Lipopolysaccharide Upregulates Renal Shiga Toxin Receptors in a Primate Model of Hemolytic Uremic Syndrome

Abstract

Background: Although Shiga toxin (Stx) mediates classical hemolytic uremic syndrome (HUS), it is not fully understood why only some subjects exposed to Stx-expressing Escherichia coli develop HUS. We have previously shown in a baboon model of Stx-mediated HUS that coadministration of lipopolysaccharide (LPS) results in an augmented host response to otherwise subtoxic Stx1 doses. We used this model to test the hypothesis that LPS upregulates renal Stx receptor (Gb₃) expression. Methods: Juvenile baboons were treated with either Stx1 (100 ng/kg), LPS (1 mg/kg as two divided doses 24 h apart), or a sham injection of saline, and sacrificed and immediately autopsied at 72 h. Renal cortical tissue Gb₃ content was quantitated by lipid extraction and thin-layer chromatography, and Stx1 and Gb₃/CD77 immunostaining was assessed by quantitative immunofluorescent microscopy. Results: Compared to saline-in jected controls, LPS administration resulted in a 2.2-fold increase in renal cortical Gb₃ by chromatography (p < 0.01), a 2.5-fold increase in Stx1 staining (p = 0.003) and a 1.7-fold increase in CD77 immunostaining (p = 0.004). Stx treatment did not significantly alter either Stx or CD77 immunostaining. Conclusion: These observations suggest that LPS primes the host for Stx-mediated renal injury by upregulating renal Gb₃ expression.

Fractalkine and CX3CR1 Mediate Leukocyte Capture by Endothelium in Response to Shiga Toxin

“…Colonic vascular damage by enterohemorrhagic E. coli may facilitate the entry of LPS and other bacterial products to the circulation, thereby promoting an inflammatory response that contributes to the pathogenesis of renal injury. In a baboon model of HUS, LPS augmented Stx toxicity by up-regulating renal expression of the Gb3 receptor (61). Consistent with these findings in nonhuman primates, both Stx2 and LPS were required to elicit a HUS-like response in mice (35)(36)(37).…”

Effects of Shiga Toxin Type 2 on a Bioengineered Three-Dimensional Model of Human Renal Tissue

“…For virtually all experiments (Fig. 1C), Stx2 was purified free of LPS, which has been used as a costimulus in a murine model of HUS (41,42) and may potentiate an Stx response by increasing the inflammatory response or increasing Gb3 receptor on the cell surface (43)(44)(45)(46). Both the cells and the tissues were treated with a range of Stx2 concentrations (1 fg to 1 g/ml) for up to 72 h with supernatant sampling occurring at 6, 24, 48, and 72 h posttreatment (Fig.…”

Distinct Physiologic and Inflammatory Responses Elicited in Baboons after Challenge with Shiga Toxin Type 1 or 2 from Enterohemorrhagic Escherichia coli

“…The bacteria colonize the intestinal lumen, with most strains forming characteristic attaching-andeffacing lesions, and the organisms may synthesize and release one or more toxins that are primary virulence factors contributing to the clinical manifestations of HUS (19). The toxins are AB 5 holotoxins, referred to as Shiga toxins due to their functional and structural similarities to Shiga toxin expressed by Shigella dysenteriae serotype 1 (4). Shiga toxin type 1 (Stx1) is essentially identical to the Shigella toxin (4), differing by one amino acid, but shares only 58% amino acid identity with Shiga toxin type 2 (Stx2).…”

“…Also, endothelial sensitivities to Stx1 and Stx2 differ depending on the vascular bed, with intestinal endothelium being more sensitive to the Shiga toxins than saphenous vein endothelium (12), and glomerular endothelial cells are about 1,000 times more sensitive to Stx2 than human umbilical vein endothelial cells (17). The mechanisms for these differences are not completely understood but may be related to receptor density, toxin effects on endoplasmic reticulum stress responses and apoptosis (22,41), or local availability of sensitizing cytokines (5,7,11).…”