The intracellular parasite Toxoplasma gondii depends on the synthesis of long‐chain and very long‐chain unsaturated fatty acids not supplied by the host cell

Abstract

SUMMARY Apicomplexa are parasitic protozoa that cause important human diseases including malaria, cryptosporidiosis and toxoplasmosis. The replication of these parasites within their target host cell is dependent on both salvage as well as de novo synthesis of fatty acids. In T. gondii, fatty acid synthesis via the apicoplast-localized FASII is essential for pathogenesis, while the role of two other fatty acid biosynthetic complexes remains unclear. Here we demonstrate that the ER-localized fatty acid elongation (ELO) is essential for parasite growth. Conditional knock-down of the non-redundant hydroxyacyl-CoA dehydratase and enoyl-CoA reductase enzymes in the ELO pathway severely repressed intracellular parasite growth. 13C-glucose and 13C-acetate labeling and comprehensive lipidomic analyses of these mutants showed a selective defect in synthesis of unsaturated long and very long chain fatty acids (LCFAs and VLCFAs) and depletion of phosphatidylinositol and phosphatidylethanolamine species containing unsaturated LCFAs and VLCFAs. This requirement for ELO pathway was by-passed by supplementing the media with specific fatty acids, indicating active, but inefficient import of host fatty acids. Our experiments highlight a gap between the fatty acid needs of the parasite and availability of specific fatty acids in the host cell that the parasite has to close using a dedicated synthesis and modification pathway.

Metabolic Cooperation of Glucose and Glutamine Is Essential for the Lytic Cycle of Obligate Intracellular Parasite Toxoplasma gondii

“…pathways (34,35). Accordingly, our bioinformatics search identified a putative acetyl-CoA synthetase (TgACS) in the parasite database (ToxoDB).…”

Apicomplexan Energy Metabolism: Carbon Source Promiscuity and the Quiescence Hyperbole

“…Indeed, computational and experimental studies show that T. gondii ACL is essential when accompanied by deletion of the other source of cytosolic acetyl-CoA, acetyl-CoA synthase (ACS) [83]. It follows that reduced levels of mitochondrial [BCKDH E1/ knockout (KO)] or cytoplasmic (ACL-ACS double KO) acetyl-CoA may have implications for the activities and balance of fatty acid biosynthesis and/or acetylation [84][85][86][87][88].…”

“…After FASII, fatty acids can be further elongated at the endoplasmic reticulum (ER) membrane [84,85], while FASI (a large cytosolic enzyme that, in many eukaryotes, is responsible for all fatty acid biosynthesis) may also contribute to fatty acid production in T. gondii. Both elongation and FASI require acetyl-CoA as a carbon donor, and this can theoretically be made in the cytosol via acylcitrate lyase (ACL, Figure 3) using citrate exported from the mitochondrion.…”

Apicoplast fatty acid synthesis is essential for pellicle formation at the end of cytokinesis in Toxoplasma gondii

“…Although T. gondii obtains lipids from the host cell (Charron and Sibley, 2002;Quittnat et al, 2004;Bisanz et al, 2006), intracellular tachyzoites also synthesize several major fatty acids de novo (Ramakrishnan et al, 2012), and both the FASII and the endoplasmic reticulum fatty acid elongation pathway (ELO) (Mazumdar et al, 2006;Ramakrishnan et al, 2012Ramakrishnan et al, , 2015 are essential for parasite survival. In contrast, the importance of the FASI pathway for parasite biology remains unclear.…”