Neutrophil elastase and proteinase-3 trigger G protein-biased signaling through proteinase-activated receptor-1 (PAR1)

Chymotrypsin activity signals to intestinal epithelium by protease-activated receptor-dependent mechanisms

BACKGROUND AND PURPOSE

Chymotrypsin is a pancreatic protease secreted into the lumen of the small intestine to digest food proteins. We hypothesized that chymotrypsin activity may be found close to epithelial cells and that chymotrypsin signals to them via protease-activated receptors (PARs). We deciphered molecular pharmacological mechanisms and gene expression regulation for chymotrypsin signalling in intestinal epithelial cells.

EXPERIMENTAL APPROACH

The presence and activity of chymotrypsin were evaluated by Western blot and enzymatic activity tests in the luminal and mucosal compartments of murine and human gut samples. The ability of chymotrypsin to cleave the extracellular domain of PAR1 or PAR2 was assessed using cell lines expressing N-terminally tagged receptors. The cleavage site of chymotrypsin on PAR1 and PAR2 was determined by HPLC-MS analysis. The chymotrypsin signalling mechanism was investigated in CMT93 intestinal epithelial cells by calcium mobilization assays and Western blot analyses of (ERK1/2) phosphorylation. The transcriptional consequences of chymotrypsin signalling were analysed on colonic organoids.

KEY RESULTS

We found that chymotrypsin was present and active in the vicinity of the colonic epithelium. Molecular pharmacological studies have shown that chymotrypsin cleaves both PAR1 and PAR2 receptors. Chymotrypsin activated calcium and ERK1/2 signalling pathways through PAR2, and this pathway promoted interleukin-10 (IL-10) up-regulation in colonic organoids. In contrast, chymotrypsin disarmed PAR1, preventing further activation by its canonical agonist, thrombin.

CONCLUSION AND IMPLICATIONS

Our results highlight the ability of chymotrypsin to signal to intestinal epithelial cells via PARs, which may have important physiological consequences in gut homeostasis.

Blockade of Proteinase-Activated Receptor 2 (PAR2) Attenuates Neuroinflammation in Experimental Autoimmune Encephalomyelitis

Proteinase-activated receptor-2 (PAR2), which modulates inflammatory responses, is elevated in the central nervous system in multiple sclerosis (MS) and in its murine model, experimental autoimmune encephalomyelitis (EAE). In PAR2-null mice, disease severity of EAE is markedly diminished. We therefore tested whether inhibiting PAR2 activation in vivo might be a viable strategy for the treatment of MS. Using the EAE model, we show that a PAR2 antagonist, the pepducin palmitoyl-RSSAMDENSEKKRKSAIK-amide (P2pal-18S), attenuates EAE progression by affecting immune cell function. P2pal-18S treatment markedly diminishes disease severity and reduces demyelination, as well as the infiltration of T-cells and macrophages into the central nervous system. Moreover, P2pal-18S decreases granulocyte-macrophage colony-stimulating factor (GM-CSF) production and T-cell activation in cultured splenocytes and prevents macrophage polarization in vitro. We conclude that PAR2 plays a key role in regulating neuroinflammation in EAE and that PAR2 antagonists represent promising therapeutic agents for treating MS and other neuroinflammatory diseases. SIGNIFICANCE STATEMENT: Proteinase-activated receptor-2 modulates inflammatory responses and is increased in multiple sclerosis lesions. We show that the proteinase-activated receptor-2 antagonist palmitoyl-RSSAMDENSEKKRKSAIK-amide reduces disease in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis by inhibiting T-cell and macrophage activation and infiltration into the central nervous system, making it a potential treatment for multiple sclerosis.

S. aureus drives itch and scratch-induced skin damage through a V8 protease-PAR1 axis

Itch is an unpleasant sensation that evokes a desire to scratch. The skin barrier is constantly exposed to microbes and their products. However, the role of microbes in itch generation is unknown. Here, we show that Staphylococcus aureus, a bacterial pathogen associated with itchy skin diseases, directly activates pruriceptor sensory neurons to drive itch. Epicutaneous S. aureus exposure causes robust itch and scratch-induced damage. By testing multiple isogenic bacterial mutants for virulence factors, we identify the S. aureus serine protease V8 as a critical mediator in evoking spontaneous itch and alloknesis. V8 cleaves proteinase-activated receptor 1 (PAR1) on mouse and human sensory neurons. Targeting PAR1 through genetic deficiency, small interfering RNA (siRNA) knockdown, or pharmacological blockade decreases itch and skin damage caused by V8 and S. aureus exposure. Thus, we identify a mechanism of action for a pruritogenic bacterial factor and demonstrate the potential of inhibiting V8-PAR1 signaling to treat itch.

Three Diseases Mediated by Different Immunopathologic Mechanisms-ANCA-Associated Vasculitis, Anti-Glomerular Basement Membrane Disease, and Immune Complex-Mediated Glomerulonephritis-A Common Clinical and Histopathologic Picture: Rapidly Progressive Crescentic Glomerulonephritis

Immune mechanisms play an important role in the pathogenesis of glomerulonephritis (GN), with autoimmunity being the main underlying pathogenetic process of both primary and secondary GN. We present three autoimmune diseases mediated by different autoimmune mechanisms: glomerulonephritis in vasculitis mediated by anti-neutrophil cytoplasmic antibodies (ANCAs), glomerulonephritis mediated by anti-glomerular basement membrane antibodies (anti-GBM antibodies), and immune complex-mediated glomerulonephritis. Some of these diseases represent a common clinical and histopathologic scenario, namely rapidly progressive crescentic glomerulonephritis. This is a severe illness requiring complex therapy, with the main role being played by therapy aimed at targeting immune mechanisms. In the absence of immune therapy, the crescents, the characteristic histopathologic lesions of this common presentation, progress toward fibrosis, which is accompanied by end-stage renal disease (ESRD). The fact that three diseases mediated by different immunopathologic mechanisms have a common clinical and histopathologic picture reveals the complexity of the relationship between immunopathologic mechanisms and their clinical expression. Whereas most glomerular diseases progress by a slow process of sclerosis and fibrosis, the glomerular diseases accompanied by glomerular crescent formation can progress, if untreated, in a couple of months into whole-nephron glomerulosclerosis and fibrosis. The outcome of different immune processes in a common clinical and histopathologic phenotype reveals the complexity of the relationship of the kidney with the immune system. The aim of this review is to present different immune processes that lead to a common clinical and histopathologic phenotype, such as rapidly progressive crescentic glomerulonephritis.

Novel mechanisms of thrombo-inflammation during infection: spotlight on neutrophil extracellular trap-mediated platelet activation

A state-of-the-art lecture titled "novel mechanisms of thrombo-inflammation during infection" was presented at the ISTH Congress in 2022. Platelet, neutrophil, and endothelial cell activation coordinate the development, progression, and resolution of thrombo-inflammatory events during infection. Activated platelets and neutrophil extracellular traps (NETs) are frequently observed in patients with sepsis and COVID-19, and high levels of NET-derived damage-associated molecular patterns (DAMPs) correlate with thrombotic complications. NET-associated DAMPs induce direct and indirect platelet activation, which in return potentiates neutrophil activation and NET formation. These coordinated interactions involve multiple receptors and signaling pathways contributing to vascular and organ damage exacerbating disease severity. This state-of-the-art review describes the main mechanisms by which platelets support NETosis and the key mechanisms by which NET-derived DAMPs trigger platelet activation and the formation of procoagulant platelets leading to thrombosis. We report how these DAMPs act through multiple receptors and signaling pathways differentially regulating cell activation and disease outcome, focusing on histones and S100A8/A9 and their contribution to the pathogenesis of sepsis and COVID-19. We further discuss the complexity of platelet activation during NETosis and the potential benefit of targeting selective or multiple NET-associated DAMPs to limit thrombo-inflammation during infection. Finally, we summarize relevant new data on this topic presented during the 2022 ISTH Congress.

Human osteoarthritis knee joint synovial fluids cleave and activate Proteinase-Activated Receptor (PAR) mediated signaling

Osteoarthritis (OA) is the most prevalent joint disorder with increasing worldwide incidence. Mechanistic insights into OA pathophysiology are evolving and there are currently no disease-modifying OA drugs. An increase in protease activity is linked to progressive degradation of the cartilage in OA. Proteases also trigger inflammation through a family of G protein-coupled receptors (GPCRs) called the Proteinase-Activated Receptors (PARs). PAR signaling can trigger pro-inflammatory responses and targeting PARs is proposed as a therapeutic approach in OA. Several enzymes can cleave the PAR N-terminus, but the endogenous protease activators of PARs in OA remain unclear. Here we characterized PAR activating enzymes in knee joint synovial fluids from OA patients and healthy donors using genetically encoded PAR biosensor expressing cells. Calcium signaling assays were performed to examine receptor activation. The class and type of enzymes cleaving the PARs was further characterized using protease inhibitors and fluorogenic substrates. We find that PAR1, PAR2 and PAR4 activating enzymes are present in knee joint synovial fluids from healthy controls and OA patients. Compared to healthy controls, PAR1 activating enzymes are elevated in OA synovial fluids while PAR4 activating enzyme levels are decreased. Using enzyme class and type selective inhibitors and fluorogenic substrates we find that multiple PAR activating enzymes are present in OA joint fluids and identify serine proteinases (thrombin and trypsin-like) and matrix metalloproteinases as the major classes of PAR activating enzymes in the OA synovial fluids. Synovial fluid driven increase in calcium signaling was significantly reduced in cells treated with PAR1 and PAR2 antagonists, but not in PAR4 antagonist treated cells. OA associated elevation of PAR1 cleavage suggests that targeting this receptor may be beneficial in the treatment of OA.

Role of neutrophil interleukin-23 in spondyloarthropathy spectrum disorders

Neutrophilic inflammation is a pervasive characteristic common to spondyloarthropathies and related disorders. This inflammation manifests as Munro's microabscesses of the skin and osteoarticular neutrophilic inflammation in patients with psoriatic arthritis, intestinal crypt abscesses in patients with inflammatory bowel disease, ocular hypopyon in anterior uveitis, and neutrophilic macroscopic and microscopic inflammation in patients with Behçet's disease. Strong MHC class I associations are seen in these diseases, which represent so-called MHC-I-opathies, and these associations indicate an involvement of CD8 T-cell immunopathology that is not yet well understood. In this Personal View, we highlight emerging data suggesting that the T-cell-neutrophil axis involves both a T-cell-mediated and interleukin (IL)-17-mediated (type 17) recruitment and activation of neutrophils, and also a sequestration of activated neutrophils at disease sites that might directly amplify type 17 T-cell responses. This amplification likely involves neutrophilic production of IL-23 and proteases as well as other feedback mechanisms that could be regulated by local microbiota, pathogens, or tissue damage. This crosstalk between innate and adaptive immunity offers a novel explanation for how bacterial and fungal microbes at barrier sites could innately control type 17 T-cell development, with the aim of restoring tissue homoeostasis, and could potentially explain features of clinical disease and treatment response, such as the fast-onset action of the IL-23 pathway blockade in certain patients. This axis could be crucial to understanding non-response to IL-23 inhibitors among patients with ankylosing spondylitis, as the axial skeleton is a site rich in neutrophils and a site of haematopoiesis with myelopoiesis in adults.

Elafin and its precursor trappin-2: What is their therapeutic potential for intestinal diseases?

Elafin and its precursor trappin-2 are known for their contribution to the physiological mucosal shield against luminal microbes. Such a contribution seems to be particularly relevant in the gut, where the exposure of host tissues to heavy loads of microbes is constant and contributes to mucosa-associated pathologies. The expression of trappin-2/elafin has been shown to be differentially regulated in diseases associated with gut inflammation. Accumulating evidence has demonstrated the protective effects of trappin-2/elafin in gut intestinal disorders associated with acute or chronic inflammation, or with gluten sensitization disorders. The protective effects of trappin-2/elafin in the gut are discussed in terms of their pleiotropic modes of action: acting as protease inhibitors, transglutaminase substrates, antimicrobial peptides or as a regulator of pro-inflammatory transcription factors. Further, the question of the therapeutic potential of trappin-2/elafin delivery at the intestinal mucosa surface is raised. Whether trappin-2/elafin mucosal delivery should be considered to ensure intestinal tissue repair is also discussed.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Neutrophil Extracellular Traps in Cerebral Ischemia/Reperfusion Injury: Friend and Foe

Cerebral ischemic injury, one of the leading causes of morbidity and mortality worldwide, triggers various central nervous system (CNS) diseases, including acute ischemic stroke (AIS) and chronic ischemia-induced Alzheimer's disease (AD). Currently, targeted therapies are urgently needed to address neurological disorders caused by cerebral ischemia/reperfusion injury (CI/RI), and the emergence of neutrophil extracellular traps (NETs) may be able to relieve the pressure. Neutrophils are precursors to brain injury following ischemic stroke and exert complicated functions. NETs extracellularly release reticular complexes of neutrophils, i.e., double-stranded DNA (dsDNA), histones, and granulins. Paradoxically, NETs play a dual role, friend and foe, under different conditions, for example, physiological circumstances, infection, neurodegeneration, and ischemia/reperfusion. Increasing evidence indicates that NETs exert anti-inflammatory effects by degrading cytokines and chemokines through protease at a relatively stable and moderate level under physiological conditions, while excessive amounts of NETs release (NETosis) irritated by CI/RI exacerbate the inflammatory response and aggravate thrombosis, disrupt the blood-brain barrier (BBB), and initiates sequential neuron injury and tissue damage. This review provides a comprehensive overview of the machinery of NETs formation and the role of an abnormal cascade of NETs in CI/RI, as well as other ischemia-induced neurological diseases. Herein, we highlight the potential of NETs as a therapeutic target against ischemic stroke that may inspire translational research and innovative clinical approaches.

Granzyme K initiates IL-6 and IL-8 release from epithelial cells by activating protease-activated receptor 2

Granzyme K (GzmK) is a tryptic member of the granzyme family of chymotrypsin-like serine proteases produced by cells of the immune system. Previous studies have indicated that GzmK activates protease-activated receptor 1 (PAR1) enhancing activation of monocytes and wound healing in endothelial cells. Here, we show using peptides and full length proteins that GzmK and, to a lesser extent the related protease GzmA, are capable of activating PAR1 and PAR2. These cleavage events occur at the canonical arginine P1 residue and involve exosite interactions between protease and receptor. Despite cleaving PAR2 at the same point as trypsin, GzmK does not induce a classical Ca2+ flux but instead activates a distinct signalling cascade, involving recruitment of β-arrestin and phosphorylation of ERK. In epithelial A549 cells, PAR2 activation by GzmK results in the release of inflammatory cytokines IL-6 and IL-8. These data suggest that during an immune response GzmK acts as a pro-inflammatory regulator, rather than as a cytotoxin.

The innate immune response, microenvironment proteinases, and the COVID-19 pandemic: pathophysiologic mechanisms and emerging therapeutic targets

The coronavirus disease 2019 (COVID-19) pandemic, causing considerable mortality and morbidity worldwide, has fully engaged the biomedical community in attempts to elucidate the pathophysiology of COVID-19 and develop robust therapeutic strategies. To this end, the predominant research focus has been on the adaptive immune response to COVID-19 infections stimulated by mRNA and protein vaccines and on the duration and persistence of immune protection. In contrast, the role of the innate immune response to the viral challenge has been underrepresented. This overview focuses on the innate immune response to COVID-19 infection, with an emphasis on the roles of extracellular proteases in the tissue microenvironment. Proteinase-mediated signaling caused by enzymes in the extracellular microenvironment occurs upstream of the increased production of inflammatory cytokines that mediate COVID-19 pathology. These enzymes include the coagulation cascade, kinin-generating plasma kallikrein, and the complement system, as well as angiotensin-generating proteinases of the renin–angiotensin system. Furthermore, in the context of several articles in this Supplement elucidating and detailing the trajectory of diverse profibrotic pathways, we extrapolate these insights to explore how fibrosis and profibrotic pathways participate importantly in the pathogenesis of COVID-19. We propose that the lessons garnered from understanding the roles of microenvironment proteinases in triggering the innate immune response to COVID-19 pathology will identify potential therapeutic targets and inform approaches to the clinical management of COVID-19. Furthermore, the information may also provide a template for understanding the determinants of COVID-19–induced tissue fibrosis that may follow resolution of acute infection (so-called “long COVID”), which represents a major new challenge to our healthcare systems.

Proteinase-activated receptor-1 antagonist attenuates brain injury via regulation of FGL2 and TLR4 after intracerebral hemorrhage in mice

Proteinase-activated receptor-1 (PAR1) antagonist plays a protective effect in brain injury. We investigated the potential function and mechanisms of PAR1 antagonist in ICH-induced brain injury. Results showed that PAR1 antagonist protected against neurobehavior deficits, brain edema and BBB integrity in ICH mice via activating JNK/ERK/p38 MAPK signaling pathway at 24h after ICH. In addition, ICH resulted in the increase of FGL2 and TLR4 expression over time, and phosphorylated JNK, ERK and p38 MAPK expression. Suppression of FGL2 and TLR4 alleviated brain injury and decreased the expression of p-JNK, p-ERK, p-p38 MAPK and p-IKKα at 24 h after ICH; while overexpression of them showed the opposite result. Moreover, the protective effect of PAR1 antagonist on ICH-induced brain injury was blocked by FGL2 or TLR4 overexpression, and the levels of p-JNK, p-ERK and p-p38 MAPK were inhibited. Furthermore, PAR1 antagonist combined with TLR4 antagonist markedly alleviated brain injury after ICH at 72h. Overall, PAR1 antagonist protected against short-term brain injury, and the effect of PAR1 antagonist on ICH-induced brain injury was mediated by FGL2 or TLR4.

Flavonoids as inhibitors of human neutrophil elastase

Elastase is a proteolytic enzyme belonging to the family of hydrolases produced by human neutrophils, monocytes, macrophages, and endothelial cells. Human neutrophil elastase is known to play multiple roles in the human body, but an increase in its activity may cause a variety of diseases. Elastase inhibitors may prevent the development of psoriasis, chronic kidney disease, respiratory disorders (including COVID-19), immune disorders, and even cancers. Among polyphenolic compounds, some flavonoids and their derivatives, which are mostly found in herbal plants, have been revealed to influence elastase release and its action on human cells. This review focuses on elastase inhibitors that have been discovered from natural sources and are biochemically characterised as flavonoids. The inhibitory activity on elastase is a characteristic of flavonoid aglycones and their glycoside and methylated, acetylated and hydroxylated derivatives. The presented analysis of structure-activity relationship (SAR) enables the determination of the chemical groups responsible for evoking an inhibitory effect on elastase. Further study especially of the in vivo efficacy and safety of the described natural compounds is of interest in order to gain better understanding of their health-promoting potential.

Platelet-Mediated NET Release Amplifies Coagulopathy and Drives Lung Pathology During Severe Influenza Infection

The influenza A virus (IAV) causes a respiratory tract infection with approximately 10% of the population infected by the virus each year. Severe IAV infection is characterized by excessive inflammation and tissue pathology in the lungs. Platelet and neutrophil recruitment to the lung are involved in the pathogenesis of IAV, but the specific mechanisms involved have not been clarified. Using confocal intravital microscopy in a mouse model of IAV infection, we observed profound neutrophil recruitment, platelet aggregation, neutrophil extracellular trap (NET) production and thrombin activation within the lung microvasculature in vivo. Importantly, deficiency or antagonism of the protease-activated receptor 4 (PAR4) reduced platelet aggregation, NET production, and neutrophil recruitment. Critically, inhibition of thrombin or PAR4 protected mice from virus-induced lung tissue damage and edema. Together, these data imply thrombin-stimulated platelets play a critical role in the activation/recruitment of neutrophils, NET release and directly contribute to IAV pathogenesis in the lung.

Neutrophilic inflammation during lung development disrupts elastin assembly and predisposes adult mice to COPD

Emerging evidence indicates that early life events can increase the risk for developing chronic obstructive pulmonary disease (COPD). Using an inducible transgenic mouse model for NF-κB activation in the airway epithelium, we found that a brief period of inflammation during the saccular stage (P3-P5) but not alveolar stage (P10-P12) of lung development disrupted elastic fiber assembly, resulting in permanent reduction in lung function and development of a COPD-like lung phenotype that progressed through 24 months of age. Neutrophil depletion prevented disruption of elastic fiber assembly and restored normal lung development. Mechanistic studies uncovered a role for neutrophil elastase (NE) in downregulating expression of critical elastic fiber assembly components, particularly fibulin-5 and elastin. Further, purified human NE and NE-containing exosomes from tracheal aspirates of premature infants with lung inflammation downregulated elastin and fibulin-5 expression by saccular-stage mouse lung fibroblasts. Together, our studies define a critical developmental window for assembling the elastin scaffold in the distal lung, which is required to support lung structure and function throughout the lifespan. Although neutrophils play a well-recognized role in COPD development in adults, neutrophilic inflammation may also contribute to early-life predisposition to COPD.

Metformin Prevents Hyperglycemia-Associated, Oxidative Stress-Induced Vascular Endothelial Dysfunction: Essential Role for the Orphan Nuclear Receptor Human Nuclear Receptor 4A1 (Nur77)

Vascular pathology is increased in diabetes because of reactive-oxygen-species (ROS)-induced endothelial cell damage. We found that in vitro and in a streptozotocin diabetes model in vivo, metformin at diabetes-therapeutic concentrations (1-50 µM) protects tissue-intact and cultured vascular endothelial cells from hyperglycemia/ROS-induced dysfunction typified by reduced agonist-stimulated endothelium-dependent, nitric oxide-mediated vasorelaxation in response to muscarinic or proteinase-activated-receptor 2 agonists. Metformin not only attenuated hyperglycemia-induced ROS production in aorta-derived endothelial cell cultures but also prevented hyperglycemia-induced endothelial mitochondrial dysfunction (reduced oxygen consumption rate). These endothelium-protective effects of metformin were absent in orphan-nuclear-receptor Nr4a1-null murine aorta tissues in accord with our observing a direct metformin-Nr4a1 interaction. Using in silico modeling of metformin-NR4A1 interactions, Nr4a1-mutagenesis, and a transfected human embryonic kidney 293T cell functional assay for metformin-activated Nr4a1, we identified two Nr4a1 prolines, P505/P549 (mouse sequences corresponding to human P501/P546), as key residues for enabling metformin to affect mitochondrial function. Our data indicate a critical role for Nr4a1 in metformin's endothelial-protective effects observed at micromolar concentrations, which activate AMPKinase but do not affect mitochondrial complex-I or complex-III oxygen consumption rates, as does 0.5 mM metformin. Thus, therapeutic metformin concentrations requiring the expression of Nr4a1 protect the vasculature from hyperglycemia-induced dysfunction in addition to metformin's action to enhance insulin action in patients with diabetes. SIGNIFICANCE STATEMENT: Metformin improves diabetic vasodilator function, having cardioprotective effects beyond glycemic control, but its mechanism to do so is unknown. We found that metformin at therapeutic concentrations (1-50µM) prevents hyperglycemia-induced endothelial dysfunction by attenuating reactive oxygen species-induced damage, whereas high metformin (>250 µM) impairs vascular function. However, metformin's action requires the expression of the orphan nuclear receptor NR4A1/Nur77. Our data reveal a novel mechanism whereby metformin preserves diabetic vascular endothelial function, with implications for developing new metformin-related therapeutic agents.

A KLK4 proteinase substrate capture approach to antagonize PAR1

Proteinase-activated receptor-1 (PAR1), triggered by thrombin and other serine proteinases such as tissue kallikrein-4 (KLK4), is a key driver of inflammation, tumor invasiveness and tumor metastasis. The PAR1 transmembrane G-protein-coupled receptor therefore represents an attractive target for therapeutic inhibitors. We thus used a computational design to develop a new PAR1 antagonist, namely, a catalytically inactive human KLK4 that acts as a proteinase substrate-capture reagent, preventing receptor cleavage (and hence activation) by binding to and occluding the extracellular R41-S42 canonical PAR1 proteolytic activation site. On the basis of in silico site-saturation mutagenesis, we then generated KLK4S207A,L185D, a first-of-a-kind 'decoy' PAR1 inhibitor, by mutating the S207A and L185D residues in wild-type KLK4, which strongly binds to PAR1. KLK4S207A,L185D markedly inhibited PAR1 cleavage, and PAR1-mediated MAPK/ERK activation as well as the migration and invasiveness of melanoma cells. This 'substrate-capturing' KLK4 variant, engineered to bind to PAR1, illustrates proof of principle for the utility of a KLK4 'proteinase substrate capture' approach to regulate proteinase-mediated PAR1 signaling.

IL-31 and IL-8 in Cutaneous T-Cell Lymphoma: Looking for Their Role in Itch

The itch associated with cutaneous T-cell lymphoma (CTCL), including Mycosis Fungoides (MF) and Sézary syndrome (SS), is often severe and poorly responsive to treatment with antihistamines. Recent studies have highlighted the possible role of interleukins in nonhistaminergic itch. We investigated the role of IL-31 and IL-8 in CTCL, concerning disease severity and associated itch. Serum samples of 27 patients with CTCL (17 MF and 10 SS) and 29 controls (blood donors) were analyzed for interleukin- (IL-) 31 and IL-8; correlations with disease and itch severity were evaluated. IL-31 serum levels were higher in CTCL patients than in controls and higher in SS than in MF. Also, serum IL-31 levels were higher in patients with advanced disease compared to those with early disease, and they correlated positively with lactate dehydrogenase and beta 2-microglobulin levels, as well as with the Sézary cell count. Itch affected 67% of CTCL patients (MF: 47%; SS: 100%). Serum IL-31 levels were higher in itching patients than in controls and in patients without itching. There was no association between serum IL-8 and disease severity, nor with itching. Serum IL-8 levels correlated positively with peripheral blood leukocyte and neutrophil counts in CTCL patients. Our study suggests a role for IL-31 in CTCL-associated itch, especially in advanced disease and SS, offering a rational target for new therapeutic approaches. Increased serum IL-8 observed in some patients may be related to concomitant infections, and its role in exacerbating itch by recruiting neutrophils and promoting the release of neutrophil proteases deserves further investigation.

Sex-dependent role of microglia in disulfide high mobility group box 1 protein-mediated mechanical hypersensitivity

ABSTRACT

High mobility group box 1 protein (HMGB1) is increasingly regarded as an important player in the spinal regulation of chronic pain. Although it has been reported that HMGB1 induces spinal glial activation in a Toll-like receptor (TLR)4-dependent fashion, the aspect of sexual dimorphisms has not been thoroughly addressed. Here, we examined whether the action of TLR4-activating, partially reduced disulfide HMGB1 on microglia induces nociceptive behaviors in a sex-dependent manner. We found disulfide HMGB1 to equally increase microglial Iba1 immunoreactivity in lumbar spinal dorsal horn in male and female mice, but evoke higher cytokine and chemokine expression in primary microglial culture derived from males compared to females. Interestingly, TLR4 ablation in myeloid-derived cells, which include microglia, only protected male mice from developing HMGB1-induced mechanical hypersensitivity. Spinal administration of the glial inhibitor, minocycline, with disulfide HMGB1 also prevented pain-like behavior in male mice. To further explore sex difference, we examined the global spinal protein expression using liquid chromatography-mass spectrometry and found several antinociceptive and anti-inflammatory proteins to be upregulated in only male mice subjected to minocycline. One of the proteins elevated, alpha-1-antitrypsin, partially protected males but not females from developing HMGB1-induced pain. Targeting downstream proteins of alpha-1-antitrypsin failed to produce robust sex differences in pain-like behavior, suggesting that several proteins identified by liquid chromatography-mass spectrometry are required to modulate the effects. Taken together, the current study highlights the importance of mapping sex dimorphisms in pain mechanisms and point to processes potentially involved in the spinal antinociceptive effect of microglial inhibition in male mice.

The RGS-RhoGEFs control the amplitude of YAP1 activation by serum

Actin-dependent mechanisms drive the nuclear translocation of Yap1 to enable its co-activation of transcription factors that induce pro-growth and survival programs. While Rho GTPases are necessary for the nuclear import of YAP1, the relevant Guanine Exchange Factors (GEFs) and GTPase Activating Proteins (GAPs) that connect this process to upstream signaling are not well defined. To this end, we measured the impact of expressing sixty-seven RhoGEFs and RhoGAPs on the YAP1 dependent activity of a TEAD element transcriptional reporter. Robust effects by all three members of the regulator of G-protein signaling (RGS) domain containing RhoGEFs (ArhGEF1, ArhGEF11 and ArhGEF12) prompted studies relating their known roles in serum signaling onto the regulation of Yap1. Under all conditions examined, ArhGEF12 preferentially mediated the activation of YAP1/TEAD by serum versus ArhGEF1 or ArhGEF11. Conversely, ArhGEF1 in multiple contexts inhibited both basal and serum elevated YAP1 activity through its GAP activity for Gα₁₃. The sensitivity of such inhibition to cellular density and to low states of serum signaling supports that ArhGEF1 is a context dependent regulator of YAP1. Taken together, the relative activities of the RGS-RhoGEFs were found to dictate the degree to which serum signaling promotes YAP1 activity.

Deciphering the Role of the Coagulation Cascade and Autophagy in Cancer-Related Thrombosis and Metastasis

Thrombotic complications are the second leading cause of death among oncology patients worldwide. Enhanced thrombogenesis has multiple origins and may result from a deregulation of megakaryocyte platelet production in the bone marrow, the synthesis of coagulation factors in the liver, and coagulation factor signaling upon cancer and the tumor microenvironment (TME). While a hypercoagulable state has been attributed to factors such as thrombocytosis, enhanced platelet aggregation and Tissue Factor (TF) expression on cancer cells, further reports have suggested that coagulation factors can enhance metastasis through increased endothelial-cancer cell adhesion and enhanced endothelial cell activation. Autophagy is highly associated with cancer survival as a double-edged sword, as can both inhibit and promote cancer progression. In this review, we shall dissect the crosstalk between the coagulation cascade and autophagic pathway and its possible role in metastasis and cancer-associated thrombosis formation. The signaling of the coagulation cascade through the autophagic pathway within the hematopoietic stem cells, the endothelial cell and the cancer cell are discussed. Relevant to the coagulation cascade, we also examine the role of autophagy-related pathways in cancer treatment. In this review, we aim to bring to light possible new areas of cancer investigation and elucidate strategies for future therapeutic intervention.

Endothelial Protease Activated Receptor 1 (PAR1) Signalling Is Required for Lymphocyte Transmigration across Brain Microvascular Endothelial Cells

Lymphocyte transendothelial migration (TEM) relies on ICAM-1 engagement on the luminal surface of the endothelial cells (ECs). In blood–brain barrier (BBB) ECs, ICAM-1 triggers TEM signalling, including through JNK MAP kinase and AMP-activated protein kinase (AMPK), which lead to the phosphorylation and internalisation of the adherens junction protein VE-cadherin. In addition to ICAM-1, G protein-coupled receptors (GPCRs) are also required for lymphocytes TEM across BBB ECs. Here, we investigated the role of protease activated GPCRs (PARs) and found a specific role for PAR1 in support of lymphocyte TEM across BBB ECs in vitro. PAR1 requirement for TEM was confirmed using protease inhibitors, specific small molecule and peptide antagonists, function blocking antibodies and siRNA-mediated knockdown. In BBB ECs, PAR1 stimulation led to activation of signalling pathways essential to TEM; notably involving JNK and endothelial nitric oxide synthase (eNOS), with the latter downstream of AMPK. In turn, nitric oxide production through eNOS was essential for TEM by modulating VE-cadherin on Y731. Collectively, our data showed that non-canonical PAR1 activation by a lymphocyte-released serine protease is required for lymphocyte TEM across the BBB in vitro, and that this feeds into previously established ICAM-1-mediated endothelial TEM signalling pathways.

Netting Liver Disease: Neutrophil Extracellular Traps in the Initiation and Exacerbation of Liver Pathology

The liver plays a vital role in the immune system. Its unique position in the portal circulation and the architecture of the hepatic sinusoids, in combination with the wide-ranged population of immunocompetent cells, make the liver function as an immune filter. To aid in pathogen clearance, once challenged, the liver initiates the rapid recruitment of a wide variety of inflammatory cells, including neutrophils. These neutrophils, in conjunction with platelets, facilitate the release of neutrophil extracellular traps (NETs), which are web-like structures of decondensed nuclear DNA, histones, and neutrophil proteins. NETs function as both a physical and a chemical barrier, binding and killing pathogens circulating in the blood stream. In addition to their antimicrobial role, NETs also bind platelets, activate coagulation, and exacerbate host inflammatory response. This interplay between inflammation and coagulation drives microvascular occlusion, ischemia, and (sterile) damage in liver disease. Although direct clinical evidence of this interplay is scarce, preliminary studies indicate that NETs contribute to progression of liver disease and (thrombotic) complications. Here, we provide an overview of the pathological mechanisms of NETs in liver disease. In addition, we summarize clinical evidence for NETs in different disease etiologies and complications of liver disease and discuss the possible implications for the use of NETs as a diagnostic marker and a therapeutic target in liver disease.

Biased signaling in platelet G-protein coupled receptors

Platelets are small megakaryocyte-derived, anucleate, disk-like structures that play an outsized role in human health and disease. Both a decrease in the number of platelets and a variety of platelet function disorders result in petechiae or bleeding that can be life threatening. Conversely, the inappropriate activation of platelets, within diseased blood vessels, remains the leading cause of death and morbidity by affecting heart attacks and stroke. The fine balance of the platelet state in healthy individuals is controlled by a number of receptor-mediated signaling pathways that allow the platelet to rapidly respond and maintain haemostasis. G-protein coupled receptors (GPCRs) are particularly important regulators of platelet function. Here we focus on the major platelet-expressed GPCRs and discuss the roles of downstream signaling pathways (e.g., different G-protein subtypes or β-arrestin) in regulating the different phases of the platelet activation. Further, we consider the potential for selectively targeting signaling pathways that may contribute to platelet responses in disease through development of biased agonists. Such selective targeting of GPCR-mediated signaling pathways by drugs, often referred to as biased signaling, holds promise in delivering therapeutic interventions that do not present significant side effects, especially in finely balanced physiological systems such as platelet activation in haemostasis.

Role of the Helix-8 and C-Terminal Tail in Regulating Proteinase Activated Receptor 2 Signaling

The C-terminal tail of G-protein-coupled receptors (GPCR) contain important regulatory sites that enable interaction with intracellular signaling effectors. Here we examine the relative contribution of the C-tail serine/threonine phosphorylation sites (Ser^383-385, Ser³⁸⁷-Thr³⁹²) and the helix-8 palmitoylation site (Cys³⁶¹) in signaling regulation downstream of the proteolytically activated GPCR, PAR2. We examined Gα_q/11-coupled calcium signaling, β-arrestin-1/-2 recruitment, and MAPK activation (p44/42 phosphorylation) by wild-type and mutant receptors expressed in a CRISPR/Cas9 PAR2-knockout HEK-293 cell background with both peptide stimulation of the receptor (SLIGRL-NH₂) as well as activation with its endogenous trypsin revealed a tethered ligand. We find that alanine substitution of the membrane proximal serine residues (Ser^383-385Ala) had no effect on SLIGRL-NH₂- or trypsin-stimulated β-arrestin recruitment. In contrast, alanine substitutions in the Ser³⁸⁷-Thr³⁹² cluster resulted in a large (∼50%) decrease in β-arrestin-1/-2 recruitment triggered by the activating peptide, SLIGRL-NH₂, but was without an effect on trypsin-activated β-arrestin-1/-2 recruitment. Additionally, we find that alanine substitution of the helix-8 cysteine residue (Cys³⁶¹Ala) led to a large decrease in both Gα_q/11 coupling and β-arrestin-1/-2 recruitment to PAR2. Furthermore, we show that Gα_q/11 inhibition with YM254890, inhibited ERK phosphorylation by PAR2 agonists, while genetic deletion of β-arrestin-1/-2 by CRISPR/Cas9 enhanced MAPK activation. Knockout of β-arrestins also enhanced Gα_q/11-mediated calcium signaling. In line with these findings, a C-tail serine/threonine mutant that has decreased β-arrestin recruitment also showed enhanced ERK activation. Thus, our studies point to multiple mechanisms that regulate β-arrestin interaction with PAR2 and highlight differences in regulation of tethered-ligand- and peptide-mediated activation of this receptor.

Granzyme A in Chikungunya and Other Arboviral Infections

Granzyme A (GzmA) is secreted by cytotoxic lymphocytes and has traditionally been viewed as a mediator of cell death. However, a growing body of data suggests the physiological role of GzmA is promotion of inflammation. Here, we show that GzmA is significantly elevated in the sera of chikungunya virus (CHIKV) patients and that GzmA levels correlated with viral loads and disease scores in these patients. Serum GzmA levels were also elevated in CHIKV mouse models, with NK cells the likely source. Infection of mice deficient in type I interferon responses with CHIKV, Zika virus, or dengue virus resulted in high levels of circulating GzmA. We also show that subcutaneous injection of enzymically active recombinant mouse GzmA was able to mediate inflammation, both locally at the injection site as well as at a distant site. Protease activated receptors (PARs) may represent targets for GzmA, and we show that treatment with PAR antagonist ameliorated GzmA- and CHIKV-mediated inflammation.

Plasma Proteins and Platelets Modulate Neutrophil Clearance of Malaria-Related Hemozoin Crystals

Hemozoin is an insoluble crystalline pigment produced by the malaria parasite Plasmodia upon digesting host hemoglobin inside red blood cells. Red blood cell rupture releases hemozoin crystals into the circulation from where they are cleared by phagocytes such as neutrophils. We speculated that plasma proteins would affect the ability of neutrophils to clear hemozoin crystals. To test this, we cultured human blood neutrophils with hemozoin ex vivo and found that neutrophils ingested hemozoin (0.1-1 µm crystal size) in a dose-dependent manner into phagosomes and vesicles/vacuoles, resulting in morphological changes including nuclear enlargement, and vesicle formation, but not cell membrane rupture or release of neutrophil extracellular traps. The presence of human plasma significantly inhibited the ability of neutrophils to ingest hemozoin crystals. Platelet-poor plasma further inhibited the uptake of hemozoin by neutrophils. Selective exposure to fibrinogen completely replicated the plasma effect. Taken together, neutrophils cleared hemozoin crystals from the extracellular space via endocytosis into phagosomes and vesicles without inducing the release of neutrophil extracellular traps. However, human plasma components such as fibrinogen limited hemozoin clearance, whereas the presence of platelets augmented this process. These factors may influence the pro-inflammatory potential of hemozoin crystals in malaria.

Triggering of protease-activated receptors (PARs) induces alternative M2 macrophage polarization with impaired plasticity

Protease-activated receptors (PARs) have been described in a wide diversity of vertebrate cells, including human immune cells. Macrophages are pivotal cells in the host-pathogen interaction and their polarization in M1 or M2 cells has been described as a new central paradigm in the immune response to pathogens. In this context, we explored the involvement of PAR activation by serine proteases on M1/M2 macrophage differentiation and their impact on the Th1/Th2 cytokine profile in response to Mycobacterium tuberculosis antigen. Our results demonstrate that the serine proteases, thrombin and trypsin, induce interleukin (IL)-4 release from human monocytes, together with upregulation of the macrophage mannose receptor (CD206) in the same way that alternative M2a differentiated cells with M-CSF/IL-4. Protease stimulation of monocytes in the presence of PAR-1 (SCH-79797) or PAR-2 (FSLLRY-NH2) antagonists abolished IL-4 release from monocytes, whereas the use of the peptide agonist for PAR-1 (SFLLRNPNDKYEPF-NH2) or PAR-2 (SLIGKV-NH2) induced the secretion of IL-4 at a level comparable to thrombin or trypsin. When these protease-induced M2 macrophages from healthy human PPD + donors were co-cultured with autologous lymphocyte population in the presence of Mycobacterium tuberculosis antigen, we found a consistent inhibition of IFN-γ/IL-12 release together with persistent IL-4 expression, in contrast to the expected Th1 profile obtained with M2a macrophages. To our knowledge, this is the first observation that proteolytic activation of PAR1/2 receptors in monocytes induces M2-like macrophages with impaired plasticity and their implication in the driving of the Th1/Th2 cytokine profile.

Iterative Optimization of the Cyclic Peptide SFTI-1 Yields Potent Inhibitors of Neutrophil Proteinase 3

Neutrophils produce at least four serine proteases that are packaged within azurophilic granules. These enzymes contribute to antimicrobial defense and inflammation but can be destructive if their activities are not properly regulated. Accordingly, they represent therapeutic targets for several diseases, including chronic obstructive pulmonary disease, cystic fibrosis, and rheumatoid arthritis. In this study, we focused on proteinase 3 (PR3), a neutrophil protease with elastase-like specificity, and engineered potent PR3 inhibitors based on the cyclic peptide sunflower trypsin inhibitor-1 (SFTI-1). We used an iterative optimization approach to screen targeted substitutions at the P1, P2, P2', and P4 positions of SFTI-1, and generated several new inhibitors with K _i values in the low nanomolar range. These SFTI-variants show high stability in human serum and are attractive leads for further optimization.

Protease-Activated Receptor 1 Deletion Causes Enhanced Osteoclastogenesis in Response to Inflammatory Signals through a Notch2-Dependent Mechanism

We found that protease-activated receptor 1 (PAR1) was transiently induced in cultured osteoclast precursor cells. Therefore, we examined the bone phenotype and response to resorptive stimuli of PAR1-deficient (knockout [KO]) mice. Bones and bone marrow-derived cells from PAR1 KO and wild-type (WT) mice were assessed using microcomputed tomography, histomorphometry, in vitro cultures, and RT-PCR. Osteoclastic responses to TNF-α (TNF) challenge in calvaria were analyzed with and without a specific neutralizing Ab to the Notch2-negative regulatory region (N2-NRR Ab). In vivo under homeostatic conditions, there were minimal differences in bone mass or bone cells between PAR1 KO and WT mice. However, PAR1 KO myeloid cells demonstrated enhanced osteoclastogenesis in response to receptor activator of NF-κB ligand (RANKL) or the combination of RANKL and TNF. Strikingly, in vivo osteoclastogenic responses of PAR1 KO mice to TNF were markedly enhanced. We found that N2-NRR Ab reduced TNF-induced osteoclastogenesis in PAR1 KO mice to WT levels without affecting WT responses. Similarly, in vitro N2-NRR Ab reduced RANKL-induced osteoclastogenesis in PAR1 KO cells to WT levels without altering WT responses. We conclude that PAR1 functions to limit Notch2 signaling in responses to RANKL and TNF and moderates osteoclastogenic response to these cytokines. This effect appears, at least in part, to be cell autonomous because enhanced osteoclastogenesis was seen in highly purified PAR1 KO osteoclast precursor cells. It is likely that this pathway is involved in regulating the response of bone to diseases associated with inflammatory signals.

Microenvironment proteinases, proteinase-activated receptor regulation, cancer and inflammation

We propose that in the microenvironment of inflammatory tissues, including tumours, extracellular proteinases can modulate cell signalling in part by regulating proteinase-activated receptors (PARs). We have been exploring this mechanism in a variety of inflammation and tumour-related settings that include tumour-derived cultured cells from prostate and bladder cancer, as well as immune inflammatory cells that are involved in the pathology of inflammatory diseases including multiple sclerosis. Our work showed that proteinase signalling via the PARs affects prostate and bladder cancer-derived tumour cell behaviour and can regulate calcium signalling in human T-cell and macrophage-related inflammatory cells as well as in murine splenocytes. Further, we found that the tumour-derived prostate cancer cells and immune-related cells (Jurkat, THP1, mouse splenocytes) can produce PAR-regulating proteinases (including kallikreins: kallikrein-related peptidases), that can control tissue function by both a paracrine and autocrine mechanism. We suggest that this PAR-driven signalling process involving secreted microenvironment proteinases can play a key role in cancer and inflammatory diseases including multiple sclerosis.

Protease-activated receptor-1 impedes prostate and intestinal tumor progression in mice

Essentials Protease activated receptor-1 (PAR-1) has been proposed to drive cancer progression. Surprisingly, PAR-1 deletion accelerated tumor progression in two distinct experimental settings. PAR-1 deletion was shown to limit the apoptosis of transformed epithelial cells. Thrombin- and activated protein C-mediated PAR-1 activation have unique effects on tumor cell biology. SUMMARY: Background Multiple studies have implicated protease-activated receptor-1 (PAR-1), a G-protein-coupled receptor activated by proteolytic cleavage of its N-terminus, as one target coupling thrombin-mediated proteolysis to tumor progression. Objective To analyze the role of PAR-1 in the setting of two distinct spontaneously developing tumor models in mice. Methods We interbred PAR-1-deficient mice with Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice, which spontaneously develop prostate tumors, and adenomatous polyposis coli Min (APCMin/+ ) mice, which spontaneously develop intestinal adenomas. Results Analyses of TRAMP mice with advanced disease (30 weeks) revealed that PAR-1 deficiency resulted in significantly larger and more aggressive prostate tumors. Prostates collected at an earlier time point (12 weeks of age) revealed that PAR-1 promotes apoptosis in transformed epithelia. In vitro analyses of TRAMP-derived cells revealed that activated protein C-mediated PAR-1 cleavage can induce tumor cell apoptosis, suggesting that tumor cell-intrinsic PAR-1 functions can limit tumor progression. Paralleling results in TRAMP mice, PAR-1-deficient APCMin/+ mice developed three-fold more adenomas than PAR-1-expressing mice, and the adenomas that formed were significantly larger. Moreover, loss of PAR-1 expression was shown to limit apoptosis in transformed intestinal epithelial cells. Conclusions Together, these results demonstrate a previously unrecognized role for PAR-1 in impeding tumor progression in vivo. These results also offer a cautionary note suggesting that long-term PAR-1 inhibition could increase malignancy risk in some contexts.

A bronchoprotective role for Rgs2 in a murine model of lipopolysaccharide-induced airways inflammation

Background

Asthma exacerbations are associated with the recruitment of neutrophils to the lungs. These cells release proteases and mediators, many of which act at G protein-coupled receptors (GPCRs) that couple via Gq to promote bronchoconstriction and inflammation. Common asthma therapeutics up-regulate expression of the regulator of G protein signalling (RGS), RGS2. As RGS2 reduces signaling from Gq-coupled GPCRs, we have defined role(s) for this GTPase-activating protein in an acute neutrophilic model of lung inflammation.

Methods

Wild type and Rgs2^−/− C57Bl6 mice were exposed to nebulized lipopolysaccharide (LPS). Lung function (respiratory system resistance and compliance) was measured using a SCIREQ flexivent small animal ventilator. Lung inflammation was assessed by histochemistry, cell counting and by cytokine and chemokine expression in bronchoalveolar lavage (BAL) fluid.

Results

Lipopolysaccharide inhalation induced transient airways hyperreactivity (AHR) and neutrophilic lung inflammation. While AHR and inflammation was greatest 3 h post-LPS exposure, BAL neutrophils persisted for 24 h. At 3 h post-LPS inhalation, multiple inflammatory cytokines (CSF2, CSF3, IL6, TNF) and chemokines (CCL3, CCL4, CXCL1, CXCL2) were highly expressed in the BAL fluid, prior to declining by 24 h. Compared to wild type counterparts, Rgs2^−/− mice developed significantly greater airflow resistance in response to inhaled methacholine (MCh) at 3 h post-LPS exposure. At 24 h post-LPS exposure, when lung function was recovering in the wild type animals, MCh-induced resistance was increased, and compliance decreased, in Rgs2^−/− mice. Thus, Rgs2^−/− mice show AHR and stiffer lungs 24 h post-LPS exposure. Histological markers of inflammation, total and differential cell counts, and major cytokine and chemokine expression in BAL fluid were similar between wild type and Rgs2^−/− mice. However, 3 and 24 h post-LPS exposure, IL12B expression was significantly elevated in BAL fluid from Rgs2^−/− mice compared to wild type animals.

Conclusions

While Rgs2 is bronchoprotective in acute neutrophilic inflammation, no clear anti-inflammatory effect was apparent. Nevertheless, elevated IL12B expression in Rgs2^−/− animals raises the possibility that RGS2 could dampen Th1 responses. These findings indicate that up-regulation of RGS2, as occurs in response to inhaled corticosteroids and long-acting β₂-adrenoceptor agonists, may be beneficial in acute neutrophilic exacerbations of airway disease, including asthma.

Electronic supplementary material

The online version of this article (10.1186/s13223-018-0266-5) contains supplementary material, which is available to authorized users.

Role of the blood coagulation cascade in hepatic fibrosis

Liver is the primary source of numerous proteins that are critical for normal function of the blood coagulation cascade. Because of this, diseases of the liver, particularly when affiliated with severe complications like cirrhosis, are associated with abnormalities of blood clotting. Although conventional interpretation has inferred cirrhosis as a disorder of uniform bleeding risk, it is now increasingly appreciated as a disease wherein the coagulation cascade is precariously rebalanced. Moreover, prothrombotic risk factors are also associated with a more rapid progression of fibrosis in humans, suggesting that coagulation proteases participate in disease pathogenesis. Indeed, strong evidence drawn from experimental animal studies indicates that components of the coagulation cascade, particularly coagulation factor Xa and thrombin, drive profibrogenic events, leading to hepatic fibrosis. Here, we concisely review the evidence supporting a pathologic role for coagulation in the development of liver fibrosis and the potential mechanisms involved. Further, we highlight how studies in experimental animals may shed light on emerging clinical evidence, suggesting that beneficial effects of anticoagulation could extend beyond preventing thrombotic complications to include reducing pathologies like fibrosis.

Pleiotropic effects of the hemostatic system

Atherothrombosis is characterized by the inflammatory process of atherosclerosis combined with a hypercoagulable state leading to superimposed thrombus formation. In atherosclerotic plaques, cell signaling can occur via protease-activated receptors (PARs), four of which have been identified so far (PAR1-PAR4). Proteases that are able to activate PARs can be produced systemically, but also at the sites of lesions, and they include thrombin and activated factor X. After PAR activation, downstream signaling can lead to both proinflammatory effects and a hypercoagulable state. Which specific effect occurs depends on the type of protease and activated PAR, and the site of activation. Hypercoagulable effects are mainly exerted through PAR1 and PAR4, whereas proinflammatory responses are mostly seen after PAR1 and PAR2 activation. PAR signaling pathways contribute to atherothrombosis, suggesting that inhibition of these pathways possibly prevents cardiovascular events based on this pathophysiological mechanism. In this review, we highlight the pathways by which PAR activation leads to proinflammatory responses and a hypercoagulable state. Furthermore, we give an overview of potential pharmacological treatment targets that promote vascular protection.

Neutrophil Elastase Subverts the Immune Response by Cleaving Toll-Like Receptors and Cytokines in Pneumococcal Pneumonia

Excessive activation of neutrophils results in the release of neutrophil elastase (NE), which leads to lung injury in severe pneumonia. Previously, we demonstrated a novel immune subversion mechanism involving microbial exploitation of this NE ability, which eventually promotes disruption of the pulmonary epithelial barrier. In the present study, we investigated the effect of NE on host innate immune response. THP-1-derived macrophages were stimulated with heat-killed Streptococcus pneumoniae or lipopolysaccharide in the presence or absence of NE followed by analysis of toll-like receptor (TLR) and cytokine expression. Additionally, the biological significance of NE was confirmed in an in vivo mouse intratracheal infection model. NE downregulated the gene transcription of multiple cytokines in THP-1-derived macrophages through the cleavage of TLRs and myeloid differentiation factor 2. Additionally, NE cleaved inflammatory cytokines and chemokines. In a mouse model of intratracheal pneumococcal challenge, administration of an NE inhibitor significantly increased proinflammatory cytokine levels in bronchoalveolar lavage fluid, enhanced bacterial clearance, and improved survival rates. Our work indicates that NE subverts the innate immune response and that inhibition of this enzyme may constitute a novel therapeutic option for the treatment of pneumococcal pneumonia.

PAR1 biased signaling is required for activated protein C in vivo benefits in sepsis and stroke

Activated protein C (APC) cleaves protease-activated receptor 1 (PAR1) in vitro at R46 to initiate beneficial cell signaling; however, thrombin and APC can cleave at R41. To elucidate PAR1-dependent aspects of the pharmacologic in vivo mechanisms of APC, we generated C57BL/6 mouse strains carrying QQ41 or QQ46 point mutations in PAR1 (F2r gene). Using these strains, we determined whether or not recombinant murine signaling-selective APC mutants would reduce septic death or provide neuroprotection against ischemic stroke when mice carried PAR1-homozygous mutations that prevent cleavage at either R41 or R46. Intercrossing PAR1+/R46Q mice generated expected numbers of PAR1+/+, PAR1+/R46Q, and R46Q/R46Q offspring whereas intercrossing PAR1+/R41Q mice gave decreased R41Q/R41Q homozygotes (resembling intercrossing PAR1+/PAR1-knockout mice). QQ41-PAR1 and QQ46-PAR1 brain endothelial cells showed the predicted retention or loss of cellular responses to thrombin receptor-activating peptide, thrombin, or APC for each PAR1 mutation. In sepsis studies, exogenous APC reduced mortality from 50% to 10% in Escherichia coli-induced pneumonia for wild-type (Wt) PAR1 and QQ41-PAR1 mice (P < .01) but had no benefit for QQ46-PAR1 mice. In transient distal middle cerebral artery occlusion stroke studies, exogenous APC significantly reduced infarct size, edema, and neuronal apoptosis for Wt mice and QQ41-PAR1 mice but had no detectable benefits for mice carrying QQ46-PAR1. In functional studies of forelimb-asymmetry and foot-fault tests at 24 hours after stroke induction, signaling-selective APC was beneficial for Wt and QQ41-PAR1 mice but not QQ46-PAR1 mice. These results support the concept that APC-induced, PAR1-dependent biased signaling following R46 cleavage is central to the in vivo benefits of APC.

Proteinases and their receptors in inflammatory arthritis: an overview

Proteinases are enzymes with established roles in physiological and pathological processes such as digestion and the homeostasis, destruction and repair of tissues. Over the past few years, the hormone-like properties of circulating proteinases have become increasingly appreciated. Some proteolytic enzymes trigger cell signalling via proteinase-activated receptors, a family of G protein-coupled receptors that have been implicated in inflammation and pain in inflammatory arthritis. Proteinases can also regulate ion flux owing to the cross-sensitization of transient receptor potential cation channel subfamily V members 1 and 4, which are associated with mechanosensing and pain. In this Review, the idea that proteinases have the potential to orchestrate inflammatory signals by interacting with receptors on cells within the synovial microenvironment of an inflamed joint is revisited in three arthritic diseases: osteoarthritis, spondyloarthritis and rheumatoid arthritis. Unanswered questions are highlighted and the therapeutic potential of modulating this proteinase-receptor axis for the management of disease in patients with these types of arthritis is also discussed.

BMSCs ameliorate septic coagulopathy by suppressing inflammation in cecal ligation and puncture-induced sepsis

Sepsis is an aggressive and life-threatening systemic inflammatory response with a high mortality. Inflammation and coagulation play crucial roles in the pathogenesis of sepsis in a mutually promoting manner. Unlike other single-target molecular therapies that have no obvious effects on clinical sepsis, bone marrow stromal cell (BMSC) therapy offers a broader spectrum of activities ranging from immune and inflammation suppression to tissue regeneration. In this report, we demonstrate that BMSC injection attenuates septic coagulopathy. It decreased the mortality, mitigated lung injury and reduced the surge of proinflammatory factors in mice with sepsis induced by cecal ligation and puncture (CLP). An in vitro cell model also revealed that co-culture with BMSCs reduced secretion of proinflammatory factors and injury of endothelial cells in response to lipopolysaccharide (LPS), an endotoxin of gram-negative bacteria. Together, our results demonstrate that BMSCs suppress sepsis-induced inflammation, endothelial dysfunction and defective coagulation.

rBmTI-6 attenuates pathophysiological and inflammatory parameters of induced emphysema in mice

Protease/anti-protease imbalance is the main pathogenic mechanism of emphysema and protease inhibitors have been recognized as potential molecules to treat the disease conditions. In this work the rBmTI-6 first domain (rBmTI-6-D1), a recombinant Kunitz-type serine proteinase inhibitor, was used to verify its effect in prevention or minimization of PPE-induced emphysema in mice. C57BL/6 mice were submitted to a PPE-induced emphysema model and treated with rBmTI-6-D1 before the emphysema development. We showed that the rBmTI-6-D1 treatment was sufficient to avoid the loss of elastic recoil, an effective decrease in alveolar enlargement and in the number of macrophages and lymphocytes in bronchoalveolar lavage fluid. Proteolytic analysis showed a significant increase in elastase activity in PPE-VE (induced emphysema) group that is controlled by rBmTI-6-D1. Kallikrein activity was decreased in the PPE-rBmTI6 (induced emphysema and inhibitor treated) group when compared to PPE-VE group. Although rBmTI-6-D1, did not present a neutrophil elastase (NE) inhibitory activity, the results show that the inhibitor interfered in the pathway of NE secretion in PPE-emphysema mice model. The role of rBmTI-6-D1 in the prevention of emphysema development in the mice model, apparently, is related with a control of inflammatory response due the trypsin/kallikrein inhibitory activity of rBmTI-6-D1.

Proteinase 3 expression on the neutrophils of patients with paroxysmal nocturnal hemoglobinuria

Proteinase 3 (PR3) is released from neutrophils and regulates platelet activity, which is associated with cluster of differentiation (CD)177 antigen (NB1), a glycosylphosphatidylinositol-linked protein. In the present study, the effect of PR3 on thrombosis in paroxysmal nocturnal hemoglobinuria (PNH) and PNH-aplastic anemia (AA) syndrome was explored. The expression of PR3 and NB1 on CD59^- neutrophils was detected by flow cytometry, immunofluorescence (IF), reverse transcription-quantitative polymerase chain reaction analysis and western blotting. Serum levels of PR3, proteinase-activated receptor 1 (PAR1) and D-Dimer were measured using ELISAs. The expression of PR3 and NB1 on the plasma membrane of CD59^- neutrophils in patients with PNH/PNH-AA was significantly lower compared with their expression on CD59⁺ neutrophils in patients and controls (P=0.001). However, no correlation between PR3 and NB1 expression was identified. IF staining further demonstrated partially positive PR3 expression on CD59^- neutrophils. The serum level of PR3 in patients was identified to be significantly decreased compared with healthy controls (P<0.0001), and significantly negatively correlated with PAR1 (r=-0.456; P=0.043) and D-Dimer (r=-0.503; P=0.028) levels. The mRNA and protein levels of PR3 on PNH clones did not change significantly compared with the control group. In conclusion, PR3 expression on the plasma membrane of neutrophils and in the serum of patients with PNH/PNH-AA decreased, which may result in increased PAR1 expression and increased clotting. The present study provides the basis for further study on platelets in PNH.

Platelet-neutrophil interactions as drivers of inflammatory and thrombotic disease

Neutrophils are well known for their role in infection and inflammatory disease and are first responders at sites of infection or injury. Platelets have an established role in hemostasis and thrombosis and are first responders at sites of vascular damage. However, neutrophils are increasingly recognized for their role in thrombosis, while the immunemodulatory properties of platelets are being increasingly studied. Platelets and neutrophils interact during infection, inflammation and thrombosis and modulate each other’s functions. This review will discuss the consequences of platelet–neutrophil interactions in infection, thrombosis, atherosclerosis and tissue injury and repair.

Paradigm of Biased PAR1 (Protease-Activated Receptor-1) Activation and Inhibition in Endothelial Cells Dissected by Phosphoproteomics

OBJECTIVE

Thrombin is the key serine protease of the coagulation cascade and mediates cellular responses by activation of PARs (protease-activated receptors). The predominant thrombin receptor is PAR1, and in endothelial cells (ECs), thrombin dynamically regulates a plethora of phosphorylation events. However, it has remained unclear whether thrombin signaling is exclusively mediated through PAR1. Furthermore, mechanistic insight into activation and inhibition of PAR1-mediated EC signaling is lacking. In addition, signaling networks of biased PAR1 activation after differential cleavage of the PAR1 N terminus have remained an unresolved issue.

APPROACH AND RESULTS

Here, we used a quantitative phosphoproteomics approach to show that classical and peptide activation of PAR1 induce highly similar signaling, that low thrombin concentrations initiate only limited phosphoregulation, and that the PAR1 inhibitors vorapaxar and parmodulin-2 demonstrate distinct antagonistic properties. Subsequent analysis of the thrombin-regulated phosphosites in the presence of PAR1 inhibitors revealed that biased activation of PAR1 is not solely linked to a specific G-protein downstream of PAR1. In addition, we showed that only the canonical thrombin PAR1 tethered ligand induces extensive early phosphoregulation in ECs.

CONCLUSIONS

Our study provides detailed insight in the signaling mechanisms downstream of PAR1. Our data demonstrate that thrombin-induced EC phosphoregulation is mediated exclusively through PAR1, that thrombin and thrombin-tethered ligand peptide induce similar phosphoregulation, and that only canonical PAR1 cleavage by thrombin generates a tethered ligand that potently induces early signaling. Furthermore, platelet PAR1 inhibitors directly affect EC signaling, indicating that it will be a challenge to design a PAR1 antagonist that will target only those pathways responsible for tissue pathology.