Four distinct pathways of hemoglobin uptake in the malaria parasite Plasmodium falciparum

Abstract

During the bloodstage of malaria infection, the parasite internalizes and degrades massive amounts of hemoglobin from the host red blood cell. Using serial thin-section electron microscopy and threedimensional reconstruction, we demonstrate four independent, but partially overlapping, hemoglobin-uptake processes distinguishable temporally, morphologically, and pharmacologically. Early ring-stage parasites undergo a profound morphological transformation in which they fold, like a cup, onto themselves and in so doing take a large first gulp of host cell cytoplasm. This event, which we term the ''Big Gulp,'' appears to be independent of actin polymerization and marks the first step in biogenesis of the parasite's lysosomal compartment-the food vacuole. A second, previously identified uptake process, uses the cytostome, a well characterized and morphologically distinct structure at the surface of the parasite. This process is more akin to classical endocytosis, giving rise to small (<0.004 fl) vesicles that are marked by the early endosomal regulatory protein Rab5a. A third process, also arising from cytostomes, creates long thin tubes previously termed cytostomal tubes in an actin-dependent manner. The fourth pathway, which we term phagotrophy, is similar to the Big Gulp in that it more closely resembles phagocytosis, except that phagotrophy does not require actin polymerization. Each of these four processes has aspects that are unique to Plasmodium, thus opening avenues to antimalarial therapy.actin ͉ endocytosis ͉ food vacuole ͉ cytosome ͉ transport

Development and host cell modifications of Plasmodium falciparum blood stages in four dimensions

“…This agrees with observations indicating multiple digestive compartments in rings, whereas only a single large FV is found in later stages 3,7 . No evidence was found for the closure of the central cavity, a process termed the 'big gulp' that was proposed to create the single FV of trophozoites 8 . We find that the central cavity persists into the mid trophozoite stage as a structure independent of the FV or the multiple FVs in earlier stages (Figs 3 and 4a, Supplementary Movies 2 and 6).…”

“…The second phase, the 'trophozoite stage' , is characterized by rapid parasite growth and the appearance of haemozoin (remnant of digested haemoglobin) in the food vacuole (FV). The mode of haemoglobin internalization is still debated and might include several distinct processes [7][8][9] . Finally, the parasite enters the 'schizont stage' during which it generates up to 32 daughter merozoites that, after rupture of the host cell, invade new erythrocytes.…”

Influence of type IV pilus retraction on the architecture of the Neisseria gonorrhoeae-infected cell cortex

“…Two changes of 1.3 % (v/v) DMP-30 (Ladd Research) in Epon were followed by overnight incubation at 60 uC. Samples were glued onto a chuck, cut into 70 nm serial sections (Elliott, 2007), and prepared as previously described (Elliott et al, 2008). Serial sections were imaged on a Phillips CM-12S transmission electron microscope.…”

“…We further probed GC-microvilli interactions using the technique of serial ultrathin sectioning, TEM, and 3D image reconstruction (Elliott et al, 2008). A431 epithelial cells were infected and processed as described above.…”

Inhibiting Plasmodium falciparum growth and heme detoxification pathway using heme-binding DNA aptamers

“…Previous microscopy data indicate that early ring stage parasites are actively sampling the red cell cytosol, as demonstrated by their ability to take up non-toxic fluorescent and biotinylated dextrans from preloaded RBCs (23,34); similarly, ultrastructural and biochemical studies provide convincing evidence for hemozoin formation in ring-stage parasites (26, 37-39). More recent work in this area describes 4 distinct pathways used by P. falciparum to take up RBC cytosolic components, namely: (i) the ''big gulp'' (BG); (ii) small Hb vacuoles (SHV); (iii) cytostomal tubes; and (iv) phagotrophic uptake (40). The BG and SHV mechanisms, in particular, are active during the early ring stages and could account for uptake of concentrations of preloaded aptamers inhibitory to hemozoin formation occurring during ring-stage parasites.…”