Plasmodium berghei sporozoites in nonreplicative vacuole are eliminated by a PI3P ‐mediated autophagy‐independent pathway

Abstract

The protozoan parasite Plasmodium, causative agent of malaria, invades hepatocytes by invaginating the host cell plasma membrane and forming a parasitophorous vacuole membrane (PVM). Surrounded by this PVM, the parasite undergoes extensive replication. Parasites inside a PVM provoke the Plasmodium-associated autophagyrelated (PAAR) response. This is characterised by a long-lasting association of the autophagy marker protein LC3 with the PVM, which is not preceded by phosphatidylinositol 3-phosphate (PI3P)-labelling. Prior to productive invasion, sporozoites transmigrate several cells and here we describe that a proportion of traversing sporozoites become trapped in a transient traversal vacuole, provoking a host cell response that clearly differs from the PAAR response. These trapped sporozoites provoke PI3P-labelling of the surrounding vacuolar membrane immediately after cell entry, followed by transient LC3-labelling and elimination of the parasite by lysosomal acidification. Our data suggest that this PI3P response is not only restricted to sporozoites trapped during transmigration but also affects invaded parasites residing in a compromised vacuole. Thus, host cells can employ a pathway distinct from the previously described PAAR response to efficiently recognise and eliminate Plasmodium parasites.

Plasmodium sporozoites on the move: Switching from cell traversal to productive invasion of hepatocytes

“…It should be noted that CT‐deficient mutant sporozoites can accumulate inside TVs, resulting in an apparent increase in total invasion events, although productive invasion is not affected (Risco‐Castillo et al, 2015; Steel et al, 2018), thus, making it difficult to distinguish between both invasion modes. Of note, the formation of TVs has been documented with P. yoelii and P. berghei sporozoites, in both hepatic and nonhepatic cells (Bindschedler et al, 2020; Risco‐Castillo et al, 2015), but has not been reported so far with P. falciparum . While the presence of a membrane surrounding intracellular sporozoites is insufficient to discriminate between TVs and PVs, the exclusion of host membrane proteins from the vacuole membrane is a distinctive feature of PVs (Risco‐Castillo et al, 2015).…”

Secretory Organelle Function in the Plasmodium Sporozoite

“…postinfection (Figure 3) [43,44]. Two studies based on live imaging highlighted that Plasmodium yoelii (Py) and Pb sporozoites form a transient vacuole (TV) during CT [44,45]. The acidification of the TV is believed to activate the micronemal perforin-like protein 1 (PLP1/Spect2), which lyses the TV membrane and might also subsequently wound the plasma membrane at the exit point [44].…”

“…The acidification of the TV is believed to activate the micronemal perforin-like protein 1 (PLP1/Spect2), which lyses the TV membrane and might also subsequently wound the plasma membrane at the exit point [44]. PLP1 mutants remain trapped in the TV and are degraded by proteases delivered upon the fusion of lysosomes with the TV [44,45]. CelTOS, known to have an important role in CT [20,21] partially dependent on its function in motility [21], is also suggested to be involved in cell membrane disruption after egressing the TV, as it displays pore-forming capabilities [46].…”

Autophagy Pathways in the Genesis of Plasmodium-Derived Microvesicles: A Double-Edged Sword?

“…They allow the parasite (i) to escape hepatocyte elimination strategies, and (ii) to use host cell nutrients and develop alternative scavenging pathways for its survival [ 5 , 6 , 35 , 36 ]. As summarized in Figure 1 A, the following two host cell pathways for clearing the parasite are triggered during Pb A sporozoite development in the liver: (1) in the early intrahepatic stage, parasites inside a TV, or in a deficient PV, are cleared by the induction of a PI3P-associated sporozoite elimination (PASE) process that differs from autophagy, but induces a lysosomal acidification pathway; (2) in the late intrahepatic stage, the PV membrane (PVM) engulfed parasite is targeted by LAP-like non-conventional autophagy that occurs independently of PI3K, RB1-inducible coiled-coil 1 (Rb1cc1), and Ulk1, and without the formation of reactive oxygen species (ROS) ( Figure 1 A) [ 37 , 38 , 39 , 40 ]. The absence of PI3K and Becn1 (beclin 1, autophagy related) in this process argues in favor of the involvement of alternative non-canonical autophagy, distinct from LAP, in the elimination of the parasite during this late hepatic stage [ 37 , 41 ].…”