BIOLOGICAL ALTERATIONS OF RAT PODOCYTES CULTURED UNDER BASOLATERAL HYDROSTATIC-PRESSURE

In vivo, glomerular visceral epithelial cells (GVEC), or podocytes, ar e morphologically highly differentiated cells which are in close conta ct with adjacent cells by complex interdigitating foot processes. In v itro, the dedifferentiated appearance of podocytes hampers investigati ons on podocyte structure and function. Cultured podocytes resemble si mple epithelium in several ways with apical tight junctions and absenc e of foot processes. The morphological resemblances between GVEC early in embryonic development, in proteinuric diseases and in cultured cel ls are striking, but the mechanisms involved in these (de)differentiat ion processes are poorly understood. A common feature of GVEC in these various states of dedifferentiation is their altered exposure to or e ven total lack of hydrostatic pressure, suggesting that this may be on e of the parameters involved in GVEC differentiation. In this study we investigated whether basolateral hydrostatic pressure could affect GV EC biology in vitro. We therefore exposed cultured GVEC grown on porou s supports to basolateral hydrostatic pressure and investigated morpho logy with scanning and transmission electron microscopy, expression of specific podocyte markers and their biological responses to a model s timulus, the cytokine IFN-gamma. Morphologically, monolayers of pressu rized GVEC contained large regions of whirl like, raised cell formatio ns. Individual cells in these formations had a rounded morphology and pore-like indentations between adjacent cells were observed. Cell-cell contacts were often found more basally and intercellular spaces were widened. Moreover, protein expression of pressurized monolayers was al tered, as demonstrated by regions of cells with decreased keratin expr ession. Finally, upon exposure to the model stimulus IFN-gamma, the pr essurized as compared to the control GVEC demonstrated a 3-fold increa sed expression of MHC class II and a strongly decreased sensitivity to the toxic effects of IFN-gamma. In conclusion, we found several indic ations that hydrostatic pressure can affect podocyte biology in vitro and similar mechanisms may account for podocyte biology in vivo. The s trikingly altered morphology and biology of pressurized GVEC suggest t hat this culture system can be quite relevant for future studies with cultured GVEC.