Characterization of the Tubovesicular Network in Plasmodium vivax Liver Stage Hypnozoites and Schizonts.

Kayla Sylvester,Benoît Witkowski,Dennis E Kyle,Emily R Derbyshire,Mckenna C Crawford,Steven P Maher,Amélie Vantaux,Dora Posfai,Michael K Tran

doi:10.3389/fcimb.2021.687019

Abstract

Plasmodium is a genus of apicomplexan parasites which replicate in the liver before causing malaria. Plasmodium vivax can also persist in the liver as dormant hypnozoites and cause clinical relapse upon activation, but the molecular mechanisms leading to activation have yet to be discovered. In this study, we use high-resolution microscopy to characterize temporal changes of the P. vivax liver stage tubovesicular network (TVN), a parasitophorous vacuole membrane (PVM)-derived network within the host cytosol. We observe extended membrane clusters, tubules, and TVN-derived vesicles present throughout P. vivax liver stage development. Additionally, we demonstrate an unexpected presence of the TVN in hypnozoites and observe some association of this network to host nuclei. We also reveal that the host water and solute channel aquaporin-3 (AQP3) associates with TVN-derived vesicles and extended membrane clusters. AQP3 has been previously shown to localize to the PVM of P. vivax hypnozoites and liver schizonts but has not yet been shown in association to the TVN. Our results highlight host-parasite interactions occur in both dormant and replicating liver stage P. vivax forms and implicate AQP3 function during this time. Together, these findings enhance our understanding of P. vivax liver stage biology through characterization of the TVN with an emphasis on the presence of this network in dormant hypnozoites.

Highlights

Apicomplexans constitute a large group of parasitic protozoans that cause diseases, including the five species of Plasmodium that cause human malaria
Schizont and hypnozoite populations are of similar sizes and are difficult to distinguish before 6 dpi, but our analysis suggested tubovesicular network (TVN) features were more abundant in smaller sized parasites when observed at 8 dpi
While few exoerythrocytic forms (EEFs) were noted with a growth area between 60 μm2 and 200 μm2 at this time, these forms were excluded from classification of hypnozoite or schizont to ensure no ambiguity between the two forms

Summary

Introduction

Apicomplexans constitute a large group of parasitic protozoans that cause diseases, including the five species of Plasmodium that cause human malaria. Sporozoites transform and rapidly replicate to yield tens of thousands of merozoites from a single schizont (Frischknecht et al, 2004; Prudêncio et al, 2006; Ejigiri and Sinnis, 2009; Ploemen et al, 2009). This stage is asymptomatic but a prerequisite to the infection of red blood cells (RBCs) that leads to disease. Efforts to identify compounds capable of inhibiting hypnozoites are hampered by our limited understanding of the molecular pathways that enable parasite survival and activation during this stage

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