INFLUENCE OF OSMOTIC-STRESS ON HEAT-SHOCK PROTEIN-25 AND PROTEIN-72 IN MOUSE MESANGIAL CELLS

Previous studies have shown intense staining for heat shock protein 25 (HSP25) in the extraglomerular mesangium (EGM). Because relationships are believed to exist between osmotic stress, expression of HSP25, an d protection against stress and because the EGM may be exposed to high local tonicity, we examined the expression of HSP25 and the major str ess-inducible and cytoprotective HSP72 in mouse mesangial cells and em bryonic lung fibroblasts (3T3) after exposure to hypertonic stress (ad dition of 150 mM NaCl to the medium for two to seven days). Mesangial: but not 3T3, cells expressed high levels of HSP25 already under contr ol conditions, whereas neither cell line contained HSP72. Hypertonic t reatment neither enhanced (mesangial cells) or induced (3T3 cells) HSP 25 expression. HSP72, however; was induced strongly in 3T3 cells, but only minimally in mesangial cells. The high level of HSP25 in mesangia l cells thus seems not to be a consequence of high tonicity in the EGM because cultured mesangial cells express HSP25 already under control conditions, and osmotic stress did not induce HSP25 in either cell lin e. Furthermore, high amounts of HSP25 seem to reduce the requirement f or HSP72 after stress exposure, suggesting that, in mesangial cells, H SP25 might assume some functions of HSP72.