SHIGA TOXIN-1 ELICITS DIVERSE BIOLOGIC RESPONSES IN MESANGIAL CELLS

Background. Shiga toxin 1 (Stx1) is a causative agent in hemolytic ure mic syndrome (HUS). Its receptor, the glycosphingolipid elobotriaosylc eramide (Gb(3)), is expressed on cultured human endothelial and mesang ial cells. Mesangial cell injury in HUS ranges from mild cellular edem a to severe mesangiolysis and eventual glomerulosclerosis. We hypothes ized that, in addition to endothelial cells, mesangial cells are targe ts of Stx1. Methods. Human mesangial cells were exposed to Stx1. Prote in synthesis was measured using [S-35]-methionine/cysteine. Cell viabi lity was measured as the lysosomal uptake of Neutral Red. Monocyte che motactic peptide (MCP-1) mRNA and protein were analyzed by Northern bl otting and ELISA. Results. Stx1 (0.25 to 2500 ng/ml) resulted in a dos e-dependent inhibition of protein synthesis. This effect of Stx1 was p otentiated by preincubation of the cells with interleukin-1 alpha (IL- 1 alpha; 2 ng/ml) or tumor necrosis-alpha (TNF-alpha; 500 U/ml). Stx1 had little effect on mesangial cell viability during the first 24 hour s of exposure to Stx1. However, prolonged incubation with Stx1 for 48 and 72 hours resulted in a 68% and 80% decrease in cell-viability, res pectively. Stx1 elicited a dose and time dependent increase in the lev els of MCP-I mRNA, an effect that was potentiated by preincubation wit h IL-1 alpha. Conclusion. These data indicate that mesangial cells are susceptible to the effects of Stx1 ill vitro. Stx1 exerts a spectrum of biologic effects on mesangial cells ranging from activation of chem okine genes to a lethal toxic injury. Immunoinflammatory cytokines pot entiate the effects of Stx1. Thus, glomerular pathology in HUS may als o result from a direct effect of Stx1 on mesangial cells.