Renal Proximal Tubular Epithelial Cell Transforming Growth Factor-β1 Generation and Monocyte Binding

With increasing awareness of the importance of renal cortical interstitial fibrosis, interest has focused on the mechanisms that stimulate generation of profibrotic factors including transforming growth factor (TGF)-β1, by resident cells, such as proximal tubular epithelial cells (PTCs). Infiltration of monocytes, has been implicated in the pathogenesis of a wide variety of renal diseases, however, how interaction between monocytes and PTCs may affect the generation of TGF-β1 by the resident cell is unknown. We demonstrate that monocytes stimulate TGF-β1 transcription and protein synthesis by PTCs. This was dependent on direct cell contact and TGF-β1 transcriptional activation that was dependent on ICAM-1 binding of unstimulated monocytes. This was mimicked by antibody cross-linking of PTC surface ICAM-1. We have previously identified hyaluronan (HA)-based structures on the surface of PTCs, both primary cultures and the HK-2 cell line. Removal of cell-surface HA increased ICAM-1-dependent monocyte binding and stimulation of TGF-β1 synthesis. Furthermore, we demonstrate that binding of monocytes to HA-based structures on the cell surface of HK-2 cells interferes with this response. In summary, we have demonstrated that HA-based pericellular structures down-regulate proinflammatory and profibrotic responses by modulation of monocyte-driven ICAM-1-dependent cell activation and TGF-β1 generation.