Extracellular Vesicle Abundance, but Not a High Aggregation-Prone Peptide Cargo, Is Associated with Dihydroartemisinin Exposure in .

Our understanding of the molecular mechanisms undergirding artemisinin (ART) resistance in is currently based on two organizing principles: reduced hemoglobin trafficking into the digestive food vacuole, resulting in lower levels of activated ART, and increased tolerance to ART-induced oxidative stress in the infected erythrocyte. We had previously proposed an extracellular vesicle (EV) export model of ART resistance in . This model predicts that EV abundance will be altered by ART exposure and that the peptide cargo of EVs from the ART-exposed condition will be enriched with aggregation-prone peptides. We tested the predictions of the EV export hypothesis in this study using in vitro culture assays of an ART-resistant transgenic line engineered on a 3D7 background (R561H) and a 3D7 knock-out line (PfVps60KO) with deficient EV production phenotype. EV enrichment was obtained from in vitro parasite culture supernatants via a series of ultracentrifugation and filtration steps, followed by size exclusion chromatography. A quality check on EVs was performed using dynamic light scattering. Liquid chromatography with tandem mass spectrometry was used to determine the proteome cargo from extracted EVs, and parasite peptides were queried for aggregation-prone tendency using open-access software. We report that dihydroartemisinin (DHA) exposure was positively correlated with EV abundance (coefficient estimate = 1038.58, confidence interval of 194.86-1882.30, and -value = 0.018) and suggests that EV biogenesis is part of the parasite's response to DHA/ART. Furthermore, our findings suggest the expression of a non-constitutive DHA-induced alternate EV biogenesis pathway as the PfVps60KO was observed to produce the highest number of EVs under DHA exposure. Finally, we show that EVs from both ART-susceptible and resistant parasites under DHA exposure carry a cargo of Chorein N-terminal domain-containing protein (PF3D7_1021700) with a high aggregation-prone index (prion-like domain [PrLD] score = 26.5) out of nine identified parasite peptides. The former of these findings is in concordance with the EV export hypothesis, which posits that the removal of DHA/ART-induced aggregated and/or misfolded peptides is critical to the parasite's survival under DHA/ART exposure. This observation further implicates EVs in the development of the ART-resistant phenotype. However, the finding of one aggregation-prone peptide out of the nine parasite proteins in the EV cargo does not sufficiently support the EV export hypothesis. Future replicates of this study and further interrogations of the EV export hypothesis are needed.