A key role for lipoic acid synthesis duringPlasmodiumliver stage development

Abstract

SUMMARY The successful navigation of malaria parasites through their life cycle, which alternates between vertebrate hosts and mosquito vectors, requires a complex interplay of metabolite synthesis and salvage pathways. Using the rodent parasite Plasmodium berghei, we have explored the synthesis and scavenging pathways for lipoic acid, a short-chain fatty acid derivative that regulates the activity of α-ketoacid dehydrogenases including pyruvate dehydrogenase. In Plasmodium, lipoic acid is either synthesized de novo in the apicoplast or is scavenged from the host into the mitochondrion. Our data show that sporozoites lacking the apicoplast lipoic acid protein ligase LipB are markedly attenuated in their infectivity for mice, and in vitro studies document a very late liver stage arrest shortly before the final phase of intra-hepatic parasite maturation. LipB-deficient asexual blood stage parasites show unimpaired rates of growth in normal in vitro or in vivo conditions. However, these parasites showed reduced growth in lipid-restricted conditions induced by treatment with the lipoic acid analog 8-bromo-octanoate or with the lipid-reducing agent clofibrate. This finding has implications for understanding Plasmodium pathogenesis in malnourished children that bear the brunt of malarial disease. This study also highlights the potential of exploiting lipid metabolism pathways for the design of genetically attenuated sporozoite vaccines.

Fatty acid metabolism in the Plasmodium apicoplast: Drugs, doubts and knockouts

“…This view was supported by genetic and biochemical studies in Plasmodium and T. gondii, which demonstrated loss of FASII impacted only PDH lipoylation [45,165], and lipoic acid scavenged from the medium contributed uniquely to lipoylation of mitochondrial enzyme complexes [83,85]. However, in addition to decreasing PDH lipoylation, both the P. falciparum and P. berghei LipB knockouts displayed a lesser but significant reduction in the lipoylation of mitochondrial enzymes [84,164]. These findings challenge the view that apicoplast and mitochondrial lipoic acid metabolism act in strict isolation, and indicate further research is required to fully understand the role of LipB and the lipoic acid synthesis pathway beyond the apicoplast.…”

“…In P. berghei, disruption of LipB had no effect on bloodstage growth, but again led to a substantial decrease in PDH lipoylation [164]. Beyond the bloodstage, loss of PbLipB resulted in defects only in late liver stage development, with knockout sporozoites typically failing to establish a patent infection in mice [164]. As this phenotype mirrored that of the PDH and FASII knockouts in rodent models [97][98][99][100], it indicated the defect most likely resulted from disruption of FASII [164].…”

“…However, as PDH lipoylation was not completely abolished in the PfLipB knockout, it suggested another enzyme could partially complement for its loss, and LplA2 was subsequently identified as a second but less efficient source of apicoplast octanoyl transferase activity [84] (see Section 3.3). In P. berghei, disruption of LipB had no effect on bloodstage growth, but again led to a substantial decrease in PDH lipoylation [164]. Beyond the bloodstage, loss of PbLipB resulted in defects only in late liver stage development, with knockout sporozoites typically failing to establish a patent infection in mice [164].…”

“…Beyond the bloodstage, loss of PbLipB resulted in defects only in late liver stage development, with knockout sporozoites typically failing to establish a patent infection in mice [164]. As this phenotype mirrored that of the PDH and FASII knockouts in rodent models [97][98][99][100], it indicated the defect most likely resulted from disruption of FASII [164]. However, as the PbLipB knockout was less attenuated than the FASII knockouts, it suggested FASII activity was not completely abolished, and indicated the reduced level of PDH lipoylation maintained in the line was sufficient to allow some parasites to successfully complete liver stage development.…”

Type II Fatty Acid Biosynthesis Is Essential for Plasmodium falciparum Sporozoite Development in the Midgut of Anopheles Mosquitoes

“…On the other hand, P. berghei liver-stage parasites lacking FabI in C57BL/6 mice or FabB/F in either BALB/c or C57BL/6 mice were severely but incompletely attenuated, resulting in breakthrough infection that developed into normal blood-stage growth (11,14). Furthermore, deletion of P. yoelii genes coding for the apicoplast-targeted pyruvate dehydrogenase complex (PDH) (18), which is essential for the creation of acetyl-coenzyme A (CoA), a precursor of FAS-II, as well as deletion of the gene coding for P. berghei apicoplast-targeted octanoyl transferase (19), which is necessary for the lipoylation of the PDH E2 subunit, led to late liver-stage arrest (19,20). Thus, studies on models of rodent malaria have shown that the deletion of genes involved in all aspects of FAS-II cause growth arrest during liver-stage development.…”