Ectopic Expression of Plasmodium vivax vir Genes in P. falciparum Affects Cytoadhesion via Increased Expression of Specific var Genes

Plasmodium falciparum-infected erythrocytes (PfIEs) adhere to endothelial cell receptors (ECRs) of blood vessels mainly via PfEMP1 proteins to escape elimination via the spleen. Evidence suggests that P. vivax-infected reticulocytes (PvIRs) also bind to ECRs, presumably enabled by VIR proteins, as shown by inhibition experiments and studies with transgenic P. falciparum expressing vir genes. To test this hypothesis, our study investigated the involvement of VIR proteins in cytoadhesion using vir gene-expressing P. falciparum transfectants. Those VIR proteins with a putative transmembrane domain were present in Maurer's clefts, and some were also present in the erythrocyte membrane. The VIR protein without a transmembrane domain (PVX_050690) was not exported. Five of the transgenic P. falciparum cell lines, including the one expressing PVX_050690, showed binding to CD36. We observed highly increased expression of specific var genes encoding PfEMP1s in all CD36-binding transfectants. These results suggest that ectopic vir expression regulates var expression through a yet unknown mechanism. In conclusion, the observed cytoadhesion of P. falciparum expressing vir genes depended on PfEMP1s, making this experimental unsuitable for characterizing VIR proteins.

Adhesion between P. falciparum infected erythrocytes and human endothelial receptors follows alternative binding dynamics under flow and febrile conditions

Characterizing the adhesive dynamics of Plasmodium falciparum infected erythrocytes (IEs) to different endothelial cell receptors (ECRs) in flow is a big challenge considering available methods. This study investigated the adhesive dynamics of IEs to five ECRs (CD36, ICAM-1, P-selectin, CD9, CSA) using simulations of in vivo-like flow and febrile conditions. To characterize the interactions between ECRs and knobby and knobless IEs of two laboratory-adapted P. falciplarum isolates, cytoadhesion analysis over time was performed using a new tracking bioinformatics method. The results revealed that IEs performed rolling adhesion exclusively over CD36, but exhibited stationary binding to the other four ECRs. The absence of knobs affected rolling adhesion both with respect to the distance travelled by IEs and their velocity. Knobs played a critical role at febrile temperatures by stabilizing the binding interaction. Our results clearly underline the complexity of the IE-receptor interaction and the importance of knobs for the survival of the parasite at fever temperatures, and lead us to propose a new hypothesis that could open up new strategies for the treatment of malaria.

Characterisation of Plasmodium falciparum populations selected on the human endothelial receptors P-selectin, E-selectin, CD9 and CD151

The ability of the parasite Plasmodium falciparum to evade the immune system and be sequestered within human small blood vessels is responsible for severe forms of malaria. The sequestration depends on the interaction between human endothelial receptors and P. falciparum erythrocyte membrane protein 1 (PfEMP1) exposed on the surface of the infected erythrocytes (IEs). In this study, the transcriptomes of parasite populations enriched for parasites that bind to human P-selectin, E-selectin, CD9 and CD151 receptors were analysed. IT4_var02 and IT4_var07 were specifically expressed in IT4 parasite populations enriched for P-selectin-binding parasites; eight var genes (IT4_var02/07/09/13/17/41/44/64) were specifically expressed in isolate populations enriched for CD9-binding parasites. Interestingly, IT4 parasite populations enriched for E-selectin- and CD151-binding parasites showed identical expression profiles to those of a parasite population exposed to wild-type CHO-745 cells. The same phenomenon was observed for the 3D7 isolate population enriched for binding to P-selectin, E-selectin, CD9 and CD151. This implies that the corresponding ligands for these receptors have either weak binding capacity or do not exist on the IE surface. Conclusively, this work expanded our understanding of P. falciparum adhesive interactions, through the identification of var transcripts that are enriched within the selected parasite populations.

The effects of the painkiller diclofenac and hypoxia on gene transcription and antioxidant system in the gills of three-spined stickleback

Aquatic organisms face multiple stressors in natural ecosystems. More and more often painkillers are detected in surface waters since their prescription has increased worldwide within the last years. Here we examined the effects of the non-steroidal anti-inflammatory drug (NSAID) diclofenac and hypoxia on three-spined sticklebacks (Gasterosteus aculeatus). We exposed sticklebacks to an environmentally relevant concentration of diclofenac (1μg/L) for 14days, to 24h of hypoxia (2.0mg O2/L), and a combination of both. Hypoxia and diclofenac both can be associated with oxidative stress in fish, but it is unclear whether they would act synergistically. Expression analysis of genes related to antioxidant response, hypoxia response, and chemical metabolism in gills showed that diclofenac alone had little effect, while the combination of hypoxia and diclofenac affected transcript levels most, indicating synergistic effects of these stressors. Of the antioxidant enzymes, only superoxide dismutase activity remained unchanged by treatments, while glutathione peroxidase (GPx) was the most affected antioxidant response on both the transcript and activity levels. Our results suggest that diclofenac may lead to suppressed catalase (CAT) activity but increased GPx activity, probably as compensatory mechanism to remove increasing H2O2 in the gills, and that this response is not affected by hypoxia. The activities of lactate dehydrogenase, CAT, and GPx also showed temporal variability during treatments, which can be attributable to tissue-specific circadian rhythms. Our study shows how responses to NSAIDs and hypoxia can interact in fish, suggesting that getting more insight into temporal variation and about the different levels of regulation of environmental responses is necessary in future studies.

Hypoxia and the pharmaceutical diclofenac influence the circadian responses of three-spined stickleback

Pollution with low concentrations of pharmaceuticals, especially when combined with low-oxygen conditions (hypoxia), is a threat to aquatic ecosystems worldwide. The non-steroidal anti-inflammatory drug diclofenac is commonly detected in wastewater effluents, and has potential to accumulate in the bile of fish. Diclofenac has been shown to activate aryl hydrocarbon receptor (AHR), which induces transcription in the metabolic enzyme cytochrome P450 1a (cyp1a). Previously, crosstalk has been shown to occur between AHR and hypoxia inducible factor 1 (HIF-1). In addition, both of these transcription factors interact with the proteins regulating circadian (24-h) rhythms in vertebrates. Yet little is known about the significance of these interactions during simultaneous exposure to chemicals and hypoxia in fish in vivo. We exposed wild-caught three-spined sticklebacks (Gasterosteus aculeatus) to diclofenac (1 μg/L, 14 days), hypoxia (2.0 mg/L, up to 24h) and the combination of both. We then analyzed markers of chemical biotransformation (EROD activity, cyp1a and ahr mRNA levels), glycolysis (lactate dehydrogenase (LDH) enzyme activity, ldh and enolase 1a mRNA levels), and the transcription of core circadian clock genes clock and period 1 in liver tissue. Samples were taken at three time points during the light period in order to address disturbances in the circadian variation of metabolic processes. The results show that mRNA levels and LDH activity tended to be lowest before the dark period, but this pattern was disturbed by hypoxia and diclofenac. Diclofenac and hypoxia co-exposure induced EROD activity more strongly than diclofenac exposure alone, while cyp1a mRNA level was increased also by hypoxia and diclofenac alone. LDH activity and mRNA expression showed a clear time-dependent response during hypoxia, which is consistent with the previously suggested decreased accumulation of HIF-1 during the dark period. Furthermore, LDH activity and transcription was disturbed by diclofenac, indicating important effects of environmental pollutants in disturbing natural acclimation. This study demonstrates the need for more studies to understand the potential disturbances in endogenous rhythms caused by environmental pollution in natural populations.