Epithelial-to-mesenchymal transition and slit function of mesothelial cells are regulated by the cross talk between mesothelial cells and endothelial cells

Proteomic study of mesothelial and endothelial cross-talk: key lessons

INTRODUCTION

The peritoneum, pleura, and pericardium are yet understudied multicellular systems where mesothelial cells (MCs) and endothelial cells (ECs) are in close proximity. Crosstalk between these cell types likely plays role in molecular transport, immunological reactions, and metabolic processes in health, disease, and therapeutic intervention.

AREAS COVERED

In this review, we discuss recent proteomic efforts to characterize the crosstalk between MC and EC. We describe the proteomic methods necessary for investigation of crosstalk between MC and EC, as well as the in-vitro models that can be employed. Potential experimental approaches range from conditioned medium, via co-culture on semi-permeable membranes, to 3D cell culture based organoid models. While the biological and clinical relevance of the models may increase with their ability to mimic close cell communication, the practicality of these complex experiments corresponds vice versa, making standardization more difficult and expensive.

EXPERT OPINION

Currently, data and reports on mesothelial-to-endothelial crosstalk are still very scarce. In our opinion, the in-vitro model using semi-permeable cell culture inserts will allow to establish a basic understanding of cellular crosstalk that may occur between those cell types. Later-on, more sophisticated 3D cell cultures may be better able to simulate the transport dynamics within the peritoneal membrane.

TGF-β1-VEGF-A pathway induces neoangiogenesis with peritoneal fibrosis in patients undergoing peritoneal dialysis

The characteristic features of chronic peritoneal injury with peritoneal dialysis (PD) are submesothelial fibrosis and neoangiogenesis. Transforming growth factor (TGF)β and vascular endothelial growth factor (VEGF)-A are the main mediators of fibrosis and neoangiogenesis, respectively; however, the effect of the interaction between them on the peritoneum is not well known. In this study, we investigated the relationship between TGF-β1 and VEGF-A in inducing peritoneal fibrosis by use of human tissues and dialysate, cultured cells, and animal models. The VEGF-A concentration correlated with the dialysate-to-plasma ratio of creatinine (D/P Cr) ( P < 0.001) and TGF-β1 ( P < 0.001) in human PD effluent. VEGF-A mRNA levels increased significantly in the peritoneal tissues of human ultrafiltration failure (UFF) patients and correlated with number of vessels ( P < 0.01) and peritoneal thickness ( P < 0.001). TGF-β1 increased VEGF-A production in human mesothelial cell lines and fibroblast cell lines, and TGF-β1-induced VEGF-A was suppressed by TGF-β receptor I (TGFβR-I) inhibitor. Incremental peak values of VEGF-A mRNA stimulated by TGF-β1 in human cultured mesothelial cells derived from PD patients with a range of peritoneal membrane functions correlated with D/P Cr ( P < 0.05). To evaluate the regulatory mechanisms of VEGF-A and neoangiogenesis in vivo, we administered TGFβR-I inhibitor intraperitoneally in a rat chlorhexidine-induced peritoneal injury (CG) model. TGFβR-I inhibitor administration in the CG model decreased peritoneal thickness ( P < 0.001), the number of vessels ( P < 0.001), and VEGF-A levels ( P < 0.05). These results suggest that neoangiogenesis is associated with fibrosis through the TGF-β1-VEGF-A pathway in mesothelial cells and fibroblasts. These findings are important when considering the strategy for management of UFF in PD patients.

Apoptosis inhibitor of macrophage ameliorates fungus-induced peritoneal injury model in mice

Fungal peritonitis in a patient on peritoneal dialysis (PD) is a refractory injury accompanied by severe inflammation, predisposing patients to a poor prognosis. Defective clearance of necrotic tissue interferes with amelioration of tissue injury and induces abnormal tissue remodeling. In the recent reports, apoptosis inhibitor of macrophage (AIM, also called CD5L) prevents obesity, hepatocellular carcinoma and acute kidney injury. Here, we investigated potential roles of AIM in prevention of progression of fungal peritonitis models. AIM^−/− mice subjected to zymosan-induced peritonitis exhibited progressive inflammation and sustained peritoneal necrosis tissue on day 28 after the disease induction, whereas there was an improvement in AIM^+/+ mice. This appeared to be caused by deposition of AIM at the necrotic peritoneum in AIM^+/+ mice. In vitro, AIM enhanced the engulfment of necrotic debris by macrophages derived from zymosan-induced peritonitis, M1- and M2a-like bone marrow derived macrophages, as well as by mesothelial cells. In addition, administration of recombinant AIM dramatically ameliorated severe inflammation associated with necrosis in zymosan-induced peritonitis of AIM^−/− mice. Our observations suggest that AIM appears to be involved in the repair process of zymosan-induced peritonitis, and thus, could be the basis of development of new therapeutic strategies for PD-related fungal peritonitis.

Progress in cell culture systems for pathological research

Cell culture is a well-established standard technique and a fundamental tool in biology and medicine. Establishment of a novel culture method by meeting various challenges can sometimes open up new fields of cell biology and medicine. An artificial microenvironment for cultured cells is made up of complicated factors, including cytokines, scaffold material type, cell-cell interactions, and physical stress. To replicate the tissue architecture, cell-cell interactions, and specific physical microenvironment, we previously demonstrated the effectiveness of a three-dimensional culture system, and further established two simple culture systems: air-liquid interface (ALI) and fluid flow stress (FFS). A three-dimensional collagen gel culture system can replicate cell-cell interactions in vitro. As skin is constantly exposed to air, the ALI system closely mimicked the skin microenvironment and maintained the homeostasis of the epidermis and dermis. The ALI culture system also revealed the possibility of skin regeneration through ectopic mesenchymal cell involvement. Fluid streaming and shear stress were recently demonstrated to constitute the critical microenvironment for various cell types. The FFS system demonstrated that fluid streaming induced epithelial-mesenchymal transition of mesothelial cells, leading to peritoneal fibrosis. Our novel culture systems will hopefully open up new fields of regenerative medicine and pathological research.

Development of an oxygenation culture method for activating the liver-specific functions of HepG2 cells utilizing a collagen vitrigel membrane chamber

We recently developed a collagen vitrigel membrane (CVM) chamber possessing a scaffold composed of high-density collagen fibrils. In this study, we first confirmed that the advantage of CVM chamber in comparison to the traditional culture chamber with porous polyethylene terephthalate membrane is to preserve a culture medium poured in its inside even though the under side is not a liquid phase but solid and gas phases. Subsequently, we designed three different culture systems to grow HepG2 cells in a culture medium (liquid phase) on the CVM which the under side is a culture medium, a plastic surface (solid phase) or 5 % CO₂ in air (gas phase) and aimed to develop a brief culture method useful for activating the liver-specific functions and analyzing the pharmacokinetics of fluorescein diacetate. HepG2 cells cultured for 2 days on the liquid–solid interface and subsequently for 1 day on the liquid–gas interface represented excellent cell viability and morphology in comparison to the others, and remarkably improved albumin secretion and urea synthesis to almost the same level of freshly isolated human hepatocytes and CYP3A4 activity to about half the level of differentiated HepaRG cells. Also, the cells rapidly absorbed fluorescein diacetate, distributed it in cytosol, metabolized it into fluorescein, and speedily excreted fluorescein into both bile canaliculus-like networks and extracellular solution. These data suggest that hepatic structure and functions of monolayered HepG2 cells can be induced within a day after the oxygenation from beneath the CVM.

Rapamycin Protects from Type-I Peritoneal Membrane Failure Inhibiting the Angiogenesis, Lymphangiogenesis, and Endo-MT

Preservation of peritoneal membrane (PM) is essential for long-term survival in peritoneal dialysis (PD). Continuous presence of PD fluids (PDF) in the peritoneal cavity generates chronic inflammation and promotes changes of the PM, such as fibrosis, angiogenesis, and lymphangiogenesis. Mesothelial-to-mesenchymal transition (MMT) and endothelial-to-mesenchymal transition (Endo-MT) seem to play a central role in this pathogenesis. We speculated that Rapamycin, a potent immunosuppressor, could be beneficial by regulating blood and lymphatic vessels proliferation. We demonstrate that mice undergoing a combined PD and Rapamycin treatment (PDF + Rapa group) presented a reduced PM thickness and lower number of submesothelial blood and lymphatic vessels, as well as decreased MMT and Endo-MT, comparing with their counterparts exposed to PD alone (PDF group). Peritoneal water transport in the PDF + Rapa group remained at control level, whereas PD effluent levels of VEGF, TGF-β, and TNF-α were lower than in the PDF group. Moreover, the treatment of mesothelial cells with Rapamycin in vitro significantly decreased VEGF synthesis and selectively inhibited the VEGF-C and VEGF-D release when compared with control cells. Thus, Rapamycin has a protective effect on PM in PD through an antifibrotic and antiproliferative effect on blood and lymphatic vessels. Moreover, it inhibits Endo-MT and, at least partially, MMT.

Fluid dwell impact induces peritoneal fibrosis in the peritoneal cavity reconstructed in vitro

Peritoneal fluid dwell impacts the peritoneum by creating an abnormal physiological microenvironment. Little is known about the precise effects of fluid dwell on the peritoneum, and no adequate in vitro models to analyze the impact of fluid dwell have been established. In this study, we developed a peritoneal fluid dwell model combined with an artificial peritoneal cavity and fluid stirring generation system to clarify the effects of different dwelling solutions on the peritoneum over time. To replicate the peritoneal cavity, we devised a reconstructed peritoneal cavity utilizing a mesothelial layer, endothelial layer, and collagen membrane chamber. The reconstructed peritoneal cavity was infused with Dulbecco's modified Eagle's medium, saline, lactated Ringer's solution or peritoneal dialysis solution with repeated 4-h dwells for 10 or 20 consecutive days. The above-described solutions induced epithelial-mesenchymal transition (EMT) and hyperplasia of mesothelial cells. All solution types modulated nitric oxide synthase activities in mesothelial and endothelial cells and nitric oxide concentrations in dwelling solutions. Inhibition of nitric oxide synthase activity acted synergistically on mesothelial EMT and hyperplasia. The present findings suggest that solutions infused into the peritoneal cavity are likely to affect nitric oxide production in the peritoneum and promote peritoneal fibrosis. Our newly devised peritoneal cavity model should be a promising tool for understanding peritoneal cellular kinetics and homeostasis.