Smad7 transgene attenuates peritoneal fibrosis in uremic rats treated with peritoneal dialysis

Investigating the therapeutic effects and mechanisms of Roxadustat on peritoneal fibrosis Based on the TGF-β/Smad pathway

Peritoneal fibrosis (PF) is particularly common in individuals undergoing peritoneal dialysis (PD). Fibrosis of the parenchymal tissue typically progresses slowly. Therefore, preventing and reducing the advancement of fibrosis is crucial for effective patient treatment. Roxadustat is a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI), primarily used to treat and improve renal anemia. Recent studies have found that HIF-1α possesses antioxidant activity and exerts a certain protective effect in ischemic heart disease and spinal cord injury, while it can also delay the progression of pulmonary and renal fibrosis. This study establishes the mice model through intraperitoneal injection of 4.25 % peritoneal dialysate fluid (PDF) and explores the therapeutic effects of Roxadustat by inducing TGF-β1-mediated epithelial-mesenchymal transition (EMT) in Met-5A cells. The aim is to investigate the protective role and mechanisms of Roxadustat against PD-related PF. We observed thicker peritoneal tissue and reduced permeability in animals with PD-related PF samples. This was accompanied by heightened inflammation, which Roxadustat alleviated by lowering the levels of inflammatory cytokines (IL-6, TNF-α). Furthermore, Roxadustat inhibited EMT in PF mice and TGF-β1-induced Met-5A cells, as evidenced by decreased expression of fibrotic markers, such as fibronectin, collagen I, and α-SMA, alongside an elevation in the expression of the epithelial marker, E-cadherin. Roxadustat also significantly decreased the expression of TGF-β1 and the phosphorylation of p-Smad2 and p-Smad3. In conclusion, Roxadustat ameliorates peritoneal fibrosis through the TGF-β/Smad pathway.

Autophagy in peritoneal fibrosis

Peritoneal dialysis (PD) is a widely accepted renal replacement therapy for patients with end-stage renal disease (ESRD). Morphological and functional changes occur in the peritoneal membranes (PMs) of patients undergoing long-term PD. Peritoneal fibrosis (PF) is a common PD-related complication that ultimately leads to PM injury and peritoneal ultrafiltration failure. Autophagy is a cellular process of "self-eating" wherein damaged organelles, protein aggregates, and pathogenic microbes are degraded to maintain intracellular environment homeostasis and cell survival. Growing evidence shows that autophagy is involved in fibrosis progression, including renal fibrosis and hepatic fibrosis, in various organs. Multiple risk factors, including high-glucose peritoneal dialysis solution (HGPDS), stimulate the activation of autophagy, which participates in PF progression, in human peritoneal mesothelial cells (HPMCs). Nevertheless, the underlying roles and mechanisms of autophagy in PF progression remain unclear. In this review, we discuss the key roles and potential mechanisms of autophagy in PF to offer novel perspectives on future therapy strategies for PF and their limitations.

Reprogramming of Mesothelial-Mesenchymal Transition in Chronic Peritoneal Diseases by Estrogen Receptor Modulation and TGF-β1 Inhibition

In chronic peritoneal diseases, mesothelial-mesenchymal transition is determined by cues from the extracellular environment rather than just the cellular genome. The transformation of peritoneal mesothelial cells and other host cells into myofibroblasts is mediated by cell membrane receptors, Transforming Growth Factor β1 (TGF-β1), Src and Hypoxia-inducible factor (HIF). This article provides a narrative review of the reprogramming of mesothelial mesenchymal transition in chronic peritoneal diseases, drawing on the similarities in pathophysiology between encapsulating peritoneal sclerosis and peritoneal metastasis, with a particular focus on TGF-β1 signaling and estrogen receptor modulators. Estrogen receptors act at the cell membrane/cytosol as tyrosine kinases that can phosphorylate Src, in a similar way to other receptor tyrosine kinases; or can activate the estrogen response element via nuclear translocation. Tamoxifen can modulate estrogen membrane receptors, and has been shown to be a potent inhibitor of mesothelial-mesenchymal transition (MMT), peritoneal mesothelial cell migration, stromal fibrosis, and neoangiogenesis in the treatment of encapsulating peritoneal sclerosis, with a known side effect and safety profile. The ability of tamoxifen to inhibit the transduction pathways of TGF-β1 and HIF and achieve a quiescent peritoneal stroma makes it a potential candidate for use in cancer treatments. This is relevant to tumors that spread to the peritoneum, particularly those with mesenchymal phenotypes, such as colorectal CMS4 and MSS/EMT gastric cancers, and pancreatic cancer with its desmoplastic stroma. Morphological changes observed during mesothelial mesenchymal transition can be treated with estrogen receptor modulation and TGF-β1 inhibition, which may enable the regression of encapsulating peritoneal sclerosis and peritoneal metastasis.

IL-6 trans-signaling drives a STAT3-dependent pathway that leads to structural alterations of the peritoneal membrane

IL-6 is a vital inflammatory factor in the peritoneal cavity of patients undergoing peritoneal dialysis (PD). The present study examined the effect of IL-6 trans-signaling on structural alterations of the peritoneal membrane. We investigated whether the epithelial-to-mesenchymal transition (EMT) process of human peritoneal mesothelial cells (HPMCs) and the production of proangiogenic factors were controlled by IL-6 trans-signaling. Its role in the peritoneal alterations was detected in a mouse model. The morphology of HPMCs and levels of cytokines in PD effluent were also explored. Stimulation of HPMCs with the IL-6 and soluble IL-6 receptor complex (IL-6/S) promoted the EMT process of HPMCs depending on the STAT3 pathway. In a coculture system of HPMCs and human umbilical vein endothelial cells, IL-6/S mediated the production of VEGF and angiopoietins so as to downregulate the expression of endothelial junction molecules and finally affect vascular permeability. Daily intraperitoneal injection of high glucose-based dialysis fluid induced peritoneal fibrosis, angiogenesis, and macrophage infiltration in a mouse model, accompanied by phosphorylation of STAT3. Blockade of IL-6 trans-signaling prevented these peritoneum alterations. The fibroblast-like appearance of HPMCs ex vivo was upregulated in patients undergoing prevalent PD accompanied by increasing levels of IL-6, VEGF, and angiopoietin-2 in the PD effluent. Taken together, these findings identified a critical link between IL-6 trans-signaling and structural alterations of the peritoneal membrane, and it might be a potential target for the treatment of patients undergoing PD who have developed peritoneal alterations.

Genetic or pharmacologic blockade of enhancer of zeste homolog 2 inhibits the progression of peritoneal fibrosis

Dysregulation of histone methyltransferase enhancer of zeste homolog 2 (EZH2) has been implicated in the pathogenesis of many cancers. However, the role of EZH2 in peritoneal fibrosis remains unknown. We investigated EZH2 expression in peritoneal dialysis (PD) patients and assessed its role in peritoneal fibrosis in cultured human peritoneal mesothelial cells (HPMCs) and murine models of peritoneal fibrosis induced by chlorhexidine gluconate (CG) or high glucose peritoneal dialysis fluid (PDF) by using 3-deazaneplanocin A (3-DZNeP), and EZH2 conditional knockout mice. An abundance of EZH2 was detected in the peritoneum of patients with PD associated peritonitis and the dialysis effluent of long-term PD patients, which was positively correlated with expression of TGF-β1, vascular endothelial growth factor, and IL-6. EZH2 was found highly expressed in the peritoneum of mice following injury by CG or PDF. In both mouse models, treatment with 3-DZNeP attenuated peritoneal fibrosis and inhibited activation of several profibrotic signaling pathways, including TGF-β1/Smad3, Notch1, epidermal growth factor receptor and Src. EZH2 inhibition also inhibited STAT3 and nuclear factor-κB phosphorylation, and reduced lymphocyte and macrophage infiltration and angiogenesis in the injured peritoneum. 3-DZNeP effectively improved high glucose PDF-associated peritoneal dysfunction by decreasing the dialysate-to-plasma ratio of blood urea nitrogen and increasing the ratio of dialysate glucose at 2 h after PDF injection to initial dialysate glucose. Moreover, delayed administration of 3-DZNeP inhibited peritoneal fibrosis progression, reversed established peritoneal fibrosis and reduced expression of tissue inhibitor of metalloproteinase 2, and matrix metalloproteinase-2 and -9. Finally, EZH2-KO mice exhibited less peritoneal fibrosis than EZH2-WT mice. In HPMCs, treatment with EZH2 siRNA or 3-DZNeP suppressed TGF-β1-induced upregulation of α-SMA and Collagen I and preserved E-cadherin. These results indicate that EZH2 is a key epigenetic regulator that promotes peritoneal fibrosis. Targeting EZH2 may have the potential to prevent and treat peritoneal fibrosis. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Tamoxifen and bone morphogenic protein-7 modulate fibrosis and inflammation in the peritoneal fibrosis model developed in uremic rats

Background

Peritoneal fibrosis (PF) represents a long-term complication of peritoneal dialysis (PD), affecting peritoneal membrane (PM) integrity and function. Understanding the mechanisms underlying PF development in an uremic environment aiming alternative therapeutic strategies for treating this process is of great interest. The aim of this study was to analyze the effects of tamoxifen (TAM) and recombinant BMP7 (rBMP7) in an experimental model of PF developed in uremic rats.

Methods

To mimic the clinical situation of patients on long-term PD, a combo model, characterized by the combination of PF and CKD with severe uremia, was developed in Wistar rats. PF was induced by intraperitoneal (IP) injections of chlorhexidine gluconate (CG), and CKD was induced by an adenine-rich diet. Uremia was confirmed by severe hypertension, increased blood urea nitrogen (BUN> 120 mg/dL) and serum creatinine levels (> 2 mg/dL). Uremic rats with PF were treated with TAM (10 mg/Kg by gavage) or BMP7 (30 μg/Kg, IP). Animals were followed up for 30 days.

Results

CG administration in uremic rats induced a striking increase in PM thickness, neoangiogenesis, demonstrated by increased capillary density, and failure of ultrafiltration capacity. These morphological and functional changes were blocked by TAM or rBMP7 treatment. In parallel, TAM and rBMP7 significantly ameliorated the PM fibrotic response by reducing α-SMA, extracellular matrix proteins and TGF-ß expression. TAM or rBMP7 administration significantly inhibited peritoneal Smad3 expression in uremic rats with PF, prevented Smad3 phosphorylation, and induced a remarkable up-regulation of Smad7, an intracellular inhibitor of TGFβ/Smad signaling, contributing to a negative modulation of profibrotic genes. Both treatments were also effective in reducing local inflammation, possibly by upregulating IκB-α expression in the PM of uremic rats with PF. In vitro experiments using primary peritoneal fibroblasts activated by TGF-ß confirmed the capacity of TAM or rBMP7 in blocking inflammatory mediators, such as IL-1ß expression.

Conclusions

In conclusion, these findings indicate important roles of TGF-ß/Smad signaling in PF aggravated by uremia, providing data regarding potential therapeutic approaches with TAM or rBMP7 to block this process.

Electronic supplementary material

The online version of this article (10.1186/s10020-019-0110-5) contains supplementary material, which is available to authorized users.

Effect of Bletilla striata on the Prevention of Postoperative Peritoneal Adhesions in Abrasion-Induced Rat Model

Postoperative peritoneal adhesions (PPAs) constitute a common complication of abdominal surgery with a high incidence. Bletilla striata (BS) is an important hemostatic drug used in China for nearly 2000 years. The purpose of this study was to investigate the effect of Bletilla striata on postoperative intestinal adhesion in rats. PPA was induced by cecal wall abrasion, and Bletilla striata was injected to observe its effect on adhesion in rats. The adhesion and inflammation score were assessed through visual observation and histopathologic evaluation. The levels of interleukin-1 (IL-1β), tumor necrosis factor (TNF-α), and interleukin-17F (IL-17F) in abdominal cavity and interleukin-6 (IL-6) in plasma were measured by enzyme-linked immunosorbent assay (ELISA) at 6 hours, 12 hours, 24 hours, and 1 week after operation. The tissue level of transforming growth factor beta-1 (TGF-β1) was also determined by ELISA on the seventh day after surgery. The expressions of collagen and TNF-α were, respectively, detected by Masson trichrome staining and immunohistochemical staining. The expression of TGF-β1 and alpha smooth muscle actin (α-SMA) was detected by Western blot. The result showed that Bletilla striata has obvious preventive effect on PPAs and celiac inflammation of PPAs. Bletilla striata could significantly reduce the level of IL-17F abdominal cavity and IL-6 in plasma. Masson trichrome staining and immunohistochemical staining results showed that Bletilla striata also decreased the expression of TNF-α and collagen. Western blot results showed that Bletilla striata decreased the expression of α-SMA and TGF-β1. Our results suggest that Bletilla striata decreased the development of abdominal adhesion in abrasion-induced model of rats and reduced the expression of the important substance which increased in PPAs. Bletilla striata can be further studied as a new and cheaper antiadhesive substance.

ERK1/2-Dependent Gene Expression Contributing to TGFβ-Induced Lens EMT

PURPOSE

This study aims to highlight some of the genes that are differentially regulated by ERK1/2 signaling in TGFβ-induced EMT in lens, and their potential contribution to this pathological process.

MATERIALS AND METHODS

Rat lens epithelial explants were cultured with or without TGFβ over a 3-day-culture period to induce EMT, in the presence or absence of UO126 (ERK1/2 signaling inhibitor), both prior to TGFβ-treatment, or 24 or 48 hours after TGFβ treatment. Smad2/3-nuclear immunolabeling was used to indicate active TGFβ signaling, and quantitative RT-PCR was used to analyze changes in the different treatment groups in expression of the following representative genes: TGFβ signaling (Smad7, Smurf1, and Rnf111), epithelial markers (Pax6, Cdh1, Zeb1, and Zeb2), cell survival/death regulators (Bcl2, Bax, and Bad) and lens mesenchymal markers (Mmp9, Fn1, and Col1a1), over the 3 days of culture.

RESULTS

ERK1/2 was found to regulate the expression of Smurf1, Smad7, Rnf11, Cdh1, Pax6, Zeb1, Bcl2, Bax, and Bad genes in lens cells. TGFβ signaling was evident by nuclear localization of Smad2/3 and this was effectively blocked by pre-treatment with UO126, but not by post-treatment with this ERK1/2 signaling inhibitor. TGFβ induced the expression of its signaling partners (Smad7, Smurf1, and Rnf111), as well as lens mesenchymal genes (Mmp9, Fn1, and Col1a1), consistent with its role in inducing an EMT. These TGFβ-responsive signaling genes, as well as the mesenchymal markers, were all positively regulated by ERK1/2-activity. The expression levels of the lens epithelial genes we examined, and genes that were associated with cell death/survival, were not directly impacted by TGFβ.

CONCLUSIONS

TGFβ-mediated ERK1/2 signaling positively modulates the expression of mesenchymal genes in lens epithelial explants undergoing EMT, in addition to regulating TGFβ-mediated regulatory genes. Independent of TGFβ, ERK1/2 activity can also regulate the expression of endogenous lens epithelial genes, highlighting its potential key role in regulation of both normal and pathological lens cellular processes.

Hypoxia, cytokines and stromal recruitment: parallels between pathophysiology of encapsulating peritoneal sclerosis, endometriosis and peritoneal metastasis

Peritoneal response to various kinds of injury involves loss of peritoneal mesothelial cells (PMC), danger signalling, epithelial-mesenchymal transition and mesothelial-mesenchymal transition (MMT). Encapsulating peritoneal sclerosis (EPS), endometriosis (EM) and peritoneal metastasis (PM) are all characterized by hypoxia and formation of a vascularized connective tissue stroma mediated by vascular endothelial growth factor (VEGF). Transforming growth factor-β1 (TGF-β1) is constitutively expressed by the PMC and plays a major role in the maintenance of a transformed, inflammatory micro-environment in PM, but also in EPS and EM. Persistently high levels of TGF-β1 or stimulation by inflammatory cytokines (interleukin-6 (IL-6)) induce peritoneal MMT, adhesion formation and fibrosis. TGF-β1 enhances hypoxia inducible factor-1α expression, which drives cell growth, extracellular matrix production and cell migration. Disruption of the peritoneal glycocalyx and exposure of the basement membrane release low molecular weight hyaluronan, which initiates a cascade of pro-inflammatory mediators, including peritoneal cytokines (TNF-α, IL-1, IL-6, prostaglandins), growth factors (TGF-α, TGF-β, platelet-derived growth factor, VEGF, epidermal growth factor) and the fibrin/coagulation cascade (thrombin, Tissue factor, plasminogen activator inhibitor [PAI]-1/2). Chronic inflammation and cellular transformation are mediated by damage-associated molecular patterns, pattern recognition receptors, AGE-RAGE, extracellular lactate, pro-inflammatory cytokines, reactive oxygen species, increased glycolysis, metabolomic reprogramming and cancer-associated fibroblasts. The pathogenesis of EPS, EM and PM shows similarities to the cellular transformation and stromal recruitment of wound healing.

Anti-fibrotic effects of valproic acid in experimental peritoneal fibrosis

Background

Progressive fibrous thickening of the peritoneal membrane is a complication of long-term peritoneal dialysis (PD). TGF-β/Smad pathway activation, inflammation, and neoangiogenesis play important roles in peritoneal membrane (PM) changes induced by PD. Recently, histone deacetilase inhibitors (HDACi) have shown anti-fibrotic and anti-inflammatory effects in different experimental models. These drugs prevent deacetylation of histones causing a loosen chromatin, which in turn induce the expression of some anti-fibrotic genes. In addition, acetylation may increase the activity of proteins involved in tissue fibrosis, such as Smad7. Here, we explored the effect of valproic acid (VPA), an HDACi, on the development of peritoneal fibrosis (PF) in rats.

Methods

PF was induced by daily intraperitoneal injections of 0.1% chlorhexidine gluconate (CG) for 15 consecutive days. Male Wistar rats (250–300 g) were divided into 3 groups: CONTROL, control rats receiving only vehicle; PF, peritoneal fibrosis induced in rats; PF+VPA, rats with PF treated with VPA (300 mg/kg/day by gavage). PF was assessed by Masson’s trichrome staining. Inflammation and fibrosis-associated factors were assessed by immunohistochemistry, immunofluorescence, multiplex analysis, and qPCR.

Results

Treatment with VPA significantly reduced PM thickness and the expression of myofibroblasts, besides preventing loss of ultrafiltration capacity of the PM. The upregulation of profibrotic factors (TGF-β, fibronectin, and Smad3) in the PF group was significantly ameliorated by VPA. VPA modulated the TGF/Smad pathway, inhibiting phosphorylated Smad3 expression and inducing an increased Smad7 expression in the FP+VPA group. The neoangiogenesis and the expression of proinflammatory cytokines (TNF-α, IL-1β, MCP-1) observed in the PF group was significantly reduced by VPA.

Conclusions

Our results indicate that VPA suppressed experimental PF through modulation of the TGF-β/Smad pathway. Interestingly, VPA treatment induced a higher expression of antifibrotic factors, such as Smad7. These results suggest that VPA may represent a potential strategy for treating long term PD complications.

A prospective, proteomics study identified potential biomarkers of encapsulating peritoneal sclerosis in peritoneal effluent

Encapsulating peritoneal sclerosis (EPS) is a potentially devastating complication of peritoneal dialysis (PD). Diagnosis is often delayed due to the lack of effective and accurate diagnostic tools. We therefore examined peritoneal effluent for potential biomarkers that could predict or confirm the diagnosis of EPS and would be valuable in stratifying at-risk patients and driving appropriate interventions. Using prospectively collected samples from the Global Fluid Study and a cohort of Greek PD patients, we utilized 2D SDSPAGE/ MS and iTRAQ to identify changes in the peritoneal effluent proteome from patients diagnosed with EPS and controls matched for treatment exposure. We employed a combinatorial peptide ligand library to compress the dynamic range of protein concentrations to aid identification of low-abundance proteins. In patients with stable membrane function, fibrinogen γ-chain and heparan sulphate proteoglycan core protein progressively increased over time on PD. In patients who developed EPS, collagen-α1(I), γ-actin and Complement factors B and I were elevated up to five years prior to diagnosis. Orosomucoid-1 and a2-HS-glycoprotein chain-B were elevated about one year before diagnosis, while apolipoprotein A-IV and α1-antitrypsin were decreased compared to controls. Dynamic range compression resulted in an increased number of proteins detected with improved resolution of protein spots, compared to the full fluid proteome. Intelectin-1, dermatopontin, gelsolin, and retinol binding protein-4 were elevated in proteome-mined samples from patients with EPS compared to patients that had just commenced peritoneal dialysis. Thus, prospective analysis of peritoneal effluent uncovered proteins indicative of inflammatory and pro-fibrotic injury worthy of further evaluation as diagnostic/prognostic markers.

Targeted AAV5-Smad7 gene therapy inhibits corneal scarring in vivo

Corneal scarring is due to aberrant activity of the transforming growth factor β (TGFβ) signaling pathway following traumatic, mechanical, infectious, or surgical injury. Altered TGFβ signaling cascade leads to downstream Smad (Suppressor of mothers against decapentaplegic) protein-mediated signaling events that regulate expression of extracellular matrix and myogenic proteins. These events lead to transdifferentiation of keratocytes into myofibroblasts through fibroblasts and often results in permanent corneal scarring. Hence, therapeutic targets that reduce transdifferentiation of fibroblasts into myofibroblasts may provide a clinically relevant approach to treat corneal fibrosis and improve long-term visual outcomes. Smad7 protein regulates the functional effects of TGFβ signaling during corneal wound healing. We tested that targeted delivery of Smad7 using recombinant adeno-associated virus serotype 5 (AAV5-Smad7) delivered to the corneal stroma can inhibit corneal haze post photorefractive keratectomy (PRK) in vivo in a rabbit corneal injury model. We demonstrate that a single topical application of AAV5-Smad7 in rabbit cornea post-PRK led to a significant decrease in corneal haze and corneal fibrosis. Further, histopathology revealed lack of immune cell infiltration following AAV5-Smad7 gene transfer into the corneal stroma. Our data demonstrates that AAV5-Smad7 gene therapy is relatively safe with significant potential for the treatment of corneal disease currently resulting in fibrosis and impaired vision.

Active compounds extracted from extra virgin olive oil counteract mesothelial-to-mesenchymal transition of peritoneal mesothelium cells exposed to conventional peritoneal dialysate: in vitro and in vivo evidences

During peritoneal dialysis (PD), peritoneal mesothelial cells undergo a transition from an epithelial phenotype to a mesenchymal phenotype that, together with the inflammatory process, promotes tissue fibrosis and a failure of peritoneal membrane function. To date, there is no definitive treatment for the progressive thickening and angiogenesis of the peritoneal membrane associated with PD. In this study we tested, in vitro and in vivo, the ability of active compounds extracted from extra virgin olive oil (AC-EVOO) to counteract the mesothelial-to-mesenchymal transition process (MMT) observed in mesothelial cells chronically exposed to the conventional peritoneal dialysate (DL). In particular, we used a cultivar from southern Italy known to have a high polyphenol content. Our results showed that, in mesothelial cells exposed to DL, the combined treatment with AC-EVOO prevented the genic and protein upregulation of key mesenchymal and inflammatory markers, as well as the MCs' migratory capacity. Concomitantly, we tested the antifibrotic efficacy of AC-EVOO in mesothelial cells obtained from effluents of patients undergoing PD, whose "fibroblast-like" phenotype was defined by flow-cytometry assay. We observed that in these cells AC-EVOO significantly mitigated, but did not reverse, the MMT process. In conclusion, our preliminary results suggest that AC-EVOO can interfere with critical factors in the process of differentiation, preventing myofibroblast formation, but once fibrosis has already progressed it is unable to promote the redifferentiation to the epithelial phenotype. Further studies are needed to establish whether AC-EVOO could represent a new therapeutic target to prevent peritoneal fibrosis.

Diverse properties of the mesothelial cells in health and disease

Mesothelial cells (MCs) form the superficial anatomic layer of serosal membranes, including pleura, pericardium, peritoneum, and the tunica of the reproductive organs. MCs produce a protective, non-adhesive barrier against physical and biochemical damages. MCs express a wide range of phenotypic markers, including vimentin and cytokeratins. MCs play key roles in fluid transport and inflammation, as reflected by the modulation of biochemical markers such as transporters, adhesion molecules, cytokines, growth factors, reactive oxygen species and their scavengers. MCs synthesize extracellular matrix related molecules, and the surface of MC microvilli secretes a highly hydrophilic protective barrier, "glycocalyx", consisting mainly of glycosaminoglycans. MCs maintain a balance between procoagulant and fibrinolytic activation by producing a whole range of regulators, can synthetize fibrin and therefore form adhesions. Synthesis and recognition of hyaluronan and sialic acids might be a new insight to explain immunoactive and immunoregulatory properties of MCs. Epithelial to mesenchymal transition of MCs may involve serosal repair and remodeling. MCs might also play a role in the development and remodeling of visceral adipose tissue. Taken together, MCs play important roles in health and disease in serosal cavities of the body. The mesothelium is not just a membrane and should be considered as an organ.

Molecular insights on the effect of TGF-β1/-β3 in human corneal fibroblasts

Transforming growth factor β (TGF-β) plays a critical role in wound healing and the pathogenesis of fibrosis (scarring). Three isoforms of TGF-β have been identified in mammals. Previous studies have shown that the addition of TGF-β1 (T1) or -β2 (T2) to human corneal fibroblasts (HCF) cultured in a 3-dimensional construct resulted in a fibrotic matrix, while the addition of TGF-β3 (T3) resulted in the production of enhanced non-fibrotic matrix as compared to control (Vitamin C [VitC] only). In the current investigation, we undertook the molecular comparison of fibrosis-related gene expression in T1 or T3-treated HCF to gain further insights into the regulation and roles of these two isoforms on the fibrotic response. HCF were cultured in 100 mm dishes in basic medium (Eagles minimum essential medium [EMEM] with 10% fetal bovine serum [FBS]). At 70-80% confluency, cells were exposed to basic medium with 0.5 mM 2-O-α-d-glucopyranosyl-l-ascorbic acid (VitC) ± 2 ng/ml of T1 or T3. After 4 h or 3 days, cells were harvested, and mRNA or protein was isolated. Fibrosis related mRNA levels were assayed using a commercial qRT-PCR Array. Selected proteins were examined using Western blotting (WB). Experiments were performed 6 times for the qRT-PCR and 4 times for WB for each condition. qRT-PCR results showed that most of the fibrosis-related genes were up or downregulated in HCF exposed to T1 or T3 as compared with VitC control. At 4 h, only Smad7 expression was significantly altered in T3-treated HCF, compared to T1, and at 3 days, five genes were altered. WB confirmed that T1 significantly decreased Smad7 expression compared to T3 and control, and that the expression of thrombospondin-1 in T3-stimulated HCF was enhanced compared to T1-treated cells. Finally, both T1 and T3 decreased Smad3 expression dramatically at both time points. At early time points, T1 and T3 have similar effects on expression of fibrosis related genes; however, with a longer exposure, an increasing number of genes were differentially expressed. Interestingly, most of the differentially expressed gene products are secreted by the cells and may be related to the modulation of extracellular matrix.

Inhibition of EGF Receptor Blocks the Development and Progression of Peritoneal Fibrosis

Inhibitors of EGF receptor (EGFR) have antifibrotic effects in several organs, but the effect of these inhibitors on the development of peritoneal fibrosis is unknown. Here, we explored the therapeutic effect of gefitinib, a specific inhibitor of EGFR, on the development and progression of peritoneal fibrosis in a rat model. Daily intraperitoneal injections of chlorhexidine gluconate induced peritoneal fibrosis, indicated by thickening of the submesothelial area with an accumulation of collagen fibrils and activation of myofibroblasts, accompanied by time-dependent phosphorylation of EGFR. Administration of gefitinib immediately after injury prevented the onset of peritoneal fibrosis and delayed administration after the onset of peritoneal fibrosis halted fibrosis progression. Gefitinib treatment abrogated the increased phosphorylation of EGFR, Smad3, signal transducer and activator of transcription 3, and NF-κB during peritoneal fibrosis; it also inhibited the accompanying overproduction of TGF-β1 and proinflammatory cytokines and the infiltration of macrophages to the injured peritoneum. Moreover, gefitinib significantly reduced the peritoneal increase of CD31-positive blood vessels and vascular EGF-positive cells after injury. Finally, gefitinib also attenuated high glucose-induced peritoneal fibrosis in rats and abrogated TGF-β1-induced phosphorylation of Smad3 and the epithelial-to-mesenchymal transition of cultured human peritoneal mesothelial cells. These results demonstrate that EGFR contributes to peritoneal fibrosis, inflammation, and angiogenesis, suggesting that EGFR inhibitors may have therapeutic potential in attenuating peritoneal fibrosis.

Endoplasmic reticulum stress as a novel target to ameliorate epithelial-to-mesenchymal transition and apoptosis of human peritoneal mesothelial cells

Epithelial-to-mesenchymal transition (EMT) and apoptosis of peritoneal mesothelial cells are known to be the earliest mechanisms of peritoneal fibrosis in peritoneal dialysis (PD). Endoplasmic reticulum (ER) stress with an unfolded protein response is regarded to have a role in the development of organ fibrosis. To investigate the potential role of ER stress as a target to prevent and/or delay the development of peritoneal fibrosis, we examined the effect of ER stress on EMT or apoptosis of human peritoneal mesothelial cells (HPMCs) and elucidated the mechanisms underlying the protective effect of ER stress preconditioning on TGF-β1-induced EMT. ER stress inducers, tunicamycin (TM) and thapsigargin (TG), induced EMT with Smad2/3 phosphorylation, an increased nuclear translocation of β-catenin and Snail expression. Low concentrations of TM and TG did not induce apoptosis within 48 h; however, high concentrations of TM- (>1 ng/ml) and TG- (>1 nM) induced apoptosis at 12 h with a persistent increase in C/EBP homologous protein. TGF-β1 induced EMT and apoptosis in HPMCs, which was ameliorated by taurine-conjugated ursodeoxycholic acid, an ER stress blocker. Interestingly, pre-treatment with TM or TG for 4 h also protected the cells from TGF-β1-induced EMT and apoptosis, demonstrating the role of ER stress as an adaptive response to protect HPMCs from EMT and apoptosis. Peritoneal mesothelial cells isolated from PD patients displayed an increase in GRP78/94, which was correlated with the degree of EMT. These findings suggest that the modulation of ER stress in HPMCs could serve as a novel approach to ameliorate peritoneal damage in PD patients.

The PPARβ/δ agonist GW501516 attenuates peritonitis in peritoneal fibrosis via inhibition of TAK1-NFκB pathway in rats

Peritoneal fibrosis is a common consequence of long-term peritoneal dialysis (PD), and peritonitis is a factor in its onset. Agonist-bound peroxisome proliferator-activated receptors (PPARs) function as key regulators of energy metabolism and inflammation. Here, we examined the effects of PPARβ/δ agonist GW501516 on peritonitis in a rat peritoneal fibrosis model. Peritoneal fibrosis secondary to inflammation was induced into uremic rats by daily injection of Dianeal 4.25% PD solutions along with six doses of lipopolysaccharide before commencement of GW501516 treatment. Normal non-uremic rats served as control, and all rats were fed with a control diet or a GW501516-containing diet. Compared to control group, exposure to PD fluids caused peritoneal fibrosis that was accompanied by increased mRNA levels of monocyte chemoattractant protein-1, tumor necrotic factor-α, and interleukin-6 in the uremic rats, and these effects were prevented by GW501516 treatment. Moreover, GW501516 was found to attenuate glucose-stimulated inflammation in cultured rat peritoneal mesothelial cells via inhibition of transforming growth factor-β-activated kinase 1 (TAK1), and nuclear factor kappa B (NFκB) signaling pathway (TAK1-NFκB pathway), a main inflammation regulatory pathway. In conclusion, inhibition of TAK1-NFκB pathway with GW501516 may represent a novel therapeutic approach to ameliorate peritonitis-induced peritoneal fibrosis for patients on PD.

AKT regulation of mesothelial-to-mesenchymal transition in peritoneal dialysis is modulated by Smurf2 and deubiquitinating enzyme USP4

Background

Transforming growth factor-β1 (TGF-β1) plays a key role in mesothelial-to-mesenchymal transition (MMT) during peritoneal dialysis (PD). However, the role of Akt in MMT transformation in PD is not clear.

Results

In this study, we observed that the phosphorylated form of protein kinase B (Akt), termed as pAkt, was up-regulated in the peritoneum of mice undergoing PD. It was associated with thickening of the peritoneum and up-regulation of TGF-β1. Upregulation of pAkt paralleled with the increased expression of Smad ubiquitination regulatory factor 2 (Smurf2), Vimentin and fibronectin (FN), and decreased expression of mothers against decapentaplegic homolog 7 (Smad7) and Zonula Occludens protein 1(ZO-1) in mice undergoing PD treatment and in TGF-β1 induced human peritoneal mesothelial cells (HPMCs). These changes were reversed with the treatment of a PI3K/Akt inhibitor LY294002 in vivo or in cells transfected with Akt dominant-negative (Akt-DN) plasmids in vitro. Increased Smurf2 expression in HPMCs, induced by TGF-β1 was accompanied with altered expression of Transforming growth factor receptor I (TβR-I), Smad7, ZO-1, Vimentin and FN via Akt modulation. In addition, inhibition of Ubiquitin carboxyl-terminal hydrolase 4 (USP4) decreased TGF- β1-induced expression of TβR-I and reversed the altered expression of Smad7, Smurf2, ZO-1 and Vimentin. Moreover, TGF-β1 accentuated the interactions between Smurf2 and Smad7, while reduced the association between TβR-I and Smurf2. These interactions were reversed by the treatment of Akt-DN and USP4 siRNA, respectively.

Conclusions

These data implied that Akt mediated MMT in PD via Smurf2 modulation/and or Smad7 degradation while conceivably maintaining the TβRI stability, most likely by the USP4.

Increased peritoneal damage in glyoxalase 1 knock-down mice treated with peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is limited by peritoneal fibrosis and ultrafiltration failure. This is in part caused by the high concentration of glucose degradation products (GDPs) present in PD fluids (PDF) as a consequence of heat sterilization. Existing research in long-term PD has mainly dealt with the toxicity induced by GDPs and the development of therapeutic strategies to reduce the cellular burden of GDPs. Currently, there are few data regarding the potential role of detoxification systems of GDP in PD. In this study, the role of glyoxalase 1 (Glo1), the major detoxification pathway for dicarbonyl-derived GD such as methylglyoxal (MG) and glyoxal (Gx), was investigated in vivo using heterozygous knock-down mice for Glo1 (Glo1(-/+)).

METHODS

Wild-type (WT) and Glo1(-/+) mice were repeatedly treated with PDF containing low and high amounts of GDP, particularly with respect to the content of dicarbonyls. After 12 weeks of treatment with PDF, peritoneal damage and function were evaluated.

RESULTS

Glo1(-/+) mice treated with PDF showed increased formation of advanced glycation endproduct (AGE) when compared with WT mice, particularly the Gx-derived AGE, carboxymethyl-lysine. This was associated with increased inflammation, neovascularization, increased peritoneal fibrosis and impaired peritoneal function.

CONCLUSIONS

This study suggests a pivotal and underestimated role for Glo1 as a detoxifying enzyme in GDP-associated peritoneal toxicity in PD. The indirect and direct modulation of Glo1 may therefore offer a new therapeutic option in prevention of GDP-induced peritoneal damage in PD.

MicroRNA-29b inhibits peritoneal fibrosis in a mouse model of peritoneal dialysis

TGF-β/Smad3 signaling plays a pivotal role in the pathogenesis of peritoneal fibrosis associated with peritoneal dialysis (PD). MicroRNA-29 (miR-29) is known as a potent downstream inhibitor of TGF-β/Smad3 in renal fibrosis. In this study, we examined the therapeutic potential for miR-29b on PD-related peritoneal fibrosis in a mouse model of PD induced by daily infusion of 4.25% dextrose-containing PD fluid (PDF). MiR-29b-expressing plasmid was delivered into the peritoneum via an ultrasound-microbubble-mediated system before and at day 14 after PDF. We found that mice on PD developed peritoneal fibrosis with impaired peritoneal function, which was associated with a loss of miR-29b. In contrast, overexpression of miR-29b before the PDF infusion showed a protective effect on peritoneal fibrosis including EMT and prevented peritoneal dysfunction. Moreover, delayed miR-29b treatment until peritoneal fibrosis was established at day 14 also halted the progression of peritoneal fibrosis at day 28. Further studies identified that blockade of the Sp1-TGF-β/Smad3 pathway may be a mechanism by which miR-29b inhibited peritoneal fibrosis. In conclusion, treatment with miR-29b may represent a novel and effective therapy for PD-associated peritoneal fibrosis.

Compare the effects of intravenous and intraperitoneal mesenchymal stem cell transplantation on ultrafiltration failure in a rat model of chronic peritoneal dialysis

AIM

The purpose of this study was to compare the possible healing effects of intraperitoneal (IP) and intravenous (IV) mesenchymal stem cell (MSC) transplantation on ultrafiltration failure (UFF) in a chronic rat model of peritoneal dialysis (PD).

METHODS

Rats were initially divided into two groups. The UFF-group received once-daily IP injections of 20 mL of 3.86% glucose PD solution for six weeks to stimulate the development of UFF, and a control group received no injections. The UFF group was sub-divided into four groups: an UFF-C group, a MSC-IP group, a MSC-IV group and a placebo (P) group. Peritoneal equilibration tests (PETs) and peritoneal biopsies were performed in the control and UFF-C groups. MSCs were administered by IP injection in the MSC-IP group and by IV injection in the MSC-IV group. The P group received IP injection of placebo. PETs and peritoneal biopsies were performed in the MSC-IP, MSC-IV and P groups at the three weeks after receiving MSCs or placebo.

RESULTS

When compared with the control group, ultrafiltration capacity significantly decreased, and the submesothelial thickness increased in the UFF-C and P group, but there were no differences between the control and MSC-IP and MSC-IV groups. The rate of glucose transport was high in the UFF-C and P group compared with the control group, and D/PCr rates in the UFF-C and P group were lower than in the control group. However, D/D0glucose was higher and D/PCr was lower in the MSC-IP group than in the UFF-C and P groups, but D/D0glucose rate of MSC-IV group similar to UFF-C and P groups and there was no difference between MSC-IV group and the other groups in terms of D/PCr rates. The MSC-IP, MSC-IV and P groups had significantly decreased tumor necrosis factor α concentrations compared with the UFF-C group. MSC-IP group had lower levels of TGF-β1 compared with the P group; MSC-IP group had also lower levels of interleukin-6 compared with UFF-C group.

CONCLUSION

The UFF group had a high permeability UFF. These results showed that IV and IP MSC transplantation exerted positive effects on UFF in a chronic rat model of PD. However, healing effect of small solute transport in MSC-IP group was better than MSC-IV group. IP MSC transplantation may be more effective than IV MSC transplantation for the renewal of the peritoneum in chronic PD patients with UFF.

Nanotechnology and adeno-associated virus-based decorin gene therapy ameliorates peritoneal fibrosis

Peritoneal dialysis (PD) is a life-sustaining therapy for end-stage renal disease (ESRD), used by 10-15% of the dialysis population worldwide. Peritoneal fibrosis (PF) is a known complication of long-term PD and frequently follows episodes of peritonitis, rendering the peritoneal membrane inadequate for dialysis. Transforming growth factor (TGF)-β is an inducer of fibrosis in several tissues and organs, and its overexpression has been correlated with PF. Animal models of peritonitis have shown an increase in expression of TGF-β in the peritoneal tissue. Decorin, a proteoglycan and component of the extracellular matrix, inactivates TGF-β, consequently reducing fibrosis in many tissues. Recently, gold nanoparticles (GNP) have been used for drug delivery in a variety of settings. In the present study, we tested the possibility that GNP-delivered decorin gene therapy ameliorates zymosan-mediated PF. We created a PF model using zymosan-induced peritonitis. Rats were treated with no decorin, GNP-decorin, or adeno-associated virus-decorin (AAV-decorin) and compared with controls. Tissue samples were then stained for Masson's trichrome, enface silver, and hematoxylin and eosin, and immunohistochemistry was carried out with antibodies to TGF-β1, α-smooth muscle actin (α-SMA), and VEGF. Animals which were treated with GNP-decorin and AAV-decorin gene therapy had significant reductions in PF compared with untreated animals. Compared with untreated animals, the treated animals had better preserved peritoneal mesothelial cell size, a significant decrease in peritoneal thickness, and decreased α-SMA. Quantitative PCR measurements showed a significant decrease in the peritoneal tissue levels of α-SMA, TGF-β, and VEGF in treated vs. untreated animals. This study shows that both GNP-delivered and AAV-mediated decorin gene therapies significantly decrease PF in vivo in a rodent model. This approach has important clinical translational potential in providing a therapeutic strategy to prevent PF in PD patients.

A pathogenetic role for endothelin-1 in peritoneal dialysis-associated fibrosis

In patients undergoing peritoneal dialysis (PD), chronic exposure to nonphysiologic PD fluids elicits low-grade peritoneal inflammation, leading to fibrosis and angiogenesis. Phenotype conversion of mesothelial cells into myofibroblasts, the so-called mesothelial-to-mesenchymal transition (MMT), significantly contributes to the peritoneal dysfunction related to PD. A number of factors have been described to induce MMT in vitro and in vivo, of which TGF-β1 is probably the most important. The vasoconstrictor peptide endothelin-1 (ET-1) is a transcriptional target of TGF-β1 and mediates excessive scarring and fibrosis in several tissues. This work studied the contribution of ET-1 to the development of peritoneal damage and failure in a mouse model of PD. ET-1 and its receptors were expressed in the peritoneal membrane and upregulated on PD fluid exposure. Administration of an ET receptor antagonist, either bosentan or macitentan, markedly attenuated PD-induced MMT, fibrosis, angiogenesis, and peritoneal functional decline. Adenovirus-mediated overexpression of ET-1 induced MMT in human mesothelial cells in vitro and promoted the early cellular events associated with peritoneal dysfunction in vivo. Notably, TGF-β1-blocking peptides prevented these actions of ET-1. Furthermore, a positive reciprocal relationship was observed between ET-1 expression and TGF-β1 expression in human mesothelial cells. These results strongly support a role for an ET-1/TGF-β1 axis as an inducer of MMT and subsequent peritoneal damage and fibrosis, and they highlight ET-1 as a potential therapeutic target in the treatment of PD-associated dysfunction.

Opposing roles for Smad2 and Smad3 in peritoneal fibrosis in vivo and in vitro

Peritoneal fibrosis is a major cause of ultrafiltration failure in patients receiving continuous ambulatory peritoneal dialysis. Transforming growth factor (TGF)-β1 is an important mediator in this process; however, its signaling mechanisms had not been explored. Thus, we examined TGF-β1/Smad signaling in human peritoneal biopsy specimens associated with continuous ambulatory peritoneal dialysis. We found that TGF-β/Smad2/3 signaling was highly activated in patients with increased collagen deposition and thickening of the peritoneal membrane who were receiving continuous ambulatory peritoneal dialysis. Long-term exposure of wild-type mice to 4.25% peritoneal dialysis solution for 30 days induced significant peritoneal fibrosis with impaired peritoneal equilibrium, which was prevented in Smad3 knockout mice. In contrast, conditional Smad2 gene deletion in the peritoneum exacerbated peritoneal fibrosis and dysfunction. The contrasting roles of Smad2 and Smad3 in peritoneal fibrosis were also examined in vitro. Cultured mesothelial cells from Smad3 knockout mice were resistant to TGF-β1-induced collagen I production and the transition toward a myofibroblast phenotype as seen in wild-type cells, whereas Smad2 deficiency in mesothelial cells failed to modulate the profibrotic response to TGF-β1. In conclusion, this study found activation of TGF-β/Smad signaling in peritoneal fibrosis in patients receiving continuous ambulatory peritoneal dialysis and identifies opposing roles for Smad2 and Smad3 in peritoneal dialysis-associated peritoneal fibrosis. These findings provide a mechanistic basis for future therapies targeting TGF-β/Smad signaling in peritoneal fibrosis.

Mesenchymal Conversion of Mesothelial Cells Is a Key Event in the Pathophysiology of the Peritoneum during Peritoneal Dialysis

Peritoneal dialysis (PD) is a therapeutic option for the treatment of end-stage renal disease and is based on the use of the peritoneum as a semipermeable membrane for the exchange of toxic solutes and water. Long-term exposure of the peritoneal membrane to hyperosmotic PD fluids causes inflammation, loss of the mesothelial cells monolayer, fibrosis, vasculopathy, and angiogenesis, which may lead to peritoneal functional decline. Peritonitis may further exacerbate the injury of the peritoneal membrane. In parallel with these peritoneal alterations, mesothelial cells undergo an epithelial to mesenchymal transition (EMT), which has been associated with peritoneal deterioration. Factors contributing to the bioincompatibility of classical PD fluids include the high content of glucose/glucose degradation products (GDPs) and their acidic pH. New generation low-GDPs-neutral pH fluids have improved biocompatibility resulting in better preservation of the peritoneum. However, standard glucose-based fluids are still needed, as biocompatible solutions are expensive for many potential users. An alternative approach to preserve the peritoneal membrane, complementary to the efforts to improve fluid biocompatibility, is the use of pharmacological agents protecting the mesothelium. This paper provides a comprehensive review of recent advances that point to the EMT of mesothelial cells as a potential therapeutic target to preserve membrane function.

Mesenchymal stem cells ameliorate experimental peritoneal fibrosis by suppressing inflammation and inhibiting TGF-β1 signaling

Mesenchymal stem cells (MSCs) are multipotent adult stem cells that have regenerative capability and exert paracrine actions on damaged tissues. Since peritoneal fibrosis is a serious complication of peritoneal dialysis, we tested whether MSCs suppress this using a chlorhexidine gluconate model in rats. Although MSCs isolated from green fluorescent protein–positive rats were detected for only 3 days following their injection, immunohistochemical staining showed that MSCs suppressed the expression of mesenchymal cells, their effects on the deposition of extracellular matrix proteins, and the infiltration of macrophages for 14 days. Moreover, MSCs reduced the functional impairment of the peritoneal membrane. Cocultures of MSCs and human peritoneal mesothelial cells using a Transwell system indicated that the beneficial effects of MSCs on the glucose-induced upregulation of transforming growth factor-β1(TGF-β1) and fibronectin mRNA expression in the human cells were likely due to paracrine actions. Preincubation in MSC-conditioned medium suppressed TGF-β1-induced epithelial-to-mesenchymal transition, α-smooth muscle actin, and the decrease in zonula occludens-1 in cultured human peritoneal mesothelial cells. Although bone morphogenic protein 7 was not detected, MSCs secreted hepatocyte growth factor and a neutralizing antibody to this inhibited TGF-β1 signaling. Thus, our findings imply that MSCs ameliorate experimental peritoneal fibrosis by suppressing inflammation and TGF-β1 signaling in a paracrine manner.

Transcriptional patterns in peritoneal tissue of encapsulating peritoneal sclerosis, a complication of chronic peritoneal dialysis

Encapsulating peritoneal sclerosis (EPS) is a devastating complication of peritoneal dialysis (PD), characterized by marked inflammation and severe fibrosis of the peritoneum, and associated with high morbidity and mortality. EPS can occur years after termination of PD and, in severe cases, leads to intestinal obstruction and ileus requiring surgical intervention. Despite ongoing research, the pathogenesis of EPS remains unclear. We performed a global transcriptome analysis of peritoneal tissue specimens from EPS patients, PD patients without EPS, and uremic patients without history of PD or EPS (Uremic). Unsupervised and supervised bioinformatics analysis revealed distinct transcriptional patterns that discriminated these three clinical groups. The analysis identified a signature of 219 genes expressed differentially in EPS as compared to PD and Uremic groups. Canonical pathway analysis of differentially expressed genes showed enrichment in several pathways, including antigen presentation, dendritic cell maturation, B cell development, chemokine signaling and humoral and cellular immunity (P value<0.05). Further interactive network analysis depicted effects of EPS-associated genes on networks linked to inflammation, immunological response, and cell proliferation. Gene expression changes were confirmed by qRT-PCR for a subset of the differentially expressed genes. EPS patient tissues exhibited elevated expression of genes encoding sulfatase1, thrombospondin 1, fibronectin 1 and alpha smooth muscle actin, among many others, while in EPS and PD tissues mRNAs encoding leptin and retinol-binding protein 4 were markedly down-regulated, compared to Uremic group patients. Immunolocalization of Collagen 1 alpha 1 revealed that Col1a1 protein was predominantly expressed in the submesothelial compact zone of EPS patient peritoneal samples, whereas PD patient peritoneal samples exhibited homogenous Col1a1 staining throughout the tissue samples. The results are compatible with the hypothesis that encapsulating peritoneal sclerosis is a distinct pathological process from the simple peritoneal fibrosis that accompanies all PD treatment.

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.

Benfotiamine protects against peritoneal and kidney damage in peritoneal dialysis

Residual renal function and the integrity of the peritoneal membrane contribute to morbidity and mortality among patients treated with peritoneal dialysis. Glucose and its degradation products likely contribute to the deterioration of the remnant kidney and damage to the peritoneum. Benfotiamine decreases glucose-induced tissue damage, suggesting the potential for benefit in peritoneal dialysis. Here, in a model of peritoneal dialysis in uremic rats, treatment with benfotiamine decreased peritoneal fibrosis, markers of inflammation, and neovascularization, resulting in improved characteristics of peritoneal transport. Furthermore, rats treated with benfotiamine exhibited lower expression of advanced glycation endproducts and their receptor in the peritoneum and the kidney, reduced glomerular and tubulointerstitial damage, and less albuminuria. Increased activity of transketolase in tissue and blood contributed to the protective effects of benfotiamine. In primary human peritoneal mesothelial cells, the addition of benfotiamine led to enhanced transketolase activity and decreased expression of advanced glycation endproducts and their receptor. Taken together, these data suggest that benfotiamine protects the peritoneal membrane and remnant kidney in a rat model of peritoneal dialysis and uremia.

Synergistic attenuation of myocardial fibrosis in spontaneously hypertensive rats by joint treatment with benazepril and candesartan

Benazepril, an angiotensin-converting enzyme inhibitor, and candesartan, an angiotensin receptor blocker, are common drugs for treating hypertension. This study aimed to investigate the enhanced attenuation of myocardial fibrosis in spontaneously hypertensive rats (SHRs) possibly induced by joint treatment with benazepril and candesartan and the possible involvement of transforming growth factor beta1 (TGF-beta1)-Smad signaling pathway. SHRs were treated with benazepril at 10 mg.kg.d, candesartan at 4 mg.kg.d, and a combination of 2 drugs at half dose, respectively, for 12 weeks. Echocardiography and histology indicated that joint treatment with 2 drugs more significantly inhibited myocardial fibrosis in SHRs than either monotherapy, as evidenced by the changes in cardiac structural parameters, ultrasonic integrated backscatters, collagen volume fraction, and perivascular collagen area. The collagen analyses further revealed that significant decreases in total collagen concentration, the ratio of collagen type I to type III, and collagen cross-linking were found after the enhanced attenuation of myocardial fibrosis. Western blot analysis showed that the protein expression of TGF-beta1 and Smad3 was significantly decreased after joint treatment with 2 drugs. We conclude that synergistic attenuation of myocardial fibrosis in SHRs is produced by combined use of benazepril and candesartan possibly through the modulation of TGF-beta/Smad signaling proteins.

Non-viral Smad7 gene delivery and attenuation of postoperative peritoneal adhesion in an experimental model

BACKGROUND

Postoperative intra-abdominal adhesion is associated with high morbidity and mortality. Smad7, a protein that occupies a strategic position in fibrogenesis, inhibits the transforming growth factor (TGF) beta/Smad signalling pathway. In this study the therapeutic potential of exogenous Smad7 in preventing fibrogenesis in postoperative intra-abdominal adhesion was investigated.

METHODS

Intra-abdominal adhesion was induced in a rodent model by peritoneal abrasion. Smad7 was delivered into the peritoneal cavity by a non-viral ultrasound-microbubble-mediated naked gene transfection system. The effect of Smad7 transgene on adhesion formation was studied by measuring changes in TGF-beta, fibrogenic factors, alpha-SMA and Smad2/3 activation in the anterior abdominal wall.

RESULTS

Four weeks after surgical abrasion, all rats developed significant peritoneal adhesion with enhanced TGF-beta expression, increased levels of extracellular matrix components and activated myofibroblasts, accompanied by decreased Smad7 expression and increased Smad2/3 activation. In rats treated with the Smad7 transgene, the incidence and severity of peritoneal adhesion were significantly reduced, with biochemical downregulation of fibrogenic factors and inhibition of Smad2/3 activation. Serial quantitation using magnetic resonance imaging revealed a significant reduction in adhesion areas from day 14 onwards.

CONCLUSION

Ultrasound-microbubble-mediated gene transfection provides timely targeted gene delivery for the treatment of postoperative peritoneal adhesions.

Impaired TGF-beta signalling enhances peritoneal inflammation induced by E. coli in rats

BACKGROUND

Peritonitis is a common and severe complication of peritoneal dialysis (PD). Although TGF-beta is a key mediator in peritoneal fibrosis with chronic PD, its role in acute peritoneal inflammation remains unclear.

METHODS

Potential role of TGF-beta signalling in acute peritonitis was investigated in a rat model by infecting peritoneum with E. coli and in primary culture of peritoneal mesothelial cells (PMC) by LPS.

RESULTS

We found that a single infection of E. coli caused an acute, but transient peritonitis by a significant increase in ascites white blood cells (WBC), peritoneal CD45+ leukocytes, upregulation of TNFalpha, activation of NF-kappaB/p65 and impaired peritoneal function (all P < 0.01). Interestingly, spontaneous recovery of acute peritonitis occurred with upregulation of TGF-beta1 and activation of Smad2/3, suggesting a protective role of TGF-beta signalling in acute peritonitis. This was demonstrated by the finding that blockade of the TGF-beta signalling pathway with gene transfer of Smad7 inactivated peritoneal Smad2/3 but worsened E. coli-induced, NF-kappaB-dependent peritoneal inflammation and peritoneal dysfunction (all P < 0.01). Furthermore, studies in vitro also found that impaired TGF-beta signalling by overexpressing Smad7 in PMC were able to overcome the inhibitory effect of TGF-beta on LPS-induced, NF-kappaB-mediated peritoneal inflammation.

CONCLUSION

Results from this study demonstrate that TGF-beta signalling is essential in protection against acute peritoneal inflammation induced by bacterial infection.

Treatment of established peritoneal fibrosis by gene transfer of Smad7 in a rat model of peritoneal dialysis

BACKGROUND/AIMS

It has been shown that blockade of TGF-beta1 signaling with Smad7 prevents experimental peritoneal fibrosis. The present study investigated whether Smad7 has a therapeutic effect on established peritoneal fibrosis associated with peritoneal dialysis (PD).

METHODS

A rat model of peritoneal fibrosis was induced by a daily intraperitoneal infusion of 4.25% Dianeal. After peritoneal fibrosis had been established on day 14, groups of 6 rats were treated intraperitoneally with gene transfer of Smad7 or control plasmids using an ultrasound-microbubble-mediated system for 2 weeks until day 28. In addition, a group of 6 diseased rats was euthanized on day 14 before treatment as the basal disease control.

RESULTS

Compared to the control-treatment animals on day 28, real-time PCR, Western blot, and confocal microscopy revealed that Smad7 gene transfer significantly attenuated the increased peritoneal fibrosis including the thickening of fibrotic peritoneum, accumulation of alpha-SMA and collagen I, and an improvement in peritoneal dysfunction (all p < 0.05). Importantly, Smad7 treatment also improved the severity of peritoneal fibrosis and functional impairment when compared to those on day 14 before treatment (all p < 0.05). Inhibition of the established peritoneal fibrosis by Smad7 was associated with an abrogation of TGF-beta signaling and upregulation of TGF-beta1 and PAI-1.

CONCLUSIONS

Smad7 gene therapy is able to inhibit established peritoneal fibrosis in a rat model of PD. Results from this study suggest that Smad7 may be a therapeutic agent for the treatment of peritoneal fibrosis associated with PD.

Update on Mechanisms of Ultrafiltration Failure

Ultrafiltration failure (UFF) continues to be a major complication of peritoneal dialysis (PD), particularly long-term PD. Continuous exposure to bioincompatible PD solutions causes inflammation of the peritoneal membrane, which progressively undergoes fibrosis and angiogenesis and, ultimately, UFF. There is emerging evidence that epithelial–mesenchymal transition (EMT) of peritoneal mesothelial cells (MCs) may play an important role in the failure of peritoneal membrane function. Submesothelial myofibroblasts originating from MCs through EMT and from activated resident fibroblasts participate in inflammatory responses, extracellular matrix accumulation, and angiogenesis. High glucose and glucose degradation products from PD solutions are responsible for production of transforming growth factor β (TGFβ) and vascular endothelial growth factor (VEGF) by MCs, which induce EMT. Leptin and receptor for advanced glycation end-products (AGEs) augment myofibroblastic conversion through the TGFβ signaling system.

A reduction in osmotic conductance in addition to increased solute transport causes UFF. This situation may be caused by loss of aquaporin (AQP) function and formation of the submesothelial fibrotic layer. During PD, AQP1 plays an essential role in water permeability and ultrafiltration (UF), modulating processes such as endothelial permeability and angiogenesis. During a hypertonic dwell, AQP1 mediates 50% of UF. Insufficient AQP1 function may be causative for inadequate UFF. A significant amount of evidence from animal studies now exists to show that mast cells communicate with fibroblasts and are implicated in fibrogenesis, angiogenesis, and UFF. However, it is not confirmed in human studies that mast cells contribute to the fibrosis seen in the peritoneum of PD patients.

The patterns of UFF in PD patients depend on duration of treatment. Inherently high small-solute transport status is associated with hypoalbuminemia and a greater comorbidity index. However, most of the variability in peritoneal transport remains unexplained, pointing to the potential role of genetic factors. Gene polymorphisms associated with peritoneal membrane transport have been identified. Recent studies have shown that VEGF, interleukin-6, endothelial NO synthase, AGE receptor, and RAS gene polymorphisms are associated with transport properties in PD patients. Current insights into the mechanisms of UFF will provide rationales for new therapeutic strategies.

Mineralocorticoid receptor blockade ameliorates peritoneal fibrosis in new rat peritonitis model

Peritoneal fibrosis (PF) is an important complication of long-term peritoneal dialysis. Although mineralocorticoid and mineralocorticoid receptor (MR) have attracted increasing attention in the field of vascular injury, including the heart, kidney, and vessels, little is known about the role of mineralocorticoid in PF. This work was designed to explore the effects of MR blockade on PF. We developed a new model of PF in rats based on mechanical scraping of the peritoneum. This model is characterized by acute-phase inflammation (neutrophil and macrophage infiltration on days 0–3) and late-phase PF (α-smooth muscle actin-positive fibroblast infiltration, type III collagen accumulation, and neoangiogenesis on days 7–14). Peritoneal thickening peaked on day 14. MR was expressed in rat peritoneum and a rat fibroblast cell line. Expression of its effector kinase [serum- and glucocorticoid-induced kinase-1 (Sgk1)], transforming growth factor-β (TGF-β), plasminogen activator inhibitor-1 (PAI-1), and CD31-positive vessels increased during the course of PF. Rats were treated with spironolactone, angiotensin receptor blockade (ARB), or angiotensin-converting enzyme inhibitor (ACEI)-ARB-spironolactone starting at 6 h after peritoneal scraping. All parameters, including peritoneal thickening, number of macrophages and CD31-positive vessels, and expression of monocyte chemoattractant protein-1, TGF-β, PAI-1, and Sgk1, were significantly suppressed by spironolactone (10 mg·kg−1·day−1). The effects of spironolactone (10 and 20 mg·kg−1·day−1) were very similar to those of triple blockade. ARB, but not ACEI, significantly reduced peritoneal thickening. Furthermore, peritoneal function assessed by peritoneal equilibration test was significantly improved by spironolactone. Our results suggest that MR is a potential target to prevent inflammation-induced PF in patients on peritoneal dialysis.