Shiga toxin 1 elicits diverse biologic responses in mesangial cells

Shiga toxin 1 (Stx1) is a causative agent in hemolytic uremic syndrome (HUS). Its receptor, the glycosphingolipid globotriaosylceramide (Gb3), is expressed on cultured human endothelial and mesangial cells. Mesangial cell injury in HUS ranges from mild cellular edema to severe mesangiolysis and eventual glomerulosclerosis. We hypothesized that, in addition to endothelial cells, mesangial cells are targets of Stx1.

Human mesangial cells were exposed to Stx1. Protein synthesis was measured using [35S]-methionine/cysteine. Cell viability was measured as the lysosomal uptake of Neutral Red. Monocyte chemotactic peptide (MCP-1) mRNA and protein were analyzed by Northern blotting and ELISA.

Stx1 (0.25 to 2500 ng/ml) resulted in a dose-dependent inhibition of protein synthesis. This effect of Stx1 was potentiated by preincubation of the cells with interleukin-1alpha (IL-1alpha; 2 ng/ml) or tumor necrosis-alpha (TNF-alpha; 500 U/ml). Stx1 had little effect on mesangial cell viability during the first 24 hours of exposure to Stx1. However, prolonged incubation with Stx1 for 48 and 72 hours resulted in a 68% and 80% decrease in cell-viability, respectively. Stx1 elicited a dose and time dependent increase in the levels of MCP-1 mRNA, an effect that was potentiated by preincubation with IL-1alpha.

These data indicate that mesangial cells are susceptible to the effects of Stx1 in vitro. Stx1 exerts a spectrum of biologic effects on mesangial cells ranging from activation of chemokine genes to a lethal toxic injury. Immunoinflammatory cytokines potentiate the effects of Stx1. Thus, glomerular pathology in HUS may also result from a direct effect of Stx1 on mesangial cells.