Plasmodium vivax inhibits erythroid cell growth through altered phosphorylation of the cytoskeletal protein ezrin.

BACKGROUND: The underlying causes of severe malarial anaemia are multifactorial. In previously reports, Plasmodium vivax was found to be able to directly inhibited erythroid cell proliferation and differentiation. The molecular mechanisms underlying the suppression of erythropoiesis by P. vivax are remarkably complex and remain unclear. In this study, a phosphoproteomic approach was performed to dissect the molecular mechanism of phosphoprotein regulation, which is involved in the inhibitory effect of parasites on erythroid cell development. METHODS: This study describes the first comparative phosphoproteome analysis of growing erythroid cells (gECs), derived from human haematopoietic stem cells, exposed to lysates of infected erythrocytes (IE)/uninfected erythrocytes (UE) for 24, 48 and 72 h. This study utilized IMAC phosphoprotein isolation directly coupled with LC MS/MS analysis. RESULTS: Lysed IE significantly inhibited gEC growth at 48 and 72 h and cell division resulting in the accumulation of cells in G0 phase. The relative levels of forty four phosphoproteins were determined from gECs exposed to IE/UE for 24-72 h and compared with the media control using the label-free quantitation technique. Interestingly, the levels of three phosphoproteins: ezrin, alpha actinin-1, and Rho kinase were significantly (p < 0.05) altered. These proteins display interactions and are involved in the regulation of the cellular cytoskeleton. Particularly affected was ezrin (phosphorylated at Thr567), which is normally localized to gEC cell extension peripheral processes. Following exposure to IE, for 48-72 h, the ezrin signal intensity was weak or absent. This result suggests that phospho-ezrin is important for actin cytoskeleton regulation during erythroid cell growth and division. CONCLUSIONS: These findings suggest that parasite proteins are able to inhibit erythroid cell growth by down-regulation of ezrin phosphorylation, leading to ineffective erythropoiesis ultimately resulting in severe malarial anaemia. A better understanding of the mechanisms of ineffective erythropoiesis may be beneficial in the development of therapeutic strategies to prevent severe malarial anaemia.

Acute erythroid toxicity in visceral leishmaniasis: a rare complication of antimonial therapy.

The spectrum of side-effects of sodium stibogluconate is well described, however, little is known regarding the acute erythroid toxicity caused by this drug. We hereby present a case with this unusual complication of antimonial therapy. A 6-year-old male with leishmaniasis was started on parenteral sodium stibogluconate. During the course of treatment, his hemoglobin (Hb) dropped from 7.2 g/dl to 3.5 g/dl. Bone-marrow aspirate showed karyorrhexis in many erythroid precursors with several Leishmania donovanii bodies. Sodium stibogluconate was stopped and amphotericin-B was started. Four days after the cessation of the antimonials, the patient's Hb improved to 5 gm/dl with a corrected reticulocyte count of 10% indicating bone-marrow erythroid regeneration. The exact mechanism of this acute erythroid toxicity of sodium stibogluconate remains unexplored.

Hematopoietic features and apoptosis in the bone marrow of severe Plasmodium falciparum-infected patients: preliminary study.

The mechanism of anemia in severe falciparum malaria is still not completely understood. The purpose of this study was to determine whether apoptosis in the erythroid lineage causes anemia in falciparum malaria. Bone marrow aspirated from 8 severe falciparum malaria patients, 3 normal volunteers and 5 retrospective normal bone marrow smears were investigated. By light microscopic study, 5 of 8 hyperparasitemic patients had hypocellular bone marrows and erythroid hypoplasia, whereas the other 3 patients had normal cellularity. The mean myeloid : erythroid ratio of these 5 patients was significantly (p < or = 0.05) higher than normal. Apoptosis of bone marrow nucleated cells (BMNC) could be determined from the exposure of phosphatidylserine (PS) on the cell membrane but not DNA fragmentation (180-250 bp) or ultrastructural morphology. The percentages of apoptotic BMNC and apoptotic erythroid cells in bone marrow from each patient and controls varied from low to high, and were not associated with parasitemia. This study suggests that destruction of erythroid lineage, particularly through apoptosis regulation, cannot solely account for anemia in falciparum malaria.