Functional Relevance of the Switch of VEGF Receptors/Co-Receptors during Peritoneal Dialysis-Induced Mesothelial to Mesenchymal Transition

María Luisa Pérez-Lozano,Rafael Selgas,Pilar Sandoval,José Antonio Sánchez-Tomero,José Antonio Jiménez-Heffernan,Patricia Albar-Vizcaíno,Ángela Rynne-Vidal,Manuel López-Cabrera,Abelardo Aguilera,Pedro L Majano

doi:10.1371/journal.pone.0060776

Abstract

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.

Highlights

Peritoneal dialysis (PD) is a therapeutic option for the treatment of end-stage renal disease and is based on the use of the peritoneal membrane (PM) as a permeable barrier across which ultrafiltration and diffusion take place [1], [2]
We have previously shown that effluent-derived mesothelial cells (MCs) produce vascular endothelial growth factor (VEGF) spontaneously and that the mesenchymal transition (MMT) process of MCs is associated with strong VEGF up-regulation [10], [11]
We have previously shown that during the MMT process there is a strong up-regulation of VEGF and that high levels of VEGF production by effluent-derived MCs correlated with high transport rates in PD patients [10]

Summary

Introduction

Peritoneal dialysis (PD) is a therapeutic option for the treatment of end-stage renal disease and is based on the use of the peritoneal membrane (PM) as a permeable barrier across which ultrafiltration and diffusion take place [1], [2]. Continuous exposure of the PM to non-physiologic PD fluids, as well as episodes of peritonitis and hemoperitoneum, may cause inflammation and injury to the PM, which progressively undergoes denudation of the mesothelial cell (MC) monolayer, submesothelial fibrosis and angiogenesis. These structural alterations may lead to the loss of the PM dialytic function [2], [3]. We have previously shown that effluent-derived MCs produce vascular endothelial growth factor (VEGF) spontaneously and that the MMT process of MCs is associated with strong VEGF up-regulation [10], [11]. We demonstrated that high levels of VEGF production by effluent MCs correlated with high transport rates in PD patients [11], [12]

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Results

Conclusion