[Retracted] TGF‑β1 induces peritoneal fibrosis by activating the Smad2 pathway in mesothelial cells and promotes peritoneal carcinomatosis

Following the publication of this paper, it was drawn to the Editor's attention by a concerned reader that the fluorescence microscopy data shown in Fig. 6A and B were strikingly similar to data appearing in different form in Fig. 7 in a previously published paper [Lv Z‑D, Na D, Liu F‑N, Du Z‑M, Sun Z, Li Z, Ma X‑Y, Wang Z‑N and Xu H‑M: Induction of gastric cancer cell adhesion through transforming growth factor‑beta1‑mediated peritoneal fibrosis. J Exp Clin Cancer Res 29: 139, 2010], which featured some of the same authors, although the data were shown to portray results obtained under different experimental conditions. Furthermore, the data in Fig. 7A for the 'TGF‑β1' and the 'TGF‑β1 + siRNAcon' experiments contained an overlapping section, such that these data appeared to have been derived from the same original source, even though they were intended to show the results from differently performed experiments. Owing to the fact that the contentious data in the above article had already been published prior to its submission to International Journal of Molecular Medicine, and due to a lack of overall confidence in the presented data, the Editor has decided that this paper should be retracted from the Journal. After having been in contact with the authors, they accepted the decision to retract the paper. The Editor apologizes to the readership for any inconvenience caused. [International Journal of Molecular Medicine 29: 373‑379, 2012; DOI: 10.3892/ijmm.2011.852].

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.

Nintedanib attenuates peritoneal fibrosis by inhibiting mesothelial-to-mesenchymal transition, inflammation and angiogenesis

Nintedanib, an Food and Drug Administration (FDA) approved multiple tyrosine kinase inhibitor, exhibits an anti-fibrotic effect in lung and kidneys. Its effect on peritoneal fibrosis remains unexplored. In this study, we found that nintedanib administration lessened chlorhexidine gluconate (CG)-induced peritoneal fibrosis and reduced collagen I and fibronectin expression. This coincided with suppressed phosphorylation of platelet-derived growth factor receptor, fibroblast growth factor receptors, vascular endothelial growth factor receptor and Src family kinase. Mechanistically, nintedanib inhibited injury-induced mesothelial-to-mesenchymal transition (MMT), as demonstrated by decreased expression of α-smooth muscle antigen and vimentin and preserved expression of E-cadherin in the CG-injured peritoneum and cultured human peritoneal mesothelial cells exposed to transforming growth factor-β1. Nintedanib also suppressed expression of Snail and Twist, two transcription factors associated with MMT in vivo and in vitro. Moreover, nintedanib treatment inhibited expression of several cytokines/chemokines, including tumour necrosis factor-α, interleukin-1β and interleukin-6, monocyte chemoattractant protein-1 and prevented infiltration of macrophages to the injured peritoneum. Finally, nintedanib reduced CG-induced peritoneal vascularization. These data suggest that nintedanib may attenuate peritoneal fibrosis by inhibiting MMT, inflammation, and angiogenesis and have therapeutic potential for the prevention and treatment of peritoneal fibrosis in patients on peritoneal dialysis.

Alpha-1 antitrypsin inhibits formaldehyde-induced apoptosis of human peritoneal mesothelial cells

BACKGROUND

The alpha-1 antitrypsin (AAT) protein has an important role in the anti-inflammatory and apoptotic response. AAT inhibits not only serine proteases but also cysteine and aspartic proteases. Apoptosis results from the sequential activation of cysteine proteases of the caspase family. This study aimed to evaluate the effect of AAT on formaldehyde-induced apoptosis of human peritoneal mesothelial cells (HPMCs).

METHODS

HPMCs were cultured and treated with formaldehyde (250 µM) to induce apoptosis. In the AAT group, the cultured HPMCs were pretreated with AAT (2 mg/mL) for 1 h before formaldehyde treatment. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays to determine cell viability, and flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assays to detect apoptosis. The MTT assays were used to find optimal concentrations of formaldehyde and AAT. We measured caspase-3 activity and used Western blotting to estimate Bcl-2 and Bad expression.

RESULTS

Flow cytometry and TUNEL assays revealed that formaldehyde exposure significantly increased apoptosis compared with the control treatment, but pretreatment with AAT significantly inhibited this effect. Compared with the control, caspase-3 activity was significantly increased and the ratio of Bcl-2 to Bad expression significantly decreased following treatment with formaldehyde. However, caspase-3 activity was significantly lower and the Bcl-2 to Bad expression ratio higher in the AAT group than in the formaldehyde-only group.

CONCLUSION

AAT inhibits formaldehyde-induced apoptosis of HPMCs via a caspase-mediated pathway. These data support a potential use for AAT as a therapeutic agent for the inhibition of peritoneal cell apoptosis during peritoneal dialysis.

Autophagy promotes fibrosis and apoptosis in the peritoneum during long-term peritoneal dialysis

Long-term peritoneal dialysis is accompanied by functional and histopathological alterations in the peritoneal membrane. In the long process of peritoneal dialysis, high-glucose peritoneal dialysis solution (HGPDS) will aggravate the peritoneal fibrosis, leading to decreased effectiveness of peritoneal dialysis and ultrafiltration failure. In this study, we found that the coincidence of elevated TGF-β1 expression, autophagy, apoptosis and fibrosis in peritoneal membrane from patients with peritoneal dialysis. The peritoneal membranes from patients were performed with immunocytochemistry and transmission electron microscopy. Human peritoneal mesothelial cells were treated with 1.5%, 2.5% and 4.25% HGPDS for 24 hrs; Human peritoneal mesothelial cells pre-treated with TGF-β1 (10 ng/ml) or transfected with siRNA Beclin1 were treated with 4.25% HGPDS or vehicle for 24 hrs. We further detected the production of TGF-β1, activation of TGF-β1/Smad2/3 signalling, induction of autophagy, EMT, fibrosis and apoptosis. We also explored whether autophagy inhibition by siRNA targeting Beclin 1 reduces EMT, fibrosis and apoptosis in human peritoneal mesothelial cells. HGPDS increased TGF-β1 production, activated TGF-β1/Smad2/3 signalling and induced autophagy, fibrosis and apoptosis hallmarks in human peritoneal mesothelial cells; HGPDS-induced Beclin 1-dependent autophagy in human peritoneal mesothelial cells; Autophagy inhibition by siRNA Beclin 1 reduced EMT, fibrosis and apoptosis in human peritoneal mesothelial cells. Taken all together, these studies are expected to open a new avenue in the understanding of peritoneal fibrosis, which may guide us to explore the compounds targeting autophagy and achieve the therapeutic improvement of PD.

IL-6 promotes epithelial-to-mesenchymal transition of human peritoneal mesothelial cells possibly through the JAK2/STAT3 signaling pathway

Long-term peritoneal dialysis (PD) therapy results in functional and structural alteration of the peritoneal membrane, including epithelial-to-mesenchymal transition (EMT). Interleukin 6 (IL-6) is a local pleiotropic cytokine, hypothesized to play an important role in EMT. This study was designed to investigate the role of IL-6 in EMT and peritoneal membrane dysfunction in long-term PD patients by assessing the level of IL-6 in dialysate and exploring the relationship between IL-6, the related signaling pathway JAK2/STAT3, and EMT, using in vitro cellular and molecular techniques. Plasma and dialysate levels of IL-6 were significantly higher in PD ultrafiltration failure patients compared with patients without ultrafiltration failure and were negatively correlated with measures of PD adequacy. In vitro IL-6 treatment changed human peritoneal mesothelial cell phenotype from a typical cobblestone-like to a fibroblast-like appearance and increased cell viability. IL-6 treatment increased α-smooth muscle actin and vascular endothelial growth factor expression but decreased E-cadherin expression. IL-6 treatment activated the JAK/STAT signaling pathway. However, the JAK2/STAT3 inhibitor WP1066 prevented IL-6-induced activation of the JAK2/STAT3 pathway and EMT. We conclude that IL-6 promotes the EMT process, possibly by activating the JAK2/STAT3 signaling pathway. IL-6 may serve as a novel therapeutic target for preventing EMT, and preservation of the peritoneal membrane may arise from these studies.

Interference of peritoneal dialysis fluids with cell cycle mechanisms

INTRODUCTION

Peritoneal dialysis fluids (PDF) differ with respect to osmotic and buffer compound, and pH and glucose degradation products (GDP) content. The impact on peritoneal membrane integrity is still insufficiently described. We assessed global genomic effects of PDF in primary human peritoneal mesothelial cells (PMC) by whole genome analyses, quantitative real-time polymerase chain reaction (RT-PCR) and functional measurements.

METHODS

PMC isolated from omentum of non-uremic patients were incubated with conventional single chamber PDF (CPDF), lactate- (LPDF), bicarbonate- (BPDF) and bicarbonate/lactate-buffered double-chamber PDF (BLPDF), icodextrin (IPDF) and amino acid PDF (APDF), diluted 1:1 with medium. Affymetrix GeneChip U133Plus2.0 (Affymetrix, CA, USA) and quantitative RT-PCR were applied; cell viability was assessed by proliferation assays.

RESULTS

The number of differentially expressed genes compared to medium was 464 with APDF, 208 with CPDF, 169 with IPDF, 71 with LPDF, 45 with BPDF and 42 with BLPDF. Out of these genes 74%, 73%, 79%, 72%, 47% and 57% were downregulated. Gene Ontology (GO) term annotations mainly revealed associations with cell cycle (p = 10(-35)), cell division, mitosis, and DNA replication. One hundred and eighteen out of 249 probe sets detecting genes involved in cell cycle/division were suppressed, with APDF-treated PMC being affected the most regarding absolute number and degree, followed by CPDF and IPDF. Bicarbonate-containing PDF and BLPDF-treated PMC were affected the least. Quantitative RT-PCR measurements confirmed microarray findings for key cell cycle genes (CDK1/CCNB1/CCNE2/AURKA/KIF11/KIF14). Suppression was lowest for BPDF and BLPDF, they upregulated CCNE2 and SMC4. All PDF upregulated 3 out of 4 assessed cell cycle repressors (p53/BAX/p21). Cell viability scores confirmed gene expression results, being 79% of medium for LPDF, 101% for BLPDF, 51% for CPDF and 23% for IPDF. Amino acid-containing PDF (84%) incubated cells were as viable as BPDF (86%).

CONCLUSION

In conclusion, PD solutions substantially differ with regard to their gene regulating profile and impact on vital functions of PMC, i.e. on cells known to be essential for peritoneal membrane homeostasis.

Alterations of intercellular junctions in peritoneal mesothelial cells from patients undergoing dialysis: effect of retinoic Acid

BACKGROUND

Dialysis patients are classified according to their peritoneal permeability as low transporter (LT, low solute permeability) or high transporter (HT, high solute permeability). Tight junction (TJ) proteins are critical to maintain ions, molecules and water paracellular transport through peritoneum. Exposure to peritoneal dialysis solutions causes damage to TJ in human peritoneal mesothelial cells (HPMCs). We analyzed the quantity, distribution and function of TJ proteins: claudin-1, -2 and -8, ZO-1 and occludin, in HPMC cultures from LT and HT patients. Since all-trans retinoic acid (ATRA) might modify the expression of TJ proteins, we studied its effect on HPMCs.

METHODS

Control HPMCs were isolated from human omentum, while HT or LT cells were obtained from dialysis effluents. Cells were cultured in presence of ATRA 0, 50 or 100 nM. Transepithelial electrical resistance (TER) measurement, immunostaining and Western blot analyses were performed.

RESULTS

HT exhibited lower TER than control and LT monolayers. Immunofluorescence for TJ was weak and discontinuous along the cell contour, in LT and HT. Furthermore, claudin-1, occludin and ZO-1 expressions were decreased. In all groups, claudin-2 was localized at nuclei. We observed that ATRA improved TJ distribution and increased TJ expression in HT. This retinoid did not modify claudin-2 and -8 expressions. All-trans retinoic acid decreased TER in HT, but had no effect in LT.

CONCLUSIONS

Tight junctions were altered in HPMCs from dialyzed patients. The HT monolayer has lower TER than LT, which might be associated with the peritoneal permeability in these patients. ATRA might be a therapeutic alternative to maintain mesothelial integrity, since it improved TJ localization and expression.