Role of coagulation factor Xa and protease-activated receptor 2 in human mesangial cell proliferation

The Many Faces of Protease-Activated Receptor 2 in Kidney Injury

Protease-activated receptor 2 (PAR2) is a seven-transmembrane, G-protein-coupled receptor that is activated by coagulation proteases such as factor VIIa and factor Xa and other serine proteases. It is a potential therapeutic target for kidney injury, as it enhances inflammatory and fibrotic responses via the nuclear factor-kappa B and mitogen-activated protein kinase cascades. The body of knowledge regarding the role of PAR2 in kidney disease is currently growing, and its role in various kidney disease models, such as acute kidney injury, renal fibrosis, diabetic kidney disease, aging, and thrombotic microangiopathy, has been reported. Here, we review the literature to better understand the various aspects of PAR2 in kidney disease.

Coagulation, Protease-Activated Receptors, and Diabetic Kidney Disease: Lessons from eNOS-Deficient Mice

Endothelial nitric oxide synthase (eNOS) dysfunction is known to exacerbate the progression and prognosis of diabetic kidney disease (DKD). One of the mechanisms through which this is achieved is that low eNOS levels are associated with hypercoagulability, which promotes kidney injury. In the extrinsic coagulation cascade, the tissue factor (factor III) and downstream coagulation factors, such as active factor X (FXa), exacerbate inflammation through activation of the protease-activated receptors (PARs). Recently, it has been shown that the lack of or reduced eNOS expression in diabetic mice, as a model of advanced DKD, increases renal tissue factor levels and PAR1 and 2 expression in their kidneys. Furthermore, pharmaceutical inhibition or genetic deletion of coagulation factors or PARs ameliorated inflammation in DKD in mice lacking eNOS. In this review, we summarize the relationship between eNOS, coagulation, and PARs and propose a novel therapeutic option for the management of patients with DKD.

Use of Non-vitamin K Antagonist Oral Anticoagulants for Stroke Prevention across the Stroke Spectrum: Progress and Prospects

Multiple randomized controlled trials and many real-world evidence studies have consistently shown that non-vitamin K antagonist oral anticoagulants (NOACs) are preferable to vitamin K antagonists for thromboembolic stroke prevention in the majority of patients with atrial fibrillation (AF). However, their role in the management of patients with AF and comorbidities, as well as in other patient populations with a high risk of stroke, such as patients with prior embolic stroke of undetermined source (ESUS) and those with atherosclerosis, is less clear. There is now increasing evidence suggesting that NOACs have a beneficial effect in the prevention of stroke in patients with AF and comorbidities, such as renal impairment and diabetes. In addition, while studies investigating the efficacy and safety of NOACs for the prevention of secondary stroke in patients with a history of ESUS demonstrated neutral results, subanalyses suggested potential benefits in certain subgroups of patients with ESUS. One NOAC, rivaroxaban, has also recently been found to be effective in reducing the risk of stroke in patients with chronic cardiovascular disease including coronary artery disease and peripheral artery disease, further broadening the patient groups that may benefit from NOACs. In this article, we will review recent evidence for the use of NOACs across the stroke spectrum in detail, and discuss the progress and future prospects in the different stroke areas.

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.

Shenkang Injection protects against diabetic nephropathy in streptozotocin (STZ)-induced mice through enhancement of anti-oxidant and anti-inflammatory activities

Objective

To investigate the protective effects and possible mechanisms of Shenkang Injection (SKI) on the diabetic nephropathy in streptozotocin-induced mice.

Methods

STZ with the feeding of high fat diet (HFD) was used to induce diabetic mice. The balb/c mice and diabetic mice were then randomly divided into five groups: (1) control group, (2) model group, (3) alprostadil (Alp, 1.5 μg/kg) group, (4) SKI (30 ml/kg) group, (5) Alp (1.5 μg/kg) + SKI (15 ml/kg) group. After six weeks' treatment, blood, urine and kidney tissues were collected for biochemical assay, ELISA assay, and pathological analysis.

Results

Diabetic mice exhibited evident manifestations of diabetic nephropathy (DN), as indicated by increased 24-h urine volume, urinary albumin and kidney weight index (P < 0.01), which could be attenuated by SKI treatment (P < 0.01). SKI was further found to improve abnormal morphology in glomerulus with increased glomerular volume and to decrease urinary N-acetyl-b-D-glucpsaminidase (NAG), β2-microglobulin (β2-MG), and kidney injury molecules-1 (KIM-1) levels (P < 0.05, P < 0.01). Plasma levels of anti-oxidant enzymes significantly reduced in the diabetic mice, and those decreases could be reversed by SKI and Alp treatments. Additionally, SKI obviously suppressed the diabetes-induced increases of pro-inflammatory cytokines (IL-6, IL-1β and TNF-α) (P < 0.01). Meanwhile, SKI was found to effectively attenuate the diabetes-induced coagulation dysfunction, as evidenced by lengthening prothrombin and thrombin time, and decreasing plasma levels of fibrinogen (FIB), 6-K-PGF1α and thromboxane B2 (TXB2) (P < 0.05, P < 0.01). With SKI and Alp combined treatment, the anti-oxidant activities and improvements of coagulation dysfunction were enhanced.

Conclusion

SKI possesses a remarkable property to prevent diabetic nephropathy. The improvements of kidney function and hypercoagulability by SKI were enhanced with Alp combined treatment. The molecular mechanisms underlying the protection of SKI against DN may be related to enhancing the anti-oxidant and anti-inflammatory activities, and improving the coagulation dysfunction.

Endothelium structure and function in kidney health and disease

The kidney harbours different types of endothelia, each with specific structural and functional characteristics. The glomerular endothelium, which is highly fenestrated and covered by a rich glycocalyx, participates in the sieving properties of the glomerular filtration barrier and in the maintenance of podocyte structure. The microvascular endothelium in peritubular capillaries, which is also fenestrated, transports reabsorbed components and participates in epithelial cell function. The endothelium of large and small vessels supports the renal vasculature. These renal endothelia are protected by regulators of thrombosis, inflammation and complement, but endothelial injury (for example, induced by toxins, antibodies, immune cells or inflammatory cytokines) or defects in factors that provide endothelial protection (for example, regulators of complement or angiogenesis) can lead to acute or chronic renal injury. Moreover, renal endothelial cells can transition towards a mesenchymal phenotype, favouring renal fibrosis and the development of chronic kidney disease. Thus, the renal endothelium is both a target and a driver of kidney and systemic cardiovascular complications. Emerging therapeutic strategies that target the renal endothelium may lead to improved outcomes for both rare and common renal diseases.

Biomarkers and the role of mast cells as facilitators of inflammation and fibrosis in chronic kidney disease

Chronic kidney disease (CKD) is a clinical syndrome with many adverse sequelae and is currently a major global health and economic burden. Regardless of aetiology, inflammation and fibrosis are common manifestations of CKD. Unfortunately, the underlying pathophysiological mechanisms are poorly understood, and robust prognostic and early diagnostic biomarkers of CKD are lacking. One immune cell population that has received little attention in the context of CKD is mast cells (MCs). This mini review will examine the role of MCs as facilitators of kidney inflammation and fibrosis, propose a mechanistic structure for MCs in CKD, and give consideration to biomarkers specific for MC activation that can be deployed clinically. MCs are derived from haematopoietic stem cells. They are characterised by electron-dense granules in the cytoplasm, filled with preformed mediators. MCs can synthesise a range of bio-active compounds. Activation of MCs modulates an innate immune and adaptive effector response. Increased MC counts have been observed in animal models of kidney disease and a range of kidney diseases in humans where MC presence has been linked to biomarkers of kidney function and tissue damage. To further implicate MCs in CKD, several chemokines, cytokines and proteases released by MCs have been observed in their own right in various kidney diseases and linked to progressive CKD. One compound released by MCs that is of particular interest is the MC-specific protease tryptase. This protease is capable of activating the G-protein coupled receptor (GPCR) protease activated receptor-2 (PAR-2). PAR-2 is widely expressed throughout the kidney and highly expressed in the tubular epithelial cells where its activation induces robust inflammatory and fibrotic responses. Novel prognostic and diagnostic biomarkers of CKD are needed. MC-specific proteases [tryptase, chymase and carboxypeptidase A3 (CPA3)] are easily detectable in the blood but questionably in the urine. This review aims to promote these as prognostic and diagnostic biomarkers in the context of CKD.

Protease-activated receptors (PARs): mechanisms of action and potential therapeutic modulators in PAR-driven inflammatory diseases

Inflammatory diseases have become increasingly prevalent with industrialization. To address this, numerous anti-inflammatory agents and molecular targets have been considered in clinical trials. Among molecular targets, protease-activated receptors (PARs) are abundantly recognized for their roles in the development of chronic inflammatory diseases. In particular, several inflammatory effects are directly mediated by the sensing of proteolytic activity by PARs.

PARs belong to the seven transmembrane domain G protein-coupled receptor family, but are unique in their lack of physiologically soluble ligands. In contrast with classical receptors, PARs are activated by N-terminal proteolytic cleavage. Upon removal of specific N-terminal peptides, the resulting N-termini serve as tethered activation ligands that interact with the extracellular loop 2 domain and initiate receptor signaling. In the classical pathway, activated receptors mediate signaling by recruiting G proteins. However, activation of PARs alternatively lead to the transactivation of and signaling through receptors such as co-localized PARs, ion channels, and toll-like receptors.

In this review we consider PARs and their modulators as potential therapeutic agents, and summarize the current understanding of PAR functions from clinical and in vitro studies of PAR-related inflammation.

MEK5/ERK5 signaling inhibition increases colon cancer cell sensitivity to 5-fluorouracil through a p53-dependent mechanism

The MEK5/ERK5 signaling pathway is emerging as an important contributor to colon cancer onset, progression and metastasis; however, its relevance to chemotherapy resistance remains unknown. Here, we evaluated the impact of the MEK5/ERK5 cascade in colon cancer cell sensitivity to 5-fluorouracil (5-FU). Increased ERK5 expression was correlated with poor overall survival in colon cancer patients. In colon cancer cells, 5-FU exposure impaired endogenous KRAS/MEK5/ERK5 expression and/or activation. In turn, MEK5 constitutive activation reduced 5-FU-induced cytotoxicity. Using genetic and pharmacological approaches, we showed that ERK5 inhibition increased caspase-3/7 activity and apoptosis following 5-FU exposure. Mechanistically, this was further associated with increased p53 transcriptional activation of p21 and PUMA. In addition, ERK5 inhibition increased the response of HCT116 p53^+/+ cells to 5-FU, but failed to sensitize HCT116 p53^−/− cells to the cytotoxic effects of this chemotherapeutic agent, suggesting a p53-dependent axis mediating 5-FU sensitization. Finally, ERK5 inhibition using XMD8-92 was shown to increase the antitumor effects of 5-FU in a murine subcutaneous xenograft model, enhancing apoptosis while markedly reducing tumor growth. Collectively, our results suggest that ERK5-targeted in hibition provides a promising therapeutic approach to overcome resistance to 5-FU-based chemotherapy and improve colon cancer treatment.

miR-143 or miR-145 overexpression increases cetuximab-mediated antibody-dependent cellular cytotoxicity in human colon cancer cells

miR-143 and miR-145 are downregulated in colon cancer. Here, we tested the effect of restoring these miRNAs on sensitization to cetuximab in mutant KRAS (HCT116 and SW480) and wild-type KRAS (SW48) colon cancer cells. We evaluated cetuximab-mediated antibody-dependent cellular cytotoxicity (ADCC) and the modulation of signaling pathways involved in immune effector cell-mediated elimination of cancer cells. Stable miR-143 or miR-145 overexpression increased cell sensitivity to cetuximab, resulting in a significant increase of cetuximab-mediated ADCC independently of KRAS status. Importantly, HCT116 cells overexpressing these miRNAs triggered apoptosis in result of cetuximab-mediated ADCC, effected by peripheral blood mononuclear cells (p < 0.01). This was associated with increased apoptosis and caspase-3/7 activity, and reduced Bcl-2 protein expression (p < 0.01). In addition, caspase inhibition abrogated cetuximab-mediated ADCC in HCT116 cells overexpressing either miR-143 or miR-145 (p < 0.01). Furthermore, Bcl-2 silencing led to high level of cetuximab-mediated ADCC, compared to control siRNA (p < 0.05). Importantly, granzyme B inhibition, abrogated cetuximab-mediated ADCC, reducing caspase-3/7 activity (p < 0.01). Collectively, our data suggests that re-introduction of miR-143 or miR-145 may provide a new approach for development of therapeutic strategies to re-sensitize colon cancer cells to cetuximab by stimulating cetuximab-dependent ADCC to induce cell death.

(3'R)-hydroxytabernaelegantine C: A bisindole alkaloid with potent apoptosis inducing activity in colon (HCT116, SW620) and liver (HepG2) cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Tabernaemontana elegans Stapf. (Apocynaceae) is a medicinal plant traditionally used in African countries to treat cancer.

AIMS OF THE STUDY

To discover new apoptosis inducing lead compounds from T. elegans and provide scientific validation of the ethnopharmacological use of this plant.

MATERIALS AND METHODS

Through fractionation, (3'R)-hydroxytaberanelegantine C (1), a vobasinyl-iboga bisindole alkaloid, was isolated from a cytotoxic alkaloid fraction of the methanol extract of T. elegans roots. Its structure was identified by spectroscopic methods, mainly 1D and 2D NMR experiments. Compound 1 was evaluated for its ability to induce apoptosis in HCT116 and SW620 colon and HepG2 liver carcinoma cells. The cell viability of compound 1 was evaluated by the MTS and lactate dehydrogenase (LDH) assays. Induction of apoptosis was analyzed through Guava ViaCount assay, by flow cytometry, caspase-3/7 activity assays and evaluation of nuclear morphology by Hoechst staining. To determine the molecular pathways elicited by 1 exposure, immunoblot analysis was also performed.

RESULTS

(3'R)-hydroxytaberanelegantine C (1) displayed strong apoptosis induction activity as compared to 5-fluorouracil (5-FU), the most used anticancer agent in colorectal cancer treatment. In the MTS assay, compound 1 exhibited IC₅₀ values similar or lower than 5-FU in the three cell lines tested. The IC₅₀ value of 1 was also calculated in CCD18co normal human colon fibroblasts. The lactate dehydrogenase assay showed increased LDH release by compound 1, and the Guava ViaCount assay revealed that 1 significantly increased the incidence of apoptosis to a further extent than 5-FU. Moreover, the induction of apoptosis was corroborated by evaluation of nuclear morphology by Hoechst staining and caspase-3/7 activity assays of 1 treated cells. As expected, in immunoblot analysis, compound 1 treatment led to poly(ADP-ribose) polymerase cleavage. This was accompanied by decreased anti-apoptotic proteins Bcl-2 and XIAP steady state levels in all three cancer cell lines tested.

CONCLUSIONS

Compound 1 showed remarkable induction of apoptosis in HCT116, SW620 and HepG2 cells. Together, the results suggest that compound 1 is a promising lead structure for inducing apoptosis.

Protease-activated receptor 2 exacerbates adenine-induced renal tubulointerstitial injury in mice

Hypercoagulability is associated with chronic kidney disease (CKD). Tissue factor/factor VIIa complex and factor Xa in the coagulation cascade are known to activate protease-activated receptor 2 (PAR2), and to cause inflammation and tissue injury. Although PAR2 is highly expressed in the kidney, it is unclear whether PAR2 plays a pathogenic role in CKD. To test this, we fed the mice lacking Par2 (F2rl1^-/-) and wild type (F2rl1^+/+) mice with adenine diet to induce tubulointerstitial injury, a hallmark of CKD. Adenine-treated mice showed severe renal dysfunction, tubular atrophy, and fibrosis. Fibrin deposition and the expression of tissue factor and PARs markedly increased in their kidneys. Lack of Par2 attenuated renal histological damage and reduced the expression levels of genes related to inflammation, fibrosis, and oxidative stress. Our data indicate that PAR2 is critically important in the pathogenesis of adenine-induced tubular injury. PAR2 antagonists under development could be useful to treat and prevent CKD.

Why, when and how should immunosuppressive therapy considered in patients with immunoglobulin A nephropathy?

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. Lifelong mesangial deposition of IgA1 complexes subsist inflammation and nephron loss, but the complex pathogenesis in detail remains unclear. In regard to the heterogeneous course, classical immunosuppressive and specific therapeutic regimens adapted to the loss of renal function will here be discussed in addition to the essential common renal supportive therapy. Renal supportive therapy alleviates secondary, surrogate effects or sequelae on renal function and proteinuria of high intraglomerular pressure and subsequent nephrosclerosis by inhibition of the renin angiotensin system (RAASB). In patients with physiological (ΔGFR < 1·5 ml/min/year) or mild (ΔGFR 1·5-5 ml/min/year) decrease of renal function and proteinuric forms (> 1 g/day after RAASB), corticosteroids have shown a reduction of proteinuria and might protect further loss of renal function. In patients with progressive loss of renal function (ΔGFR > 3 ml/min within 3 months) or a rapidly progressive course with or without crescents in renal biopsy, cyclophosphamide with high-dose corticosteroids as induction therapy and azathioprine maintenance has proved effective in one randomized controlled study of a homogeneous cohort in loss of renal function (ΔGFR). Mycophenolic acid provided further maintenance in non-randomized trials. Differentiated, precise, larger, randomized, placebo-controlled studies focused on the loss of renal function in the heterogeneous forms of IgAN are still lacking. Prospectively, fewer toxic agents will be necessary in the treatment of IgAN.

Vobasinyl-Iboga Alkaloids from Tabernaemontana elegans: Cell Cycle Arrest and Apoptosis-Inducing Activity in HCT116 Colon Cancer Cells

Phytochemical investigation of the roots of the African medicinal plant Tabernaemontana elegans led to the isolation of three new (1-3) and two known (4 and 5) bisindole alkaloids of the vobasinyl-iboga type. The structures of 1-3 were assigned by spectroscopic methods, mainly using 1D and 2D NMR experiments. All of the isolated compounds were evaluated for their cytotoxicity against HCT116 colon and HepG2 liver carcinoma cells by the MTS metabolism assay. Compounds 1-3 and 5 were found to be cytotoxic to HCT116 colon cancer cells, displaying IC₅₀ values in the range 8.4 to >10 μM. However, the compounds did not display significant cytotoxicity against HepG2 cancer cells. The cytotoxicity of compounds 1-3 and 5 was corroborated using a lactate dehydrogenase assay. Hoechst staining and nuclear morphology assessment and caspase-3/7 activity assays were also performed for investigating the activity of compounds 1-3 and 5 as apoptosis inducers. The induced inhibition of proliferation of HCT116 cells by compounds 1 and 2 was associated with G1 phase arrest, while compounds 3 and 5 induced G2/M cell cycle arrest. These results showed that the new vobasinyl-iboga alkaloids 1-3 and compound 5 are strong inducers of apoptosis and cell cycle arrest in HCT116 colon cancer cells.

Increased phosphatidylserine-exposing microparticles and their originating cells are associated with the coagulation process in patients with IgA nephropathy

BACKGROUND

Relatively little information is available about phosphatidylserine positive (PS(+)) microparticles (MPs) and their originating cells in IgA nephropathy (IgAN) despite well-established intraglomerular coagulation. Our objectives were to detect PS exposure on MP membranes and MP-origin cells and to evaluate its role in procoagulant activity (PCA) and fibrin formation and their association with pathological lesions in the disease.

METHODS

Patients with IgAN and healthy controls were studied. Lactadherin was used to quantify PS exposure on MPs and MP-origin cells. PCA of MPs and MP-origin cells was evaluated by clotting time and purified coagulation complex assays. Fibrin production was determined by turbidity. PS exposure, fibrin strands and FVa/Xa binding were observed on MPs/cells using confocal microscopy.

RESULTS

Using flow cytometry, we found that IgAN patients had high levels of PS(+) MPs derived from lymphocytes, monocytes, neutrophils, platelets, erythrocytes and endothelial cells (ECs). The PS exposure on MP-origin cells also increased in these patients. MPs and MP-origin cells (leukocytes, platelets and erythrocytes) isolated from IgAN patients and ECs cultured with IgAN serum had a significantly shorter median coagulation time (P < 0.001), higher median intrinsic FXa (P < 0.001) and higher thrombin (P < 0.001) generation than controls. These coagulation functional assays were associated with the glomerular lesions. The lesions were also correlated with glomerular fibrin deposition (all P < 0.05). In the presence of patient MPs or their related cells, fibrin formation peaked faster with a higher maximum turbidity when compared with healthy controls. Blocking PS with lactadherin in the IgAN group prolonged coagulation time to control levels, inhibited the PCA up to 80% and markedly reduced fibrin formation. More importantly, we observed that fibrin strands formed on MPs and ECs in the same regions that bound lactadherin, similar to the FVa/Xa costaining.

CONCLUSIONS

We find that high levels of PS(+) MPs and the MP-origin cells are associated with the coagulation process in IgAN, and this may provide a previously unrecognized contribution to intraglomerular coagulation.

The emerging role of coagulation proteases in kidney disease

A role of coagulation proteases in kidney disease beyond their function in normal haemostasis and thrombosis has long been suspected, and studies performed in the past 15 years have provided novel insights into the mechanisms involved. The expression of protease-activated receptors (PARs) in renal cells provides a molecular link between coagulation proteases and renal cell function and revitalizes research evaluating the role of haemostasis regulators in renal disease. Renal cell-specific expression and activity of coagulation proteases, their regulators and their receptors are dynamically altered during disease processes. Furthermore, renal inflammation and tissue remodelling are not only associated, but are causally linked with altered coagulation activation and protease-dependent signalling. Intriguingly, coagulation proteases signal through more than one receptor or induce formation of receptor complexes in a cell-specific manner, emphasizing context specificity. Understanding these cell-specific signalosomes and their regulation in kidney disease is crucial to unravelling the pathophysiological relevance of coagulation regulators in renal disease. In addition, the clinical availability of small molecule targeted anticoagulants as well as the development of PAR antagonists increases the need for in-depth knowledge of the mechanisms through which coagulation proteases might regulate renal physiology.

[Roles of coagulation pathway and factor Xa in chronic kidney disease (CKD)]

Considering that fibrin deposition is observed in glomerulonephritis as well as in diabetic nephropathy, we performed studies to clarify the roles of the coagulation pathway and the active type of coagulation factor X (factor Xa) in the development of chronic kidney disease (CKD) using animal models. Factor Xa activates various cell types through protease-activated receptor 2 (PAR2). Several in vitro studies have demonstrated that PAR2 can mediate factor Xa signaling, but not thrombin signaling. Coagulation processes proceed together with the extracellular matrix (ECM) accumulation through factor V expression in rat Thy-1 nephritis. DX-9065a, a factor Xa inhibitor, suppresses this type of glomerulonephritis. The factor Xa inhibitor danaparoid ameliorated proteinuria, cellular proliferation, and fibrin deposition in lipopolysaccharide (LPS)-triggered activation of High IgA (HIGA) strain of ddY mice. Another factor Xa inhibitor, fondaparinux, suppressed urinary protein, glomerular hypertrophy, and connective tissue growth factor (CTGF), and ECM protein deposition together with angiogenesis in diabetic db/db mice. Finally, in the model of peritoneal fibrosis, fondaparinux treatment decreased the thickness of submesothelial fibrotic tissue and angiogenesis. In consideration of the results to potential human therapy, factor Xa regulation may be promising for the treatment of the aggravation in glomerulonephritis and of the early phase of diabetic nephropathy. In the near future, novel factor Xa inhibitors with the characteristics of oral administration and biliary elimination may appear in the clinical use for treatment of cardiovascular diseases.

Coagulation and coagulation signalling in fibrosis

Following tissue injury, a complex and coordinated wound healing response comprising coagulation, inflammation, fibroproliferation and tissue remodelling has evolved to nullify the impact of the original insult and reinstate the normal physiological function of the affected organ. Tissue fibrosis is thought to result from a dysregulated wound healing response as a result of continual local injury or impaired control mechanisms. Although the initial insult is highly variable for different organs, in most cases, uncontrolled or sustained activation of mesenchymal cells into highly synthetic myofibroblasts leads to the excessive deposition of extracellular matrix proteins and eventually loss of tissue function. Coagulation was originally thought to be an acute and transient response to tissue injury, responsible primarily for promoting haemostasis by initiating the formation of fibrin plugs to enmesh activated platelets within the walls of damaged blood vessels. However, the last 20years has seen a major re-evaluation of the role of the coagulation cascade following tissue injury and there is now mounting evidence that coagulation plays a critical role in orchestrating subsequent inflammatory and fibroproliferative responses during normal wound healing, as well as in a range of pathological contexts across all major organ systems. This review summarises our current understanding of the role of coagulation and coagulation initiated signalling in the response to tissue injury, as well as the contribution of uncontrolled coagulation to fibrosis of the lung, liver, kidney and heart. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

PR3 and elastase alter PAR1 signaling and trigger vWF release via a calcium-independent mechanism from glomerular endothelial cells

Neutrophil proteases, proteinase-3 (PR3) and elastase play key roles in glomerular endothelial cell (GEC) injury during glomerulonephritis. Endothelial protease-activated receptors (PARs) are potential serine protease targets in glomerulonephritis. We investigated whether PAR1/2 are required for alterations in GEC phenotype that are mediated by PR3 or elastase during active glomerulonephritis. Endothelial PARs were assessed by flow cytometry. Thrombin, trypsin and agonist peptides for PAR1 and PAR2, TFLLR-NH(2) and SLIGKV-NH(2,) respectively, were used to assess alterations in PAR activation induced by PR3 or elastase. Endothelial von Willebrand Factor (vWF)release and calcium signaling were used as PAR activation markers. Both PR3 and elastase induced endothelial vWF release, with elastase inducing the highest response. PAR1 peptide induced GEC vWF release to the same extent as PR3. However, knockdown of PARs by small interfering RNA showed that neither PAR1 nor PAR2 activation caused PR3 or elastase-mediated vWF release. Both proteases interacted with and disarmed surface GEC PAR1, but there was no detectable interaction with cellular PAR2. Neither protease induced a calcium response in GEC. Therefore, PAR signaling and serine protease-induced alterations in endothelial function modulate glomerular inflammation via parallel but independent pathways.

Roles of coagulation pathway and factor Xa in the progression of diabetic nephropathy in db/db mice

The active type of coagulation factor X (factor Xa) activates various cell-types through protease-activated receptor 2 (PAR2). We previously reported that a factor Xa inhibitor could suppress Thy-1 nephritis. Considering that fibrin deposition is observed in diabetic nephropathy as well as in glomerulonephritis, this study examined the roles of the coagulation pathway and factor Xa in the development of diabetic nephropathy using type 2 diabetic model mice. Diabetic (db/db) and normoglycemic (m+/m+) mice were immunohistochemically evaluated for their expression/deposition of PAR2, transforming growth factor (TGF)-β, fibrin, extracellular matrix (ECM) proteins, and CD31 at week 20. Significantly greater numbers of PAR2-positive cells and larger amounts of fibronectin, and collagen IV depositions were observed in the glomeruli of db/db mice than those in m+/m+ mice. Next, expression of PAR2 versus deposition of collagen IV and fibronectin was compared between week 20 and week 30, and the number of PAR2-positive cells in the glomeruli decreased in contrast with the increased accumulation of ECM proteins. In an intervention study, fondaparinux, a factor Xa inhibitor, was subcutaneously administered for ten weeks from week 10 to 20. Fondaparinux treatment significantly suppressed urinary protein, glomerular hypertrophy, fibrin deposition, expression of connective tissue growth factor, and ECM proteins deposition together with CD31-positive capillaries. These results suggest that coagulation pathway and glomerular PAR2 expression are upregulated in the early phase of diabetes, together with the increase of profibrotic cytokines expression, ECM proteins deposition and CD-31-positive vessels. Factor Xa inhibition may ameliorate glomerular neoangiogenesis and ECM accumulation in diabetic nephropathy.

Profiling gene expression induced by protease-activated receptor 2 (PAR2) activation in human kidney cells

Protease-Activated Receptor-2 (PAR2) has been implicated through genetic knockout mice with cytokine regulation and arthritis development. Many studies have associated PAR2 with inflammatory conditions (arthritis, airways inflammation, IBD) and key events in tumor progression (angiogenesis, metastasis), but they have relied heavily on the use of single agonists to identify physiological roles for PAR2. However such probes are now known not to be highly selective for PAR2, and thus precisely what PAR2 does and what mechanisms of downstream regulation are truly affected remain obscure. Effects of PAR2 activation on gene expression in Human Embryonic Kidney cells (HEK293), a commonly studied cell line in PAR2 research, were investigated here by comparing 19,000 human genes for intersecting up- or down-regulation by both trypsin (an endogenous protease that activates PAR2) and a PAR2 activating hexapeptide (2f-LIGRLO-NH(2)). Among 2,500 human genes regulated similarly by both agonists, there were clear associations between PAR2 activation and cellular metabolism (1,000 genes), the cell cycle, the MAPK pathway, HDAC and sirtuin enzymes, inflammatory cytokines, and anti-complement function. PAR-2 activation up-regulated four genes more than 5 fold (DUSP6, WWOX, AREG, SERPINB2) and down-regulated another six genes more than 3 fold (TXNIP, RARG, ITGB4, CTSD, MSC and TM4SF15). Both PAR2 and PAR1 activation resulted in up-regulated expression of several genes (CD44, FOSL1, TNFRSF12A, RAB3A, COPEB, CORO1C, THBS1, SDC4) known to be important in cancer. This is the first widespread profiling of specific activation of PAR2 and provides a valuable platform for better understanding key mechanistic roles of PAR2 in human physiology. Results clearly support the development of both antagonists and agonists of human PAR2 as potential disease modifying therapeutic agents.

Membranoproliferative glomerulonephritis and a rare bleeding disorder: Factor X deficiency

Factor X (FX) deficiency is a rare hereditary coagulation disorder. This is the first case report on the association of FX deficiency and membranoproliferative glomerulonephritis (MPGN) type I. The patient, a 17-year-old male, presented with edema, hypertension, and microscopic hematuria, followed by a mild upper respiratory tract infection. Laboratory tests revealed: serum creatinine 1.6 mg/dl, serum albumin 2.80 g/dl, C3 16 mg/dl and proteinuria (1,800 mg/day). The renal biopsy showed MPGN type I. The coagulation profile prior to percutaneous renal biopsy revealed prolonged prothrombin time and activated partial thromboplastin time values. The patient was given fresh frozen plasma and vitamin K before the biopsy. Further evaluation showed the functional activity of FX was 7% of the norm. This case emphasizes the need for routine coagulation screening before percutaneous renal biopsy.

Protease-activated receptor 2 blocking peptide counteracts endotoxin-induced inflammation and coagulation and ameliorates renal fibrin deposition in a rat model of acute renal failure

Glomerular and microvascular thrombosis due to the activation of inflammation and coagulation pathway contribute to the occurrence of acute renal failure in sepsis. The protease-activated receptors (PARs) have been shown to play an important role in the interplay between inflammation and coagulation. We hypothesized that PAR-2 blocking would improve glomerular and vascular thrombosis by attenuating inflammation and coagulation, leading to the prevention of acute renal failure, and assessed the effects of the PAR-2 blocking peptide (PAR-2 BP) in a rat model of LPS-induced acute renal failure. Levels of TNF-alpha were significantly expressed 1 h after LPS administration, followed by 1) an increase in levels of tissue factor, factor VIIa, factor Xa, thrombin and plasminogen activator inhibitor 1; 2) unchanged levels of tissue factor pathway inhibitor; and 3) subsequent deposition of fibrin in kidney tissues, which led to the elevation of creatinine and blood urea nitrogen. Time-dependent PAR-2 expression was observed at both the gene and protein levels. Immunoreactivities of PAR-2 and fibrin were observed in the glomerulus and small arteries. Protease-activated receptor blocking peptide suppressed TNF-alpha elevation and attenuated activation of the coagulation, thus leading to a decrease in fibrin formation and its deposition in the glomerulus. However, the levels of creatinine and blood urea nitrogen remained unchanged. These results show that PAR-2 plays a key role in the inflammatory and coagulation process of LPS-induced renal failure; however, PAR-2 inhibition alone does not affect improvement in the renal function.

The coagulation factor Xa/protease activated receptor-2 axis in the progression of liver fibrosis: a multifaceted paradigm

Hepatic fibrosis is a common response to virtually all forms of chronic liver injury independent of the etiologic agent. Despite the relatively large population of patients suffering from hepatic fibrosis and cirrhosis, no efficient and well-tolerated drugs are available for the treatment of this disorder. The lack of efficient treatment options is at least partly because the underlying cellular mechanisms leading to hepatic fibrosis are only partly understood. It is thus of pivotal importance to better understand the cellular processes contributing to the progression of hepatic fibrosis. Interestingly in this perspective, a common feature of fibrotic disease of various organs is the activation of the coagulation cascade and hepatic fibrosis is also accompanied by a local hypercoagulable state. Activated blood coagulation factors directly target liver cells by activating protease-activated receptors (PAR) thereby inducing a plethora of cellular responses like (among others) proliferation, migration and extracellular matrix production. Coagulation factor driven PAR activation thus establishes a potential link between activation of the coagulation cascade and the progression of fibrosis. The current review focuses on blood coagulation factor Xa and summarizes the variety of cellular functions induced by factor Xa-driven PAR-2 activation and the subsequent consequences for tissue repair and hepatic fibrosis.

Factor Xa stimulates proinflammatory and profibrotic responses in fibroblasts via protease-activated receptor-2 activation

Coagulation proteases have been suggested to play a role in the pathogenesis of tissue remodeling and fibrosis. We therefore assessed the proinflammatory and fibroproliferative effects of coagulation protease factor (F)Xa. We show that FXa elicits a signaling response in C2C12 and NIH3T3 fibroblasts. FXa-induced ERK1/2 phosphorylation was dependent on protease-activated receptor (PAR)-2 cleavage because desensitization with a PAR-2 agonist (trypsin) but not a PAR-1 agonist (thrombin) abolished FXa-induced signal transduction and PAR-2 siRNA abolished FXa-induced ERK1/2 phosphorylation. The PAR-2-dependent cellular effects of FXa led to fibroblast proliferation, migration, and differentiation into myofibroblasts, as demonstrated by the expression of alpha-smooth muscle actin and desmin, followed by the secretion of the cytokines monocyte chemotactic protein-1 and interleukin-6 as well as the expression of the fibrogenic proteins transforming growth factor-beta and fibronectin. To assess the relevance of FXa-induced proliferation and cell migration, we examined the effect of FXa in a wound scratch assay. Indeed, FXa facilitated wound healing in a PAR-2- and ERK1/2-dependent manner. Taken together, these results support the notion that, beyond its role in coagulation, FXa-dependent PAR-2 cleavage might play a role in the progression of tissue fibrosis and remodeling.

Proteinases and signalling: pathophysiological and therapeutic implications via PARs and more

Proteinases like thrombin, trypsin and tissue kallikreins are now known to regulate cell signaling by cleaving and activating a novel family of G-protein-coupled proteinase-activated receptors (PARs 1-4) via exposure of a tethered receptor-triggering ligand. On their own, short synthetic PAR-selective PAR-activating peptides (PAR-APs) mimicking the tethered ligand sequences can activate PARs 1, 2 and 4 and cause physiological responses both in vitro and in vivo. Using the PAR-APs as sentinel probes in vivo, it has been found that PAR activation can affect the vascular, renal, respiratory, gastrointestinal, musculoskeletal and nervous systems (both central and peripheral nervous system) and can promote cancer metastasis and invasion. In general, responses triggered by PARs 1, 2 and 4 are in keeping with an innate immune inflammatory response, ranging from vasodilatation to intestinal inflammation, increased cytokine production and increased or decreased nociception. Further, PARs have been implicated in a number of disease states, including cancer and inflammation of the cardiovascular, respiratory, musculoskeletal, gastrointestinal and nervous systems. In addition to activating PARs, proteinases can cause hormone-like effects by other signalling mechanisms, like growth factor receptor activation, that may be as important as the activation of PARs. We, therefore, propose that the PARs themselves, their activating serine proteinases and their associated signalling pathways can be considered as attractive targets for therapeutic drug development. Thus, proteinases in general must now be considered as 'hormone-like' messengers that can signal either via PARs or other mechanisms.

Proinflammatory and proliferative responses of human proximal tubule cells to PAR-2 activation

Despite the abundant expression of protease-activated receptor (PAR)-2 in the kidney, its relevance to renal physiology is not well understood. A role for this receptor in inflammation and cell proliferation has recently been suggested in nonrenal tissues. The aims of this study were to demonstrate that human proximal tubule cells (PTC) express functional PAR-2 and to investigate whether its activation can mediate proinflammatory and proliferative responses in these cells. Primary human PTC were cultured under serum-free conditions with or without the PAR-2-activating peptide SLIGKV-NH2 (up to 800 microM), a control peptide, VKGILS-NH2 (200 microM), or trypsin (0.01-100 nM). PAR-2 expression (RT-PCR), intracellular Ca2+ mobilization (fura-2 fluorimetry), DNA synthesis (thymidine incorporation), fibronectin production (ELISA, Western blotting), and monocyte chemotactic protein (MCP)-1 secretion (ELISA) were measured. Trypsinogen expression in kidney and PTC cultures was determined by immunohistochemistry and Western blotting. In the kidney PTC were the predominant cell type expressing PAR-2. SLIGKV-NH2, but not VKGILS-NH2, stimulated a rapid concentration-dependent mobilization of intracellular Ca2+ and ERK1/2 phosphorylation and, by 24 h, increases in DNA synthesis, fibronectin secretion, and MCP-1 secretion. These delayed responses appeared to be independent of ERK1/2. Trypsin produced similar rapid but not delayed responses. Trypsinogen was weakly expressed by PTC in the kidney and in culture. In summary, PTC are the main site of PAR-2 expression in the human kidney. In PTC cultures SLIGKV-NH2 initiates proinflammatory and proliferative responses. Trypsinogen expressed within the kidney has the potential to contribute to PAR-2 activation in certain circumstances.

Protease-activated receptor-2 augments experimental crescentic glomerulonephritis

Protease-activated receptor-2 (PAR-2) is a cellular receptor expressed prominently on epithelial, mesangial, and endothelial cells in the kidney and on macrophages. PAR-2 is activated by serine proteases such as trypsin, tryptase, and coagulation factors VIIa and Xa. It induces pleiotropic effects including vasodilatation, increasing plasminogen activator inhibitor (PAI-1) expression, mesangial cell proliferation, and cytokine production by macrophages. The role of PAR-2 in renal inflammation was studied in antiglomerular basement membrane antibody-induced crescentic glomerulonephritis (CGN) using PAR-2-deficient (PAR-2(-/-)) mice and wild-type littermate controls. PAR-2(-/-) mice had reduced crescent formation, proteinuria, and serum creatinine compared with wild-type mice 21 days after initiation of CGN. Glomerular accumulation of CD4(+) T cells and macrophages and the number of proliferating cells in glomeruli were similar in both groups. Glomerular fibrin deposition was significantly reduced in PAR-2(-/-) mice, and this was associated with reduced renal plasminogen activator inhibitor expression and increased renal matrix-metalloprotinase-9 activity. These results demonstrate a proinflammatory role for PAR-2 in CGN that is independent of effects on glomerular leukocyte recruitment and mesangial cell proliferation. PAR-2-mediated augmentation of renal plasminogen activator inhibitor expression and inhibition of matrix-metalloprotinase-9 activity may contribute to increased glomerular fibrin accumulation and glomerular injury in CGN.

Coagulation factor Xa drives tumor cells into apoptosis through BH3-only protein Bim up-regulation

Coagulation Factor (F)Xa is a serine protease that plays a crucial role during blood coagulation by converting prothrombin into active thrombin. Recently, however, it emerged that besides this role in coagulation, FXa induces intracellular signaling leading to different cellular effects. Here, we show that coagulation factor (F)Xa drives tumor cells of epithelial origin, but not endothelial cells or monocytes, into apoptosis, whereas it even enhances fibroblast survival. FXa signals through the protease activated receptor (PAR)-1 to activate extracellular-signal regulated kinase (ERK) 1/2 and p38. This activation is associated with phosphorylation of the transcription factor CREB, and in tumor cells with up-regulation of the BH3-only pro-apoptotic protein Bim, leading to caspase-3 cleavage, the main hallmark of apoptosis. Transfection of tumor cells with dominant negative forms of CREB or siRNA for either PAR-1, Bim, ERK1 and/or p38 inhibited the pro-apoptotic effect of FXa. In fibroblasts, FXa-induced PAR-1 activation leads to down-regulation of Bim and pre-treatment with PAR-1 or Bim siRNA abolishes proliferation. We thus provide evidence that beyond its role in blood coagulation, FXa plays a key role in cellular processes in which Bim is the central player in determining cell survival.

Soluble fibrin formation in the mesangial area of IgA nephropathy

BACKGROUND

Fibrin monomer and its derivatives in blood are found in an early stage of thrombosis. When they are produced in blood, they form complexes with fibrinogen, and they exist as soluble complexes named soluble fibrin (SF). As final insoluble products, cross-linked fibrin (XFb) is often observed in mesangial areas in active types of human glomerulonephritis. To clarify the mechanisms of mesangial SF production and its relationship to XFb deposition in IgA nephropathy (IgAN), an immunohistochemical study was conducted.

METHODS

Nineteen patients with IgAN were studied. XFb was detected in renal biopsy specimens using anti-d-dimer antibody combined with plasmin exposure. SF was detected with a monoclonal antibody (IF-43), and factor V was detected with a specific rabbit antibody. The relationships of SF staining to the disease activity index, XFb deposition, and factor V staining was evaluated.

RESULTS

XFb, factor V, and SF were observed in the mesangium in 14, 11, and 8, respectively, of a total of 19 specimens. SF had frequent staining in the proliferating areas, showing a significant relationship to XFb or factor V (P < 0.05). Furthermore, XFb, factor V, and SF depositions were markedly correlated with disease activity (P < 0.001 in each case).

CONCLUSIONS

These findings suggest that SF is formed in the mesangial area in active IgA nephropathy accompanied by mesangial proliferation, in particular, in its early stage.

Potential physiological and pathophysiological roles for protease-activated receptor-2 in the kidney (Review Article)

The protease-activated receptor-2 (PAR-2), the second of four members of a unique subfamily of G-protein coupled receptors, is abundantly expressed in the kidney. In a similar manner to other PAR cleavage of its extracellular N-terminus exposes a tethered ligand, SLIGKV in humans, which acts as an intramolecular ligand to activate itself. In the kidney, PAR-2 expression has been variably reported in collecting duct cells, mesangial cells, interstitial fibroblasts, vascular endothelial cells, vascular smooth muscle cells and proximal tubular cells. Despite this renal expression data, the function of PAR-2 in the kidney remains unknown. More than 15 different mammalian serine proteases have been shown to activate PAR-2 in an in vitro setting, but it is still unclear which of these are physiologically relevant activators of PAR-2 in specific tissues. Their identification could provide novel therapeutic targets. PAR-2 activates a number of down-stream signalling molecules that include protein kinase C, extracellular signal regulated kinase and nuclear factor kappa-B. Proteases that can activate PAR-2 are generated and released from cells during injury, inflammation and malignancy and can thus signal to cells under these conditions. Potential physiological and pathophysiological roles for PAR-2 in the kidney include the regulation of inflammation, blood flow, and ion transport and tissue protection, repair and fibrosis. In this review the potential roles of PAR-2 in the kidney are highlighted and discussed.

Roles of coagulation pathway and factor Xa in rat mesangioproliferative glomerulonephritis

Tissue factor initiates the extrinsic coagulation pathway by activating coagulation factor X to factor Xa, and factor V is a cofactor for the prothrombin activation by factor Xa. As factor Xa is known to promote the proliferation of mesangial cells in culture, the roles of the coagulation pathway and factor Xa were studied in an animal model of mesangioproliferative glomerulonephritis (MsPGN). MsPGN was induced in Wistar rats by an intravenous injection of anti-Thy 1.1 monoclonal antibody, OX-7. To clarify the role of factor Xa in MsPGN, a specific factor Xa inhibitor, DX-9065a, was injected intravenously at 2.5 or 10 mg/kg at the same time as OX-7, and kidney involvement was assessed by immunohistological analyses. We also examined p44/42 mitogen-activated protein (MAP) kinase activation. Time-course study revealed that expressions of tissue factor, factor V, and protease-activated receptor 2 (PAR2) were peaked on day 3, followed by factor X accumulation and mesangial proliferation. DX-9065a treatment significantly ameliorated proteinuria in a dose-dependent manner on day 8. Histological analyses showed a significant reduction in the size of glomeruli, the total number of glomerular cells, and crescent formation by DX-9065a treatment. Macrophage infiltration, which was rapidly observed on day 1 in disease control rats was not inhibited on days 1-3 by DX-9065a treatment, however it was suppressed on days 5-8. The deposition of fibrin, the number of PCNA-positive cells, and phosphorylation of p44/42 MAP kinase were markedly increased in the disease control group, whereas they were significantly reduced in the treatment group. Tissue factor and factor V induction may accelerate MsPGN through the activation and accumulation of factor X via proinflammatory and procoagulant mechanisms, and the inhibition of factor Xa would be a promising method to regulate the disease process.

Angiotensin II receptor blockade ameliorates mesangioproliferative glomerulonephritis in rats through suppression of CTGF and PAI-1, independently of the coagulation system

BACKGROUND

Previously we observed that the coagulation system promotes matrix protein accumulation through transforming growth factor (TGF)-beta and connective tissue growth factor (CTGF) expression in rat mesangioproliferative glomerulonephritis (MsPGN). Angiotensin II receptor blockers (ARBs) are known to suppress matrix accumulation in experimental MsPGN. In the present study, we investigated whether ARB suppresses MsPGN through inhibition of these profibrotic cytokines, and in relation to coagulation and fibrinolytic systems.

METHODS

MsPGN was induced in Wistar rats by intravenous injection of anti-Thy-1.1 monoclonal antibody, OX-7. As an ARB, olmesartan was orally administered in rat feed from the day of OX-7 injection (day 0) to day 8, when rats were sacrificed and kidney specimens were collected. The degrees of cellular proliferation, matrix production, coagulation factors, and inhibitory factor of fibrinolysis were evaluated.

RESULTS

Although blood pressure did not change in the normal, disease control, or treatment groups, the amount of urinary protein was significantly decreased in the ARB-treated groups, compared with the disease control group (p < 0.05). alpha-Smooth muscle actin expression was suppressed significantly in the treatment groups (p < 0.001). Blue-staining areas of trichrome, the number of proliferating cell nuclear antigen (PCNA)- or ED-1-positive cells, fibronectin and plasminogen activator inhibitor type 1 in glomeruli significantly decreased in the treatment groups (p < 0.05, respectively); however, fibrin-related antigen and factor V depositions were not suppressed in the treatment groups.

CONCLUSIONS

These results suggest that the ARB drug would ameliorate MsPGN in vivo, at least partly through CTGF and plasminogen activator inhibitor type 1 suppression, and independently of the local coagulation system in glomeruli.