Environmental Cues Modulate Microglial Cell Behavior Upon Shiga Toxin 2 From Enterohemorrhagic Escherichia coli Exposure

Abstract

Shiga toxin (Stx) produced by enterohemorrhagic E. coli produces hemolytic uremic syndrome and encephalopathies in patients, which can lead to either reversible or permanent neurological abnormalities, or even fatal cases depending on the degree of intoxication. It has been observed that the inflammatory component plays a decisive role in the severity of the disease. Therefore, the objective of this work was to evaluate the behavior of microglial cell primary cultures upon Stx2 exposure and heat shock or lipopolysaccharide challenges, as cues which modulate cellular environments, mimicking fever and inflammation states, respectively. In these contexts, activated microglial cells incorporated Stx2, increased their metabolism, phagocytic capacity, and pro-inflammatory profile. Stx2 uptake was associated to receptor globotriaosylceramide (Gb3)-pathway. Gb3 had three clearly distinguishable distribution patterns which varied according to different contexts. In addition, toxin uptake exhibited both a Gb3-dependent and a Gb3-independent binding depending on those contexts. Altogether, these results suggest a fundamental role for microglial cells in pro-inflammatory processes in encephalopathies due to Stx2 intoxication and highlight the impact of environmental cues.

Cognitive Deficits Found in a Pro-inflammatory State are Independent of ERK1/2 Signaling in the Murine Brain Hippocampus Treated with Shiga Toxin 2 from Enterohemorrhagic Escherichia coli

“…According to the present data, in our encephalopathy murine model, the deleterious effect produced by Stx2 together with LPS [10,11,16,29] suggests a potentially synergistic action rather than an additive one (Fig 6). While both toxins induced the activation and translocation of NF-κB to the nucleus, they performed it independently through two distinct pathways: LPS activated the ERK1/2 pathway, and Stx2 activated an ERK1/2-independent pathway.…”

“…Considering previous reports [9][10][11], Stx2 may damage hippocampal neurons in at least two ways: first, Stx2 binds to the canonical Gb3 receptor localized in CA1 hippocampal neurons; and, second, indirectly by an inflammatory process with MG playing a fundamental role [10]. Indeed, we have recently reported in an in vitro model that Stx2 is up-taken by MG through its receptor Gb3, which produces an increase in MG metabolism, phagocytic capacity and pro-inflammatory cytokine release [29].…”

Cognitive deficits found in a pro-inflammatory state are independent of ERK 1/2 signaling in the murine brain hippocampus treated with Shiga toxin 2 from enterohemorrhagicEscherichia Coli

“…Considering previous reports [9–11], Stx2 may damage hippocampal neurons in at least two ways: first, Stx2 binds to the canonical Gb3 receptor localized in CA1 hippocampal neurons; and, second, indirectly by an inflammatory process with MG playing a fundamental role [10]. Indeed, we have recently reported in an in vitro model that Stx2 is up-taken by MG through its receptor Gb3, which produces an increase in MG metabolism, phagocytic capacity and pro-inflammatory cytokine release [29].…”

Role of Globotriaosylceramide in Physiology and Pathology

“…In rat microglial primary cultures, Stx2 is incorporated through Gb3-dependent and independent pathways. Recent work by Berdasco et al (2019) confirmed the presence of Gb3 in microglia primary cultures and showed that these cells have context-specific reactions to Stx2 which included either a fever condition or the presence of endotoxin upon treatment with Stx2. The metabolic and functional states, as well as the subcellular distribution and expression of Gb3, vary according to the context, promoting the expression of pro-inflammatory cytokines and microglial phagocytic capacity ( Berdasco et al, 2019 ).…”

“…Recent work by Berdasco et al (2019) confirmed the presence of Gb3 in microglia primary cultures and showed that these cells have context-specific reactions to Stx2 which included either a fever condition or the presence of endotoxin upon treatment with Stx2. The metabolic and functional states, as well as the subcellular distribution and expression of Gb3, vary according to the context, promoting the expression of pro-inflammatory cytokines and microglial phagocytic capacity ( Berdasco et al, 2019 ). In addition, in Vero, Burkitt’s lymphoma, Caco-2 and Hep-2 cell lines, the binding of Stx to Gb3 induces cytotoxic effects by inhibiting protein synthesis and inducing apoptosis and necrosis ( Karpman et al, 1998 ; Jones et al, 2000 ; Silberstein et al, 2011 ).…”