Funktionale Charakterisierung der Patatin-ähnlichen Phospholipase PNPLA1 in den Blut- und Sexualstadien des humanpathogenen Malariaerregers Plasmodium falciparum

• Functional characterization of the patatin-like phospholipase PNPLA1 in the blood and sexual stages of the human malaria parasite Plasmodium falciparum

Flammersfeld, Ansgar; Pradel, Gabriele (Thesis advisor); Antonin, Wolfram (Thesis advisor); Spehr, Marc (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020

Abstract

The malaria pathogen P. falciparum displays a well-regulated lipid metabolism required to ensure its survival in the human host as well as in the mosquito vector. Therefore, proteins involved in synthesis and acquisition of phospholipids were extensively studied in the past and represent prime targets for malaria therapeutics. In contrast, not much is known about phospholipases, which may have potentially important functions in membrane dynamics, host cell membrane penetration, cell proliferation, and cell signaling due to their phospholipid-hydrolytic activity. In a comprehensive genome analysis carried out within the scope of this work, a total of 22 putative phospholipases were identified in the P. falciparum genome, four of which are annotated as patatin like phospholipases (PNPLA). PNPLA1, a putative PLA2, is present in the asexual and sexual blood stages and here localizes to the cytosol. PNPLA1-deficient parasites showed normal asexual replication, gametocyte development and gametogenesis. However, parasites lacking PNPLA1 formed significantly less gametocyte numbers and showed delayed development of the five maturation stages, while episomal overexpression of PNPLA1 promoted gametocyte formation. The loss of PNPLA1 function also led to a transcriptional deregulation of genes related to game to cytogenesis, including the gene encoding the key regulator of sexual commitment, the transcription factor AP2-G. Comparative lipidodomic analysis of asexual PNPLA1-deficient parasites revealed overall increased levels of major phospholipids, in particular phosphatidylcholine (PC), which is the main component of plasmodial membranes. PC synthesis is known to be pivotal for erythrocytic replication, while reduced availability of PC precursors drives the parasite into game to cytogenesis. Thus, the higher PC levels due to PNPLA1-deficiency might prevent the blood stage parasites from entering the sexual pathway. By the first characterization of a plasmodial PNPLA, the results of this thesis contribute to the elucidation of the biochemical and functional role of phospholipases in the life cycle of the malaria pathogen and deepen the understanding of the sexual differentiation pathway.