Annexin Induces Cellular Uptake of Extracellular Vesicles and Delays Disease in Escherichia coli O157:H7 Infection.

Ashmita Tontanahal,Diana Karpman,Ida Arvidsson

doi:10.3390/microorganisms9061143

Abstract

Enterohemorrhagic Escherichia coli secrete Shiga toxin and lead to hemolytic uremic syndrome. Patients have high levels of circulating prothrombotic extracellular vesicles (EVs) that expose phosphatidylserine and tissue factor and transfer Shiga toxin from the circulation into the kidney. Annexin A5 (AnxA5) binds to phosphatidylserine, affecting membrane dynamics. This study investigated the effect of anxA5 on EV uptake by human and murine phagocytes and used a mouse model of EHEC infection to study the effect of anxA5 on disease and systemic EV levels. EVs derived from human whole blood or HeLa cells were more readily taken up by THP-1 cells or RAW264.7 cells when the EVs were coated with anxA5. EVs from HeLa cells incubated with RAW264.7 cells induced phosphatidylserine exposure on the cells, suggesting a mechanism by which anxA5-coated EVs can bind to phagocytes before uptake. Mice treated with anxA5 for six days after inoculation with E. coli O157:H7 showed a dose-dependent delay in the development of clinical disease. Treated mice had lower levels of EVs in the circulation. In the presence of anxA5, EVs are taken up by phagocytes and their systemic levels are lower, and, as EVs transfer Shiga toxin to the kidney, this could postpone disease development.

Highlights

Annexins are a group of highly conserved proteins that interact with phospholipids on cellular membranes in a calcium-dependent manner [1,2]
HeLa cell-derived extracellular vesicles (EVs) incubated with RAW264.7 cells exhibited an increase in EV uptake when the EVs were pretreated with anxA5 (Figure 1c), but not when only the cells were pretreated
RAW264.7 cells had no effect on EV uptake

Summary

Introduction

Annexins are a group of highly conserved proteins that interact with phospholipids on cellular membranes in a calcium-dependent manner [1,2]. They are both intracellular and extracellular [3] and, by forming a scaffold on membranes, exert a multitude of functions affecting membrane dynamics and the cytoskeleton, stabilizing membrane defects [4], inducing membrane repair [5] and linking membranes [6]. This is enabled by its binding to phosphatidylserine (PS) and self-assembly to form a 2D-lattice on the cell surface in a calcium-dependent manner [4]

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