Disruption of a Plasmodium falciparum cyclic nucleotide phosphodiesterase gene causes aberrant gametogenesis

Abstract

SummaryPhosphodiesterase (PDE) and guanylyl cyclase (GC) enzymes are key components of the cGMP signalling pathway and are encoded in the genome of Plasmodium falciparum. Here we investigate the role of specific GC and PDE isoforms in gamete formation -a process that is essential for malaria transmission and occurs in the Anopheles mosquito midgut following feeding on an infected individual. Details of the intracellular signalling events controlling development of the male and female gametes from their precursors (gametocytes) remain sparse in P. falciparum. Previous work involving the addition of pharmacological agents to gametocytes implicated cGMP in exflagellation -the emergence of highly motile, flagellated male gametes from the host red blood cell. In this study we show that decreased GC activity in parasites having undergone disruption of the PfGCb gene had no significant effect on gametogenesis. By contrast, decreased cGMP-PDE activity during gametocyte development owing to disruption of the PfPDEd gene, led to a severely reduced ability to undergo gametogenesis. This suggests that the concentration of cGMP must be maintained below a threshold in the developing gametocyte to allow subsequent differentiation to proceed normally. The data indicate that PfPDEd plays a crucial role in regulating cGMP levels during sexual development.

The development of malaria parasites in the mosquito midgut

“…Parasites lacking GCβ were not impaired in gametogenesis, while in P . berghei revealed a severe defect in ookinete motility (Hirai et al ., 2006; Taylor et al ., 2008), indicating that GCα, not GCβ, is important for gametocyte activation.…”

“…Interestingly, deletion of the gene coding for PDEδ leads to an impaired ability of P . falciparum to undergo gametogenesis, indicating that the tight regulation of intracellular cGMP concentrations is crucial for gametocyte activation and that premature, abnormally high cGMP levels have a deleterious effect on this process (Taylor et al ., 2008). …”

Active site similarity between human and Plasmodium falciparum phosphodiesterases: considerations for antimalarial drug design

“…As a consequence, it has been suggested that targeting P. falciparum PDEs should disrupt a range of physiological processes and weaken or kill the organism [15][16][17][18][19]. Interest in this area has been focussed on understanding the role of PDEs in the parasite life cycle [15,16,20]. In addition, Yuasa and co-workers have screened compounds against PfPDEa which has identified potential starting points for medicinal chemistry [21].…”

“…Furthermore, various studies have indicated that cyclic nucleotides are likely to play a major role in the cell biology of P. falciparum (including sexual development, hepatocyte infection, gametocytogenesis, cell cycle control, and exocytosis) [15,16]. As a consequence, it has been suggested that targeting P. falciparum PDEs should disrupt a range of physiological processes and weaken or kill the organism [15][16][17][18][19]. Interest in this area has been focussed on understanding the role of PDEs in the parasite life cycle [15,16,20].…”

A synthetic cGMP-sensitive gene switch providing Viagra®-controlled gene expression in mammalian cells and mice

“…cGMP signaling is essential for cardiovascular homeostasis; it controls relaxation and proliferation in vascular smooth muscle cells (Archer et al, 1994;Yu et al, 1997) in addition to contractility and hypertrophy in cardiac myocytes (Fiedler et al, 2002;Mohan et al, 1996). cGMP signaling is also essential for a variety of human pathogens including the malaria parasite Plasmodium falciparum (Taylor et al, 2008).…”