The Role of TLR4 in M1 Macrophage-Induced Epithelial-Mesenchymal Transition of Peritoneal Mesothelial Cells.

Background/Aims: Peritoneal fibrosis is a frequent complication of peritoneal dialysis that follows inflammation. It is recognized that epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (PMCs), plays a key role in fibrogenesis. However, the relationship between inflammatory macrophages and PMCs remains elusive. In this study, we investigated the effects of different polarized macrophages on EMT of HMrSV5 PMCs. Methods: Monocytes were polarized to M1/M2 macrophages before being added to HMrSV5 in direct or indirect contact. Morphological changes of HMrSV5 were observed and toll-like receptors 4 (TLR4) on macrophage surfaces was detected using flow cytometry. EMT markers and intracellular signals of HMrSV5 cells were assessed using real time-PCR and WB. Results: The typical epithelial cell morphology of HMrSV5 disappeared after co-culture with M1 macrophages and was accompanied by decreased E-cadherin and increased α-SMA, suggesting HMrSV5 undergo EMT. These effects depended on direct contact between the two cells, as indirect contact or co-culture with M2 macrophages had no effect. Intriguingly, we found TLR4 surface receptors were activated on sorted M1 cells in co-culture, and related signal adaptors, such as TRIF, were obviously upregulated. Conclusion: Direct contact with M1 macrophages induces EMT of PMCs, during which TRIF-dependent TLR4 signaling pathway was activated.