Jeroen Bastiaans

Thrombin induces epithelial-mesenchymal transition and collagen production by retinal pigment epithelial cells via autocrine PDGF-receptor signaling.

PURPOSE De-differentiation of RPE cells into mesenchymal cells (epithelial-mesenchymal transition; EMT) and associated collagen production contributes to development of proliferative vitreoretinopathy (PVR). In patients with PVR, intraocular coagulation cascade activation occurs and may play an important initiating role. Therefore, we examined the effect of the coagulation proteins factor Xa and thrombin on EMT and collagen production by RPE cells. METHODS Retinal pigment epithelial cells were stimulated with factor Xa or thrombin and the effect on zonula occludens (ZO)-1, α-smooth muscle actin (α-SMA), collagen, and platelet-derived growth factor (PDGF)-B were determined by real-time quantitative-polymerase chain reaction (RQ-PCR), immunofluorescence microscopy, and HPLC and ELISA for collagen and PDGF-BB in culture supernatants, respectively. PDGF-receptor activation was determined by phosphorylation analysis and inhibition studies using the PDGF-receptor tyrosine kinase inhibitor AG1296. RESULTS Thrombin reduced ZO-1 gene expression (P < 0.05) and enhanced expression of the genes encoding α-SMA and the pro-alpha1 chain of collagen type-1 (P < 0.05), indicating EMT. Also, ZO-1 protein expression declined on thrombin stimulation, whereas production of α-SMA and collagen increased. In contrast to thrombin, factor Xa hardly stimulated EMT by RPE. Thrombin clearly induced PDGF-BB production and PDGF-Rβ chain phosphorylation in RPE. Moreover, AG1296 significantly blocked the effect of thrombin on EMT and collagen production. CONCLUSIONS Our findings demonstrate that thrombin is a potent inducer of EMT by RPE via autocrine activation of PDGF-receptor signaling. Coagulation cascade-induced EMT of RPE may thus contribute to the formation of fibrotic retinal membranes in PVR and should be considered as treatment target in PVR.

Factor Xa and thrombin stimulate proinflammatory and profibrotic mediator production by retinal pigment epithelial cells: a role in vitreoretinal disorders?

BackgroundVitreoretinal disorders, including proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR) and exudative age-related macular degeneration (AMD), are a major cause of visual impairment worldwide and can lead to blindness when untreated. Loss of blood-retinal barrier (BRB) integrity associated with vitreoretinal fibrin deposition, inflammation, fibrosis and neovascularization contribute to the pathophysiological processes in these disorders. Retinal pigment epithelial (RPE) cells are well recognized to contribute to vitreoretinal inflammation/fibrosis and are likely to encounter contact with coagulation factor upon loss of BRB integrity.MethodsAn extensive study was performed in which we examined the effect of factor Xa and thrombin on the production of a broad panel of cytokines/chemokines and growth factors by RPE cells. For this purpose we used the ARPE-19 cell line as well as primary RPE cells, a glass slide based array that allows simultaneous detection of 120 cytokines/chemokines and growth factors, ELISA and real-time-quantitative PCR. The involved signaling cascade was examined using specific inhibitors for protease activated receptor (PAR)1, PAR2 and nuclear factor kappa-B (NF-κB).ResultsFactor Xa and thrombin regulated the production of cytokines and growth factors (including GM-CSF, IL-6, IL-8, MCP-3, PDGF-AA, PDGF-BB, TIMP-1 and TGF-α) that fit well in the pathobiology of vitreoretinal disease. Blocking studies revealed that the effects were mediated via PAR1 induced NF-κB activation.ConclusionsOur findings suggest that factor Xa and thrombin can drive vitreoretinal inflammation and fibrosis and should be considered as treatment targets in vitreoretinal disorders such as PVR, PDR and AMD.

The Role of Thrombin in Proliferative Vitreoretinopathy

PURPOSE To determine the role of thrombin in the development of proliferative vitreoretinopathy (PVR). METHODS Vitreous was collected from patients undergoing a vitrectomy (macular holes and puckers, n = 11 [controls]; retinal detachment without PVR development following vitrectomy, n = 15 [RRD1]; retinal detachment with PVR development within 6 months after vitrectomy, n = 11 [RRD2]; and established PVR, n = 14 [PVR]). Thrombin activity in vitreous was determined using a thrombin-specific chromogenic substrate. ARPE-19 cells were stimulated with 8× diluted vitreous samples in the presence and absence of hirudin. The samples were analyzed at t = 0 and t = 24 hours for the presence of 27 cytokines/chemokines and growth factors using a multiplex approach. In comparable studies, ARPE-19 cells were stimulated for 2 hours, and mRNA expression levels for CCL2, CXCL8, GMCSF, IL6, and PDGFB were determined by real-time quantitative (RQ)-PCR. RESULTS Thrombin activity was significantly (P < 0.05) higher in vitreous of the PVR group compared to the other groups. Proliferative vitreoretinopathy vitreous stimulated the production of chemokine (C-C motif) ligand (CCL)2, chemokine (C-X-C motif) ligand (CXCL)8, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6, and platelet-derived growth factor (PDGF)-BB by ARPE-19 to significantly (P < 0.05) higher levels than vitreous from the RRD1 and RRD2 groups. These effects of PVR vitreous were significantly (P < 0.05) reduced by hirudin. These data were confirmed by mRNA studies. CONCLUSIONS Thrombin activity is increased in vitreous of patients with established PVR and is involved in the activation of proinflammatory and profibrotic pathways in RPE cells. Inhibition of thrombin activity may therefore represent a potential treatment option for proliferative vitreoretinopathy.

Mild versus strong anti-inflammatory therapy during early sepsis in mice: a matter of life and death.

Objective: A recent literature-based study suggested that low-dose corticosteroid treatment has a beneficial effect on mortality in septic patients, whereas high-dose corticosteroid treatment has not. This suggests that mild down-regulation of the inflammatory response during early sepsis may be beneficial while extensive reduction of the inflammatory response is not. To investigate this hypothesis, we examined the effect of dexamethasone in varying doses on cecal ligation and puncture-induced inflammation and mortality. Design: Animal study. Setting: University research laboratory. Subjects: Male C57BL/6 mice. Interventions: Mice were subjected to cecal ligation and puncture, and dexamethasone was administered intravenously at a dosage of 0.05 (L/DEX), 0.25 (M/DEX), or 2.5 (H/DEX) mg/kg body weight 20 mins postoperatively. Mice receiving phosphate-buffered saline served as controls. Survival was recorded up to 21 days and inflammatory markers were determined in plasma, lungs, liver, and kidney at 6 hrs following cecal ligation and puncture as well as bacterial load in blood and peritoneal fluid. Measurements and Main Results: L/DEX treatment significantly improved survival compared with control mice, whereas treatment with higher concentrations of dexamethasone (M/DEX and H/DEX) did not. Treatment with either M/DEX or H/DEX was associated with significantly (p < .05) reduced cytokine plasma levels as compared with controls at 6 hrs after cecal ligation and puncture. In addition, M/DEX or H/DEX powerfully reduced cytokine messenger RNA expression in the lung, liver, and kidney. In contrast, treatment with L/DEX was associated with a mild, but nonsignificant, reduction of cytokine plasma levels. In addition, L/DEX moderately reduced cytokine messenger RNA expression in lung, liver, and kidney tissue and reduced the occurrence of bacteremia. Conclusions: A modest down-regulation of the early sepsis-associated inflammatory response improves survival in a murine cecal ligation and puncture model. We propose that the success of anti-inflammatory therapies in a septic setting fundamentally depends on finding a treatment balance that reduces the hyperinflammation-induced pathology but still allows adequate defense against pathogens.

Ustekinumab improves psoriasis-related gene expression in noninvolved psoriatic skin without inhibition of the antimicrobial response

Background  Ustekinumab is a fully human anti‐p40 monoclonal antibody which neutralizes interleukin (IL)‐12 and IL‐23, thereby interfering with T‐helper (Th)1/Th17 pathways and keratinocyte activation, and is highly effective in the treatment of psoriasis. During ustekinumab treatment, some of our patients noticed reduced koebnerization of noninvolved skin and less new plaque formation.

Chloroquine and Hydroxychloroquine Increase Retinal Pigment Epithelial Layer Permeability

Antimalarials chloroquine (CQ) and hydroxychloroquine (HCQ) are widely used as antiinflammatory drugs, but side effects include retinopathy and vision loss. The objective of this study was to examine the effect of CQ and HCQ on the barrier integrity of retinal pigment epithelial (RPE) cell monolayers in vitro. Permeability of ARPE‐19 cell monolayers was determined using Fluorescein isothiocyanate (FITC)‐labeled dextran. The influence of CQ and HCQ on cell death and the expression tight junction molecules was examined. CQ and HCQ significantly increased ARPE‐19 monolayer permeability after 3 and 18 h, respectively, and enhanced mRNA levels for claudin‐1 and occludin. Cytotoxicity was only observed after 18 h exposure. Thus, CQ and HCQ rapidly enhance RPE barrier permeability in vitro, independent of cytotoxicity or loss of zonula occludens‐1, claudin‐1, and occludin expression. Our findings suggest that CQ/HCQ‐induced permeability of the RPE layer may contribute to blood–retinal barrier breakdown in case of CQ/HCQ‐induced retinopathy.

Retinal pigment epithelial cells display specific transcriptional responses upon TNF-α stimulation

Background/aims Tumour necrosis factor-α (TNF-α) is a key mediator of ocular inflammation and its interaction with the retinal pigment epithelium (RPE) may be a driving force in vitreoretinal disorders such as age-related macular degeneration, proliferative vitreoretinopathy (PVR) and diabetic retinopathy. Under inflammatory conditions, the ability of RPE cells to maintain the blood–retinal barrier and immune privilege may be lost and proliferation of RPE cells is facilitated. To gain insight into the effects of TNF-α on RPE cells, a gene expression study was performed. Methods ARPE-19 and HT-29 cells were stimulated with 50 ng/mL TNF-α for 6 h. Gene expression patterns were compared between stimulated and control cells using whole genome gene expression arrays. Data were analysed using Partek and OmniViz and validated using quantitative RT-PCR. Functional annotation analysis was performed using Ingenuity and DAVID. Results A total of 97 genes were uniquely modulated by TNF-α in ARPE-19 cells compared with HT-29 cells (86 upregulated and 11 downregulated). Most commonly affected biological processes were apoptosis, cell motility and cell signalling. The highest upregulated gene was EFNA1. Among the downregulated genes were transcription factors implicated in ocular development (SIX3, PAX6) and modulation of p53-mediated apoptosis (CITED2). Conclusions This study provides insight into the unique responses of RPE cells to TNF-α stimulation and suggests a role for genes involved in apoptosis and retinal epithelial development. These findings contribute to our understanding of the behaviour of RPE cells under inflammatory conditions and the crucial role of RPE cells in vitreoretinal diseases.

Factor Xa and thrombin induce epithelial-mesenchymal transition by retinal pigment epithelial cells via PDGF-Rβ signaling

Proliferative vitreoretinopathy (PVR) is an inflammatory fibrotic disorder of the retina. Retinal pigment epithelial (RPE) cells contribute to PVR development through uncontrolled proliferation and extracellular matrix production as well as cytokine secretion. Insight into factors that stimulate these processes by RPE in PVR is limited, which may explain the lack of satisfying treatment so far. Blood-retinal barrier breakdown and vascular damage are early pathobiological events of PVR. Vascular damage results in activation of the coagulation system and subretinal fluids from retinal detachment patients have been described to contain high pro-coagulant activity. The effect of coagulation proteases on RPE is however hardly studied so far. Of all proteins involved in the coagulation cascade only factor Xa and thrombin are able to induce various cellular responses via their receptors which are expressed at the cell membranes of various cell types. These receptors, the so-called protease activated receptors (PARs) consist of 4 members: PAR1, -2, -3 and -4. Cleavage of PARs results in the activation of signal transduction pathways that control multiple cellular functions like inflammation, fibrosis and tissue repair. Here we examine the effect of factor Xa and thrombin on epithelial-mesenchymal transition (EMT) by RPE. EMT is a biological process that allows epithelial cells to undergo multiple biochemical changes that enable them to assume a mesenchymal phenotype. Similar processes have also been described for RPE cells in PVR membranes. Differentiation from an epithelial phenotype into a mesenchymal phenotype results in the loss of epithelial markers like zona occludens (ZO)-1 and the enrichment of mesenchymal markers like α-smooth muscle actin (α-SMA). Another component of PVR development as a result of EMT consists of excessive production of extracellular matrix (ECM) proteins; mainly collagen subtype-I. In this study we show that factor Xa and thrombin are able to upregulate the expression of pro-fibrotic mediators like PDGF-A, -B, TGF-α and TIMP-1 by RPE cells and induce fibrotic responses known to be involved in the development of PVR. In line with these findings we also show that mainly thrombin but also factor Xa, can induce EMT by RPE via PDGF-B mediated PDGF-Rβ signaling.

Dabigatran inhibits intravitreal thrombin activity

Proliferative vitreoretinopathy (PVR) is a vitreoretinal disorder in which retinal pigment epithelial (RPE) cell activation contributes to both formation of fibrotic retinal membranes and inflammation. Vitreous of patients with PVR contains increased thrombin activity which induces profibrotic and proinflammatory programs in RPE cells. Inhibition of intravitreal thrombin activity may thus represent a therapeutic option for PVR. In this study, we examined the capacity of the clinically available direct thrombin inhibitor dabigatran to inhibit thrombin activity in vitreous fluids.