Protease-activated receptors: contribution to physiology and disease

Protease Activated Receptors and Arthritis

The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For example, thrombin, trypsin, tryptase, and neutrophil elastase cleave the extracellular N-terminus of a family of G protein-coupled receptors and the remaining tethered ligand sequence then binds to the same receptor to initiate a series of molecular signalling processes. These protease activated receptors (PARs) pervade multiple tissues and cells throughout joints where they have the potential to regulate joint homeostasis. Overall, joint PARs contribute to pain, inflammation, and structural integrity by altering vascular reactivity, nociceptor sensitivity, and tissue remodelling. This review highlights the therapeutic potential of targeting PARs to alleviate the pain and destructive nature of elevated proteases in various arthritic conditions.

CSF and serum inflammatory response and association with outcomes in spontaneous intracerebral hemorrhage with intraventricular extension: an analysis of the CLEAR-III Trial

Background

Intracerebral hemorrhage (ICH) results in a cascade of inflammatory cell activation with recruitment of peripheral leukocytes to the brain parenchyma and surrounding the hematoma. We hypothesized that in patients with ICH and intraventricular hemorrhage (IVH), a robust cerebrospinal fluid (CSF) inflammatory response occurs with leukocyte subtypes being affected by alteplase treatment and contributing to outcomes.

Methods

Serum and CSF cell counts from patients in the phase 3 Clot Lysis: Evaluating Accelerated Resolution of Intraventricular Hemorrhage (CLEAR III) trial were analyzed. CSF leukocytes were corrected for the presence of red blood cells. Trends in cell counts were plotted chronologically. Associations were evaluated between serum and CSF leukocyte subtypes and adjudicated functional outcome (modified Rankin Scale; mRS) at 30 and 180 days and bacterial infection according to treatment with intraventricular alteplase versus saline.

Results

A total of 279 and 292 patients had ≥3 differential cell counts from serum and CSF, respectively. CSF leukocyte subtypes evolved during IVH resolution with a significantly augmented inflammatory response for all subtypes in alteplase- compared to saline-treated patients. CSF leukocyte subtypes were not associated with detrimental effect on functional outcomes in the full cohort, but all were associated with poor 30-day outcome in saline-treated patients with IVH volume ≥20 mL. Higher serum lymphocytes were associated with good functional outcomes (mRS 0–3) in the entire cohort and saline-treated but not alteplase-treated group. Conversely, increased serum neutrophil-to-lymphocyte ratio (NLR) in the entire cohort and saline group was associated with worse functional outcomes. Higher median serum lymphocytes were associated with the absence of infection at 7 days.

Conclusions

Aseptic CSF inflammation after IVH involves all leukocyte subtypes. Serum lymphocytes may be associated with better outcomes by mitigating infection. Alteplase augments the inflammatory response without affecting outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02224-w.

Inhibition of PAR-2 Attenuates Neuroinflammation and Improves Short-Term Neurocognitive Functions Via ERK1/2 Signaling Following Asphyxia-Induced Cardiac Arrest in Rats

OBJECTIVE

Global cerebral ischemia-induced neuroinflammation causes neurofunctional impairment following cardiac arrest. Previous studies have demonstrated that the activation of protease-activated receptor-2 (PAR-2) contributes to neuroinflammation. In the present study, we aimed to determine the potential treatment effect of PAR-2 inhibition against neuroinflammation in the setting of asphyxial CA (ACA) in rats.

METHODS

A total of 116 adult, male Sprague-Dawley rats were randomly divided into Sham (n = 18) and ACA (n = 98) groups. Time course, short-term outcome, and mechanism studies were conducted. All drugs were delivered intranasally. The effect of PAR-2 inhibitor FSLLRY-NH2 on neurocognitive functions was assessed by neurologic deficit score, number of seizures, and T-maze test, while hippocampal neuronal degeneration was evaluated by Fluoro-Jade C staining after ACA. Western blotting was performed for the mechanism study at 24 h following ACA. Selective PAR-2 agonist (AC55541) and ERK1/2 inhibitor (PD98059) were used for intervention.

RESULTS

Inhibition of PAR-2 decreased neuroinflammation, reduced the number of degenerating hippocampal neurons and improved neurocognitive functions following ACA. PAR-2 activator alone exerted opposite effects to PAR-2 inhibitor. PAR-2 mediated the augmented brain levels of proinflammatory cytokines by promoting the phosphorylation of ERK1/2.

CONCLUSIONS

PAR-2 inhibition diminished neuroinflammation and thereby reduced hippocampal neuronal degeneration and neurocognitive impairment following ACA. This effect was at least partly mediated via the PAR-2/ERK1/2 signaling.

Using Dictyostelium to Develop Therapeutics for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) involves damage to lungs causing an influx of neutrophils from the blood into the lung airspaces, and the neutrophils causing further damage, which attracts more neutrophils in a vicious cycle. There are ∼190,000 cases of ARDS per year in the US, and because of the lack of therapeutics, the mortality rate is ∼40%. Repelling neutrophils out of the lung airspaces, or simply preventing neutrophil entry, is a potential therapeutic. In this minireview, we discuss how our lab noticed that a protein called AprA secreted by growing Dictyostelium cells functions as a repellent for Dictyostelium cells, causing cells to move away from a source of AprA. We then found that AprA has structural similarity to a human secreted protein called dipeptidyl peptidase IV (DPPIV), and that DPPIV is a repellent for human neutrophils. In animal models of ARDS, inhalation of DPPIV or DPPIV mimetics blocks neutrophil influx into the lungs. To move DPPIV or DPPIV mimetics into the clinic, we need to know how this repulsion works to understand possible drug interactions and side effects. Combining biochemistry and genetics in Dictyostelium to elucidate the AprA signal transduction pathway, followed by drug studies in human neutrophils to determine similarities and differences between neutrophil and Dictyostelium chemorepulsion, will hopefully lead to the safe use of DPPIV or DPPIV mimetics in the clinic.

Advocacy of targeting protease-activated receptors in severe coronavirus disease 2019

Identifying drug targets mitigating vascular dysfunction, thrombo-inflammation and thromboembolic complications in COVID-19 is essential. COVID-19 coagulopathy differs from sepsis coagulopathy. Factors that drive severe lung pathology and coagulation abnormalities in COVID-19 are not understood. Protein-protein interaction studies indicate that the tagged viral bait protein ORF9c directly interacts with PAR2, which modulates host cell IFN and inflammatory cytokines. In addition to direct interaction of SARS-CoV-2 viral protein with PARs, we speculate that activation of PAR by proteases plays a role in COVID-19-induced hyperinflammation. In COVID-19-associated coagulopathy elevated levels of activated coagulation proteases may cleave PARs in association with TMPRSS2. PARs activation enhances the release of cytokines, chemokines and tissue factor expression to propagate IFN-dependent inflammation, leukocyte-endothelial interaction, vascular permeability and coagulation responses. This hypothesis, corroborated by in vitro findings and emerging clinical evidence, will focus targeted studies of PAR1/2 blockers as adjuvant drugs against cytokine release syndrome and COVID-19-associated coagulopathy.

Oral Versus Gastrointestinal Mucosal Immune Niches in Homeostasis and Allostasis

Different body systems (epidermis, respiratory tract, cornea, oral cavity, and gastrointestinal tract) are in continuous direct contact with innocuous and/or potentially harmful external agents, exhibiting dynamic and highly selective interaction throughout the epithelia, which function as both a physical and chemical protective barrier. Resident immune cells in the epithelia are constantly challenged and must distinguish among antigens that must be either tolerated or those to which a response must be mounted for. When such a decision begins to take place in lymphoid foci and/or mucosa-associated lymphoid tissues, the epithelia network of immune surveillance actively dominates both oral and gastrointestinal compartments, which are thought to operate in the same immune continuum. However, anatomical variations clearly differentiate immune processes in both the mouth and gastrointestinal tract that demonstrate a wide array of independent immune responses. From single vs. multiple epithelia cell layers, widespread cell-to-cell junction types, microbial-associated recognition receptors, dendritic cell function as well as related signaling, the objective of this review is to specifically contrast the current knowledge of oral versus gut immune niches in the context of epithelia/lymphoid foci/MALT local immunity and systemic output. Related differences in 1) anatomy 2) cell-to-cell communication 3) antigen capture/processing/presentation 4) signaling in regulatory vs. proinflammatory responses and 5) systemic output consequences and its relations to disease pathogenesis are discussed.

Boosting the oxidase-like activity of platinum nanozyme in MBTH-TOOS chromogenic system for detection of trypsin and its inhibitor

Nanozymes, as a new type of artificial enzyme, have recently become a research hotspot in the field of catalysis and biomedicine. However, the application of nanozyme is limited by catalytic activity changes of different substrates and low specificity. This work shows that citrate-capped platinum nanoparticles (Cit-PtNPs) exhibit stronger oxidase-like activity than other platinum nanozymes at different pH when 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and n-ethyl-n- (2-hydroxy-3-sulfopropyl)-m-toluidine sodium salt (TOOS) were used as chromogenic substrates. This phenomenon has important reference value for different nanozymes to choose chromogenic substrates in catalysis. In MBTH-TOOS chromogenic system, MBTH (-NH) radical is first produced during the reaction through catalytic oxidation of Cit-PtNPs, which reacts with TOOS to produce a colorless compound. The blue-purple quinoid dye was produced through the dismutation of the colorless compound. The catalytic mechanism of the oxidase-like activity of Cit-PtNPs is that two-electron reduction process and four-electron reduction process are simultaneously carried out in the catalytic process. Furthermore, to solve the problem of low specificity of metal nanozymes, protamine is designed as aggregation promoter of Cit-PtNPs and the specifichydrolysis substrate of trypsin. In this work, it can achieve one-step detection of trypsin by the boosting oxidase activity of Cit-PtNPs at pH8. The catalytic activity of Cit-PtNPs is proportional to the concentration of trypsin. The linear range for trypsin is 1.0-70.0 ngmL^-1 and the limit of detection is measured to be 0.6 ngmL^-1. This novel method has also been successfully applied to the detection of inhibitors and trypsin in urine samples.

Inherited and acquired determinants of serum tryptase levels in humans

OBJECTIVE

To aid the clinician in correctly interpreting serum tryptase levels.

DATA SOURCES

Primary peer-reviewed literature.

STUDY SELECTIONS

Clinical and basic science peer-reviewed studies characterizing the genetic and physiological bases for tryptase generation, secretion, and elevation, including those describing serum tryptase levels in population-based cohort studies.

RESULTS

Clinically measured basal serum tryptase (BST) consists of ostensibly inactive alpha- and beta-tryptase precursors. The autosomal dominant genetic trait hereditary alpha-tryptasemia is the most often cause for elevated BST levels, with other acquired causes, such as renal failure and clonal myeloid diseases being far less common. Acute increases in serum tryptase levels resulting from release of mature tryptase from secretory granules is specific to mast cell degranulation but is not detected in all cases of systemic anaphylaxis.

CONCLUSION

Understanding the differences and distinguishing between acute increases in serum tryptase and chronic elevations in BST owing to inherited or acquired conditions is critical in the correct interpretation of this useful clinical biomarker.

The Role of Protease-Activated Receptor 2 in Hepatocellular Carcinoma after Hepatectomy

Background and Objectives: Protease activated receptor-2 (PAR2) is elevated in a variety of cancers and has been promoted as a potential therapeutic target. However, the clinical and prognostic values of PAR2 in hepatocellular carcinoma (HCC) are poorly characterized. This study aimed to evaluate the expression of PAR2 in HCC tissues and examine the prognostic value of PAR2 after resection in HCC. Materials and Methods: Two hundred and eight resected specimens were collected from HCC patients at Kaohsiung Chang Gung Memorial Hospital. PAR2 protein expression was assessed by western blotting in HCC tissues and matched normal tissues. The correlation between PAR2 expression and clinicopathological parameters was analyzed. Disease-free survival (DFS) and overall survival (OS) were compared using the log-rank test. A Cox regression model was used to identify independent prognostic factors. Results: PAR2 was expressed at higher levels in HCC tissues than the paired adjacent nontumor tissues. High expression of PAR2 was associated with advanced tumor, node, metastasis (TNM )stage and histological grade. Kaplan-Meier analysis indicated high PAR2 expression was associated with poorer DFS and OS compared to low PAR2 expression. Multivariate analyses indicated high PAR2 expression [hazard ratio (HR), 1.779, p = 0.006), α-fetoprotein (AFP) (HR, 1.696, p = 0.003), liver cirrhosis (HR, 1.735, p = 0.002), and advanced TNM stage (HR, 2.061, p < 0.001) were prognostic factors for DFS, and advanced TNM stage (HR, 2.741, p < 0.001) and histological grade (HR, 2.675, p = 0.002) and high PAR2 expression (HR, 1.832, p = 0.012) were significant risk factors for OS. In subgroup analyses, the combination of PAR2 expression and serum AFP provided improved prognostic ability for OS and DFS. Conclusion: Combination PAR2 and AFP predict HCC outcomes after resection. PAR2 represents a potentially clinically relevant biomarker for HCC.

Voluntary Wheel Running Partially Attenuates Early Life Stress-Induced Neuroimmune Measures in the Dura and Evoked Migraine-Like Behaviors in Female Mice

Migraine is a complex neurological disorder that affects three times more women than men and can be triggered by endogenous and exogenous factors. Stress is a common migraine trigger and exposure to early life stress increases the likelihood of developing chronic pain disorders later in life. Here, we used our neonatal maternal separation (NMS) model of early life stress to investigate whether female NMS mice have an increased susceptibility to evoked migraine-like behaviors and the potential therapeutic effect of voluntary wheel running. NMS was performed for 3 h/day during the first 3 weeks of life and initial observations were made at 12 weeks of age after voluntary wheel running (Exercise, -Ex) or sedentary behavior (-Sed) for 4 weeks. Mast cell degranulation rates were significantly higher in dura mater from NMS-Sed mice, compared to either naïve-Sed or NMS-Ex mice. Protease activated receptor 2 (PAR2) protein levels in the dura were significantly increased in NMS mice and a significant interaction of NMS and exercise was observed for transient receptor potential ankyrin 1 (TRPA1) protein levels in the dura. Behavioral assessments were performed on adult (>8 weeks of age) naïve and NMS mice that received free access to a running wheel beginning at 4 weeks of age. Facial grimace, paw mechanical withdrawal threshold, and light aversion were measured following direct application of inflammatory soup (IS) onto the dura or intraperitoneal (IP) nitroglycerin (NTG) injection. Dural IS resulted in a significant decrease in forepaw withdrawal threshold in all groups of mice, while exercise significantly increased grimace score across all groups. NTG significantly increased grimace score, particularly in exercised mice. A significant effect of NMS and a significant interaction effect of exercise and NMS were observed on hindpaw sensitivity following NTG injection. Significant light aversion was observed in NMS mice, regardless of exercise, following NTG. Finally, exercise significantly reduced calcitonin gene-related peptide (CGRP) protein level in the dura of NMS and naïve mice. Taken together, these findings suggest that while voluntary wheel running improved some measures in NMS mice that have been associated with increased migraine susceptibility, behavioral outcomes were not impacted or even worsened by exercise.

Protease-activated receptor 2 induces ROS-mediated inflammation through Akt-mediated NF-κB and FoxO6 modulation during skin photoaging

Long-term exposure to ultraviolet irradiation to skin leads to deleterious intracellular effects, including reactive oxygen species (ROS) production and inflammatory responses, causing accelerated skin aging. Previous studies have demonstrated that increased expression and activation of protease-activated receptor 2 (PAR2) and Akt is observed in keratinocyte proliferation, suggesting their potential regulatory role in skin photoaging. However, the specific underlying molecular mechanism of PAR2 and the Akt/NF-κB/FoxO6-mediated signaling pathway is not clearly defined. In this study, we first used the UVB-irradiated photoaged skin of hairless mice and observed an increase in PAR2 and Gαq expression and PI3-kinase/Akt, NF-κB, and suppressed FoxO6. Consequently, increased levels of proinflammatory cytokines and decreased levels of antioxidant MnSOD was observed. Next, to investigate PAR2-specific roles in inflammation and oxidative stress, we used photoaged hairless mice topically applied with PAR2 antagonist GB83 and photoaged PAR2 knockout mice. PAR2 inhibition and deletion significantly suppressed inflammatory and oxidative stress levels, which were associated with decreased IL-6 and IL-1β levels and increased MnSOD levels, respectively. Furthermore, NF-κB phosphorylation and decreased FoxO6 was reduced by PAR2 inhibition and deletion in vivo. To confirm the in vivo results, we conducted PAR2 knockdown and overexpression in UVB-irradiated HaCaT cells. In PAR2 knockdown cells by si-PAR2 treatment, it suppressed Akt/NF-κB and increased FoxO6, whereas PAR2 overexpression reversed these effects and subsequently modulated proinflammatory target genes. Collectively, our data define that PAR2 induces oxidative stress and inflammation through Akt-mediated phosphorylation of NF-κB (Ser536) and FoxO6 (Ser184), which could be a critical upstream regulatory mechanism in ROS-mediated inflammatory response.

The relationship between gut microbiota and proteolytic activity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease that affects 3.8-9.2% of the world population. It affects the physiology and psychology of patients and increases the burden on families, the healthcare system, society, and economic development. Presently, a large number of studies have shown that compared to healthy individuals, the composition and diversity of gut microbiota in IBS patients have changed, and the proteolytic activity (PA) in fecal supernatant and colonic mucosa of IBS patients has also increased. These findings indicate that the imbalance of intestinal microecology and intestinal protein hydrolysis is closely related to IBS. Furthermore, the intestinal flora is a key substance that regulates the PA and is associated with IBS. The current review described the intestinal microecology and intestinal proteolytic activity of patients with IBS and also discussed the effect of intestinal flora on PA. In summary, this study proposed a pivotal role of gut microbiota and PA in IBS, respectively, and provided an in-depth insight into the diagnosis and treatment targets of IBS as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

β-arrestin-dependent PI(4,5)P2 synthesis boosts GPCR endocytosis

β-arrestins regulate many cellular functions including intracellular signaling and desensitization of G protein-coupled receptors (GPCRs). Previous studies show that β-arrestin signaling and receptor endocytosis are modulated by the plasma membrane phosphoinositide lipid phosphatidylinositol-(4, 5)-bisphosphate (PI(4,5)P2). We found that β-arrestin also helped promote synthesis of PI(4,5)P2 and up-regulated GPCR endocytosis. We studied these questions with the Gq-coupled protease-activated receptor 2 (PAR2), which activates phospholipase C, desensitizes quickly, and undergoes extensive endocytosis. Phosphoinositides were monitored and controlled in live cells using lipid-specific fluorescent probes and genetic tools. Applying PAR2 agonist initiated depletion of PI(4,5)P2, which then recovered during rapid receptor desensitization, giving way to endocytosis. This endocytosis could be reduced by various manipulations that depleted phosphoinositides again right after phosphoinositide recovery: PI(4)P, a precusor of PI(4,5)P2, could be depleted at either the Golgi or the plasma membrane (PM) using a recruitable lipid 4-phosphatase enzyme and PI(4,5)P2 could be depleted at the PM using a recruitable 5-phosphatase. Endocytosis required the phosphoinositides. Knock-down of β-arrestin revealed that endogenous β-arrestin normally doubles the rate of PIP5-kinase (PIP5K) after PAR2 desensitization, boosting PI(4,5)P2-dependent formation of clathrin-coated pits (CCPs) at the PM. Desensitized PAR2 receptors were swiftly immobilized when they encountered CCPs, showing a dwell time of ∼90 s, 100 times longer than for unactivated receptors. PAR2/β-arrestin complexes eventually accumulated around the edges or across the surface of CCPs promoting transient binding of PIP5K-Iγ. Taken together, β-arrestins can coordinate potentiation of PIP5K activity at CCPs to induce local PI(4,5)P2 generation that promotes recruitment of PI(4,5)P2-dependent endocytic machinery.

Neurological Symptoms of COVID-19: The Zonulin Hypothesis

The irruption of SARS-CoV-2 during 2020 has been of pandemic proportions due to its rapid spread and virulence. COVID-19 patients experience respiratory, digestive and neurological symptoms. Distinctive symptom as anosmia, suggests a potential neurotropism of this virus. Amongst the several pathways of entry to the nervous system, we propose an alternative pathway from the infection of the gut, involving Toll-like receptor 4 (TLR4), zonulin, protease-activated receptor 2 (PAR2) and zonulin brain receptor. Possible use of zonulin antagonists could be investigated to attenuate neurological manifestations caused by SARS-CoV-19 infection.

Proteinase-activated receptor-2 (PAR2) on blood pressure and electrolyte handling in the late pregnant rat

NEW FINDINGS

What is the central question of this study? Pregnancy requires marked renal sodium and potassium retention and cumulative plasma volume expansion, in the setting of reduced blood pressure. Research in male rodents has shown that activation of PAR2 can produce peripheral vasodilatation, stimulate renal sodium chloride reabsorption and inhibit renal potassium secretion. Here, we investigate PAR2 activation in virgin and normal pregnant rats. What is the main finding and its importance? PAR2 expression and sensitivity to activation are increased in pregnancy. This implicates a possible role for PAR2 in supporting the renal/vascular adaptations of pregnancy required for normal maternal plasma volume expansion.

ABSTRACT

A healthy pregnancy involves renal and systemic haemodynamic adaptations, which allow renal sodium and potassium retention and cumulative plasma volume expansion, accompanied by a decline in blood pressure attributable to a reduction in the total peripheral vascular resistance. When these adaptations do not occur, pregnancy is compromised. The mechanisms permitting these opposing adaptations are largely unknown. Research in male rodents has shown that activation of PAR2 can produce peripheral vasodilatation, stimulate renal sodium chloride reabsorption and inhibit renal potassium secretion. Here, we investigate PAR2 activation in female virgin and normal late pregnant (LP) rats. We measured the mRNA expression of PAR2 in the renal cortex, outer medulla and inner medulla of virgin and LP rats using quantitative real-time PCR. We also measured in vivo blood pressure, natriuretic and kaliuretic responses to PAR2-activating peptide (SLIGRL-NH₂ ) in anaesthetized virgin and LP rats. We found that PAR2 mRNA was increased in the inner medulla of LP rats. We also found that LP rats had larger decreases in blood pressure and increases in net sodium retention compared with virgin rats. These findings suggest that pregnancy enhances sensitivity to the blood pressure-lowering and sodium-retaining effects of PAR2.

The Pathogenesis of Chronic Spontaneous Urticaria: The Role of Infiltrating Cells

Chronic spontaneous urticaria is characterized by a perivascular non-necrotizing cellular infiltrate around small venules of the skin. It consists primarily of CD4(+) lymphocytes, a prominence of the T helper (Th)2 subtype but also Th1 cells, with Th17 cell-derived cytokines elevated in plasma. There are also neutrophils, eosinophils, basophils, and monocytes. Chemokines derived from mast cells and activated endothelial cells drive the process. Although the role of the cellular infiltrate has not previously been addressed, each constituent can contribute to the overall pathogenesis. It is of interest that CSU responds to corticosteroid, yet, short-term steroids do not affect autoimmunity or degranulation of mast cells, and act on margination of cells along the endothelium and chemotaxis to enter the surrounding dermis. In this review, we address each cell's contribution to the overall inflammatory response, as it is currently understood, with a view toward development of therapeutic options that impede the function of critical cells and/or their secretory products.

The PAR-1 antagonist vorapaxar ameliorates kidney injury and tubulointerstitial fibrosis

Protease-activated receptor (PAR)-1 has emerged as a key profibrotic player in various organs including kidney. PAR-1 activation leads to deposition of extracellular matrix (ECM) proteins in the tubulointerstitium and induction of epithelial-mesenchymal transition (EMT) during renal fibrosis. We tested the anti-fibrotic potential of vorapaxar, a clinically approved PAR-1 antagonist for cardiovascular protection, in an experimental kidney fibrosis model of unilateral ureteral obstruction (UUO) and an AKI-to-chronic kidney disease (CKD) transition model of unilateral ischemia-reperfusion injury (UIRI), and dissected the underlying renoprotective mechanisms using rat tubular epithelial cells. PAR-1 is activated mostly in the renal tubules in both the UUO and UIRI models of renal fibrosis. Vorapaxar significantly reduced kidney injury and ameliorated morphologic changes in both models. Amelioration of kidney fibrosis was evident from down-regulation of fibronectin (Fn), collagen and α-smooth muscle actin (αSMA) in the injured kidney. Mechanistically, inhibition of PAR-1 inhibited MAPK ERK1/2 and transforming growth factor-β (TGF-β)-mediated Smad signaling, and suppressed oxidative stress, overexpression of pro-inflammatory cytokines and macrophage infiltration into the kidney. These beneficial effects were recapitulated in cultured tubular epithelial cells in which vorapaxar ameliorated thrombin- and hypoxia-induced TGF-β expression and ECM accumulation. In addition, vorapaxar mitigated capillary loss and the expression of adhesion molecules on the vascular endothelium during AKI-to-CKD transition. The PAR-1 antagonist vorapaxar protects against kidney fibrosis during UUO and UIRI. Its efficacy in human CKD in addition to CV protection warrants further investigation.

Dynamics of D-amino acid oxidase in kidney epithelial cells under amino acid starvation

D-amino acid oxidase (DAO) is a flavoenzyme catalyzing the oxidation of D-amino acid (AA)s. In the kidney, its expression is detected in proximal tubules, and DAO is considered to play a role in the conversion of D-form AAs to α-keto acids. LLC-PK1 cells, a pig renal proximal tubule cell line, were used to elucidate the regulation of DAO protein synthesis and degradation. In this study, we showed that trypsinization of LLC-PK1 cells in culture system rapidly reduced the intracellular DAO protein level to approximately 33.9% of that before treatment, even within 30 min. Furthermore, we observed that the DAO protein level was decreased when LLC-PK1 cells were subjected to AA starvation. To determine the degradation pathway, we treated the cells with chloroquine and MG132. DAO degradation was found to be inhibited by chloroquine, but not by MG132 treatment. We next examined whether or not DAO was degraded by autophagy. We found that AA starvation led to an increased accumulation of LC3-II, suggesting that DAO protein is degraded by autophagy due to AA starvation conditions. Furthermore, treatment with cycloheximide inhibited DAO protein degradation. Taken together, DAO protein is degraded by autophagy under starvation. The present study revealed the potential dynamics of DAO correlated with renal pathophysiology.

PAR-2-activated secretion by airway gland serous cells: role for CFTR and inhibition by Pseudomonas aeruginosa

Airway submucosal gland serous cells are important sites of fluid secretion in conducting airways. Serous cells also express the cystic fibrosis (CF) transmembrane conductance regulator (CFTR). Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor that activates secretion from intact airway glands. We tested if and how human nasal serous cells secrete fluid in response to PAR-2 stimulation using Ca²⁺ imaging and simultaneous differential interference contrast imaging to track isosmotic cell shrinking and swelling reflecting activation of solute efflux and influx pathways, respectively. During stimulation of PAR-2, serous cells exhibited dose-dependent increases in intracellular Ca²⁺. At stimulation levels >EC₅₀ for Ca²⁺, serous cells simultaneously shrank ∼20% over ∼90 s due to KCl efflux reflecting Ca²⁺-activated Cl^- channel (CaCC, likely TMEM16A)-dependent secretion. At lower levels of PAR-2 stimulation (<EC₅₀ for Ca²⁺), shrinkage was not evident due to failure to activate CaCC. Low levels of cAMP-elevating VIP receptor (VIPR) stimulation, also insufficient to activate secretion alone, synergized with low-level PAR-2 stimulation to elicit fluid secretion dependent on both cAMP and Ca²⁺ to activate CFTR and K⁺ channels, respectively. Polarized cultures of primary serous cells also exhibited synergistic fluid secretion. Pre-exposure to Pseudomonas aeruginosa conditioned media inhibited PAR-2 activation by proteases but not peptide agonists in primary nasal serous cells, Calu-3 bronchial cells, and primary nasal ciliated cells. Disruption of synergistic CFTR-dependent PAR-2/VIPR secretion may contribute to reduced airway surface liquid in CF. Further disruption of the CFTR-independent component of PAR-2-activated secretion by P. aeruginosa may also be important to CF pathophysiology.

Protease-activated receptor 1 as a potential therapeutic target for COVID-19

Acute respiratory disease caused by a novel coronavirus (SARS-CoV-2) has spread all over the world, since its discovery in 2019, Wuhan, China. This disease is called COVID-19 and already killed over 1 million people worldwide. The clinical symptoms include fever, dry cough, dyspnea, headache, dizziness, generalized weakness, vomiting, and diarrhea. Unfortunately, so far, there is no validated vaccine, and its management consists mainly of supportive care. Venous thrombosis and pulmonary embolism are highly prevalent in patients suffering from severe COVID-19. In fact, a prothrombotic state seems to be present in most fatal cases of the disease. SARS-CoV-2 leads to the production of proinflammatory cytokines, causing immune-mediated tissue damage, disruption of the endothelial barrier, and uncontrolled thrombogenesis. Thrombin is the key regulator of coagulation and fibrin formation. In severe COVID-19, a dysfunctional of physiological anticoagulant mechanisms leads to a progressive increase of thrombin activity, which is associated with acute respiratory distress syndrome development and a poor prognosis. Protease-activated receptor type 1 (PAR1) is the main thrombin receptor and may represent an essential link between coagulation and inflammation in the pathophysiology of COVID-19. In this review, we discuss the potential role of PAR1 inhibition and regulation in COVID-19 treatment.

Spinal PAR2 Activation Contributes to Hypersensitivity Induced by Peripheral Inflammation in Rats

The mechanisms of inflammatory pain need to be identified in order to find new superior treatments. Protease-activated receptors 2 (PAR2) and transient receptor potential vanilloid 1 (TRPV1) are highly co-expressed in dorsal root ganglion neurons and implicated in pain development. Here, we examined the role of spinal PAR2 in hyperalgesia and the modulation of synaptic transmission in carrageenan-induced peripheral inflammation, using intrathecal (i.t.) treatment in the behavioral experiments and recordings of spontaneous, miniature and dorsal root stimulation-evoked excitatory postsynaptic currents (sEPSCs, mEPSCs and eEPSCs) in spinal cord slices. Intrathecal PAR2-activating peptide (AP) administration aggravated the carrageenan-induced thermal hyperalgesia, and this was prevented by a TRPV1 antagonist (SB 366791) and staurosporine i.t. pretreatment. Additionally, the frequency of the mEPSC and sEPSC and the amplitude of the eEPSC recorded from the superficial dorsal horn neurons were enhanced after acute PAR2 AP application, while prevented with SB 366791 or staurosporine pretreatment. PAR2 antagonist application reduced the thermal hyperalgesia and decreased the frequency of mEPSC and sEPSC and the amplitude of eEPSC. Our findings highlight the contribution of spinal PAR2 activation to carrageenan-induced hyperalgesia and the importance of dorsal horn PAR2 and TRPV1 receptor interactions in the modulation of nociceptive synaptic transmission.

Emerging Roles of Protease-Activated Receptors (PARs) in the Modulation of Synaptic Transmission and Plasticity

Protease-activated receptors (PARs) are a class of G protein-coupled receptors (GPCRs) with a unique mechanism of activation, prompted by a proteolytic cleavage in their N-terminal domain that uncovers a tethered ligand, which binds and stimulates the same receptor. PARs subtypes (PAR1-4) have well-documented roles in coagulation, hemostasis, and inflammation, and have been deeply investigated for their function in cellular survival/degeneration, while their roles in the brain in physiological conditions remain less appreciated. Here, we describe PARs' effects in the modulation of neurotransmission and synaptic plasticity. Available evidence, mainly concerning PAR1-mediated and PAR2-mediated regulation of glutamatergic and GABAergic transmission, supports that PARs are important modulators of synaptic efficacy and plasticity in normal conditions.

Thrombin-PAR1 signaling in pancreatic cancer promotes an immunosuppressive microenvironment

Essentials Elimination of PDAC tumor cell PAR1 increased cytotoxic T cells and reduced tumor macrophages. PAR1KO PDAC cells are preferentially eliminated from growing tumors. Thrombin-PAR1 signaling in PDAC tumor cells drives an immunosuppressive gene signature. Csf2 and Ptgs2 are thrombin-PAR1 downstream immune suppressor genes in PDAC tumor cells. ABSTRACT: Background Pancreatic ductal adenocarcinoma (PDAC) is characterized by a prothrombotic state and a lack of host antitumor immune responsiveness. Linking these two key features, we previously demonstrated that tumor-derived coagulation activity promotes immune evasion. Specifically, thrombin-protease-activated receptor-1 (PAR1) signaling in mouse PDAC cells drives tumor growth by evading cytotoxic CD8a+ cells. Methods Syngeneic mixed cell tumor growth, transcriptional analyses, and functional tests of immunosuppressive response genes were used to identify cellular and molecular immune evasion mechanisms mediated by thrombin-PAR-1 signaling in mouse PDAC tumor cells. Results Elimination of tumor cell PAR1 in syngeneic graft studies increased cytotoxic T lymphocyte (CTL) infiltration and decreased tumor-associated macrophages in the tumor microenvironment. Co-injection of PAR1-expressing and PAR1-knockout (PAR-1KO ) tumor cells into immunocompetent mice resulted in preferential elimination of PAR-1KO cells from developing tumors, suggesting that PAR1-dependent immune evasion is not reliant on CTL exclusion. Transcriptomics analyses revealed no PAR1-dependent changes in the expression of immune checkpoint proteins and no difference in major histocompatibility complex-I cell surface expression. Importantly, thrombin-PAR1 signaling in PDAC cells upregulated genes linked to immunosuppression, including Csf2 and Ptgs2. Functional analyses confirmed that both Csf2 and Ptgs2 are critical for PDAC syngeneic graft tumor growth and overexpression of each factor partially restored tumor growth of PAR1KO cells in immunocompetent mice. Conclusions Our results provide novel insight into the mechanisms of a previously unrecognized pathway coupling coagulation to PDAC immune evasion by identifying PAR1-dependent changes in the tumor microenvironment, a PAR1-driven immunosuppressive gene signature, and Csf2 and Ptgs2 as critical PAR1 downstream targets.

A direct thrombin inhibitor, dabigatran etexilate protects from renal fibrosis by inhibiting protease activated receptor-1

Chronic kidney disease (CKD) involves interstitial fibrosis as an influential underlying pathological process associated with compromised renal function regardless of etiological cause of the injury. The tubulointerstitial fibrosis is found to be well correlated with declining renal function and its subsequent culmination into renal failure. Given the prominent role of thrombin in multiple diseases, it was tempting for us to investigate the outcome of a direct thrombin inhibitor in renal injury. We investigated the involvement of thrombin in renal injury and fibrosis by using an FDA approved orally active, direct thrombin inhibitor, dabigatran etexilate (DB). We used a robust experimental model of unilateral ureteral obstruction (UUO)-induced renal injury which shows progressive tubulointerstitial fibrosis (TIF) along with tubular injury and inflammation. The obstructed kidney showed severe TIF as compared to control kidneys. The administration of DB significantly inhibited UUO-induced collagen-1 and TIF by inhibition of thrombin activated protease activated receptor (PAR)-1 expression in fibrotic kidney. In addition, DB administration improved histoarchitecture of obstructed kidney, inhibited TGF-β and SNAI2-induced epithelial-mesenchymal transition (EMT) program. Our study highlights the importance of thrombin signalling in TIF and provides strong evidences to support the notion that a direct thrombin inhibitor ameliorates TIF by PAR-1 mediated mechanism.

Protease-activated receptor-2 ligands reveal orthosteric and allosteric mechanisms of receptor inhibition

Protease-activated receptor-2 (PAR2) has been implicated in multiple pathophysiologies but drug discovery is challenging due to low small molecule tractability and a complex activation mechanism. Here we report the pharmacological profiling of a potent new agonist, suggested by molecular modelling to bind in the putative orthosteric site, and two novel PAR2 antagonists with distinctly different mechanisms of inhibition. We identify coupling between different PAR2 binding sites. One antagonist is a competitive inhibitor that binds to the orthosteric site, while a second antagonist is a negative allosteric modulator that binds at a remote site. The allosteric modulator shows probe dependence, more effectively inhibiting peptide than protease activation of PAR2 signalling. Importantly, both antagonists are active in vivo, inhibiting PAR2 agonist-induced acute paw inflammation in rats and preventing activation of mast cells and neutrophils. These results highlight two distinct mechanisms of inhibition that potentially could be targeted for future development of drugs that modulate PAR2.

Kennedy et al. report the pharmacological and in vivo profiling of two small molecule PAR2 inhibitors and an agonist. They conclude that while the small molecule agonist and one of the inhibitors bind to the orthosteric PAR2 binding site, the other inhibitor is a negative allosteric modulator, highlighting two distinct mechanisms of inhibition that could be targeted for future development of drugs that modulate PAR2.

Platelet-derived calpain cleaves the endothelial protease-activated receptor 1 to induce vascular inflammation in diabetes

Diabetes mellitus is a major risk factor for cardiovascular disease. Platelets from diabetic patients are hyperreactive and release microparticles that carry activated cysteine proteases or calpains. Whether platelet-derived calpains contribute to the development of vascular complications in diabetes is unknown. Here we report that platelet-derived calpain1 (CAPN1) cleaves the protease-activated receptor 1 (PAR-1) on the surface of endothelial cells, which then initiates a signaling cascade that includes the activation of the tumor necrosis factor (TNF)-α converting enzyme (TACE). The latter elicits the shedding of the endothelial protein C receptor and the generation of TNF-α, which in turn, induces intracellular adhesion molecule (ICAM)-1 expression to promote monocyte adhesion. All of the effects of CAPN1 were mimicked by platelet-derived microparticles from diabetic patients or from wild-type mice but not from CAPN1^−/− mice, and were not observed in PAR-1-deficient endothelial cells. Importantly, aortae from diabetic mice expressed less PAR-1 but more ICAM-1 than non-diabetic mice, effects that were prevented by treating diabetic mice with a calpain inhibitor as well as by the platelet specific deletion of CAPN1. Thus, platelet-derived CAPN1 contributes to the initiation of the sterile vascular inflammation associated with diabetes via the cleavage of PAR-1 and the release of TNF-α from the endothelial cell surface.

Expression of Proteinase-Activated Receptor 2 During Colon Volvulus in the Horse

Large colon volvulus in horses is associated with a poor prognosis, especially when ischemic-reperfusion injury of the affected intestinal tract develops. Proteinase-activated receptor 2 (PAR₂) plays an important role in the pathogenesis of inflammation in the gastrointestinal tract. The aim of this study was to evaluate the distribution and expression of PAR₂ in colonic pelvic flexure of horses spontaneously affected by large colon volvulus (CVH group). Eight horses admitted for severe abdominal colon volvolus and which underwent surgery were included. Colon samples were collected after enterotomy. Data previously obtained from healthy horses were used as a control group. Histologic evaluation was carried out to grade the severity of the colon lesions. Immunofluorescence, western blot and quantitative polymerase chain reaction (RT-qPCR) were carried out on colon samples to evaluate PAR₂ expression. In addition, the transcriptional profile of cytokines and chemokines was evaluated using RT² Profiler™ PCR Array Horse Cytokines & Chemokines. Three out of the eight patients were euthanised due to clinical deterioration. Immunostaining for PAR² was observed in the enterocytes, intestinal glands and neurons of the submucosal and myenteric plexi. In the CVH horses, the expression of PAR₂ mesenger RNA (mRNA) did not differ significantly from that of the healthy animals; western blots of the mucosa of the colon tracts showed a clear band of the expected molecular weight for PAR₂ (~44 kDa) and a band smaller than the expected molecular weight for PAR₂ (25kDa), suggesting its activation. The gene expressions for C-X-C motif ligand 1 (CXCL1); interleukin 8 (IL8), macrophage inflammatory protein 2 beta (MIP-2BETA) were upregulated in the colic horses as compared with the colons of the healthy horses. Therefore, in the present study, the expression and activation of PAR₂ in the colons of horses in the presence of an inflammatory reaction like that occurring in those with spontaneous colon volvulus was confirmed.

High CSF thrombin concentration and activity is associated with an unfavorable outcome in patients with intracerebral hemorrhage

Background

The cerebral thrombin system is activated in the early stage after intracerebral hemorrhage (ICH). Expression of thrombin leads to concentration dependent secondary neuronal damage and detrimental neurological outcome. In this study we aimed to investigate the impact of thrombin concentration and activity in the cerebrospinal fluid (CSF) of patients with ICH on clinical outcome.

Methods

Patients presenting with space-occupying lobar supratentorial hemorrhage requiring extra-ventricular drainage (EVD) were included in our study. The CSF levels of thrombin, its precursor prothrombin and the Thrombin-Antithrombin complex (TAT) were measured using enzyme linked immune sorbent assays (ELISA). The oxidative stress marker Superoxide dismutase (SOD) was assessed in CSF. Initial clot size and intraventricular hemorrhage (IVH) volume was calculated based on by computerized tomography (CT) upon admission to our hospital. Demographic data, clinical status at admission and neurological outcome were assessed using the modified Rankin Scale (mRS) at 6-weeks and 6-month after ICH.

Results

Twenty-two consecutive patients (9 females, 11 males) with supratentorial hemorrhage were included in this study. CSF concentrations of prothrombin (p < 0.005), thrombin (p = 0.005) and TAT (p = 0.046) were statistical significantly different in patients with ICH compared to non-hemorrhagic CSF samples. CSF concentrations of thrombin 24h after ICH correlated with the mRS index after 6 weeks (r² = 0.73; < 0.005) and 6 months (r² = 0.63; < 0.005) after discharge from hospital. Thrombin activity, measured via TAT as surrogate parameter of coagulation, likewise correlated with the mRS at 6 weeks (r² = 0.54; < 0.01) and 6 months (r² = 0.66; < 0.04). High thrombin concentrations coincide with higher SOD levels 24h after ICH (p = 0.01).

Conclusion

In this study we found that initial thrombin concentration and activity in CSF of ICH patients did not correlate with ICH and IVH volume but are associated with a poorer functional neurological outcome. These findings support mounting evidence of the role of thrombin as a contributor to secondary injury formation after ICH.

Targeting of protease activator receptor-2 (PAR-2) antagonist FSLLRY-NH2 as an asthma adjuvant therapy

Asthma is a chronic inflammatory and multifactorial respiratory tract disease. It affects over 18 million adults and 6 million children in the USA with Puerto Ricans showing the highest prevalence (12%-19%). This airways illness can be triggered by an environmental stimulus such as grass pollen, fungi spores, cockroaches allergens, dust mites metabolic compounds, and importantly, by environmental proteases such as trypsin and tryptase. Because of the pivotal role of proteases in the onset of asthma pathophysiology, we focused this study on the serine Protease Activated Receptor-2 (PAR-2), a G-protein-coupled receptor widely expressed in cells across the respiratory tract. Herein, we measured the activation of PAR-2 on primary pulmonary bronchial/tracheal epithelial cells, human small airway epithelial cells, lung bronchial smooth muscle cells (with and without asthma). We tested human-derived eosinophils from 61 Puerto Rican participants (33 asthmatic and 28 non-asthmatic). As surrogate of PAR-2 activation or inhibition we used intracellular calcium mobilization assay. We hypothesized that following exposure of the PAR-2 agonist (AC264613), the studied human primary cell types will increase the mobilization of intracellular calcium levels. In contrast, we expected a decrease of the intracellular calcium levels upon exposure to a PAR-2 antagonist (FSLLRY-NH2). The Puerto Rican-derived eosinophils were analyzed for the proinflammatory markers MAPK/PI3K using flow cytometry (n = 8). As expected, the PAR-2 agonist significantly increased the activation of PAR-2 on the bronchial/tracheal epithelial cells, bronchial smooth muscle cells and human small airway epithelial cells (P = .01). The PAR-2 antagonist significantly decreased the intracellular calcium levels of these lung primary down to undetectable levels (P = .01). Remarkably, the asthmatic-derived eosinophils showed a striking 300% increase of intracellular calcium mobilization suggesting a severe response to the PAR-2 agonist stimuli in asthmatics. In contrast, there were no significant changes between groups after adding the PAR-2 antagonist. Our outcomes revealed that PAR-2 antagonist effectively inhibited the studied primary cells, expecting to decrease the immune response of eosinophils. Most importantly, our results reveal a promising role for the PAR-2 antagonist in targeting bronchial/tracheal epithelial cells, human small airway epithelial cells and bronchial smooth muscle cells with the potential to oblige an asthma adjuvant therapy.

MicroRNAs are critical in regulating smooth muscle cell mineralization and apoptosis during vascular calcification

Vascular calcification refers to the pathological deposition of calcium and phosphate minerals into the vasculature. It is prevalent in atherosclerosis, ageing, type 2 diabetes mellitus and chronic kidney disease, thus, increasing morbidity and mortality from these conditions. Vascular calcification shares similar mechanisms with bone mineralization, with smooth muscle cells playing a critical role in both processes. In the last decade, a variety of microRNAs have been identified as key regulators for the differentiation, phenotypic switch, proliferation, apoptosis, cytokine production and matrix deposition in vascular smooth muscle cells during vascular calcification. Therefore, this review mainly discusses the roles of microRNAs in the pathophysiological mechanisms of vascular calcification in smooth muscle cells and describes several interventions against vascular calcification by regulating microRNAs. As the exact mechanisms of calcification remain not fully elucidated, having a better understanding of microRNA involvement in vascular calcification may give impetus to development of novel therapeutics for the control and treatment of vascular calcification.

The Role of Thrombin in Brain Injury After Hemorrhagic and Ischemic Stroke

Thrombin is increased in the brain after hemorrhagic and ischemic stroke primarily due to the prothrombin entry from blood either with a hemorrhage or following blood-brain barrier disruption. Increasing evidence indicates that thrombin and its receptors (protease-activated receptors (PARs)) play a major role in brain pathology following ischemic and hemorrhagic stroke (including intracerebral, intraventricular, and subarachnoid hemorrhage). Thrombin and PARs affect brain injury via multiple mechanisms that can be detrimental or protective. The cleavage of prothrombin into thrombin is the key step of hemostasis and thrombosis which takes place in every stroke and subsequent brain injury. The extravascular effects and direct cellular interactions of thrombin are mediated by PARs (PAR-1, PAR-3, and PAR-4) and their downstream signaling in multiple brain cell types. Such effects include inducing blood-brain-barrier disruption, brain edema, neuroinflammation, and neuronal death, although low thrombin concentrations can promote cell survival. Also, thrombin directly links the coagulation system to the immune system by activating interleukin-1α. Such effects of thrombin can result in both short-term brain injury and long-term functional deficits, making extravascular thrombin an understudied therapeutic target for stroke. This review examines the role of thrombin and PARs in brain injury following hemorrhagic and ischemic stroke and the potential treatment strategies which are complicated by their role in both hemostasis and brain.

Influence of dabigatran on pro-inflammatory cytokines, growth factors and chemokines - Slowing the vicious circle of coagulation and inflammation

AIMS

Blood coagulation is one of the most important host-defending mechanisms in vivo by maintaining the blood pressure after injury. However, besides maintaining homeostasis, blood coagulation and the contributing factors are directly linked to pathological conditions, such as thromboembolism and inflammation, leading to cardiovascular diseases, among others. As anti-inflammatory drugs may reduce cardiovascular events, we hypothesized in this study that the direct thrombin inhibitor dabigatran may reduce cytokine, growth factor and chemokine expression in vitro.

MAIN METHODS

Initially, human whole blood was incubated in tubes for serum, EDTA plasma, and heparinized plasma. Furthermore, human PBMCs were isolated and incubated under different culture conditions, including the treatment with human serum or thrombin, respectively. The effect of the oral anticoagulant dabigatran on pro-inflammatory cytokines, growth factors and chemokines was investigated by ELISA.

KEY FINDINGS

Conditioned serum resulted in a significant alteration of the secretome's protein levels after 24 h. However, solely ANG showed a dose-dependent increment by the addition of serum (79.8 ± 9.2 ng/mL) in comparison to baseline (0.2 ± 0.2 ng/mL), as it was in trend for thrombin treatment. Furthermore, the pre-treatment of PBMCs with different doses of dabigatran significantly lowered supernatant protein levels measured. Moreover, dabigatran was shown to decrease most notably the growth factor and chemokine levels in the PBMC's secretome that were treated with 200 ng/mL thrombin in a dose-dependent manner.

SIGNIFICANCE

In conclusion, novel oral anticoagulants, such as dabigatran, could help to reduce not only procoagulatory effects in inflammatory conditions but could also reduce proinflammatory stimuli via reduced expression of cytokines and chemokines.

Macrophage TLR4 and PAR2 Signaling: Role in Regulating Vascular Inflammatory Injury and Repair

Macrophages play a central role in dictating the tissue response to infection and orchestrating subsequent repair of the damage. In this context, macrophages residing in the lungs continuously sense and discriminate among a wide range of insults to initiate the immune responses important to host-defense. Inflammatory tissue injury also leads to activation of proteases, and thereby the coagulation pathway, to optimize injury and repair post-infection. However, long-lasting inflammatory triggers from macrophages can impair the lung's ability to recover from severe injury, leading to increased lung vascular permeability and neutrophilic injury, hallmarks of Acute Lung Injury (ALI). In this review, we discuss the roles of toll-like receptor 4 (TLR4) and protease activating receptor 2 (PAR2) expressed on the macrophage cell-surface in regulating lung vascular inflammatory signaling.

Protease-activated receptor 1 (PAR1) inhibits synaptic NMDARs in mouse nigral dopaminergic neurons

Protease-activated receptor 1 (PAR1) is a G protein-coupled receptor (GPCR), whose activation requires a proteolytic cleavage in the extracellular domain exposing a tethered ligand, which binds to the same receptor thus stimulating Gα_q/11-, Gα_i/o- and Gα_12-13 proteins. PAR1, activated by serine proteases and matrix metalloproteases, plays multifaceted roles in neuroinflammation and neurodegeneration, in stroke, brain trauma, Alzheimer's diseases, and Parkinson's disease (PD). Substantia nigra pars compacta (SNpc) is among areas with highest PAR1 expression, but current evidence on its roles herein is restricted to mechanisms controlling dopaminergic (DAergic) neurons survival, with controversial data showing PAR1 either fostering or counteracting degeneration in PD models. Since PAR1 functions on SNpc DAergic neurons activity are unknown, we investigated if PAR1 affects glutamatergic transmission in this neuronal population. We analyzed PAR1's effects on NMDARs and AMPARs by patch-clamp recordings from DAergic neurons from mouse midbrain slices. Then, we explored subunit composition of PAR1-sensitive NMDARs, with selective antagonists, and mechanisms underlying PAR1-induced NMDARs modulation, by quantifying NMDARs surface expression. PAR1 activation inhibits synaptic NMDARs in SNpc DAergic neurons, without affecting AMPARs. PAR1-sensitive NMDARs contain GluN2B/GluN2D subunits. Moreover, PAR1-mediated NMDARs hypofunction is reliant on NMDARs internalization, as PAR1 stimulation increases NMDARs intracellular levels and pharmacological limitation of NMDARs endocytosis prevents PAR1-induced NMDARs inhibition. We reveal that PAR1 regulates glutamatergic transmission in midbrain DAergic cells. This might have implications in brain's DA-dependent functions and in neurological/psychiatric diseases linked to DAergic dysfunctions.

The domino effect triggered by the tethered ligand of the protease activated receptors

Protease activated receptors (PARs) are G-protein coupled receptors (GPCRs) that have a unique activation mechanism. Unlike other GPCRs that can be activated by free ligands, under physiological conditions, PARs are activated by the tethered ligand, which is a part of their N-terminus that is unmasked by proteolysis. It has been 30 years since the first member of the family, PAR1, was identified. In this review, we will discuss this unique tethered ligand mediate receptor activation of PARs in detail: how they interact with the proteases, the complex structural rearrangement of the receptors upon activation, and the termination of the signaling. We also summarize the structural studies of the PARs and how single nucleotide polymorphisms impact the receptor reactivity. Finally, we review the current strategies for inhibiting PAR function with therapeutic targets for anti-thrombosis. The focus of this review is PAR1 and PAR4 as they are the thrombin signal mediators on human platelets and therapeutics targets. We also include the structural studies of PAR2 as it informs the mechanism of action for PARs in general.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

The transient receptor potential vanilloid 4 (TRPV4) ion channel mediates protease activated receptor 1 (PAR1)-induced vascular hyperpermeability

Endothelial barrier disruption is a hallmark of tissue injury, edema, and inflammation. Vascular endothelial cells express the G protein-coupled receptor (GPCR) protease acctivated receptor 1 (PAR1) and the ion channel transient receptor potential vanilloid 4 (TRPV4), and these signaling proteins are known to respond to inflammatory conditions and promote edema through remodeling of cell-cell junctions and modulation of endothelial barriers. It has previously been established that signaling initiated by the related protease activated receptor 2 (PAR2) is enhanced by TRPV4 in sensory neurons and that this functional interaction plays a critical role in the development of neurogenic inflammation and nociception. Here, we investigated the PAR1-TRPV4 axis, to determine if TRPV4 plays a similar role in the control of edema mediated by thrombin-induced signaling. Using Evans Blue permeation and retention as an indication of increased vascular permeability in vivo, we showed that TRPV4 contributes to PAR1-induced vascular hyperpermeability in the airways and upper gastrointestinal tract of mice. TRPV4 contributes to sustained PAR1-induced Ca²⁺ signaling in recombinant cell systems and to PAR1-dependent endothelial junction remodeling in vitro. This study supports the role of GPCR-TRP channel functional interactions in inflammatory-associated changes to vascular function and indicates that TRPV4 is a signaling effector for multiple PAR family members.

Rivaroxaban, a Direct Factor Xa Inhibitor, Ameliorates Hypertensive Renal Damage Through Inhibition of the Inflammatory Response Mediated by Protease-Activated Receptor Pathway

Background

An enhanced renin‐angiotensin system causes hypertensive renal damage. Factor Xa not only functions in the coagulation cascade but also activates intracellular signaling through protease‐activated receptors (PAR). We investigated the effects of rivaroxaban, a factor Xa inhibitor, on hypertensive renal damage in hypertensive mice overexpressing renin (Ren‐TG).

Methods and Results

The 12‐ to 16‐week‐old Ren‐TG and wild‐type mice were orally administered with or without 6 or 12 mg/kg of rivaroxaban for 1 or 4 months. Plasma factor Xa was significantly increased in the Ren‐TG compared with the wild‐type mice and was reduced by 12 mg/kg of rivaroxaban (P<0.05). Urinary albumin excretion (UAE) was higher in the nontreated 8‐month‐old Ren‐TG than in the wild‐type mice (69.6±29 versus 20.1±8.2 μg/day; P<0.01). Treatment with 12 mg/kg of rivaroxaban for 4 months decreased the UAE to 38.1±13.2 μg/day (P<0.01). Moreover, rivaroxaban treatment attenuated histologic changes of glomerular hypertrophy, mesangial matrix expansion, effacement of the podocyte foot process, and thickened glomerular basement membrane in the Ren‐TG. The renal expression of PAR‐2 was increased in the Ren‐TG, but was inhibited with rivaroxaban treatment. In vitro study using the human podocytes showed that the expressions of PAR‐2 and inflammatory genes and nuclear factor–‐κB activation were induced by angiotensin II stimulation, but were inhibited by rivaroxaban. PAR‐2 knockdown by small interfering RNA also attenuated the PAR‐2‐related inflammatory gene expressions.

Conclusions

These findings indicate that rivaroxaban exerts protective effects against angiotensin II–induced renal damage, partly through inhibition of the PAR‐2 signaling‐mediated inflammatory response.

Punicalagin Ameliorates Lupus Nephritis via Inhibition of PAR2

Lupus nephritis (LN) is the most frequent phenotype in patients with systemic lupus erythematosus (SLE) and has a high rate of progression to end-stage renal disease, in spite of intensive treatment and maintenance therapies. Recent evidence suggests that protease-activated receptor-2 (PAR2) is a therapeutic target for glomerulonephritis. In this study, we performed a cell-based high-throughput screening and identified a novel potent PAR2 antagonist, punicalagin (PCG, a major polyphenol enriched in pomegranate), and evaluated the effects of PCG on LN. The effect of PCG on PAR2 inhibition was observed in the human podocyte cell line and its effect on LN was evaluated in NZB/W F1 mice. In the human podocyte cell line, PCG potently inhibited PAR2 (IC₅₀ = 1.5 ± 0.03 µM) and significantly reduced the PAR2-mediated activation of ERK1/2 and NF-κB signaling pathway. In addition, PCG significantly decreased PAR2-induced increases in ICAM-1 and VCAM-1 as well as in IL-8, IFN-γ, and TNF-α expression. Notably, the intraperitoneal administration of PCG significantly alleviated kidney injury and splenomegaly and reduced proteinuria and renal ICAM-1 and VCAM-1 expression in NZB/W F1 mice. Our results suggest that PCG has beneficial effects on LN via inhibition of PAR2, and PCG is a potential therapeutic agent for LN.

Electroacupuncture intervention of visceral hypersensitivity is involved in PAR-2-activation and CGRP-release in the spinal cord

Electroacupuncture (EA) relieves visceral hypersensitivity (VH) with underlying inflammatory bowel diseases. However, the mechanism by which EA treats ileitis-induced VH is not clearly known. To assess the effects of EA on ileitis-induced VH and confirm whether EA attenuates VH through spinal PAR-2 activation and CGRP release, goats received an injection of 2,4,6-trinitro-benzenesulfonic-acid (TNBS) solution into the ileal wall. TNBS-injected goats were allocated into VH, Sham acupuncture (Sham-A) and EA groups, while goats treated with saline instead of TNBS solution were used as the control. Goats in EA group received EA at bilateral Hou-San-Li acupoints for 0.5 h at 7 days and thereafter repeated every 3 days for 6 times. Goats in the Sham-A group were inserted with needles for 0.5 h at the aforementioned acupoints without any hand manipulation and electric stimulation. Visceromotor responses to colorectal distension, an indicator of VH, were recorded by electromyography. The terminal ileum and thoracic spinal cord (T₁₁) were sampled for evaluating ileitis at days 7 and 22, and distribution and expression-levels of PAR-2, CGRP and c-Fos on day 22. TNBS-treated-goats exhibited apparent transmural-ileitis on day 7, microscopically low-grade ileitis on day 22 and VH at days 7–22. Goats of Sham-A, VH or EA group showed higher (P < 0.01) VH at days 7–22 than the Control-goats. EA-treated goats exhibited lower (P < 0.01) VH as compared with Sham-A or VH group. Immunoreactive-cells and expression-levels of spinal PAR-2, CGRP and c-Fos in the EA group were greater (P < 0.01) than those in the Control group, but less (P < 0.01) than those in Sham-A and VH groups on day 22. Downregulation of spinal PAR-2 and CGRP levels by EA attenuates the ileitis and resultant VH.

Physiology and Pathophysiology of Itch

Itch is a topic to which everyone can relate. The physiological roles of itch are increasingly understood and appreciated. The pathophysiological consequences of itch impact quality of life as much as pain. These dynamics have led to increasingly deep dives into the mechanisms that underlie and contribute to the sensation of itch. When the prior review on the physiology of itching was published in this journal in 1941, itch was a black box of interest to a small number of neuroscientists and dermatologists. Itch is now appreciated as a complex and colorful Rubik's cube. Acute and chronic itch are being carefully scratched apart and reassembled by puzzle solvers across the biomedical spectrum. New mediators are being identified. Mechanisms blur boundaries of the circuitry that blend neuroscience and immunology. Measures involve psychophysics and behavioral psychology. The efforts associated with these approaches are positively impacting the care of itchy patients. There is now the potential to markedly alleviate chronic itch, a condition that does not end life, but often ruins it. We review the itch field and provide a current understanding of the pathophysiology of itch. Itch is a disease, not only a symptom of disease.

New PAR1 Agonist Peptide Demonstrates Protective Action in a Mouse Model of Photothrombosis-Induced Brain Ischemia

Protease-activated receptors (PARs) are involved not only in hemostasis but also in the development of ischemic brain injury. In the present work, we examined in vivo effects of a new peptide (AP9) composing Asn⁴⁷-Phen⁵⁵ of PAR1 “tethered ligand” generated by activated protein C. We chose a mouse model of photothrombosis (PT)-induced ischemia to assess AP9 effects in vivo. To reveal the molecular mechanism of AP9 action, mice lacking β-arrestin-2 were used. AP9 was injected intravenously once 10 min before PT at doses of 0.2, 2, or 20 mg/kg, or twice, that is, 10 min before and 1 h after PT at a dose of 20 mg/kg. Lesion volume was measured by magnetic resonance imaging and staining of brain sections with tetrazolium salt. Neurologic deficit was estimated using the cylinder and the grid-walk tests. Blood–brain barrier (BBB) disruption was assessed by Evans blue dye extraction. Eosin-hematoxylin staining and immunohistochemical staining were applied to evaluate the number of undamaged neurons and activated glial cells in the penumbra. A single administration of AP9 (20 mg/kg), as well as its two injections (20 mg/kg), decreased brain lesion volume. A double administration of AP9 also reduced BBB disruption and neurological deficit in mice. We did not observe the protective effect of AP9 in mice lacking β-arrestin-2 after PT. Thus, we demonstrated for the first time protective properties of a PAR1 agonist peptide, AP9, in vivo. β-Arrestin-2 was required for the protective action of AP9 in PT-induced brain ischemia.

Discovery of Novel Nonpeptidic PAR2 Ligands

Proteinase-activated receptor 2 (PAR2) is a class A G protein-coupled receptor whose activation has been associated with inflammatory diseases and cancer, thus representing a valuable therapeutic target. Pathophysiological roles of PAR2 are often characterized using peptidic PAR2 agonists. Peptidic ligands are frequently unstable in vivo and show poor bioavailability, and only a few approaches toward drug-like nonpeptidic PAR2 ligands have been described. The herein-described ligand 5a (IK187) is a nonpeptidic PAR2 agonist with submicromolar potency in a functional assay reflecting G protein activation. The ligand also showed substantial β-arrestin recruitment. The development of the compound was guided by the crystal structure of PAR2, when the C-terminal end of peptidic agonists was replaced by a small molecule based on a disubstituted phenylene scaffold. IK187 shows preferable metabolic stability and may serve as a lead compound for the development of nonpeptidic drugs addressing PAR2.

Mast cell-mediated neuroinflammation may have a role in attention deficit hyperactivity disorder (Review)

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental and behavioral disorder with a serious negative impact on the quality of life from childhood until adulthood, which may cause academic failure, family disharmony and even social unrest. The pathogenesis of ADHD has remained to be fully elucidated, leading to difficulties in the treatment of this disease. Genetic and environmental factors contribute to the risk of ADHD development. Certain studies indicated that ADHD has high comorbidity with allergic and autoimmune diseases, with various patients with ADHD having a high inflammatory status. Increasing evidence indicated that mast cells (MCs) are involved in the pathogenesis of brain inflammation and neuropsychiatric disorders. MCs may cause or aggravate neuroinflammation via the selective release of inflammatory factors, interaction with glial cells and neurons, activation of the hypothalamic-pituitary adrenal axis or disruption of the blood-brain barrier integrity. In the present review, the notion that MC activation may be involved in the occurrence and development of ADHD through a number of ways is discussed based on previously published studies. The association between MCs and ADHD appears to lack sufficient evidence at present and this hypothesis is considered to be worthy of further study, providing a novel perspective for the treatment of ADHD.

Urticaria: recommendations from the Italian Society of Allergology, Asthma and Clinical Immunology and the Italian Society of Allergological, Occupational and Environmental Dermatology

BACKGROUND

Urticaria is a disorder affecting skin and mucosal tissues characterized by the occurrence of wheals, angioedema or both, the latter defining the urticaria-angioedema syndrome. It is estimated that 12-22% of the general population has suffered at least one subtype of urticaria during life, but only a small percentage (estimated at 7.6-16%) has acute urticaria, because it is usually self-limited and resolves spontaneously without requiring medical attention. This makes likely that its incidence is underestimated. The epidemiological data currently available on chronic urticaria in many cases are deeply discordant and not univocal, but a recent Italian study, based on the consultation of a national registry, reports a prevalence of chronic spontaneous urticaria of 0.02% to 0.4% and an incidence of 0.1-1.5 cases/1000 inhabitants/year.

METHODS

We reviewed the recent international guidelines about urticaria and we described a methodologic approach based on classification, pathophysiology, impact on quality of life, diagnosis and prognosis, differential diagnosis and management of all the types of urticaria.

CONCLUSIONS

The aim of the present document from the Italian Society of Allergology, Asthma and Clinical Immunology (SIAAIC) and the Italian Society of Allergological, Occupational and Environmental Dermatology (SIDAPA) is to provide updated information to all physicians involved in diagnosis and management of urticaria and angioedema.

Inhibition of mast cell tryptase attenuates neuroinflammation via PAR-2/p38/NFκB pathway following asphyxial cardiac arrest in rats

Background

Cardiac arrest survivors suffer from neurological dysfunction including cognitive impairment. Cerebral mast cells, the key regulators of neuroinflammation contribute to neuroinflammation-associated cognitive dysfunction. Mast cell tryptase was demonstrated to have a proinflammatory effect on microglia via the activation of microglial protease-activated receptor-2 (PAR-2). This study investigated the potential anti-neuroinflammatory effect of mast cell tryptase inhibition and the underlying mechanism of PAR-2/p-p38/NFκB signaling following asphyxia-induced cardiac arrest in rats.

Methods

Adult male Sprague-Dawley rats resuscitated from 10 min of asphyxia-induced cardiac arrest were randomized to four separate experiments including time-course, short-term outcomes, long-term outcomes and mechanism studies. The effect of mast cell tryptase inhibition on asphyxial cardiac arrest outcomes was examined after intranasal administration of selective mast cell tryptase inhibitor (APC366; 50 μg/rat or 150 μg/rat). AC55541 (selective PAR-2 activator; 30 μg/rat) and SB203580 (selective p38 inhibitor; 300 μg/rat) were used for intervention. Short-term neurocognitive functions were evaluated using the neurological deficit score, number of seizures, adhesive tape removal test, and T-maze test, while long-term cognitive functions were evaluated using the Morris water maze test. Hippocampal neuronal degeneration was evaluated by Fluoro-Jade C staining.

Results

Mast cell tryptase and PAR-2 were dramatically increased in the brain following asphyxia-induced cardiac arrest. The inhibition of mast cell tryptase by APC366 improved both short- and long-term neurological outcomes in resuscitated rats. Such behavioral benefits were associated with reduced expressions of PAR-2, p-p38, NFκB, TNF-α, and IL-6 in the brain as well as less hippocampal neuronal degeneration. The anti-neuroinflammatory effect of APC366 was abolished by AC55541, which when used alone, indeed further exacerbated neuroinflammation, hippocampal neuronal degeneration, and neurologic deficits following cardiac arrest. The deleterious effects aggregated by AC55541 were minimized by p38 inhibitor.

Conclusions

The inhibition of mast cell tryptase attenuated neuroinflammation, led to less hippocampal neuronal death and improved neurological deficits following cardiac arrest. This effect was at least partly mediated via inhibiting the PAR-2/p-p38/NFκB signaling pathway. Thus, mast cell tryptase might be a novel therapeutic target in the management of neurological impairment following cardiac arrest.

Non-invasive Assessment of Fecal Stress Biomarkers in Hunting Dogs During Exercise and at Rest

Intense exercise causes to organisms to have oxidative stress and inflammation at the gastrointestinal (GI) level. The reduction in intestinal blood flow and the exercise-linked thermal damage to the intestinal mucosa can cause intestinal barrier disruption, followed by an inflammatory response. Furthermore, the adaptation to exercise may affect the gut microbiota and the metabolome of the biofluids. The aim of the present research was to evaluate the presence of a GI derangement in hunting dogs through a non-invasive sampling as a consequence of a period of intense exercise in comparison with samples collected at rest. The study included nine dogs that underwent the same training regime for hunting wild boar. In order to counterbalance physiological variations, multiple-day replicates were collected and pooled at each experimental point for each dog. The samples were collected immediately at rest before the training (T0), after 60 days of training (T1), after 60 days of hunting wild boar (T2), and finally, at 60 days of rest after hunting (T3). A number of potential stress markers were evaluated: fecal cortisol metabolites (FCMs) as a major indicator of altered physiological states, immunoglobulin A (IgA) as an indicator of intestinal immune protection, and total antioxidant activity [total antioxidant capacity (TAC)]. Since stool samples contain exfoliated cells, we investigated also the presence of some transcripts involved in GI permeability [occludin (OCLN), protease-activated receptor-2 (PAR-2)] and in the inflammatory mechanism [interleukin (IL)-8, IL-6, IL-1b, tumor necrosis factor alpha (TNFα), calprotectin (CALP), heme oxygenase-1 (HO-1)]. Finally, the metabolome and the microbiota profiles were analyzed. No variation in FCM and IgA content and no differences in OCLN and CALP gene expression between rest and training were observed. On the contrary, an increase in PAR-2 and HO-1 transcripts, a reduction in total antioxidant activity, and a different profile of microbiota and metabolomics data were observed. Collectively, the data in the present study indicated that physical exercise in our model could be considered a mild stressor stimulus.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.

Effects of low-dose unfractionated heparin on early brain injury after subarachnoid hemorrhage in mice

BACKGROUND

Sphingosine kinase (SphK) 1 has been reported as an important signaling node in anti-apoptotic signaling. Heparin is a pleiotropic drug that antagonizes many pathophysiological mechanisms. In this study, we evaluated if heparin prevents early brain injury (EBI) after subarachnoid hemorrhage (SAH) by anti-apoptotic mechanisms including SphK1.

METHODS

SAH was induced by endovascular perforation in mice, which were randomly assigned to sham-operated (n = 23), SAH + vehicle (n = 36), SAH + 10U heparin pretreatment (n = 13), SAH + 30U heparin pretreatment (n = 15), SAH + 10U heparin posttreatment (n = 31), and SAH + 30U heparin posttreatment (n = 23). At 24 hours post-SAH, neurological scores, brain water content and Evans blue extravasation were evaluated. Also, the expression of SphK, phosphorylated Akt, and cleaved caspase-3 was determined by Western blotting, and cell death was examined by terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling staining.

RESULTS

Low-dose heparin posttreatment improved neurobehavioral function, brain edema, blood-brain barrier disruption and cell death in the cortex, associated with an increase in SphK1 and phosphorylated Akt, and a decrease in cleaved caspase-3. High-dose heparin had a tendency for increased SAH severity, which obscured the neuroprotective effects by heparin.

CONCLUSIONS

Low-dose heparin posttreatment may decrease the development of post-SAH EBI through anti-apoptotic mechanisms including sphingosine-related pathway activation.