Molecular interactions between Anopheles stephensi midgut cells and Plasmodium berghei: the time bomb theory of ookinete invasion of mosquitoes

Abstract

We present a detailed analysis of the interactions between Anopheles stephensi midgut epithelial cells and Plasmodium berghei ookinetes during invasion of the mosquito by the parasite. In this mosquito, P.berghei ookinetes invade polarized columnar epithelial cells with microvilli, which do not express high levels of vesicular ATPase. The invaded cells are damaged, protrude towards the midgut lumen and suffer other characteristic changes, including induction of nitric oxide synthase (NOS) expression, a substantial loss of microvilli and genomic DNA fragmentation. Our results indicate that the parasite in¯icts extensive damage leading to subsequent death of the invaded cell. Ookinetes were found to be remarkably plastic, to secrete a subtilisin-like serine protease and the GPI-anchored surface protein Pbs21 into the cytoplasm of invaded cells, and to be capable of extensive lateral movement between cells. The epithelial damage in¯icted is repaired ef®ciently by an actin pursestring-mediated restitution mechanism, which allows the epithelium to`bud off' the damaged cells without losing its integrity. A new model, the time bomb theory of ookinete invasion, is proposed and its implications are discussed.

Nitric oxide metabolites induced in Anopheles stephensi control malaria parasite infection

“…In parallel studies, provision of L-NAME, but not D-NAME, to A. stephensi significantly decreased the percentage of apoptotic Plasmodium berghei ookinetes in the midgut lumen [4]. At later times during midgut invasion, 5% of ookinetes travel 5-6 cell diameters in the epithelium, perhaps in an effort to escape the toxic diffusible · NO and · NO metabolites [3]. This extensive movement may explain the observation that ~95% of ookinetes appear to escape the epithelium [3] yet only a few remain to survive as oocysts [reviewed in 5].…”

“…Induction of NOS expression has been correlated to ookinete invasion as revealed by diaphorase staining [1] and immunofluorescence [3]. Synthesis of · NO limits parasite development in the mosquito midgut as shown by dietary provision of a NOS inhibitor (L-NAME),in the infectious blood meal [1].…”

“…At later times during midgut invasion, 5% of ookinetes travel 5-6 cell diameters in the epithelium, perhaps in an effort to escape the toxic diffusible · NO and · NO metabolites [3]. This extensive movement may explain the observation that ~95% of ookinetes appear to escape the epithelium [3] yet only a few remain to survive as oocysts [reviewed in 5].…”

A long and winding road: The Plasmodium sporozoite's journey in the mammalian host

“…Plasmodium sporozoites are not the only Apicomplexans that can migrate through cells, although they may have perfected the process. The ookinete stage of Plasmodium [22] as well as sporozoite stages of Eimeria [23] and Toxoplasma [24] are also capable of cell traversal though these zoites appear to cause more damage to the traversed cell.…”

Cellular and molecular interactions between the apicomplexan parasitesPlasmodiumandTheileriaand their host cells

“…In both processes, a prerequisite of parasite transmigration is secretion of the parasite protein CelTOS into the cytoplasm of the traversed cell (Kariu et al, 2006). Epithelial cells traversed by ookinetes invariably die by apoptosis and are extruded into the mosquito midgut (Han et al, 2000). It may be that the damage caused by entry of the ookinete, a much broader cell than the sporozoite, cannot be overcome by membrane repair, leading to cell death by apoptosis.…”