The apicoplast link to fever-survival and artemisinin-resistance in the malaria parasite

Abstract

BackgroundThe emergence and spread of Plasmodium falciparum parasites resistant to front-line antimalarial artemisinin-combination therapies (ACT) threatens to erase the considerable gains against the disease of the last decade. We developed a new large-scale phenotypic screening pipeline and used it to carry out the first large-scale forward-genetic phenotype screen in P. falciparum to identify genes that allow parasites to survive febrile temperatures.ResultsScreening identified more than 200 P. falciparum mutants with differential responses to increased temperature. These mutants were more likely to be sensitive to artemisinin derivatives as well as to heightened oxidative stress. Major processes critical for P. falciparum tolerance to febrile temperatures and artemisinin included highly essential, conserved pathways associated with protein-folding, heat-shock and proteasome-mediated degradation, and unexpectedly, isoprenoid biosynthesis, which originated from the parasite’s algal endosymbiont-derived plastid, the apicoplast. Apicoplast-targeted genes in general were up-regulated in response to heat shock, as were other Plasmodium genes with orthologs in plant and algal genomes.ConclusionsPlasmodium falciparum parasites appear to exploit their innate febrile-response mechanisms to mediate resistance to artemisinin. Both responses depend on endosymbiotic cyanobacterium-related ancestral genes in the parasite’s genome, suggesting a link to the evolutionary origins of Plasmodium parasites in free-living ancestors.

Plasmodium falciparum resistance to ACTs: Emergence, mechanisms, and outlook

“…The free radicals and ROS generated from activation of ART can damage parasite DNA ( Gopalakrishnan and Kumar, 2015 ), and the mutations in genes associated with DNA synthesis, mismatch repair, and oxidative damage response in ART-resistant parasites in the GMS bestow these parasites a greater ability to deal with DNA damage caused by ART exposure ( Miotto et al, 2013 ; Takala-Harrison et al, 2013 ; Xiong et al, 2020 ). A recent forward genetic, phenotypic screen for heat-shock response genes using the piggyback transposon system demonstrated that the malaria parasite uses a shared crisis-response mechanism (upregulated UPR and downregulated endocytosis and ubiquitination) to relieve the build-up of damaged proteins from different stresses such as febrile temperatures and drugs ( Zhang et al, 2020 ).…”

“…Recent studies also shed light on the significance of mitochondrion and apicoplast in stress response and ART resistance ( Mok et al, 2021 ; Zhang et al, 2020 ). Mitochondria are identified as one of the cellular targets of ARTs ( Wang et al, 2010 ) and mitochondrial activity is critical for the survival and regrowth of dormant parasites after DHA exposure ( Peatey et al, 2015 ).…”

“…These facts highlight the involvement of mitochondria in regulating heme levels and dealing with ART-caused oxidative stress response. Following the finding that the fatty acid synthesis pathway in the apicoplast remains active in DHA-induced dormant parasites ( Chen et al, 2014 ), a recent genetic screen further implicated the apicoplast's critical involvement in heat-shock response and K13-mediated ART resistance ( Zhang et al, 2020 ). Especially, the isoprenoid biosynthesis pathway of the apicoplast is needed for prenylation of a restricted set of proteins (<15) that are predominated by the Rab GTPases in the blood-stage parasite ( Suazo et al, 2016 ).…”

“…The lack of prenylation disrupts Rab 5's localization, uptake and trafficking of the RBC cytoplasm to the FV, and FV integrity ( Howe et al, 2013 ; Kennedy et al, 2019 ). Thus, these studies have identified a mechanistic link between elevated isoprenoid biosynthesis and ART resistance, which involves the Rab proteins and their modification by prenylation, interactions with K13, and participation in hemoglobin endocytosis ( Zhang et al, 2020 ).…”

The PfAP2-HS transcription factor protects malaria parasites from febrile temperatures

“…Specific binding to the G-box is conferred by D1 10 , but activation of these genes during HS strictly requires D3, which is not capable of binding DNA in vitro 10 and likely participates in protein-protein interactions or dimerization 34 . Other components of the protein folding machinery necessary for HS survival [35][36][37] are constitutively expressed or induced later, but the rapid PfAP2-HS-driven response is essential to avoid irreversible damage, as parasites lacking D3 or the full protein fail to survive HS. While PfAP2-HS is not evolutionarily related with HSF1 5,8 , the conserved master regulator of the HS response from yeast to mammals, it appears to play an analogous role.…”