Three-dimensional invasion of epithelial-mesenchymal transition-positive human peritoneal mesothelial cells into collagen gel is promoted by the concentration gradient of fibronectin.

BACKGROUND: In long-term peritoneal dialysis, myofibroblast-like cells found in the interstitium of the peritoneum are assumed to be a transformed type of mesothelial cell-epithelial-mesenchymal transition-positive [EMT(+)] human peritoneal mesothelial cells (HPMCs)-because they express a mesothelial marker, cytokeratin. However, no direct evidence about how these cells are able to invade from the mesothelium has yet been obtained. AIM: In this study, we aimed to verify whether EMT(+) HPMCs would, in vitro, invade three-dimensionally along certain chemotactic factors. METHODS: We used reverse-transcriptase polymerase chain reaction to measure expression of Snail, E-cadherin, α(5)-integrin, and matrix metalloproteinase 2 (MMP2) messenger RNA (mRNA) in HPMCs exposed to 10 ng/mL transforming growth factor ß1 (TGFß1) and how that expression corresponds to cell motility, as represented by a video movie. We used the Transwell (12 µm pore diameter: Sigma-Aldrich, Tokyo, Japan) to construct a three-dimensional (3D) cell migration chamber. In the lower chamber, a concentration gradient of fibronectin (FN) or albumin(Alb) was formed in 0.1% type I collagen by diffusion (C(0)=22 nmol/L; concentration gradient: C/C(0)=0.7). All cells beneath the membrane were counted 72 hours after 5×10(4) EMT(+) HPMCs (HPMCs after a 48-hour exposure to 10 ng/mL TGFß1) had been spread in the upper chamber. RESULTS: After 72 hours, the increased motility of HPMCs resulting from their exposure to 10 ng/mL TGFß1 had returned to baseline, but they retained an elongated morphology. Expression of Snail and MMP2 mRNA reached maximum at 24 hours. Expression of E-cadherin declined, and expression of α(5)-integrin increased continuously. In the 3D invasion study, significantly enhanced invasion by EMT(+) but not EMT(-) HPMCs was clearly seen in the presence of a FN concentration gradient (p<0.01), although invasion by EMT(+) and EMT(-) HPMCs in the absence of a FN concentration gradient was not statistically significantly different. Compared with the EMT(+) control (no concentration gradient), invasion by EMT(+) HPMCs was 2.1 ± 0.5 times (p<0.05) and 1.4 ± 0.4 times (p=nonsignificant) higher along the FN and Alb concentration gradients respectively. Increased invasion along the FN concentration gradient was significantly inhibited (p<0.05) when the HPMCs were pre-incubated with 5 µg/mL RGDS (a blocker for α(5)-integrin to FN). CONCLUSIONS: We conclude that EMT(+) HPMCs invade collagen gel along the FN concentration gradient because of specific binding to RGDS receptors, which bind integrins such as α(5)-integrin, upregulating invasion-related gene expression associated with synthesis of the cytoskeleton protein α smooth muscle actin.

HPMCs induce greater intercellular delocalization of tight junction-associated proteins due to a higher susceptibility to H2O2 compared with HUVECs.

BACKGROUND: Reactive oxygen species (ROS) have been speculated as possible inducers of structural or functional changes that lead to a hyperpermeable state in patients on long-term peritoneal dialysis. This study aimed to compare localization of tight junction-associated proteins (TJPs), which relate to solute permeability characteristics, between human peritoneal mesothelial cell (HPMC) monolayers and human umbilical vein endothelial cell (HUVEC) monolayers under oxidative stress. METHODS: HPMCs and HUVECs were cultured on a polymer mesh until transepithelial electrical resistance reached a plateau. Solute permeation tests were conducted using FITC-labeled dextrans. Localization of TJPs was observed under a confocal laser scanning microscope. These experiments were carried out with/without 0.1 mmol/L H(2)O(2). In addition, ROS production as well as the amounts of intracellular reductive glutathione (GSH) and oxidative glutathione were measured. RESULTS: When the monolayers were exposed to 0.1 mmol/L H(2)O(2)/medium for 2 hours, the HPMC monolayer revealed a significant reduction in transepithelial electrical resistance (from 32.5 +/- 3.4 to 17.4 +/- 4.9 Omega.cm(2)) with delocalization of TJPs, particularly occludins. The HUVEC monolayer remained stable and exhibited an unremarkable change in TJP organization. Compared to the HUVEC monolayer, the HPMC monolayer exhibited two- to threefold higher 2',7'-dichlorofluorescein intensities that increased in a dose-dependent manner. HUVECs contained approximately 2.5-times more GSH than HPMCs. This supported the lesser production of ROS when exposed to 0.1 mmol/L H(2)O(2) for 24 hours. HUVECs used 8.03 nmol/mg GSH protein to maintain TJP localization, while only 3.75 nmol/mg GSH protein was available for the HPMCs. CONCLUSION: The HUVEC monolayer, which was less permeable to middle-to-high molecular weight solutes, was more tolerant against ROS stress than the HPMC monolayer. Availability of intracellular GSH is an important issue in maintaining the integrity of the mesothelium.