Elucidating the functions of red blood cell factors in malaria parasite invasion

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PROJECT SUMMARY/ ABSTRACT Malaria is a leading cause of morbidity and mortality globally, responsible for the deaths of hundreds of thousands of individuals per year, primarily children and pregnant women. Effective control is hampered by the lack of a vaccine and continually emerging drug resistance. Most cases of severe malaria are caused by Plasmodium falciparum, which is an obligate intracellular parasite of human red blood cells (RBCs). Therefore, critical host factors may provide an untapped source of new therapeutic targets. Red blood cell invasion is a complex process that involves interactions between several parasite ligands and host receptors, but there remains a fundamental gap in knowledge regarding the functional role(s) of RBC host factors for P. falciparum. This gap in our knowledge is, in part, due to RBCs being terminally differentiated and lacking DNA, thereby precluding conventional genetic experimentation. To surmount this roadblock, we have recently developed CRISPR-Cas9-based methods to generate null mutants in primary human hematopoietic stem cells and efficiently differentiate them ex-vivo to mature cultured RBCs (cRBCs), opening new opportunities for functional analysis of these important cells. Our objective in this proposal is to comprehensively determine the specific roles and functions of two novel RBC host factors required for P. falciparum invasion, CD44 and CD55, which were recently identified from a forward genetic screen. Our central hypothesis, supported by strong preliminary data, is that these critical surface receptors play distinct yet synergistic roles to facilitate P. falciparum invasion through their interactions with parasite ligands and subsequent signaling to the host cell. In the first aim, we will determine the precise steps involving CD44 and CD55 in P. falciparum invasion of human RBCs using live cell imaging and advanced microscopy. In the second aim, avidity-based and proximity labeling proteomic approaches will be used to identify P. falciparum and RBC binding partners for CD44 and CD55. In the final aim, we will define host RBC signaling pathways activated by P. falciparum invasion, and test their dependence on CD44 and CD55. Together, these studies will generate a comparative understanding of the mechanistic roles of two novel host factors crucial for P. falciparum invasion. In addition to revealing new insights into the fundamental cell biology of Plasmodium invasion and human RBCs, this work will stimulate new therapeutic and vaccine approaches to treat one of the most important infectious diseases of humankind.