Shiga Toxin Mediated Neurologic Changes in Murine Model of Disease

Abstract

Seizures and neurologic involvement have been reported in patients infected with Shiga toxin (Stx) producing E. coli, and hemolytic uremic syndrome (HUS) with neurologic involvement is associated with more severe outcome. We investigated the extent of renal and neurologic damage in mice following injection of the highly potent form of Stx, Stx2a, and less potent Stx1. As observed in previous studies, Stx2a brought about moderate to acute tubular necrosis of proximal and distal tubules in the kidneys. Brain sections stained with hematoxylin and eosin (H&E) appeared normal, although some red blood cell congestion was observed. Microglial cell responses to neural injury include up-regulation of surface-marker expression (e.g., Iba1) and stereotypical morphological changes. Mice injected with Stx2a showed increased Iba1 staining, mild morphological changes associated with microglial activation (thickening of processes), and increased microglial staining per unit area. Microglial changes were observed in the cortex, hippocampus, and amygdala regions, but not the nucleus. Magnetic resonance imaging (MRI) of Stx2a-treated mice revealed no hyper-intensities in the brain, although magnetic resonance spectroscopy (MRS) revealed significantly decreased levels of phosphocreatine in the thalamus. Less dramatic changes were observed following Stx1 challenge. Neither immortalized microvascular endothelial cells from the cerebral cortex of mice (bEnd.3) nor primary human brain microvascular endothelial cells were found to be susceptible to Stx1 or Stx2a. The lack of susceptibility to Stx for both cell types correlated with an absence of receptor expression. These studies indicate Stx causes subtle, but identifiable changes in the mouse brain.

Tissue Responses to Shiga Toxin in Human Intestinal Organoids

“…Although mice are resistant to Stx2a delivered by the intestinal route, they are highly susceptible to Stx injected IP and rapid weight loss is seen. 39 Stx2a injected into HIO transplants in mice lead to significant weight loss as early as day 2 after injection ( Figure 10B and C), very similar to what is seen after direct IP injection in mice. Although we were unable to assess maintenance of the epithelial barrier in the transplanted HIOs, transcytosis of Stx to the interstitial space could allow Stx to enter the circulation and access the sensitive tissue targets in the mice.…”

“…Although vascular and kidney involvement is prominent in human disease, in mice lethal disease occurs in the absence of gross pathologic changes to the vasculature or kidney. 39 However, lethal doses of Stx in mice are associated with neurologic changes, [39][40][41] and these could cause a decrease in feeding and drinking behaviors that result in weight loss. Neurologic complications also are seen in HUS, and are associated with more severe outcomes.…”

Recent Updates on Outbreaks of Shiga Toxin-Producing Escherichia coli and Its Potential Reservoirs

“…The toxins produced by STEC are classified as type 1 (Stx1) and type 2 (Stx2), and several Stx1/Stx2 subtypes and variants have been reported based on the receptor preference and toxin potency (Scheutz et al, 2012;Melton-Celsa, 2014). And among those, Stx2, which is more potent than Stx1, causes clinically severe weight loss and renal injury (Lentz et al, 2011;Pradhan et al, 2016).…”

Molecular Biology of Escherichia coli Shiga Toxins’ Effects on Mammalian Cells

“…Besides direct effects of the Stxs on endothelial cells, comprehensively reviewed by Bauwens et al [38], evidence exists that the toxins also directly act on neuronal cells [39] as well as innate [40,41] and adaptive immune cells [42]. While the clinical meaning of the former remains elusive [43], the presumptive importance of the latter effects recently became appreciated [9].…”