Abstract
Patatin-like phospholipases (PNPLAs) are highly conserved enzymes of prokaryotic and eukaryotic organisms with major roles in lipid homeostasis. The genome of the malaria parasite Plasmodium falciparum encodes four putative PNPLAs with predicted functions during phospholipid degradation. We here investigated the role of one of the plasmodial PNPLAs, a putative PLA2 termed PNPLA1, during blood stage replication and gametocyte development. PNPLA1 is present in the asexual and sexual blood stages and here localizes to the cytoplasm. PNPLA1-deficiency due to gene disruption or conditional gene-knockdown had no effect on intraerythrocytic growth, gametocyte development and gametogenesis. However, parasites lacking PNPLA1 were impaired in gametocyte induction, while PNPLA1 overexpression promotes gametocyte formation. The loss of PNPLA1 further leads to transcriptional down-regulation of genes related to gametocytogenesis, including the gene encoding the sexual commitment regulator AP2-G. Additionally, lipidomics of PNPLA1-deficient asexual blood stage parasites revealed overall increased levels of major phospholipids, including phosphatidylcholine (PC), which is a substrate of PLA2 . PC synthesis is known to be pivotal for erythrocytic replication, while the reduced availability of PC precursors drives the parasite into gametocytogenesis; we thus hypothesize that the higher PC levels due to PNPLA1-deficiency prevent the blood stage parasites from entering the sexual pathway.
Highlights
Following a first round of multiplication in the human liver, the unicellular malaria parasite Plasmodium falciparum enters the blood stream and replicates in human red blood cells (RBCs)
Because PC synthesis is pivotal for erythrocytic replication, while the reduced availability of PC precursors drives the parasite into gametocytogenesis, we hypothesize that the high PC levels due to PNPLA1deficiency prevent the blood stage parasites from entering the sexual pathway
2.4/ PNPLA1-deficiency results in an overall increase of major phospholipids Since the deficiency of PNPLA1 impaired the proper gametocytogenesis pathway, we investigated whether the parasite lipid composition was altered in the PNPLA1-knock out (KO) lines, to the putative role of the enzyme and the role of phospholipids for maintaining normal asexual blood stage growth
Summary
The gene PF3D7_0209100 of P. falciparum encodes a putative patatin-like phospholipase, termed PNPLA1, with a molecular weight of 78 kDa. When the asexual blood stages were treated with 4-BPB, significantly reduced gametocyte numbers were observed in the WT upon –SerM incubation compared the untreated WT and the solvent control (Fig. 5E). This alternative route of PC synthesis via the PMT pathway appears to be upregulated in gametocytes, explaining the higher tolerance of these stages towards serum-free medium (Brancucci et al, 2017) While these data demonstrate the high sensitivity of the plasmodial blood stages to the availability of phospholipids, we show that PNPLA1 of the parasite is involved in the phospholipid-dependent switch from asexual blood stage replication to gametocyte development. Asexual blood stage parasites lacking PNPLA1, due to conventional gene-KO or conditional gene-KD, are less responsive to triggers of gametocyte commitment, including lysoPC deficiency This loss-of-function phenotype can be mimicked by the PLA2 inhibitor 4-BPB, pointing to direct link between PNPLA1 activity and gametocyte induction. Future studies need to identify, how the malaria parasite monitors its phospholipid levels and unveil the downstream signaling pathways leading to the activation of transcriptional regulators of sexual commitment
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