BMP-7 blocks mesenchymal conversion of mesothelial cells and prevents peritoneal damage induced by dialysis fluid exposure

Smad7 gene transfer attenuates angiogenesis in peritoneal dialysis rats

AIM

Transforming growth factor-β (TGF-β) has been shown to play a role in peritoneal angiogenesis associated with peritoneal dialysis (PD). The present study investigated whether blockade of TGF-β signalling with Smad7 has a therapeutic effect on PD induced-peritoneal angiogenesis.

METHODS

A rat model of peritoneal dialysis was induced by a daily intraperitoneal injection of 4.25% Dianeal and lipopolysaccharides. PD rats were transfected with a doxycycline regulated, Smad7-expressing plasmid using an ultrasound-microbubble-mediated system on day 0 and day 14 after initiation of PD and an empty vector was used as control. Peritoneal microvessel density (MVD) in peritoneal tissue was assessed by anti-CD31 immunohistochemistry after 4 weeks of PD and peritoneal angiogenic growth factors, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) was also examined by immunofluorescence, western blot and reverse transcription-polymerase chain reaction.

RESULTS

In contrast to the normal control group, at 4 weeks after PD, PD rats displayed peritoneal lesions, peritoneal angiogenesis and increased mRNA and protein expression of VEGF, bFGF and PDGF. Smad7 gene transfer significantly attenuated the peritoneal MVD and inhibited the upregulation of VEGF, bFGF and PDGF. Moreover, inhibition of peritoneal angiogenesis by overexpression of Smad7 was associated with inhibition of phosphorylation of Smad3 and downregulation of TGF-β expression.

CONCLUSION

Smad7 gene transfer via an ultrasound-microbubble-mediated system is able to attenuate peritoneal angiogenesis in a rat model of PD. Those results suggest that blockade of the TGF-β/Smad signalling pathway may represent a novel therapeutic approach to prevent PD-induced peritoneal angiogenesis.

Role of CIP4 in high glucose induced epithelial--mesenchymal transition of rat peritoneal mesothelial cells

BACKGROUND

Peritoneal mesothelial cell (PMC) plays a key role in the process of peritoneal fibrosis. Epithelial-mesenchymal transition (EMT) of PMCs is an important mechanism of peritoneal fibrosis. Prolonged exposure to peritoneal dialysis fluid containing a high concentration of glucose may lead to EMT of PMCs. Cdc42-interacting protein-4 (CIP4) is a critical regulator of cell skeleton and downstream effector of Cdc42 and participates in EMT of tubular epithelial cells. In the present study, we investigate the possible role of CIP4 in EMT of PMC under high glucose (HG) condition in vitro and further explore the potential therapeutic point for peritoneal fibrosis.

METHODS

Rat peritoneal mesothelial cells (RPMCs) were isolated from the peritonea of rats by enzymatic digestion. Under HG conditions (1.5%, 2.5% and 4.25%), E-cadherin, α-SMA and CIP4 expression were assessed by Western blot. Effect of CIP4-siRNA and pcDNA3.1-CIP4 transfection on E-cadherin, α-SMA and CIP4 expression were also assessed respectively under 2.5% HG concentration. Cells were pretreated for 24 h with PI3K/Akt signaling inhibitor perifosine and effect of perifosine on CIP4 expression were detected by Western blot.

RESULTS

EMT induction by HG was confirmed by the prevalence of morphological changes, loss of E-cadherin, increase in α-SMA expression. CIP4-siRNA transfection can reverse EMT of RPMCs. Over-expression of CIP4 promoted characteristics similar to those commonly observed in EMT. Furthermore, the increased CIP4 in response to HG was efficiently inhibited by perifosine.

CONCLUSION

This study shows that CIP4 promotes high glucose-induced EMT through PI3K-Akt signaling pathway in RPMCs.

Anti-fibrosis effect of BMP-7 peptide functionalization on cobalt chromium alloy

Orthopedic metallic prosthetic implants are commonly made of cobalt chromium (CoCr) alloys. However, such metal-based implants are susceptible to fibrous capsule formation on the implant surface after implantation. At the bone-implant interface, this capsule can prevent implant integration, resulting in loosening and failure. Minimizing the development of such a capsule on the CoCr surface would improve direct bone-implant bonding leading to long-term implant functionality. We evaluated the anti-fibrosis effect of bone morphogenic protein-7 (BMP-7) peptide covalently bonded to CoCr alloy. This peptide, a biomimetic derivation of the knuckle epitope of BMP-7, was conjugated at the N-terminus with a cysteine amino acid. X-ray photoelectron spectroscopy (XPS) and probe binding assay were used to evaluate different stages of grafting and surface functionalization using polydopamine coating. Cellular functions were studied using fibroblast attachment, cell proliferation, and MTT assays. Fibroblasts were grown on functionalized and pristine CoCr substrates, and the efficacy of BMP-7 peptide on anti-fibrosis was analyzed via gene expression and protein expression of fibrosis markers ACTA2, Collagen 1A1, and fibronectin. The peptide functionalized substrates showed significant reduction of fibrosis markers expression after 1 week of incubation compared to controls. BMP-7 signaling pathway activation was shown by the presence of phosphorylation of Smad1/5/8. These findings may contribute to the improvement of CoCr implants in orthopedic surgery applications.

Mesothelial cells differentiate into fibroblast-like cells under the scirrhous gastric cancer microenvironment and promote peritoneal carcinomatosis in vitro and in vivo

Peritoneal metastases are one reason for the poor prognosis of scirrhous gastric cancer (SGC), and myofibroblast provides a favorable environment for the peritoneal dissemination of gastric cancer. The aim of this study was to determine whether myofibroblast originates from peritoneal mesothelial cells under the influence of the tumor microenvironment. Immunohistochemical studies of peritoneal biopsy specimens from patients with peritoneal lavage cytological (+) status demonstrate the expression of the epithelial markers cytokeratin in fibroblast-like cells entrapped in the stroma, suggesting that these cells stemmed from local conversion of mesothelial cells. To confirm this hypothesis in vitro, we co-incubated mesothelial cells with SGC or non-SGC to investigate morphology and function changes. As we expected, mesothelial cells undergo a transition from an epithelial phenotype to a mesenchymal phenotype with loss of epithelial morphology and decrease in the expression of cytokeratin and E-cadherin when exposed to conditioned medium from HSC-39, and the induction of mesothelial cells can be abolished using a neutralizing antibody to transforming growth factor-beta1 (TGF-β1) as well as by pre-treatment with SB431542. Moreover, we found that these mesothelial cells-derived cells exhibit functional properties of myofibroblasts, including the ability to increase adhesion and invasion of SGC. In summary, our current data demonstrated that mesothelial cells are a source of myofibroblasts under the SGC microenvironment which provide a favorable environment for the dissemination of gastric cancer; TGF-β1 produced by autocrine/paracrine in peritoneal cavity may play a central role in this pathogenesis.

Functional relevance of the switch of VEGF receptors/co-receptors during peritoneal dialysis-induced mesothelial to mesenchymal transition

Vascular endothelial growth factor (VEGF) is up-regulated during mesothelial to mesenchymal transition (MMT) and has been associated with peritoneal membrane dysfunction in peritoneal dialysis (PD) patients. It has been shown that normal and malignant mesothelial cells (MCs) express VEGF receptors (VEGFRs) and co-receptors and that VEGF is an autocrine growth factor for mesothelioma. Hence, we evaluated the expression patterns and the functional relevance of the VEGF/VEGFRs/co-receptors axis during the mesenchymal conversion of MCs induced by peritoneal dialysis. Omentum-derived MCs treated with TGF-β1 plus IL-1β (in vitro MMT) and PD effluent-derived MCs with non-epithelioid phenotype (ex vivo MMT) showed down-regulated expression of the two main receptors Flt-1/VEGFR-1 and KDR/VEGFR-2, whereas the co-receptor neuropilin-1 (Nrp-1) was up-regulated. The expression of the Nrp-1 ligand semaphorin-3A (Sema-3A), a functional VEGF competitor, was repressed throughout the MMT process. These expression pattern changes were accompanied by a reduction of the proliferation capacity and by a parallel induction of the invasive capacity of MCs that had undergone an in vitro or ex vivo MMT. Treatment with neutralizing anti-VEGF or anti-Nrp-1 antibodies showed that these molecules played a relevant role in cellular proliferation only in naïve omentum-derived MCs. Conversely, treatment with these blocking antibodies, as well as with recombinant Sema-3A, indicated that the switched VEGF/VEGFRs/co-receptors axis drove the enhanced invasion capacity of MCs undergoing MMT. In conclusion, the expression patterns of VEGFRs and co-receptors change in MCs during MMT, which in turn would determine their behaviour in terms of proliferation and invasion in response to VEGF.

Are the Mesothelial-to-Mesenchymal Transition, Sclerotic Peritonitis Syndromes, and Encapsulating Peritoneal Sclerosis Part of the Same Process?

Mesothelial-to-mesenchymal transition (MMT) is an autoregulated physiological process of tissue repair that in uncontrolled conditions, such as peritoneal dialysis (PD), can lead to peritoneal fibrosis. The maximum expression of sclerotic peritoneal syndromes (SPS) is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. The SPS includes a wide range of peritoneal fibrosis that appears progressively and is considered as a reversible process, while EPS does not. EPS is a serious complication of PD characterized by a progressive intra-abdominal inflammatory process that results in bridles and severe fibrous tissue formation which cover and constrict the viscera. Recent studies show that transdifferentiated mesothelial cells isolated from the PD effluent correlate very well with the clinical events such as the number of hemoperitoneum and peritonitis, as well as with PD function (lower ultrafiltration and high Cr-MTC). In addition, in peritoneal biopsies from PD patients, the MMT correlates very well with anatomical changes (fibrosis and angiogenesis). However, the pathway to reach EPS from SPS has not been fully and completely established. Herein, we present important evidence pointing to the MMT that is present in the initial peritoneal fibrosis stages and it is perpetual over time, with at least theoretical possibility that MMT initiated the fibrosing process to reach EPS.

Zinc transporter 7 induced by high glucose attenuates epithelial-to-mesenchymal transition of peritoneal mesothelial cells

Zinc (Zn) is an essential micronutrient and cytoprotectant involved in preventing many types of epithelial-to-mesenchymal transition (EMT)-driven fibrosis in vivo. The zinc-transporter family SLC30A (ZnT) is a pivotal factor in the regulation of Zn homeostasis. However, its function in EMT in peritoneal mesothelial cells (PMCs) remains unknown. This study explored the regulation of zinc transporters and the role they play in cell EMT, particularly in rat peritoneal mesothelial cells (RPMCs), surrounding glucose concentrations and the molecular mechanism involved. The effects of high glucose (HG) on zinc transporter gene expression were measured in RPMCs by real-time PCR. We explored ZnT7 (Slc30A7): the effect of ZnT7 over-expression and siRNA-mediated knock-down on HG-induced EMT was investigated as well as the underlying molecular mechanisms. Over-expression of ZnT7 resulted in significantly inhibited HG-induced EMT in RPMCs, while inhibition of ZnT7 expression using a considerable siRNA-mediated knock-down of RPMCs increased the levels of EMT. Furthermore, over-expression of ZnT7 is accompanied by down-regulation of TGF-β/Smad pathway, phospho-Smad3,4 expression levels. The finding suggests that the zinc-transporting system in RPMCs is influenced by the exposure to HG. The ZnT7 may account for the inhibition of HG-induced EMT in RPMCs, likely through targeting TGF-β/Smad signaling.

The monocyte chemoattractant protein-1 (MCP-1)/CCR2 system is involved in peritoneal dialysis-related epithelial-mesenchymal transition of peritoneal mesothelial cells

Epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (PMCs) has a role in the process of peritoneal fibrosis (PF), a serious complication in peritoneal dialysis (PD) patients. Even though monocyte chemoattractant protein-1 (MCP-1) was demonstrated to directly increase extracellular matrix (ECM) synthesis, the role of the MCP-1/CCR2 system in PD-related EMT and ECM synthesis in cultured human PMCs (HPMCs) and in an animal model of PD has never been elucidated. In vitro, HPMCs were exposed to 5.6 mM glucose (NG), NG+MCP-1 (10 ng/ml) (NG+MCP-1), or 100 mM glucose (HG) with or without CCR2 inhibitor (RS102895) (CCR2i) or a dominant-negative mutant MCP-1-expressing lentivirus (LV-mMCP-1). In vivo, PD catheters were inserted into 60 Sprague-Dawley rats, and saline (Control, C) (N=30) or 4.25% PD solution (PD) (N=30) was infused for 4 weeks. Twenty rats from each group were treated with empty LV or LV-mMCP-1 intraperitoneally. Snail, E-cadherin, α-smooth muscle actin (α-SMA), and fibronectin protein expression in HPMCs and the peritoneum was evaluated by western blot analysis. Compared with NG cells, Snail, α-SMA, and fibronectin expression was significantly increased, while E-cadherin expression was significantly decreased in HPMCs exposed to HG and NG+MCP-1, and these changes were significantly abrogated by CCR2i (P<0.05). In addition, MCP-1-induced EMT was significantly attenuated by anti-TGF-β1 antibody. In PD rats, Snail and fibronectin expression was significantly increased in the peritoneum, whereas the ratios of E-cadherin/α-SMA protein expression were significantly decreased (P<0.05). The thickness of the peritoneum and the intensity of Masson's trichrome staining in the peritoneum were also significantly higher in PD rats than in C rats (P<0.05). These changes in PD rats were significantly abrogated by LV-mMCP-1. These findings suggest that the MCP-1/CCR2 system is directly involved in PD-related EMT and ECM synthesis and that this is mediated, at least in part, via TGF-β1.

Heme oxygenase-1 attenuates epithelial-to-mesenchymal transition of human peritoneal mesothelial cells

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells has been regarded as an early mechanism of peritoneal fibrosis. A substantial and rapidly growing literature indicates that HO-1 provides the provenance for pathways that can interrupt virtually all major mechanisms of tissue injury. The effects of HO-1 expression on EMT, which plays a critical role in the development of peritoneal membrane (PM) fibrosis, are unknown and its roles in peritoneal fibrosis has not been studied, yet.

METHODS

A piece of human omentum obtained from consenting patients undergoing elective abdominal surgery was used for study. We treated the human peritoneal mesothelial cells (HPMCs) with high glucose solution and HO-1 inducer (hemin, 10 μmol/L). To further investigate the pure effect of HO-1 on EMT of mesothelium, gene transfer of recombinant Adenovirus-harboring human HO-1 (Adv-HO-1 gene) to HPMCs was done.

RESULTS

Exposure of HPMCs to HG solution resulted in an increase of the expression of mesenchymal markers such as α-smooth muscle actin (α-SMA) and was associated with a decrease in the expression of epithelial markers, E-cadherin. HO-1 protein expression was decreased in the same situation. Treatment of HPMCs with HO-1 inducer, hemin showed a dosage-dependent amelioration of HG induced changes in markers of EMT with increase of expression of HO-1. Human HO-1 gene transfection resulted in a significant increase in HO-1 expression and ameliorated HG-induced changes in expression of E-cadherin and α-SMA.

CONCLUSION

Taken together, our results suggest that HO-1 has a critical role in the modulation of peritoneal fibrosis, and, more important, the suppression of EMT. This study is the first to show the beneficial effect of HO-1 on reversing EMT in MC.

Effect of alendronate sodium on the expression of mesenchymal-epithelial transition markers in mice with liver fibrosis

The aim of this study was to explore whether alendronate sodium regulates tissue remodeling by controlling the transforming growth factor (TGF)-β1-induced epithelial-mesenchymal transition (EMT) and bone morphogenetic protein (BMP)-7-induced mesenchymal-epithelial transition (MET) in CCl₄-induced hepatic fibrosis in mice. A mouse model of CCl₄-induced hepatic fibrosis was evaluated using the hematoxylin and eosin (HE) and Masson’s trichrome staining histological methods. The activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured using an automated biochemical analyzer. The expression of TGF-β1, α-smooth muscle actin (α-SMA), BMP-7 and E-cadherin in the hepatic tissue was detected using immunohistochemistry. The mRNA and protein levels of TGF-β1, α-SMA, BMP-7, fibroblast-specific protein 1 (FSP1), E-cadherin and N-cadherin were detected using RT-PCR and western blot analysis. Immunohistochemical and molecular biochemical examination revealed that alendronate sodium significantly arrested the progression of hepatic fibrosis. Alendronate sodium caused significant amelioration of liver injury and reduced the activities of serum ALT and AST (P<0.001). Furthermore, alendronate sodium markedly reduced TGF-β1 and α-SMA mRNA expression and increased BMP-7 and E-cadherin in the mouse liver tissue (P<0.001). Alendronate sodium significantly arrested the progression of hepatic fibrosis. The underlying mechanism was associated with changes in the redox state, which remains variable in liver fibrosis, and depends on the balance between TGF-β/smad- and BMP-7-modulated mechanisms which regulate EMT and MET in multifunctional progenitors.

miRNA589 regulates epithelial-mesenchymal transition in human peritoneal mesothelial cells

Background. microRNA (miRNA, miR) are thought to interact with multiple mRNAs which are involved in the EMT process. But the role of miRNAs in peritoneal fibrosis has remained unknown. Objective. To determine if miRNA589 regulates the EMT induced by TGFβ1 in human peritoneal mesothelial cell line (HMrSV5 cells). Methods. 1. Level of miR589 was detected in both human peritoneal mesothelial cells (HPMCs) isolated from continuous ambulatory peritoneal dialysis (CAPD) patients' effluent and HMrSV5 cells treated with or without TGFβ1. 2. HMrSV5 cells were divided into three groups: control group, TGFβ1 group, and pre-miR-589+TGFβ1 group. The level of miRNA589 was determined by realtime PCR. The expressions of ZO-1, vimentin, and E-cadherin in HPMCs were detected, respectively. Results. Decreased level of miRNA589 was obtained in either HPMCs of long-term CAPD patients or HMrSV5 cells treated with TGFβ1. In vitro, TGFβ1 led to upregulation of vimentin and downregulation of ZO-1 as well as E-cadherin in HMrSV5 cells, which suggested EMT, was induced. The changes were accompanied with notably decreased level of miRNA589 in HMrSV5 cells treated with TGFβ1. Overexpression of miRNA589 by transfection with pre-miRNA589 partially reversed these EMT changes. Conclusion. miRNA589 mediates TGFβ1 induced EMT in human peritoneal mesothelial cells.

The complex regulation of TGF-β in cardiovascular disease

Transforming growth factor β (TGF-β1) is a pleiotropic cytokine with many and complex effects in cell and tissue physiology. This is made possible by a very complex and interwoven signaling system, whose regulation continues to be the focus of a growing line of research. This complex regulation translates to a key role in cardiovascular physiology, hemostasis, and the blood–vessel interface. In accordance with this, the TGF-β1 pathway appears to be deregulated in related disorders, such as atherosclerotic vascular disease and myeloproliferative syndromes. It is expected that the growing amount of experimental and clinical research will yield medical advances in the applications of knowledge of the TGF-β1 pathway to diagnosis and therapeutics.

Oral administration of recombinant adeno-associated virus-mediated bone morphogenetic protein-7 suppresses CCl(4)-induced hepatic fibrosis in mice

Fibrogenesis and hepatocyte degeneration are the main pathological processes in chronic liver diseases. Transforming growth factor-β1 (TGF-β1) is the key profibrotic cytokine in hepatic fibrosis. Bone morphogenetic protein-7 (BMP-7) is a potent antagonist of TGF-β1 and an antifibrotic factor. In this study, we generated a recombinant adeno-associated virus carrying BMP-7 (AAV-BMP-7) and tested its ability to suppress carbon tetrachloride (CCl(4))-induced hepatic fibrosis when orally administered to mice. Our results show that the ectopic expression of BMP-7 in gastrointestinal (GI) mucosa due to the AAV-BMP-7 administration led to the long-term elevation of serum BMP-7 concentrations and resulted in the drastic amelioration of CCl(4)-induced hepatic fibrosis in BALB/c mice. Immunostaining for α-smooth muscle actin (α-SMA) and desmin demonstrated that AAV-BMP-7 inhibited the activation of hepatic stellate cells (HSCs) in the fibrotic mouse liver. Moreover, the ectopic expression of BMP-7 promoted hepatocyte proliferation, as confirmed by an increase in the amount of proliferating cell nuclear antigen (PCNA)-positive hepatocytes in the mice that received AAV-BMP-7. Our results clearly indicate that BMP-7 is capable of inhibiting hepatic fibrosis and promoting hepatocyte regeneration. We suggest that oral AAV-BMP-7 could be developed into a safe, simple, and effective therapy for hepatic fibrosis.

Inhibition of transforming growth factor-activated kinase 1 (TAK1) blocks and reverses epithelial to mesenchymal transition of mesothelial cells

Peritoneal fibrosis is a frequent complication of peritoneal dialysis following repeated low grade inflammatory and pro-fibrotic insults. This pathological process may lead to ultrafiltration failure and eventually to the discontinuing of the therapy. Fibrosis is linked to epithelial to mesenchymal transition (EMT) of the peritoneal mesothelial cells, which acquire invasive and fibrogenic abilities. Here, we analyzed the role of the transforming growth factor-activated kinase-1 (TAK1) in the EMT of primary mesothelial cells from human peritoneum. The inhibition of TAK1 in mesenchymal-like mesothelial cells from the effluents of patients undergoing peritoneal dialysis led to the reacquisition of the apical to basolateral polarity, to increased expression of epithelial and to down-regulation of mesenchymal markers. TAK1 inhibition also resulted in decreased migratory/invasive abilities of effluent-derived mesothelial cells. Simultaneous inhibition of ERK1/2 and TAK1 pathways did not lead to an additive effect in the reacquisition of the epithelial phenotype. Inhibition of TAK1 also blocked EMT in vitro and reduced the levels of PAI-1, which is involved in fibrosis and invasion. Analysis of signalling pathways downstream of TAK1 involved in EMT induction, showed that TAK1 inhibition reduced the transcriptional activity of NF-κB and Smad3, as well as the phosphorylation of c-jun, while enhancing Smad1–5–8 activity. These results demonstrate that TAK1 is a cross-point in a network including different pro-EMT transcription factors, such as NF-κB, Snail, AP-1 and Smads. The identification of TAK1 as a main biochemical mediator of EMT and fibrosis in mesothelial cells from human peritoneum and the study of signalling pathways induced by its activity may be relevant in the design of new therapies aimed to counteract peritoneal fibrosis.

Influence of bicarbonate/low-GDP peritoneal dialysis fluid (BicaVera) on in vitro and ex vivo epithelial-to-mesenchymal transition of mesothelial cells

BACKGROUND

Peritoneal membrane damage induced by peritoneal dialysis (PD) is largely associated with epithelial-to-mesenchymal transition (EMT) of mesothelial cells (MCs), which is believed to be a result mainly of the glucose degradation products (GDPs) present in PD solutions.

OBJECTIVES

This study investigated the impact of bicarbonate-buffered, low-GDP PD solution (BicaVera: Fresenius Medical Care, Bad Homburg, Germany) on EMT of MCs in vitro and ex vivo.

METHODS

IN VITRO STUDIES

Omentum-derived MCs were incubated with lactate-buffered standard PD fluid or BicaVera fluid diluted 1:1 with culture medium. Ex vivo studies: From 31 patients randomly distributed to either standard or BicaVera solution and followed for 24 months, effluents were collected every 6 months for determination of EMT markers in effluent MCs.

RESULTS

Culturing of MCs with standard fluid in vitro resulted in morphology change to a non-epithelioid shape, with downregulation of E-cadherin (indicative of EMT) and strong induction of vascular endothelial growth factor (VEGF) expression. By contrast, in vitro exposure of MCs to bicarbonate/low-GDP solution had less impact on both EMT parameters. Ex vivo studies partially confirmed the foregoing results. The BicaVera group, with a higher prevalence of the non-epithelioid MC phenotype at baseline (for unknown reasons), showed a clear and significant trend to gain and maintain an epithelioid phenotype at medium- and longer-term and to show fewer fibrogenic characteristics. By contrast, the standard solution group demonstrated a progressive and significantly higher presence of the non-epithelioid phenotype. Compared with effluent MCs having an epithelioid phenotype, MCs with non-epithelioid morphology showed significantly lower levels of E-cadherin and greater levels of fibronectin and VEGF. In comparing the BicaVera and standard solution groups, MCs from the standard solution group showed significantly higher secretion of interleukin 8 and lower secretion of collagen I, but no differences in the levels of other EMT-associated molecules, including fibronectin, VEGF, E-cadherin, and transforming growth factor β1. Peritonitis incidence was similar in both groups. Functionally, the use of BicaVera fluid was associated with higher transport of small molecules and lower ultrafiltration capacity.

CONCLUSIONS

Effluent MCs grown ex vivo from patients treated with bicarbonate/low-GDP BicaVera fluid showed a trend to acquire an epithelial phenotype, with lower production of proinflammatory cytokines and chemokines (such as interleukin 8) than was seen with MCs from patients treated with a lactate-buffered standard PD solution.

Bioincompatible impact of different peritoneal dialysis fluid components and therapeutic interventions as tested in a rat peritoneal dialysis model

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this paper, we describe the impact of different factors contributing to peritoneal incompatibility of PD fluid installation including presence of a catheter, volume loading, and the PD fluid components itself. These factors initiate recruitment and activation of peritoneal immune cells such as macrophages and mast cells, as well as activation of peritoneal cells as mesothelial cells in situ. We provide an overview of PD-associated changes as seen in our rat PD-exposure model. Since these changes are partly reversible, we finally discuss therapeutic strategies in the rat PD model with possible consequences of long-term PD in the relevant human setting.

Blocking TGF-β1 protects the peritoneal membrane from dialysate-induced damage

During peritoneal dialysis (PD), mesothelial cells undergo mesothelial-to-mesenchymal transition (MMT), a process associated with peritoneal-membrane dysfunction. Because TGF-β1 can induce MMT, we evaluated the efficacy of TGF-β1-blocking peptides in modulating MMT and ameliorating peritoneal damage in a mouse model of PD. Exposure of the peritoneum to PD fluid induced fibrosis, angiogenesis, functional impairment, and the accumulation of fibroblasts. In addition to expressing fibroblast-specific protein-1 (FSP-1), some fibroblasts co-expressed cytokeratin, indicating their mesothelial origin. These intermediate-phenotype (Cyto(+)/FSP-1(+)) fibroblasts had features of myofibroblasts with fibrogenic capacity. PD fluid treatment triggered the appearance of CD31(+)/FSP-1(+) and CD45(+)/FSP-1(+) cells, suggesting that fibroblasts also originate from endothelial cells and from cells recruited from bone marrow. Administration of blocking peptides significantly ameliorated fibrosis and angiogenesis, improved peritoneal function, and reduced the number of FSP-1(+) cells, especially in the Cyto(+)/FSP-1(+) subpopulation. Conversely, overexpression of TGF-β1 in the peritoneum by adenovirus-mediated gene transfer led to a marked accumulation of fibroblasts, most of which derived from the mesothelium. Taken together, these results demonstrate that TGF-β1 drives the peritoneal deterioration induced by dialysis fluid and highlights a role of TGF-β1-mediated MMT in the pathophysiology of peritoneal-membrane dysfunction.

Effluent markers related to epithelial mesenchymal transition with adjusted values for effluent cancer antigen 125 in peritoneal dialysis patients

Objectives. Epithelial mesenchymal transition (EMT) is important for peritoneal deterioration. We evaluated the association between peritoneal solute transport rate (PSTR) and effluent markers related to EMT with adjusted values for effluent cancer antigen 125 (CA125). Methods. One hundred five incident peritoneal dialysis (PD) patients on PD for 25 (12-68) months with biocompatible solutions were included in the study. Fast peritoneal equilibration test was used to evaluate PSTR. Effluent hepatocyte growth factor (HGF), bone morphogenic protein-7 (BMP-7), vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), and CA125 at 4 h were measured. Results. Patients with dialysate/plasma creatinine ≧0.82 showed significantly higher effluent HGF (240 versus 133 pg/mL, P < .001), VEGF, IL-6, and IL6/CA125 levels than the others but no significant differences in effluent HGF/CA125, BMP-7, and BMP7/CA125 were observed. Conclusion. Increase in the effluent HGF levels as a compensatory mechanism is a marker of peritoneal deterioration, but controversy remains regarding adjusted value for CA125.

Angiogenesis in peritoneal dialysis

Long-term exposure to peritoneal dialysis fluid induces morphological alterations, including angiogenesis, leading to a loss of ultrafiltration (UF) capacity. We discuss the effect of different factors in peritoneal dialysis (PD) on angiogenesis. In addition, we describe the process of angiogenesis and the possible role of different cell types in the peritoneum upon PD contributing to new blood vessel formation. Furthermore, we review several interventions used in our rat PD exposure model to decrease angiogenesis in PD. Moreover, we show new data on the use of sunitinib to inhibit angiogenesis in this rat model. Although various interventions seem to be promising, well-randomised clinical trials showing absolute prevention of angiogenesis and UF failure are, yet, still missing. To make real progress in PD treatment, the aim should be to prevent angiogenesis as well as peritoneal fibrosis and PD-induced inflammation.

Protective measures against ultrafiltration failure in peritoneal dialysis patients

Ultrafiltration failure in patients undergoing peritoneal dialysis is a condition with an incidence that increases over time. It is related to increased cardiovascular morbidity and mortality and is a major cause of the abandonment of the treatment technique. Because the number of patients undergoing renal replacement therapy is increasing with society aging and because approximately 10% of this population is treated with peritoneal dialysis, this matter is becoming more common in everyday practice for clinicians involved in the care of patients with chronic renal failure. In this review, we summarize the available measures used to prevent and treat ultrafiltration failure and the current state of research in the field, both in the experimental and clinical settings, focusing on the possible clinical applications of recent findings.

p38 maintains E-cadherin expression by modulating TAK1-NF-kappa B during epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells is a pathological process that occurs during peritoneal dialysis. EMT leads to peritoneal fibrosis, ultrafiltration failure and eventually to the discontinuation of therapy. Signaling pathways involved in mesothelial EMT are thus of great interest, but are mostly unknown. We used primary mesothelial cells from human omentum to analyze the role of the p38 MAPK signaling pathway in the induction of EMT. The use of specific inhibitors, a dominant-negative p38 mutant and lentiviral silencing of p38α demonstrated that p38 promotes E-cadherin expression both in untreated cells and in cells co-stimulated with the EMT-inducing stimuli transforming growth factor (TGF)-β1 and interleukin (IL)-1β. p38 inhibition also led to disorganization and downregulation of cytokeratin filaments and zonula occludens (ZO)-1, whereas expression of vimentin was increased. Analysis of transcription factors that repress E-cadherin expression showed that p38 blockade inhibited expression of Snail1 while increasing expression of Twist. Nuclear translocation and transcriptional activity of p65 NF-κB, an important inducer of EMT, was increased by p38 inhibition. Moreover, p38 inhibition increased the phosphorylation of TGF-β-activated kinase 1 (TAK1), NF-κB and IκBα. The effect of p38 inhibition on E-cadherin expression was rescued by modulating the TAK1-NF-κB pathway. Our results demonstrate that p38 maintains E-cadherin expression by suppressing TAK1-NF-κB signaling, thus impeding the induction of EMT in human primary mesothelial cells. This represents a novel role of p38 as a brake or 'gatekeeper' of EMT induction by maintaining E-cadherin levels.

Low-GDP peritoneal dialysis fluid ('balance') has less impact in vitro and ex vivo on epithelial-to-mesenchymal transition (EMT) of mesothelial cells than a standard fluid

BACKGROUND

Peritoneal membrane deterioration during peritoneal dialysis (PD) is associated with epithelial-to-mesenchymal transition (EMT) of mesothelial cells (MC), which is believed to be mainly due to glucose degradation products (GDPs) present in PD solutions. Here we investigate the impact of GDPs in PD solutions on the EMT of MC in vitro and ex vivo.

METHODS

For in vitro studies, omentum-derived MC were incubated with standard PD fluid or low-GDP solution diluted 1:1 with culture medium. For ex vivo studies, 33 patients, who were distributed at random to either the 'standard' or the 'low GDP' groups, were followed over 24 months. Effluents were collected every 6 months to determine EMT markers in effluent MC.

RESULTS

Exposure of MC to standard fluid in vitro resulted in morphological change into a non-epitheloid shape, down-regulation of E-cadherin, indicative of EMT, and in a strong induction of vascular endothelial growth factor (VEGF) expression. In contrast, in vitro exposure of MC to low-GDP solution did not lead to these phenotype changes. This could be confirmed ex vivo, as the prevalence of non-epitheloid phenotype of MC in the standard group was significantly higher with increasing PD duration and MC isolated from this group showed significantly higher levels of EMT-associated molecules including fibronectin, collagen I, VEGF, IL-8 and TGF-β levels when compared with the low-GDP group. Over time, the expression of E-cadherin also decreased in the standard but increased in the low-GDP group. In addition, the levels of EMT-associated molecules (fibronectin, VEGF and IL-8) increased in the standard but decreased in the low-GDP group. A similar trend was also observed for collagen I and for TGF-β (for the first year), but did not reach global statistical significance. Accordingly, effluent MC with non-epitheloid morphology showed significantly lower levels of E-cadherin and greater levels of fibronectin, collagen I, VEGF and IL 8 when compared with MC with epitheloid phenotype. The incidence of peritonitis did not significantly influence these results. Drop-out due to technique failure was less in the 'balance' group. The functional, renal and peritoneal evaluation of patients being treated with either standard or 'balance' fluid did not show any significant difference over time.

CONCLUSIONS

MC from PD effluent of patients treated with a PD fluid containing low GDP levels show fewer signs of EMT and the respective molecules than MC from patients treated with standard fluid, indicating a better preservation of the peritoneal membrane structure and a favourable outcome in patients using low-GDP fluid. It also confirms the hypothesis that the protection of EMT by GDP-reduced fluids is also present in vivo.