Thrombin down-regulates the TGF-beta-mediated synthesis of collagen and fibronectin by human proximal tubule epithelial cells through the EPCR-dependent activation of PAR-1

Interaction of estradiol and renin-angiotensin system with microRNAs-21 and -29 in renal fibrosis: focus on TGF-β/smad signaling pathway

Kidney fibrosis is one of the complications of chronic kidney disease (CKD (and contributes to end-stage renal disease which requires dialysis and kidney transplantation. Several signaling pathways such as renin-angiotensin system (RAS), microRNAs (miRNAs) and transforming growth factor-β1 (TGF-β1)/Smad have a prominent role in pathophysiology and progression of renal fibrosis. Activation of classical RAS, the elevation of angiotensin II (Ang II) production and overexpression of AT1R, develop renal fibrosis via TGF-β/Smad pathway. While the non-classical RAS arm, Ang 1-7/AT2R, MasR reveals an anti-fibrotic effect via antagonizing Ang II. This review focused on studies illustrating the interaction of RAS with sexual female hormone estradiol and miRNAs in the progression of renal fibrosis with more emphasis on the TGF-β signaling pathway. MiRNAs, especially miRNA-21 and miRNA-29 showed regulatory effects in renal fibrosis. Also, 17β-estradiol (E2) is a renoprotective hormone that improved renal fibrosis. Beneficial effects of ACE inhibitors and ARBs are reported in the prevention of renal fibrosis in patients. Future studies are also merited to delineate the new therapy strategies such as miRNAs targeting, combination therapy of E2 or HRT, ACEis, and ARBs with miRNAs mimics and antagomirs in CKD to provide a new therapeutic approach for kidney patients.

Protease-Activated Receptor 1-Mediated Damage of Podocytes in Diabetic Nephropathy

There is clinical evidence that increased urinary serine proteases are associated with the disease severity in the setting of diabetic nephropathy (DN). Elevation of serine proteases may mediate [Ca2+]i dynamics in podocytes through the protease-activated receptors (PARs) pathway, including associated activation of nonspecific cation channels. Cultured human podocytes and freshly isolated glomeruli were used for fluorescence and immunohistochemistry stainings, calcium imaging, Western blot analysis, scanning ion conductance microscopy, and patch clamp analysis. Goto-Kakizaki, Wistar, type 2 DN (T2DN), and a novel PAR1 knockout on T2DN rat background rats were used to test the importance of PAR1-mediated signaling in DN settings. We found that PAR1 activation increases [Ca2+]i via TRPC6 channels. Both human cultured podocytes exposed to high glucose and podocytes from freshly isolated glomeruli of T2DN rats had increased PAR1-mediated [Ca2+]i compared with controls. Imaging experiments revealed that PAR1 activation plays a role in podocyte morphological changes. T2DN rats exhibited a significantly higher response to thrombin and urokinase. Moreover, the plasma concentration of thrombin in T2DN rats was significantly elevated compared with Wistar rats. T2DNPar1-/- rats were embryonically lethal. T2DNPar1+/- rats had a significant decrease in glomerular damage associated with DN lesions. Overall, these data provide evidence that, during the development of DN, elevated levels of serine proteases promote an excessive [Ca2+]i influx in podocytes through PAR1-TRPC6 signaling, ultimately leading to podocyte apoptosis, the development of albuminuria, and glomeruli damage.

ARTICLE HIGHLIGHTS

Increased urinary serine proteases are associated with diabetic nephropathy. During the development of diabetic nephropathy in type 2 diabetes, the elevation of serine proteases could overstimulate protease-activated receptor 1 (PAR1). PAR1 signaling is involved in the development of DN via TRPC6-mediated intracellular calcium signaling. This study provides fundamental knowledge that can be used to develop efficient therapeutic approaches targeting serine proteases or corresponding PAR pathways to prevent or slow the progression of diabetes-associated kidney diseases.

Early growth response factor 1 upregulates pro-fibrotic genes through activation of TGF-β1/Smad pathway via transcriptional regulation of PAR1 in high-glucose treated HK-2 cells

Tubulointerstitial fibrosis (TIF) makes a key role in diabetic kidney disease (DKD). In this study, we revealed that the expressions of Egr1 and protease-activated receptor 1 (PAR1) were increased in renal tissues of DKD rats. In vitro experiments demonstrated that both Egr1 overexpression and high glucose (HG) condition could promote the expressions of PAR1, fibronectin (FN) and collagen I (COL I). Furthermore, HG stimulation enhanced the binding capacity of Egr1 to PAR1 promoter. Both HG condition and Egr1 upregulation could increase, and thrombin inhibitor did not affect activity of TGF-β1/Smad pathway via PAR1. Collectively, Egr1 is involved in TIF of DKD partly through activating TGF-β1/Smad pathway via transcriptional regulation of PAR1 in HG treated HK-2 cells.

A phenotype driven integrative framework uncovers molecular mechanisms of a rare hereditary thrombophilia

Antithrombin resistance is a rare subtype of hereditary thrombophilia caused by prothrombin gene variants, leading to thrombotic disorders. Recently, the Prothrombin Belgrade variant has been reported as a specific variant that leads to antithrombin resistance in two Serbian families with thrombosis. However, due to clinical data scarcity and the inapplicability of traditional genome-wide association studies (GWAS), a broader perspective on molecular and phenotypic mechanisms associated with the Prothrombin Belgrade variant is yet to be uncovered. Here, we propose an integrative framework to address the lack of genomic samples and support the genomic signal from the full genome sequences of five heterozygous subjects by integrating it with subjects' phenotypes and the genes' molecular interactions. Our goal is to identify candidate thrombophilia-related genes for which our subjects possess germline variants by focusing on the resulting gene clusters of our integrative framework. We applied a Non-negative Matrix Tri-Factorization-based method to simultaneously integrate different data sources, taking into account the observed phenotypes. In other words, our data-integration framework reveals gene clusters involved with this rare disease by fusing different datasets. Our results are in concordance with the current literature about antithrombin resistance. We also found candidate disease-related genes that need to be further investigated. CD320, RTEL1, UCP2, APOA5 and PROZ participate in healthy-specific or disease-specific subnetworks involving thrombophilia-annotated genes and are related to general thrombophilia mechanisms according to the literature. Moreover, the ADRA2A and TBXA2R subnetworks analysis suggested that their variants may have a protective effect due to their connection with decreased platelet activation. The results show that our method can give insights into antithrombin resistance even if a small amount of genetic data is available. Our framework is also customizable, meaning that it applies to any other rare disease.

Emergent White Matter Degeneration in the rTg-DI Rat Model of Cerebral Amyloid Angiopathy Exhibits Unique Proteomic Changes

Cerebral amyloid angiopathy (CAA), characterized by cerebral vascular amyloid accumulation, neuroinflammation, microbleeds, and white matter (WM) degeneration, is a common comorbidity in Alzheimer disease and a prominent contributor to vascular cognitive impairment and dementia. WM loss was recently reported in the corpus callosum (CC) in the rTg-DI rat model of CAA. The current study shows that the CC exhibits a much lower CAA burden compared with the adjacent cortex. Sequential Window Acquisition of All Theoretical Mass Spectra tandem mass spectrometry was used to show specific proteomic changes in the CC with emerging WM loss and compare them with the proteome of adjacent cortical tissue in rTg-DI rats. In the CC, annexin A3, heat shock protein β1, and cystatin C were elevated at 4 months (M) before WM loss and at 12M with evident WM loss. Although annexin A3 and cystatin C were also enhanced in the cortex at 12M, annexin A5 and the leukodystrophy-associated astrocyte proteins megalencephalic leukoencephalopathy with subcortical cysts 1 and GlialCAM were distinctly elevated in the CC. Pathway analysis indicated neurodegeneration of axons, reflected by reduced expression of myelin and neurofilament proteins, was common to the CC and cortex; activation of Tgf-β1 and F2/thrombin was restricted to the CC. This study provides new insights into the proteomic changes that accompany WM loss in the CC of rTg-DI rats.

Hirudin, a thrombin inhibitor, attenuates TGF-β-induced fibrosis in renal proximal tubular epithelial cells by inhibition of protease-activated receptor 1 expression via S1P/S1PR2/S1PR3 signaling

Renal interstitial fibrosis (RIF) is the final common outcome of numerous chronic kidney diseases, contributing to end-stage renal disease. Hirudin, a thrombin inhibitor, has attracted increased attention as a potential treatment approach for renal fibrosis. The present study aimed to investigate the molecular mechanism underlying the effect of hirudin on fibrosis in renal proximal tubular epithelial cells. An in vivo mouse RIF model established using unilateral ureteral obstruction (UUO) and an in vitro of RIF using the renal tubular epithelial cell line HK-2 treated with TGF-β were used. Expressions of sphingosine-1-phosphate (S1P) receptors (S1PR)1-4 and protease-activated receptor 1 (PAR1) were measured by reverse transcription-quantitative PCR and western blotting in mice with UUO and TGF-β induced HK-2 cells. Western blotting was used to detect the expression of N-cadherin, Slug, E-cadherin, Collagen IV, fibronectin, MMP9 and monocyte chemoattractant protein-1. Immunofluorescence staining was conducted to measure α-SMA level expression. The results demonstrated that the expression levels of S1PR1, S1PR2, S1PR3, S1PR4 and PAR1 were upregulated in both TGF-β-induced HK-2 cells and renal tissues from mice with unilateral ureteral ligation. Notably, hirudin inhibited TGF-β-induced PAR1, S1PR2 and S1PR3 upregulation in both HK-2 cells and renal tissues. Additionally, the inhibition of S1PR2 and S1PR3 resulted in PAR1 downregulation. Furthermore, treatment with S1P and PAR1 agonists abolished the effect of hirudin on the expression of EMT, fibrosis-related proteins and monocyte chemoattractant protein 1. In conclusion, hirudin attenuated TGF-β-induced fibrosis in proximal renal tubular epithelial HK-2 cells by inhibiting PAR1 expression via the S1P/S1PR2/S1PR3 signaling pathway. Therefore, hirudin may be considered as a promising therapeutic agent for RIF.

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.

Comparative transcriptomic profiling of myxomatous mitral valve disease in the cavalier King Charles spaniel

BACKGROUND

Almost all elderly dogs develop myxomatous mitral valve disease by the end of their life, but the cavalier King Charles spaniel (CKCS) has a heightened susceptibility, frequently resulting in death at a young age and suggesting that there is a genetic component to the condition in this breed. Transcriptional profiling can reveal the impact of genetic variation through differences in gene expression levels. The aim of this study was to determine whether expression patterns were different in mitral valves showing myxomatous degeneration from CKCS dogs compared to valves from non-CKCS dogs.

RESULTS

Gene expression patterns in three groups of canine valves resulted in distinct separation of normal valves, diseased valves from CKCS and diseased valves from other breeds; the latter were more similar to the normal valves than were the valves from CKCS. Gene expression patterns in diseased valves from CKCS dogs were quite different from those in the valves from other dogs, both affected and normal. Patterns in all diseased valves (from CKCS and other breeds) were also somewhat different from normal non-diseased samples. Analysis of differentially expressed genes showed enrichment in GO terms relating to cardiac development and function and to calcium signalling canonical pathway in the genes down-regulated in the diseased valves from CKCS, compared to normal valves and to diseased valves from other breeds. F2 (prothrombin) (CKCS diseased valves compared to normal) and MEF2C pathway activation (CKCS diseased valves compared to non-CKCS diseased valves) had the strongest association with the gene changes. A large number of genes that were differentially expressed in the CKCS diseased valves compared with normal valves and diseased valves from other breeds were associated with cardiomyocytes including CASQ2, TNNI3 and RYR2.

CONCLUSION

Transcriptomic profiling identified gene expression changes in CKCS diseased valves that were not present in age and disease severity-matched non-CKCS valves. These genes are associated with cardiomyocytes, coagulation and extra-cellular matrix remodelling. Identification of genes that vary in the CKCS will allow exploration of genetic variation to understand the aetiology of the disease in this breed, and ultimately development of breeding strategies to eliminate this disease from the breed.

Formin mDia1 contributes to migration and epithelial-mesenchymal transition of tubular epithelial cells exposed to TGF-β1

Renal tubular epithelial cells may undergo epithelial-mesenchymal transition (EMT) in response to stimuli, such as transforming growth factor (TGF)-β1, leading to myofibroblast activation and renal fibrosis. The formin mDia1 is required for nucleation and polymerization of actin and the microtubule cytoskeleton. The present study sought to explore the role of mDia1 in EMT of tubular epithelial cells. A rat model of unilateral ureteral obstruction (UUO) was established. The expression of TGF-β1, collagen I, collagen III, and mDia1 in the kidneys was examined at day 7 after surgery. The effect of mDia1 on EMT was explored in NRK-52E cells by exposing them to TGF-β1. Increased expression of TGF-β1, collagen I, collagen III, and mDia1 was found in obstructive kidneys of UUO model rats. Exposing rat tubular epithelial cells to TGF-β1 promoted collagen I and collagen III expression but had no effect on mDia1 expression. Silencing mDia1 expression impeded epithelial cell migration as well as reduced TGF-β1, collagen, and Profilin1 expression, whereas mDia1 overexpression exerted an opposite effect. Furthermore, mDia1 regulated the expression of vimentin, α-smooth muscle actin, and E-cadherin and focal adhesion-kinase (FAK)/Src activation through Profilin1. Inhibition of the mDia1 activator RhoA by fasudil reversed EMT, and FAK/Src activation induced by mDia1. In conclusion, mDia1 regulated tubular epithelial cell migration, collagen expression, and EMT in NRK-52E cells exposed to TGF-β1. Thus, suppression of mDia1 activation might be a strategy to counteract renal fibrosis.

Therapeutic Potential of Thrombomodulin in Renal Fibrosis of Nephrotoxic Serum Nephritis in Wistar-Kyoto Rats

BACKGROUND

Recombinant human soluble thrombomodulin (rhTM) was approved in 2008 and has been used for treatment of disseminated intravascular coagulation in Japan. The antifibrotic effects of rhTM in acute exacerbation of idiopathic pulmonary fibrosis are well established, but the therapeutic potential of rhTM in renal fibrosis remains poorly understood.

METHODS

Nephrotoxic serum nephritis (NTS-N) was induced in 22 female Wistar-Kyoto (WKY) rats on day 0. Rats were administered either rhTM or vehicle intraperitoneally, every day from day 4 to day 55. Rats were sacrificed on day 56 when renal fibrosis was established and renal morphological investigations were performed. In vitro, rat renal fibroblasts (NRK-49F) were pretreated with rhTM or saline, and expression levels of profibrogenic gene induced by thrombin were analyzed by real-time reverse transcription polymerase chain reaction.

RESULTS

Compared to WKY-GN-vehicle rats, the body weights of WKY-GN-rhTM rats were significantly greater on day 55. By day 56, rhTM had significantly reduced serum creatinine levels in NTS-N. On the other hand, urinary protein excretion was comparable between the two treatment groups throughout the study. The percentage of Masson trichrome-positive areas in WKY-GN-rhTM rats was significantly lower compared to that in WKY-GN-vehicle rats. Glomerular fibrin deposition was significantly reduced in WKY-GN-rhTM rats. In addition, rhTM significantly reduced the renal cortical mRNA expression levels of TNF-α, Toll-like receptor 4, MYD88, TGF-β, αSMA, collagen I, collagen III, fibronectin, and protease-activated receptor 1 (PAR1), a thrombin receptor. In vitro, thrombin stimulation of NRK-49F cells significantly enhanced the mRNA expression levels of αSMA and PAR1, and these upregulations were significantly reduced by pretreatment with rhTM.

CONCLUSIONS

Administration of rhTM after establishment of crescentic glomerulonephritis (GN) attenuated the subsequent development of renal fibrosis in NTS-N, possibly in part by inhibiting thrombin-mediated fibrogenesis. Our results suggest that rhTM may offer a therapeutic option for limiting the progression of chronic kidney disease in crescentic GN.

Protease-activated receptor-1 contributes to renal injury and interstitial fibrosis during chronic obstructive nephropathy

End‐stage renal disease, the final stage of all chronic kidney disorders, is associated with renal fibrosis and inevitably leads to renal failure and death. Transition of tubular epithelial cells (TECs) into mesenchymal fibroblasts constitutes a proposed mechanism underlying the progression of renal fibrosis and here we assessed whether protease‐activated receptor (PAR)‐1, which recently emerged as an inducer of epithelial‐to‐mesenchymal transition (EMT), aggravates renal fibrosis. We show that PAR‐1 activation on TECs reduces the expression of epithelial markers and simultaneously induces mesenchymal marker expression reminiscent of EMT. We next show that kidney damage was reduced in PAR‐1‐deficient mice during unilateral ureter obstruction (UUO) and that PAR‐1‐deficient mice develop a diminished fibrotic response. Importantly, however, we did hardly observe any signs of mesenchymal transition in both wild‐type and PAR‐1‐deficient mice suggesting that diminished fibrosis in PAR‐1‐deficient mice is not due to reduced EMT. Instead, the accumulation of macrophages and fibroblasts was significantly reduced in PAR‐1‐deficient animals which were accompanied by diminished production of MCP‐1 and TGF‐β. Overall, we thus show that PAR‐1 drives EMT of TECs in vitro and aggravates UUO‐induced renal fibrosis although this is likely due to PAR‐1‐dependent pro‐fibrotic cytokine production rather than EMT.

Signaling Crosstalk of TGF-β/ALK5 and PAR2/PAR1: A Complex Regulatory Network Controlling Fibrosis and Cancer

Both signaling by transforming growth factor-β (TGF-β) and agonists of the G Protein-coupled receptors proteinase-activated receptor-1 (PAR1) and -2 (PAR2) have been linked to tissue fibrosis and cancer. Intriguingly, TGF-β and PAR signaling either converge on the regulation of certain matrix genes overexpressed in these pathologies or display mutual regulation of their signaling components, which is mediated in part through sphingosine kinases and sphingosine-1-phosphate and indicative of an intimate signaling crosstalk between the two pathways. In the first part of this review, we summarize the various regulatory interactions that have been discovered so far according to the organ/tissue in which they were described. In the second part, we highlight the types of signaling crosstalk between TGF-β on the one hand and PAR2/PAR1 on the other hand. Both ligand–receptor systems interact at various levels and by several mechanisms including mutual regulation of ligand–ligand, ligand–receptor, and receptor–receptor at the transcriptional, post-transcriptional, and receptor transactivation levels. These mutual interactions between PAR2/PAR1 and TGF-β signaling components eventually result in feed-forward loops/vicious cycles of matrix deposition and malignant traits that exacerbate fibrosis and oncogenesis, respectively. Given the crucial role of PAR2 and PAR1 in controlling TGF-β receptor activation, signaling, TGF-β synthesis and bioactivation, combining PAR inhibitors with TGF-β blocking agents may turn out to be more efficient than targeting TGF-β alone in alleviating unwanted TGF-β-dependent responses but retaining the beneficial ones.

Contraction-dependent TGF-β1 activation is required for thrombin-induced remodeling in human airway smooth muscle cells

AIMS

Thrombin is a serine proteinase that is not only involved in coagulation cascade, but also mediates a number of biological responses relevant to tissues repair, and induces bronchoconstriction. TGF-β plays a pivotal role in airway remodeling due to its effects on airway smooth muscle proliferation and extracellular matrix (ECM) deposition. Recently, bronchoconstriction itself is found to constitute a form of strain and is highly relevant to asthmatic airway remodeling. However, the underlying mechanisms remain unknown. Here, we investigated the role of contraction- dependent TGF-β activation in thrombin-induced remodeling in human airway smooth muscle (HASM) cells.

MATERIALS AND METHODS

Primary HASM cells were treated with or without thrombin in the absence or presence of anti-TGF-β antibody, cytochalasin D and formoterol. CFSE labeling index or CCK-8 assay were performed to test cell proliferation. RT-PCR and Western blotting were used to examined ECM mRNA level and collagen Iα1, α-actin protein expression, respectively. Immunofluorescence was also used to confirm contraction induced by thrombin in HASM cells.

KEY FINDING

Thrombin stimulation enhanced HASM cells proliferation and activated TGF-β signaling. Thrombin induced ECM mRNA and collagen Iα1 protein expression, and these effects are mediated by TGF-β. Abrogation of TGF-β activation by contraction inhibitors cytochalasin D and formoterol prevents the thrombin-induced effects.

SIGNIFICANCE

These findings suggest that contraction-dependent TGF-β activation could be a mechanism by which thrombin leads to the development of asthmatic airway remodeling. Blocking physical forces with bronchodilator would be an intriguing way in reducing airway remodeling in asthma.

Coagulation and non-coagulation effects of thrombin

Thrombin is a multifunctional serine protease produced from prothrombin, and is a key regulator in hemostatic and non-hemostatic processes. It is the main effector protease in primary hemostasis by activating platelets, and plays a key role in secondary hemostasis. Besides its well-known functions in hemostasis, thrombin also plays a role in various non-hemostatic biological and pathophysiologic processes, predominantly mediated through activation of protease-activated receptors (PARs). Depending on several factors, such as the concentration of thrombin, the duration of activation, the location of PARs, the presence of coreceptors, and the formation of PAR heterodimers, activation of the receptor by thrombin can induce different cellular responses. Moreover, thrombin can have opposing effects in the same cell; it can induce both inflammatory and anti-inflammatory signals. Owing to the complexity of thrombin's signal transduction pathways, the exact mechanism behind the dichotomy of thrombin is yet still unknown. In this review, we highlight the hemostatic and non-hemostatic functions of thrombin, and specifically focus on the non-hemostatic dual role of thrombin under various conditions and in relation to cardiovascular disease.

Protease-activated receptor-1 deficiency protects against streptozotocin-induced diabetic nephropathy in mice

Endogenously administered activated protein C ameliorates diabetic nephropathy (DN) in a protease-activated receptor-1 (PAR-1)-dependent manner, suggesting that PAR-1 activation limits the progression of DN. Activation of PAR-1 in fibroblast-like cells, however, induces proliferation and extracellular matrix production, thereby driving fibrotic disease. Considering the key role of mesangial proliferation and extracellular matrix production during DN, PAR-1 may in fact potentiate diabetes-induced kidney injury. To determine the net effect of PAR-1 in DN, streptozotocin-induced DN was studied in wild type and PAR-1 deficient mice. Subsequent mechanistic insight was obtained by assessing profibrotic responses of mesangial and tubular epithelial cells in vitro, following PAR-1 stimulation and inhibition. Despite having similar glucose levels, PAR-1 deficient mice developed less kidney damage after induction of diabetes, as evidenced by diminished proteinuria, plasma cystatin C levels, expansion of the mesangial area, and tubular atrophy. In vitro, PAR-1 signaling in mesangial cells led to increased proliferation and expression of matrix proteins fibronectin and collagen IV. Conversely, a reduction in both proliferation and fibronectin deposition was observed in diabetic PAR-1 deficient mice. Overall, we show that PAR-1 plays an important role in the development of DN and PAR-1 might therefore be an attractive therapeutic target to pursue in DN.

Human Endothelial Protein C Receptor Overexpression Protects Intraportal Islet Grafts in Mice

Islet transplantation can potentially cure type 1 diabetes mellitus, but it is limited by a shortage of human donors as well as by islet graft destruction by inflammatory and thrombotic mechanisms. A possible solution to these problems is to use genetically modified pig islets. Endothelial protein C receptor (EPCR) enhances protein C activation and regulates coagulation, inflammation, and apoptosis. We hypothesized that human EPCR (hEPCR) expression on donor islets would improve graft survival and function. Islets from an hEPCR transgenic mouse line strongly expressed the transgene, and hEPCR expression was maintained after islet isolation. Islets were transplanted from hEPCR mice and wild-type (WT) littermates into diabetic mice in a marginal-dose syngeneic intraportal islet transplantation model. The blood glucose level normalized within 5 days in 5 of 7 recipients of hEPCR islets, compared with only 2 of 7 recipients of WT islets (P < .05). Transplanted hEPCR islets had better preserved morphology and more intense insulin staining than WT grafts, and they retained transgene expression. The improved engraftment compared with WT islets suggests that inflammation and coagulation associated with the transplant process can be reduced by hEPCR expression on donor tissue.

Protease activated receptor 1 (PAR1) enhances Src-mediated tyrosine phosphorylation of NMDA receptor in intracerebral hemorrhage (ICH)

It has been demonstrated that Src could modulate NMDA receptor, and PAR1 could also affect NMDAR signaling. However, whether PAR1 could regulate NMDAR through Src under ICH has not yet been investigated. In this study, we demonstrated the role of Src-PSD95-GluN2A signaling cascades in rat ICH model and in vitro thrombin challenged model. Using the PAR1 agonist SFLLR, antagonist RLLFS and Src inhibitor PP2, electrophysiological analysis showed that PAR1 regulated NMDA-induced whole-cell currents (INMDA) though Src in primary cultured neurons. Both in vivo and in vitro results showed the elevated phosphorylation of tyrosine in Src and GluN2A and enhanced interaction of the Src-PSD95-GluN2A under model conditions. Treatment with the PAR1 antagonist RLLFS, AS-PSD95 (Antisense oligonucleotide against PSD95) and Src inhibitor PP2 inhibited the interaction among Src-PSD95-GluN2A, and p-Src, p-GluN2A. Co-application of SFLLR and AS-PSD95, PP2, or MK801 (NMDAR inhibitor) abolished the effect of SF. In conclusion, our results demonstrated that activated thrombin receptor PAR1 induced Src activation, enhanced the interaction among Src-PSD95-GluN2A signaling modules, and up-regulated GluN2A phosphorylation after ICH injury. Elucidation of such signaling cascades would possibly provide novel targets for ICH treatment.

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.

Thrombin weakens the amnion extracellular matrix (ECM) directly rather than through protease activated receptors

INTRODUCTION

Preterm premature rupture of fetal membranes (pPROM) is a major cause of preterm birth. Abruption associated thrombin production, and infection-inflammation associated cytokine production reportedly play major roles in pPROM. Utilizing an in vitro model-system we have confirmed that both thrombin and inflammatory cytokines remodel and biomechanically weaken amnion, the load-bearing component of FM. Also, we have shown thrombin directly weakens isolated amnion but cytokines weaken amnion only indirectly by initially interacting with choriodecidua and releasing unidentified soluble activator(s). This study's purpose was to determine whether thrombin weakens the isolated amnion through thrombin receptor-protease activated receptors (PARs 1,2,3,4), activation of previously secreted extracellular matrix (ECM) enzymes, or by direct action on the ECM.

METHODS

Primary amnion cells and isolated amnion were tested for PARs by immunohistochemistry, Western Blot and rtPCR. Cell-free amnion ECM was produced by devitalizing isolated amnion by exposure to UV light and subsequent freeze-thaw cycles. Devitalized amnion membrane explants were incubated with thrombin and biomechanically tested.

RESULTS

PARs were not found in amnion or amnion cells. Thrombin induced dose-dependent weakening of devitalized amnion explants. Preincubation with the thrombin inhibitor hirudin prevented thrombin-induced weakening. Thrombin converted pro-MMP2 embedded in the devitalized amnion ECM to multiple active forms. Thrombin also directly digested gelatin gels in zymograms suggesting the possibility of direct degradation of amnion ECM components.

DISCUSSION

Thrombin appears to directly weaken the amnion ECM and additionally activates stored pro-MMP2 to active forms that may further enhance amnion ECM degradation.

CONCLUSION

Thrombin weakens amnion directly rather than through PARs.

Renal and urinary levels of endothelial protein C receptor correlate with acute renal allograft rejection

The Endothelial Protein C Receptor (EPCR) is expressed on leukocytes, on endothelium of large blood vessels and to a lesser extent on capillaries. Membrane bound EPCR plays an important role in the activation of protein C which has anticoagulant, anti-inflammatory and cytoprotective effects. After cleavage by a protease EPCR is also found as a soluble protein. Acute rejection of kidney allografts can be divided in T-cell-mediated rejection (TCMR) and antibody-mediated (ABMR) rejection. The latter is characterized by strong activation of coagulation. Currently no reliable non-invasive biomarkers are available to monitor rejection.

Renal biopsies were available from 81 renal transplant patients (33 without rejection, 26 TCMR and 22 ABMR), we had access to mRNA material, matched plasma and urine samples for a portion of this cohort. Renal EPCR expression was assessed by RT-PCR and immunostaining. Plasma and urine sEPCR levels were measured by ELISA.

ABMR patients showed higher levels of EPCR mRNA than TCMR patients. EPCR expression on glomeruli was significantly elevated in ABMR patients than in TCMR or control patients. In the peritubular capillaries EPCR expression was higher in ABMR patients than in control patients. EPCR expression was higher in tubules and arteries of rejection patients than in control patients. Plasma sEPCR levels did not differ. Urine sEPCR levels were more elevated in the ABMR group than in patients with TCMR or without rejection. ROC analysis demonstrated that urinary sEPCR is appropriate to discriminate between ABMR patients and TCMR or control patients. We conclude that urinary sEPCR could be a novel non-invasive biomarker of antibody mediated rejection in renal transplantation.

Organ-specific protection against lipopolysaccharide-induced vascular leak is dependent on the endothelial protein C receptor

OBJECTIVE

To study the role of the endothelial protein C receptor (EPCR) in the modulation of susceptibility to inflammation-induced vascular leak in vivo.

APPROACH AND RESULTS

Genetically modified mice with low, <10% EPCR expression (EPCR(low)) and control mice were challenged with lipopolysaccharides in a mouse model of endotoxemia. Infrared fluorescence and quantification of albumin-bound Evans Blue in tissues and intravascular plasma volumes were used to assess plasma extravasation. Pair-wise analysis of EPCR(low) and control mice matched for sex, age, and weight allowed determination of EPCR-dependent vascular leak. Kidney, lung, and brain were the organs with highest discriminative increased Evans Blue accumulation in EPCR(low) versus control mice in response to lipopolysaccharides. Histology of kidney and lung confirmed the EPCR-specific pathology. In addition to severe kidney injury in response to lipopolysaccharides, EPCR(low) and anti-EPCR-treated wild-type mice suffered from enhanced albuminuria and profound renal hemorrhage versus controls. Intravascular volume loss at the same extent of weight loss in EPCR(low) mice compared with control mice provided proof that plasma leak was the predominant cause of Evans Blue tissue accumulation.

CONCLUSIONS

This study demonstrates an important protective role for EPCR in vivo against vascular leakage during inflammation and suggests that EPCR-dependent vascular protection is organ-specific.

Protective effects of transgenic human endothelial protein C receptor expression in murine models of transplantation

Thrombosis and inflammation are major obstacles to successful pig-to-human solid organ xenotransplantation. A potential solution is genetic modification of the donor pig to overexpress molecules such as the endothelial protein C receptor (EPCR), which has anticoagulant, anti-inflammatory and cytoprotective signaling properties. Transgenic mice expressing human EPCR (hEPCR) were generated and characterized to test this approach. hEPCR was expressed widely and its compatibility with the mouse protein C pathway was evident from the anticoagulant phenotype of the transgenic mice, which exhibited a prolonged tail bleeding time and resistance to collagen-induced thrombosis. hEPCR mice were protected in a model of warm renal ischemia reperfusion injury compared to wild type (WT) littermates (mean serum creatinine 39.0 ± 2.3 μmol/L vs. 78.5 ± 10.0 μmol/L, p < 0.05; mean injury score 31 ± 7% vs. 56 ± 5%, p < 0.05). Heterotopic cardiac xenografts from hEPCR mice showed a small but significant prolongation of survival in C6-deficient PVG rat recipients compared to WT grafts (median graft survival 6 vs. 5 days, p < 0.05), with less hemorrhage and edema in rejected transgenic grafts. These data indicate that it is possible to overexpress EPCR at a sufficient level to provide protection against transplant-related thrombotic and inflammatory injury, without detrimental effects in the donor animal.

The endothelial cell protein C receptor: cell surface conductor of cytoprotective coagulation factor signaling

Increasing evidence links blood coagulation proteins with the regulation of acute and chronic inflammatory disease. Of particular interest are vitamin K-dependent proteases, which are generated as a hemostatic response to vascular injury, but can also initiate signal transduction via interactions with vascular receptors. The endothelial cell protein C receptor (EPCR) is a multi-ligand vitamin K-dependent protein receptor for zymogen and activated forms of plasma protein C and factor VII. Although the physiological role of the EPCR-FVII(a) interaction is not well-understood, protein C binding to EPCR facilitates rapid generation of APC in response to excessive thrombin generation, and is a central requirement for the multiple signal-transduction cascades initiated by APC on both vascular endothelial and innate immune cells. Exciting recent studies have highlighted the emerging role of EPCR in modulating the cytoprotective properties of APC in a number of diverse inflammatory disorders. In this review, we describe the structure-function relationships, signal transduction pathways, and cellular interactions that enable EPCR to modulate the anticoagulant and anti-inflammatory properties of its vitamin K-dependent protein ligands, and examine the relevance of EPCR to both thrombotic and inflammation-associated disease.

Is EPCR a multi-ligand receptor? Pros and cons

In the last decade, the endothelial cell protein C/activated protein C receptor (EPCR) has received considerable attention. The role initially attributed to EPCR, i.e. the enhancement of protein C (PC) activation by the thrombin-thrombomodulin complex on the surface of the large vessels, although important, did not go beyond the haemostasis scenario. However, the discovery of the cytoprotective, anti-inflammatory and anti-apoptotic features of the activated PC (APC) and the required involvement of EPCR for APC to exert such actions did place the receptor in a privileged position in the crosstalk between coagulation and inflammation. The last five years have shown that PC/APC are not the only molecules able to interact with EPCR. Factor VII/VIIa (FVII/VIIa) and factor Xa (FXa), two other serine proteases that play a central role in haemostasis and are also involved in signalling processes influencing wound healing, tissue remodelling, inflammation or metastasis, have been reported to bind to EPCR. These observations have paved the way for an exploration of unsuspected new roles for the receptor. This review aims to offer a new image of EPCR in the light of its extended panel of ligands. A brief update of what is known about the APC-evoked EPCR-dependent cell signalling mechanisms is provided, but special care has been taken to assemble all the information available about the interaction of EPCR with FVII/VIIa and FXa.

The role of TGF-β and epithelial-to mesenchymal transition in diabetic nephropathy

Transforming Growth Factor-beta (TGF-β) is a pro-sclerotic cytokine widely associated with the development of fibrosis in diabetic nephropathy. Central to the underlying pathology of tubulointerstitial fibrosis is epithelial-to-mesenchymal transition (EMT), or the trans-differentiation of tubular epithelial cells into myofibroblasts. This process is accompanied by a number of key morphological and phenotypic changes culminating in detachment of cells from the tubular basement membrane and migration into the interstitium. Ultimately these cells reside as activated myofibroblasts and further exacerbate the state of fibrosis. A large body of evidence supports a role for TGF-β and downstream Smad signalling in the development and progression of renal fibrosis. Here we discuss a role for TGF-β as the principle effector in the development of renal fibrosis in diabetic nephropathy, focusing on the role of the TGF-β1 isoform and its downstream signalling intermediates, the Smad proteins. Specifically we review evidence for TGF-β1 induced EMT in both the proximal and distal regions of the nephron and describe potential therapeutic strategies that may target TGF-β1 activity.

Low but sustained coagulation activation ameliorates glucose-induced podocyte apoptosis: protective effect of factor V Leiden in diabetic nephropathy

Whereas it is generally perceived to be harmful, enhanced coagulation activation can also convey salutary effects. The high prevalence of the prothrombotic factor V Leiden (FVL) mutation in whites has been attributed to a positive selection pressure (eg, resulting from reduced blood loss or improved survival in sepsis). The consequences of enhanced coagulation activation, as observed in FVL carriers, on microvascular diabetic complications remain unknown. We therefore investigated the role of FVL in diabetic nephropathy. In heterozygous or homozygous diabetic FVL mice, albuminuria and indices of diabetic nephropathy were reduced compared with diabetic wild-type mice. This was associated with reduced glomerular apoptosis and preservation of podocytes in diabetic FVL-positive mice. In vitro, low-dose thrombin (50pM) prevented, whereas high-dose thrombin (20nM) aggravated, glucose-induced apoptosis in podocytes. In diabetic patients, the FVL mutation, but not the plasminogen activator inhibitor-1 4G/5G polymorphism, is associated with reduced albuminuria, which is consistent with a nephroprotective role of low but sustained thrombin generation. Consistently, anticoagulation of diabetic FVL-positive mice with hirudin abolished the nephroprotective effect. These results identify a nephroprotective function of low but sustained thrombin levels in FVL carriers, supporting a dual, context-dependent function of thrombin in chronic diseases.