Adapa, S. R. | bioRxiv Science

bioRxiv2017

Mitochondrial heteroplasmy is responsible for Atovaquone drug resistance in Plasmodium falciparum

Malaria is the most significant parasitic disease affecting humans, with 212 million cases and 429,000 deaths in 2 0151, and resistance to existing drugs endangers the global malaria elimination campaign. Atovaquone (ATO) is a safe and potent antimalarial drug that acts on cytochrome b (cyt. b) of the mitochondrial electron transport chain (mtETC) in Plasmodium falciparum, yet treatment failures result in resistance-conferring SNPs in cyt. b. Herein we report that rather than the expected de novo selection of resistance, previously unknown mitochondrial diversity is the genetic mechanism responsible for resistance to ATO, and potentially other cyt. b targeted drugs. We found that P. falciparum harbors cryptic cyt. b. Y268S alleles in the multicopy ([~]22 copies) mitochondrial genome prior to drug treatment, a phenomenon known as mitochondrial heteroplasmy. Parasites with cryptic Y268S alleles readily evolve into highly resistant parasites with >95% Y268S copies under in vitro ATO selection. Further we uncovered high mitochondrial diversity in a global collection of 1279 genomes in which heteroplasmic polymorphisms were >3-fold more prevalent than homoplasmic SNPs. Moreover, significantly higher mitochondrial genome copy number was found in Asia (e.g., Cambodia) versus Africa (e.g., Ghana). Similarly, ATO drug selections in vitro induced >3-fold mitochondrial copy number increases in ATO resistant lines. Hidden mitochondrial diversity is a previously unknown mechanism of antimalarial drug resistance and characterization of mitochondrial heteroplasmy will be of paramount importance in combatting resistance to antimalarials targeting the electron transport chain.

cell biology↗

bioRxiv2017

Transmission Expression Signature in Nascent Plasmodium vivax Blood Stage Infection

The lack of a continuous in vitro culture system for Plasmodium vivax severely limits our knowledge of pathophysiology of the most widespread malaria parasite. To gain direct understanding of P. vivax human infections, we used Next Generation Sequencing data mining to unravel parasite in vivo expression profiles for P. vivax, and P. falciparum as comparison. We performed cloud and local computing to extract parasite transcriptomes from publicly available raw data of human blood samples. We developed a Poisson Modelling (PM) method to confidently identify parasite derived transcripts in mixed RNAseq signals of infected host tissues. We successfully retrieved and reconstructed parasite transcriptomes from infected patient blood as early as the first blood stage cycle; and the same methodology did not recover any significant signal from controls. Surprisingly, these first generation blood parasites already show strong signature of transmission, which indicates the commitment from asexual-to-sexual stages. Further, we develop mathematical models for P. vivax and P. falciparum to assess the epidemiological impact of possible 7-day early stage transmission and P. vivax complex life cycle. The study uncovers the earliest onset of P. vivax blood pathogenesis and highlights the challenges of P. vivax eradication programs.\n\nAuthor summaryWe discovered that P. vivax in vivo parasitemia is associated with gametocytogenesis expression signature within the first blood stage cycle, that is, eight days from a mosquito bite. Our results suggest that asexual-to-sexual commitment may happen with first generation merozoite infection. This allows for the possibility of transmission at this early stage, much earlier than for P. falciparum. Our novel mathematical model accounts for multiple unique aspects of P. vivax biology to advance our understanding of expected disease prevalence, and compares the results to those of P. falciparum. We demonstrate that given the presence of asymptotical carriers and the possibility of relapses, earlier parasite transmission is capable of increasing the spread of disease within human populations. In summary, P. vivax gametogenesis has the potential to fast track the transmission cycle, which will drive enhanced propagation of the disease during the transmission season and clinical relapses.

systems biology↗