Brain endothelial barrier disruption during cerebral malaria

Summary Cerebral malaria is a serious complication of Plasmodium falciparum infection where infected red blood cells (iRBC) adhere to brain endothelial cells, eventually leading to disruption of the blood-brain barrier integrity. Our previous work has identified that P. falciparum-iRBC do not cause the death of brain-microvascular endothelial cells (HBMEC) in vitro, but induce specific signaling causing the disruption of inter-endothelial junctions and resulting in the loss of barrier function. We have also observed that hemozoin, a crystallized byproduct of the digestion of hemoglobin by the parasite, induces the disruption of inter-cellular HBMEC junctions when it was isolated from P. falciparum-iRBC, but not when it was synthetized in vitro. These findings suggest that natural hemozoin may serve as a carrier for P. falciparum active biomolecules that are the ultimate cause the disruption of the brain endothelium. To define the role of natural hemozoin in the disruption of brain endothelial barrier during cerebral malaria we will characterize this effect in vitro and determine whether hemozoin acts as a carrier for other bioactive parasite-derived molecules. The identification of specific bioactive molecules will be attempted. The activity of natural hemozoin will be validated in an in vitro model of the human BBB neuro-endothelial environment, which represents the complexity of the neurovascular unit, as a physiological model to mimic the microenvironment of cerebral malaria. The transcriptomic analysis of endothelial cells in the neurovascular unit model of cerebral malaria will allow the identification of candidate genes and pathways involved in brain endothelial barrier disruption. We have also observed that P. falciparum iRBC modulate the cholesterol synthesis pathway in HBMEC and that inhibition of the enzyme farnesyl transferase in this pathway prevents endothelial barrier disruption by P. falciparum-iRBC in vitro and reduces neurological signs and mortality induced by cerebral malaria in mice. We will validate these results in the neurovascular unit model and define the role of farnesyl transferase mediated brain endothelial barrier disruption by downregulating expression of farnesyl transferase in vitro and by studying the development of cerebral malaria in mice conditionally deficient for this enzyme in endothelial cells. To investigate the mechanism underlying barrier disruption by farnesyl transferase we will perform an unbiassed farnesylation screen to identify candidate substrates of this enzyme that will be functionally validated. In parallel, the role of RhoGTPases, which are typically involved in endothelial barrier integrity, will be defined in the context of cerebral malaria in vitro and in mice. Since no specific therapies are available for cerebral malaria, understanding the molecular mechanisms mediating the loss of brain endothelial barrier integrity in response to P. falciparum is essential for the development of much needed adjunctive treatments for this syndrome.