also a physiologic ligand for the Tyro/axl/Mer-family of receptor tyrosine kinases that mediate an anti-inflammatory regulatory loop of dendritic cell and monocyte inflammatory function.

CONCLUSIONS

The immune-regulatory capacity of the protein C pathway and its individual components emerge as the dominant action of this pathway in the setting of severe inflammation.

Carboxypeptidase U (TAFIa): a new drug target for fibrinolytic therapy?

Procarboxypeptidase U (TAFI) is a recently discovered plasma procarboxypeptidase that upon activation by thrombin or thrombin-thrombomodulin turns into a potent antifibrinolytic enzyme. Its prominent bridging function between coagulation and fibrinolysis raised the interest of many research groups and of the pharmaceutical industry. The development of carboxypeptidase U (CPU) inhibitors as profibrinolytic agents is an attractive concept and possibilities for rational drug design will become more readily available in the near future as a result of the recently published crystal structure. Numerous studies have been performed and many of them show beneficial effects of CPU inhibitors for the improvement of endogenous fibrinolysis in different animal sepsis and thrombosis models. CPU inhibitors combined with tissue-type plasminogen activator (t-PA) seem to increase the efficiency of pharmacological thrombolysis allowing lower dosing of t-PA and subsequently fewer bleeding complications. This review will focus on recently obtained in vivo data and the benefits/risks of targeting CPU for the treatment of thrombotic disorders.

Site-specific carboxypeptidase B1 tyrosine nitration and pathophysiological implications following its physical association with nitric oxide synthase-3 in experimental sepsis

LPS-induced sepsis results in oxidative modification and inactivation of carboxypeptidase B1 (CPB1). In this study, immunoprecipitated CPB1 was probed for tyrosine nitration using monoclonal nitrotyrosine-specific Abs in a murine model of LPS-induced sepsis. Tyrosine nitration of CPB1 was significantly reduced in the presence of NO synthase (NOS) inhibitors and the xanthine oxidase (XO) inhibitor allopurinol and in NOS-3 knockout (KO) mice. CPB1 tyrosine nitration and loss of activity by the concerted action of NOS-3 and XO were also confirmed in vitro using both the NO donor 3-morpholinosydnonimine and peroxynitrite. Liquid chromatography/tandem mass spectrometry data indicated five sites of tyrosine nitration in vitro including Tyr(248), the tyrosine at the catalytic site. The site- and protein-specific nitration of CPB1 and the possible high nitration yield to inactivate it were elucidated by confocal microscopy. The studies indicated that CPB1 colocalized with NOS-3 in the cytosol of sinus-lining cells in the red pulp of the spleen. Further analysis of CPB1-immunoprecipitated samples indicated immunoreactivity to a monoclonal NOS-3 Ab, suggesting protein complex formation with CPB1. XO and NOS inhibitors and NOS-3 KO mice injected with LPS had decreased levels of C5a in spleens of septic mice, indicating peroxynitrite as a possible cause for CPB1 functional alteration. Thus, CPB1 colocalization, coupling, and proximity to NOS-3 in the sinus-lining cells of spleen red pulp could explain the site-specific tyrosine nitration and inactivation of CPB1. These results open up new avenues for the investigation of several enzymes involved in inflammation and their site-specific oxidative modifications by protein-protein interactions as well as their role in sepsis.

The group migration of Dictyostelium cells is regulated by extracellular chemoattractant degradation

Starvation of Dictyostelium induces a developmental program in which cells form an aggregate that eventually differentiates into a multicellular structure. The aggregate formation is mediated by directional migration of individual cells that quickly transition to group migration in which cells align in a head-to-tail manner to form streams. Cyclic AMP acts as a chemoattractant and its production, secretion, and degradation are highly regulated. A key protein is the extracellular phosphodiesterase PdsA. In this study we examine the role and localization of PdsA during chemotaxis and streaming. We find that pdsA(-) cells respond chemotactically to a narrower range of chemoattractant concentrations compared with wild-type (WT) cells. Moreover, unlike WT cells, pdsA(-) cells do not form streams at low cell densities and form unusual thick and transient streams at high cell densities. We find that the intracellular pool of PdsA is localized to the endoplasmic reticulum, which may provide a compartment for storage and secretion of PdsA. Because we find that cAMP synthesis is normal in cells lacking PdsA, we conclude that signal degradation regulates the external cAMP gradient field generation and that the group migration behavior of these cells is compromised even though their signaling machinery is intact.

Functional analysis of mutant variants of thrombin-activatable fibrinolysis inhibitor resistant to activation by thrombin or plasmin

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) defines a pathway that functionally links the coagulation and fibrinolytic cascades. TAFI is activated by proteolytic cleavage, a reaction that can be performed by thrombin and plasmin, but most efficiently by thrombin in complex with the endothelial cofactor thrombomodulin (TM). The respective roles of these activators in regulating the TAFI pathway are largely unknown.

OBJECTIVE AND METHODS

In the present study, we constructed and expressed mutant variants of TAFI that have key substitutions in the amino acids surrounding the scissile Arg92-Ala93 bond.

RESULTS AND CONCLUSIONS

We identified variants that showed patterns of resistance to specific activators. For example, the P91S, R92K and S90P variants exhibited specific impairment of activation by thrombin or thrombin-TM, thrombin alone, and thrombin alone or plasmin, respectively. The variants that we tested also showed antifibrinolytic potentials that can be rationalized in terms of which enzymes are capable of activating them. On the other hand, certain predictions from peptide studies of mutations that would be expected to interfere with plasmin cleavage were not satisfied by our data, indicating that protein context, as well as the identity of amino acids at protease cleavage sites, dictates protease specificity.