Mid-Liver Stage Arrest of Plasmodium falciparum Schizonts in Primary Porcine Hepatocytes.

Saskia C Van Der Boor,Geert-Jan Van Gemert,Alex E J Hanssen,Teun Bousema,Johannes H W De Wilt,Annie S P Yang,Robert W Sauerwein,Youri M Van Waardenburg,Matthew B B Mccall

doi:10.3389/fcimb.2022.834850

Abstract

During co-evolution Plasmodium parasites and vertebrates went through a process of selection resulting in defined and preferred parasite-host combinations. As such, Plasmodium falciparum (Pf) sporozoites can infect human hepatocytes while seemingly incompatible with host cellular machinery of other species. The compatibility between parasite invasion ligands and their respective human hepatocyte receptors plays a key role in Pf host selectivity. However, it is unclear whether the ability of Pf sporozoites to mature in cross-species infection also plays a role in host tropism. Here we used fresh hepatocytes isolated from porcine livers to study permissiveness to Pf sporozoite invasion and development. We monitored intra-hepatic development via immunofluorescence using anti-HSP70, MSP1, EXP1, and EXP2 antibodies. Our data shows that Pf sporozoites can invade non-human hepatocytes and undergo partial maturation with a significant decrease in schizont numbers between day three and day five. A possible explanation is that Pf sporozoites fail to form a parasitophorous vacuolar membrane (PVM) during invasion. Indeed, the observed aberrant EXP1 and EXP2 staining supports the presence of an atypical PVM. Functions of the PVM include the transport of nutrients, export of waste, and offering a protective barrier against intracellular host effectors. Therefore, an atypical PVM likely results in deficiencies that may detrimentally impact parasite development at multiple levels. In summary, despite successful invasion of porcine hepatocytes, Pf development arrests at mid-stage, possibly due to an inability to mobilize critical nutrients across the PVM. These findings underscore the potential of a porcine liver model for understanding the importance of host factors required for Pf mid-liver stage development.

Highlights

Plasmodium falciparum (Pf) is the causative agent for most of the mortality and morbidity associated with malaria
While there is an abundant number of parasite proteins implicated in sporozoite entry into hepatocytes such as circumsporozoite protein (CSP) [reviewed in (Sinnis and Coppi, 2007)], apical merozoite antigen 1 (AMA1), merozoite apical erythrocyte-binding ligand (MAEBL) (Yang et al, 2017), and the thrombospondin-related anonymous protein (TRAP) (Ejigiri et al, 2012), many of the corresponding host ligands remain to be identified
We show that Pf is capable of traversing, invading and partially maturing in non-human porcine hepatocytes

Summary

Introduction

Plasmodium falciparum (Pf) is the causative agent for most of the mortality and morbidity associated with malaria. While there is an abundant number of parasite proteins implicated in sporozoite entry into hepatocytes such as circumsporozoite protein (CSP) [reviewed in (Sinnis and Coppi, 2007)], apical merozoite antigen 1 (AMA1), merozoite apical erythrocyte-binding ligand (MAEBL) (Yang et al, 2017), and the thrombospondin-related anonymous protein (TRAP) (Ejigiri et al, 2012), many of the corresponding host ligands remain to be identified It is unclear why Pf sporozoites show exclusive human tropism, with natural infection appearing limited to humans (Liu et al, 2016; Sato, 2021), unlike their rodent malaria counterparts P. yoelii (Py) and P. berghei (Pb) (Prudencio et al, 2011). We investigated whether Pf sporozoites can invade and mature in porcine hepatocytes

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Conclusion