Role of lipid signaling in microneme exocytosis facilitating plasmodium invasion into host erythrocytes

Abstract

Malaria continues to be a major threat to human health killing thousands of people every newlineyear. It is caused by an intracellular obligate protozoan parasite, Plasmodium. Out of the newlinefive species of Plasmodium known to cause malaria in humans, Plasmodium falciparum newlineis the deadliest, causing maximum number of deaths. In humans, P. falciparum life cycle newlineis divided into two stages, liver and blood. Blood stage is the clinically significant stage. newlineDuring this stage, P. falciparum infects and multiplies within host erythrocytes. The newlineprocess of invasion is mediated by specific interactions between parasite proteins newlineharbored in apical organelles of invasive merozoites called micronemes and the receptors newlinepresent on host erythrocytes. The timely, regulated discharge of such parasite proteins newlinefrom micronemes to the merozoite surface enables receptor engagement and is the key to newlinesuccessful invasion. Microneme discharge is triggered by a rise in cytosolic calcium newline(Ca2+) following the activation of phospholipase C (PLC) leading to production of two newlinesecond messengers, Diacylglycerol (DAG) and Inositol triphosphate (IP3). DAG is newlineconverted by DAG kinase (DGK) to Phosphatidic acid (PA), which has been linked to newlineregulate exocytosis, in a wide variety of cell types. PA is rapidly converted to DAG by a newlinephosphatase, type-2 Phosphatidic Acid Phosphatase, PAP2. Together, DGK and PAP2 newlineregulate PA dynamics. In this thesis work, we detect and confirm the expression of DGK newlineand PAP2 homologue in P. falciparum and characterize them functionally. Exposure of newlinemerozoites to extracellular like ionic conditions results in rise in DAG and PA levels in newlinethe parasite. We demonstrate that production of PA by P. falciparum DGK (PfDGK1) newlineplays a key role in regulation of microneme discharge in P. falciparum merozoites. We newlineshow that treatment of P. falciparum merozoites with specific DGK inhibitor blocks newlineproduction of PA and inhibits microneme discharge as well as erythrocyte invasion. newlineFurthermore, we demonstrate that PA interacts with P. falciparum calcium