Malaria proteases mediate inside-out egress of gametocytes from red blood cells following parasite transmission to the mosquito

Abstract

SummaryMalaria parasites reside in human erythrocytes within a parasitophorous vacuole. The parasites are transmitted from the human to the mosquito by the uptake of intraerythrocytic gametocytes during a blood meal, which in the midgut become activated by external stimuli and subsequently egress from the enveloping erythrocyte. Gametocyte egress is a crucial step for the parasite to prepare for fertilization, but the molecular mechanisms of egress are not well understood. Via electron microscopy, we show that Plasmodium falciparum gametocytes exit the erythrocyte by an inside-out type of egress. The parasitophorous vacuole membrane (PVM) ruptures at multiple sites within less than a minute following activation, a process that requires a temperature drop and parasite contact with xanthurenic acid. PVM rupture can also be triggered by the ionophore nigericin and is sensitive to the cysteine protease inhibitor E-64d. Following PVM rupture the subpellicular membrane begins to disintegrate. This membrane is specific to malaria gametocytes, and disintegration is impaired by the aspartic protease inhibitor EPNP and the cysteine/serine protease inhibitor TLCK. Approximately 15 min post activation, the erythrocyte membrane ruptures at a single breaking point, which can be inhibited by inhibitors TLCK and TPCK. In all cases inhibitor treatment results in interrupted gametogenesis.

ThePlasmodium falciparumblood stages acquire factor H family proteins to evade destruction by human complement

“…While in MZs and in non‐activated intraerythrocytic gametocytes GAP50 localizes to the IMC, the protein relocates to the gamete plasmalemma upon activation (Simon et al , 2013). During this time, the IMC disintegrates to leave the newly formed gametes defined by a single membrane (Sologub et al , 2011). Consequently, antibodies directed against GAP50 are able to reduce FH binding to the gamete surface and inhibit parasite transmission from the human to the mosquito, making GAP50 a promising new candidate for transmission blocking vaccines (Simon et al , 2013).…”

The development of malaria parasites in the mosquito midgut

“…Signals inducing gamete formation include a drop of temperature by approximately 5 °C, which is mandatory for gametocyte activation, and the presence of the mosquito‐derived molecule xanthurenic acid (XA), a metabolic intermediate of the tryptophan catabolism. An additional trigger of gametogenesis is the increase of extracellular pH from 7.2 to about 8 (Kawamoto et al ., 1991; Billker et al ., 1997, 1998; Garcia et al ., 1998; Sologub et al ., 2011). …”

“…Gametocytes egress from the erythrocyte via an inside‐out mode, during which the membrane of the PV (PVM) ruptures prior to the opening of the erythrocyte membrane (EM). PVM rupture occurs at multiple sites and is a Ca 2+ ‐independent event that takes less than 2 min following parasite uptake by the mosquito (Sologub et al ., 2011). Electron‐dense vesicles, the osmiophilic bodies, can be observed accumulating underneath the rupture sites, which disappear simultaneously with the disintegration of the PVM, while the activated gametocytes are rounding‐up (Sologub et al ., 2011; reviewed in Wirth and Pradel, 2012).…”

“…This event occurs approximately 6 min post‐activation of the gametocyte and results in the release of the erythrocyte cytoplasm; hence, the gamete is then contained by the EM only (Deligianni et al ., 2013; Wirth et al ., 2014). Approximately 15 min after uptake by the blood‐feeding mosquito, the EM opens and releases the fertile gamete (Sologub et al ., 2011; Wirth et al ., 2014; reviewed in Wirth and Pradel, 2012). …”

Biology of Malaria Parasites

“…The half life of the gametocytes has been estimated to be between 2 and 3 days but some are known to persist for up to four weeks. [ 18,19 ] The five recognized morphological stages were first described by Field and Shute in 1956.…”