Toxoplasma gondii is an obligate intracellular parasite that invades host cells, creating a parasitophorous vacuole where it communicates with the host cell cytosol through the parasitophorous vacuole membrane. The lytic cycle of the parasite starts with its exit from the host cell followed by gliding motility, conoid extrusion, attachment, and invasion of another host cell. Here, we report that Ca²⁺ oscillations occur in the cytosol of the parasite during egress, gliding, and invasion, which are critical steps of the lytic cycle. Extracellular Ca²⁺ enhances each one of these processes. We used tachyzoite clonal lines expressing genetically encoded calcium indicators combined with host cells expressing transiently expressed calcium indicators of different colors, and we measured Ca²⁺ changes in both parasites and host simultaneously during egress. We demonstrated a link between cytosolic Ca²⁺ oscillations in the host and in the parasite. Our approach also allowed us to measure two new features of motile parasites, which were enhanced by Ca²⁺ influx. This is the first study showing, in real time, Ca²⁺ signals preceding egress and their direct link with motility, an essential virulence trait.

Serpentine receptors comprise a large family of membrane receptors distributed over diverse organisms, such as bacteria, fungi, plants and all metazoans. However, the presence of serpentine receptors in protozoan parasites is largely unknown so far. In the present study we performed a genome-wide search for proteins containing seven transmembrane domains (7-TM) in the human malaria parasite Plasmodium falciparum and identified four serpentine receptor-like proteins. These proteins, denoted PfSR1, PfSR10, PfSR12 and PfSR25, show membrane topologies that resemble those exhibited by members belonging to different families of serpentine receptors. Expression of the pfsrs genes was detected by Real Time PCR in P. falciparum intraerythrocytic stages, indicating that they potentially code for functional proteins. We also found corresponding homologues for the PfSRs in five other Plasmodium species, two primate and three rodent parasites. PfSR10 and 25 are the most conserved receptors among the different species, while PfSR1 and 12 are more divergent. Interestingly, we found that PfSR10 and PfSR12 possess similarity to orphan serpentine receptors of other organisms. The identification of potential parasite membrane receptors raises a new perspective for essential aspects of malaria parasite host cell infection.

TSSA (trypomastigote small surface antigen) is a polymorphic mucin-like molecule displayed on the surface of Trypanosoma cruzi trypomastigote forms. To evaluate its functional properties, we undertook comparative biochemical and genetic approaches on isoforms present in parasite stocks from extant evolutionary lineages (CL Brener and Sylvio X-10). We show that CL Brener TSSA, but not the Sylvio X-10 counterpart, exhibits dose-dependent and saturable binding towards non-macrophagic cell lines. This binding triggers Ca2+-based signalling responses in the target cell while providing an anchor for the invading parasite. Accordingly, exogenous addition of either TSSA-derived peptides or specific antibodies significantly inhibits invasion of CL Brener, but not Sylvio X-10, trypomastigotes. Non-infective epimastigote forms, which do not express detectable levels of TSSA, were stably transfected with TSSA cDNA from either parasite stock. Although both transfectants produced a surface-associated mucin-like TSSA product, epimastigotes expressing CL Brener TSSA showed a ~2-fold increase in their attachment to mammalian cells. Overall, these findings indicate that CL Brener TSSA functions as a parasite adhesin, engaging surface receptor(s) and inducing signalling pathways on the host cell as a prerequisite for parasite internalization. More importantly, the contrasting functional features of TSSA isoforms provide one appealing mechanism underlying the differential infectivity of T. cruzi stocks.

Cisplatin is a chemotherapy drug widely used in the treatment of solid tumors. However, nephrotoxicity has been reported in about one-third of patients undergoing cisplatin therapy. Proximal tubules are the main target of cisplatin toxicity and cellular uptake; elimination of this drug can modulate renal damage. Organic transporters play an important role in the transport of cisplatin into the kidney and organic cations transporter 2 (OCT-2) has been shown to be one of the most important transporters to play this role. On the other hand, multidrug and toxin extrusion 1 (MATE-1) transporter is the main protein that mediates the extrusion of cisplatin into the urine. Cisplatin nephrotoxicity has been shown to be enhanced by increased OCT-2 and/or reduced MATE-1 activity. Peroxisome proliferator-activated receptor alpha (PPAR-α) is the transcription factor which controls lipid metabolism and glucose homeostasis; it is highly expressed in the kidneys and interacts with both MATE-1 and OCT-2. Considering the above, we treated wild-type and PPAR-α knockout mice with cisplatin in order to evaluate the severity of nephrotoxicity. Cisplatin induced renal dysfunction, renal inflammation, apoptosis and tubular injury in wild-type mice, whereas PPAR-α deletion protected against these alterations. Moreover, we observed that cisplatin induced down-regulation of organic transporters MATE-1 and OCT-2 and that PPAR-α deletion restored the expression of these transporters. In addition, PPAR-α knockout mice at basal state showed increased MATE-1 expression and reduced OCT-2 levels. Here, we show for the first time that PPAR-α deletion protects against cisplatin nephrotoxicity and that this protection is via modulation of the organic transporters MATE-1 and OCT-2.