Phosphodiesterase delta governs the mechanical properties of erythrocytes infected with Plasmodium falciparum gametocytes.

To persist in the blood circulation and to be available for mosquitoes, Plasmodium falciparum gametocytes modify the deformability and the permeability of their erythrocyte host via cyclic AMP (cAMP) signaling pathway. Cyclic nucleotide levels are tightly controlled by phosphodiesterases (PDE), however in Plasmodium these proteins are poorly characterized. Here, we characterize the P. falciparum phosphodiesterase delta (PfPDEδ) and we investigate its role in the cAMP signaling-mediated regulation of gametocyte-infected erythrocyte mechanical properties. Our results revealed that PfPDEδ is a dual-function enzyme capable of hydrolyzing both cAMP and cGMP, with a higher affinity for cAMP. We also show that PfPDEδ is the most expressed PDE in mature gametocytes and we propose that it is located in parasitophorous vacuole at the interface between the host cell and the parasite. We conclude that PfPDEδ is the master regulator of both the increase in deformability and the inhibition of channel activity in mature gametocyte stages, and may therefore play a crucial role in the persistence of mature gametocytes in the bloodstream.

The Phosphodiesterase Inhibitor Tadalafil Promotes Splenic Retention of Plasmodium falciparum Gametocytes in Humanized Mice.

The persistence of erythrocytes infected with Plasmodium falciparum gametocytes in the bloodstream is closely related to the modulation of their mechanical properties. New drugs that increase the stiffness of infected erythrocytes may thus represent a novel approach to block malaria parasite transmission. The phosphodiesterase inhibitor tadalafil has been shown to impair the ability of infected erythrocytes to circulate in an in vitro model for splenic retention. Here, we used a humanized mouse model to address in vivo the effect of tadalafil on the circulation kinetics of mature gametocyte-infected erythrocytes. We show that stiff immature gametocyte-infected erythrocytes are retained in the spleen of humanized mice at rates comparable to that of the in vitro model. Accordingly, tadalafil-induced stiffening of mature gametocyte-infected erythrocytes impairs their circulation in the bloodstream and triggers their retention by the spleen. These in vivo results validate that tadalafil is a novel drug lead potentially capable of blocking malaria parasite transmission by targeting GIE mechanical properties.

Tadalafil impacts the mechanical properties of Plasmodium falciparum gametocyte-infected erythrocytes.

Plasmodium falciparum gametocytes modify the mechanical properties of their erythrocyte host to persist for several weeks in the blood circulation and to be available for mosquitoes. These changes are tightly regulated by the plasmodial phosphodiesterase delta that decreases both the stiffness and the permeability of the infected host cell. Here, we address the effect of the phosphodiesterase inhibitor tadalafil on deformability and permeability of gametocyte-infected erythrocytes. We show that this inhibitor drastically increases isosmotic lysis of gametocyte-infected erythrocytes and impairs their ability to circulate in an in vitro model for splenic retention. These findings indicate that tadalafil represents a novel drug lead potentially capable of blocking malaria parasite transmission by impacting gametocyte circulation.

Plasmodium falciparum sexual parasites regulate infected erythrocyte permeability.

To ensure the transport of nutrients necessary for their survival, Plasmodium falciparum parasites increase erythrocyte permeability to diverse solutes. These new permeation pathways (NPPs) have been extensively characterized in the pathogenic asexual parasite stages, however the existence of NPPs has never been investigated in gametocytes, the sexual stages responsible for transmission to mosquitoes. Here, we show that NPPs are still active in erythrocytes infected with immature gametocytes and that this activity declines along gametocyte maturation. Our results indicate that NPPs are regulated by cyclic AMP (cAMP) signaling cascade, and that the decrease in cAMP levels in mature stages results in a slowdown of NPP activity. We also show that NPPs facilitate the uptake of artemisinin derivatives and that phosphodiesterase (PDE) inhibitors can reactivate NPPs and increase drug uptake in mature gametocytes. These processes are predicted to play a key role in P. falciparum gametocyte biology and susceptibility to antimalarials.

Increased circulation time of Plasmodium falciparum underlies persistent asymptomatic infection in the dry season.

The dry season is a major challenge for Plasmodium falciparum parasites in many malaria endemic regions, where water availability limits mosquito vectors to only part of the year. How P. falciparum bridges two transmission seasons months apart, without being cleared by the human host or compromising host survival, is poorly understood. Here we show that low levels of P. falciparum parasites persist in the blood of asymptomatic Malian individuals during the 5- to 6-month dry season, rarely causing symptoms and minimally affecting the host immune response. Parasites isolated during the dry season are transcriptionally distinct from those of individuals with febrile malaria in the transmission season, coinciding with longer circulation within each replicative cycle of parasitized erythrocytes without adhering to the vascular endothelium. Low parasite levels during the dry season are not due to impaired replication but rather to increased splenic clearance of longer-circulating infected erythrocytes, which likely maintain parasitemias below clinical and immunological radar. We propose that P. falciparum virulence in areas of seasonal malaria transmission is regulated so that the parasite decreases its endothelial binding capacity, allowing increased splenic clearance and enabling several months of subclinical parasite persistence.