Effect of intercellular adhesion molecule-1 and hyaluronic acid on monocyte-renal tubular epithelial cell adhesion induced by tumor necrosis factor α

Objective To investigate the effect of tumor necrosis factor ot (TNF-α) on monocyte-renal tubular epithelial cell adhesion and to explore its associated mechanism. Methods Human renal proximal tubular epithelial cell line (HK2 cells)and monocyte cell line (U937)were used to perform cell co-culture. TNF-α (10 μg/L)was used to stimulate HK2 cells and then U937 was put into the HK2 monolayers. Three locational parts of hyaluronan around HK2 cells were extracted by different ways and the HA expression was detected by enzyme-linked binding protein assay. Monocyte adhesion was detected by florescence recording assay. Flow cytometry was applied to assess intercellular adhesion molecule-1 (ICAM-1) expression in HK2 cells. Results Stimulation of HK2 cells with TNF-α significantly increased U937 binding to HK2 cell monolayer [(2.25±0.05) folds vs control, P<0.01]. Incubation of TNF-α (10 μg/L) with HK2 cells for 24 hours did not induce the change of total HA expression surrounding the HK2 cells, whereas HA redistribution happened with conditioned medium fraction (CM-HA) increased [(1.17±0.16) fold vs control, P<0.05], the pericellular fraction (trypsin extract fraction, TE-HA) decreased (83%±11% vs control, P<0.05) and the remaining cells-associated HA (cell associated fraction, CA) did not change significantly. In addition, pre-treatment of HK2 cells with TNF-α significantly increased the ICAM-1 expression [(1.85±0.22) folds vs control, P<0.01] and ICAM-1-dependent monocytes binding. Removal of HA from the surface of confluent monolayers of HK2 cells by hyaluronidase before addition of U937 cells increased monocyte binding[ (1.35±0.06) folds vs control, P<0.05]. In contrast, the presence of either sICAM-1 (400 μg/L) or anti-CDI8 antibody (10 mg/L) led to a significant decrease in ICAM-1-dependent monocyte binding (78%±7%, P<0.05; 75%±8%, P<0.01 vs those before adding sICAM-1 or anti-CD18 antibody, respectively). Conclusion HA redistribution induced by TNF-α may facilitate ICAM-1-dependent monocyte-epithelium binding, and pericellular HA plays a protective role in monocyte-driven tissue inflammation.