Shiga toxin 1 induces on lipopolysaccharide-treated astrocytes the release of tumor necrosis factor-alpha that alter brain-like endothelium integrity.

The hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia and renal dysfunction. The typical form of HUS is generally associated with infections by Gram-negative Shiga toxin (Stx)-producing Escherichia coli (STEC). Endothelial dysfunction induced by Stx is central, but bacterial lipopolysaccharide (LPS) and neutrophils (PMN) contribute to the pathophysiology. Although renal failure is characteristic of this syndrome, neurological complications occur in severe cases and is usually associated with death. Impaired blood-brain barrier (BBB) is associated with damage to cerebral endothelial cells (ECs) that comprise the BBB. Astrocytes (ASTs) are inflammatory cells in the brain and determine the BBB function. ASTs are in close proximity to ECs, hence the study of the effects of Stx1 and LPS on ASTs, and the influence of their response on ECs is essential. We have previously demonstrated that Stx1 and LPS induced activation of rat ASTs and the release of inflammatory factors such as TNF-α, nitric oxide and chemokines. Here, we demonstrate that rat ASTs-derived factors alter permeability of ECs with brain properties (HUVECd); suggesting that functional properties of BBB could also be affected. Additionally, these factors activate HUVECd and render them into a proagregant state promoting PMN and platelets adhesion. Moreover, these effects were dependent on ASTs secreted-TNF-α. Stx1 and LPS-induced ASTs response could influence brain ECs integrity and BBB function once Stx and factors associated to the STEC infection reach the brain parenchyma and therefore contribute to the development of the neuropathology observed in HUS.

Shiga toxin 1-induced inflammatory response in lipopolysaccharide-sensitized astrocytes is mediated by endogenous tumor necrosis factor alpha.

Hemolytic-uremic syndrome (HUS) is generally caused by Shiga toxin (Stx)-producing Escherichia coli. Endothelial dysfunction mediated by Stx is a central aspect in HUS development. However, inflammatory mediators such as bacterial lipopolysaccharide (LPS) and polymorphonuclear neutrophils (PMN) contribute to HUS pathophysiology by potentiating Stx effects. Acute renal failure is the main feature of HUS, but in severe cases, patients can develop neurological complications, which are usually associated with death. Although the mechanisms of neurological damage remain uncertain, alterations of the blood-brain barrier associated with brain endothelial injury is clear. Astrocytes (ASTs) are the most abundant inflammatory cells of the brain that modulate the normal function of brain endothelium and neurons. The aim of this study was to evaluate the effects of Stx type 1 (Stx1) alone or in combination with LPS in ASTs. Although Stx1 induced a weak inflammatory response, pretreatment with LPS sensitized ASTs to Stx1-mediated effects. Moreover, LPS increased the level of expression of the Stx receptor and its internalization. An early inflammatory response, characterized by the release of tumor necrosis factor alpha (TNF-alpha) and nitric oxide and PMN-chemoattractant activity, was induced by Stx1 in LPS-sensitized ASTs, whereas activation, evidenced by higher levels of glial fibrillary acid protein and cell death, was induced later. Furthermore, increased adhesion and PMN-mediated cytotoxicity were observed after Stx1 treatment in LPS-sensitized ASTs. These effects were dependent on NF-kappaB activation or AST-derived TNF-alpha. Our results suggest that TNF-alpha is a pivotal effector molecule that amplifies Stx1 effects on LPS-sensitized ASTs, contributing to brain inflammation and leading to endothelial and neuronal injury.