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      Thrombin Is a Pro-Fibrotic Factor for Rat Renal Fibroblasts in vitro

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          Background: Generation of thrombin occurs in response to parenchymal injury. Thrombin not only converts plasma fibrinogen into an insoluble fibrin clot, but also potentially augments inflammation through receptor-mediated activity. This study examines whether thrombin may potentially exacerbate fibrosis by upregulating the function of interstitial fibroblasts in vitro. Methods: Fibroblasts were isolated by explant outgrowth culture of rat kidneys. Subcultured cells were grown in DMEM+10% FCS supplemented with 0.1–0.5 U/ml thrombin. Functional parameters examined included kinetics (thymidine incorporation and change in cell number), differentiation (Western blotting for α-smooth muscle actin; αSMA), expression of procollagen α1(I) (Northern blotting) and contraction of collagen I lattices. RT-PCR was used to characterise expression of protease-activated receptors (PAR) previously implicated in thrombin’s cellular effects. Results: Cell population growth was increased 66 ± 41 and 47 ± 41% by 0.1 and 0.5 U/ml thrombin respectively (both p < 0.05 vs. basal). Likewise, 0.5 U/ml thrombin increased corrected procollagen α1(I) expression 2.4-fold (p < 0.05 vs. basal) and exacerbated the ability of fibroblasts to contract collagen matrix (p < 0.05 vs. basal). These effects were not associated with any change in expression of the myofibroblast marker αSMA. Effects on cell number were inhibited by treatment with ( D)-Phe-Pro-Arg-chloromethylketone HCl (PPACK) suggesting that functional effects were mediated by serine protease activity. PAR-1 was the only fully functional known thrombin receptor expressed by these cells. Conclusion: Thrombin is a potential unrecognised fibroblast agonist in renal disease. Further studies of thrombin and its receptors may yield valuable insights into the pathogenesis of interstitial fibrosis.

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          Thrombin signalling and protease-activated receptors.

          How does the coagulation protease thrombin regulate cellular behaviour? The protease-activated receptors (PARs) provide one answer. In concert with the coagulation cascade, these receptors provide an elegant mechanism linking mechanical information in the form of tissue injury or vascular leakage to cellular responses. Roles for PARs are beginning to emerge in haemostasis and thrombosis, inflammation, and perhaps even blood vessel development.
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            The role of tubulointerstitial injury in chronic renal failure.

            Progressive renal failure results from a triad of glomerulosclerosis, tubulointerstitial fibrosis and vascular sclerosis. The mechanisms by which tubules are injured, and by which the tubular epithelial cell then excites interstitial inflammation culminating in fibroblast activation and fibrosis have become increasingly understood. Most current methods to prevent progressive glomerulosclerosis would inherently prevent tubular injury and interstitial fibrosis. The behaviour and control of the renal fibroblast is being investigated, with the potential for direct interference with its functions.
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              Protease-Activated Receptor 1 Mediates Thrombin-Dependent, Cell-Mediated Renal Inflammation in Crescentic Glomerulonephritis

              Protease-activated receptor (PAR)-1 is a cellular receptor for thrombin that is activated after proteolytic cleavage. The contribution of PAR-1 to inflammatory cell–mediated renal injury was assessed in murine crescentic glomerulonephritis (GN). A pivotal role for thrombin in this model was demonstrated by the capacity of hirudin, a selective thrombin antagonist, to attenuate renal injury. Compared with control treatment, hirudin significantly reduced glomerular crescent formation, T cell and macrophage infiltration, fibrin deposition, and elevated serum creatinine, which are prominent features of GN. PAR-1–deficient (PAR-1−/−) mice, which have normal coagulation, also showed significant protection from crescentic GN compared with wild-type mice. The reductions in crescent formation, inflammatory cell infiltration, and serum creatinine were similar in PAR-1−/− and hirudin-treated mice, but hirudin afforded significantly greater protection from fibrin deposition. Treatment of wild-type mice with a selective PAR-1–activating peptide (TRAP) augmented histological and functional indices of GN, but TRAP treatment did not alter the severity of GN in PAR−/− mice. These results indicate that activation of PAR-1 by thrombin or TRAP amplifies crescentic GN. Thus, in addition to its procoagulant role, thrombin has proinflammatory, PAR-1–dependent effects that augment inflammatory renal injury.

                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                October 2005
                08 June 2005
                : 101
                : 2
                : e42-e49
                aDepartment of Nephrology, The Royal Melbourne Hospital, bDepartment of Medicine, and cSchool of Veterinary Science, University of Melbourne, Melbourne, Australia
                86228 Nephron Exp Nephrol 2005;101:e42–e49
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 5, References: 30, Pages: 1
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/86228
                Original Paper


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