Binding of Plasmodium falciparum to CD36 can be shielded by the glycocalyx

Casper Hempel,Jørgen Anders Lindholm Kurtzhals,Trine Staalsø,Christian William Wang

doi:10.1186/s12936-017-1844-6

Casper Hempel, Jørgen Anders Lindholm Kurtzhals + Show 2 more

Open Access

https://doi.org/10.1186/s12936-017-1844-6

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Abstract

BackgroundPlasmodium falciparum-infected erythrocytes sequester in the microcirculation due to interaction between surface-expressed parasite proteins and endothelial receptors. Endothelial cells are covered in a carbohydrate-rich glycocalyx that shields against undesired leukocyte adhesion. It was investigated if the cellular glycocalyx affects the binding of P. falciparum-infected erythrocytes to CD36 in vitro.MethodsGlycocalyx growth was followed in vitro by using azido sugars and cationized ferritin detecting O-glycoproteins and negatively charged proteoglycans, respectively. P. falciparum (clone FCR3/IT) was selected on Chinese hamster ovary (CHO) cells transfected with human CD36. Cytoadhesion to CHO CD36 at 1–4 days after seeding was quantified by using a static binding assay.ResultsThe glycocalyx thickness of CHO cells increased during 4 days in culture as assessed by metabolic labelling of glycans with azido sugars and with electron microscopy studying the binding of cationized ferritin to cell surfaces. The functional importance of this process was addressed in binding assays by using CHO cells transfected with CD36. In parallel with the maturation of the glycocalyx, antibody-binding to CD36 was inhibited, despite stable expression of CD36. P. falciparum selected for CD36-binding recognized CD36 on CHO cells on the first day in culture, but the binding was lost after 2–4 days.ConclusionThe endothelial glycocalyx affects parasite cytoadhesion in vitro, an effect that has previously been ignored. The previously reported loss of glycocalyx during experimental malaria may play an important role in the pathogenesis of malaria complications by allowing the close interaction between infected erythrocytes and endothelial receptors.

Highlights

Plasmodium falciparum-infected erythrocytes sequester in the microcirculation due to interaction between surface-expressed parasite proteins and endothelial receptors
The cytoadhesion is mediated by variant surface antigens (VSA) that the parasites export to the erythrocyte surface [7]
The present study examined the effect that the glycocalyx may have on parasite cytoadhesion

Summary

Introduction

Plasmodium falciparum-infected erythrocytes sequester in the microcirculation due to interaction between surface-expressed parasite proteins and endothelial receptors. Endothelial cells are covered in a carbohydrate-rich glycocalyx that shields against undesired leukocyte adhesion It was investigated if the cellular glycocalyx affects the binding of P. falciparum-infected erythrocytes to CD36 in vitro. During the intra erythrocytic part of their life cycle Plasmodium spp. invade erythrocytes and remodel the erythrocytic surface both in terms of exposed proteins, nanoprotrusions (‘knobs’) and rigidity [6] These changes render the infected erythrocytes susceptible to splenic removal and cytoadhesion to endothelial cells in the microcirculation is essential for parasite survival. It is well known that the endothelial glycocalyx shields leukocytes and platelets from undesired binding to the endothelium [17, 18] This led to the proposal that cytoadhesion of parasite-infected erythrocytes may be affected by the glycocalyx [19]. The glycocalyx grows continuously during in vitro culture [20] and in order to assess how this affected cytoadhesion a simple culture system was used to quantify changes in parasite binding to CD36 as a consequence of glycocalyx growth on Chinese hamster ovary (CHO) cells

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