RNA-Seq Analysis Illuminates the Early Stages ofPlasmodiumLiver Infection

Abstract

24The apicomplexan parasites Plasmodium spp. are the causative agents of malaria, a disease 25 that poses a significant global health burden. Plasmodium spp. initiate infection of the human host 26 by transforming and replicating within hepatocytes. This liver stage (LS) is poorly understood 27 when compared to other Plasmodium life stages, which has hindered our ability to target these 28 parasites for disease prevention. We conducted an extensive RNA-seq analysis throughout the 29 Plasmodium berghei LS, covering as early as 2 hours post infection (hpi) and extending to 48 hpi. 30Our data revealed that hundreds of genes are differentially expressed at 2 hpi, and that multiple 31 genes shown to be important for later infection are upregulated as early as 12 hpi. Using 32 hierarchical clustering along with co-expression analysis, we identified clusters functionally 33 enriched for important liver-stage processes such as interactions with the host cell and redox 34 homeostasis. Furthermore, some of these clusters were highly correlated to the expression of 35ApiAP2 transcription factors, while showing enrichment of mostly uncharacterized DNA binding 36 motifs. This finding presents potential LS targets for these transcription factors, while also hinting 37 at alternative uncharacterized DNA binding motifs and transcription factors during this stage. Our 38 work presents a window into the previously undescribed transcriptome of Plasmodium upon host 39 hepatocyte infection to enable a comprehensive view of the parasite's LS. These findings also 40 provide a blueprint for future studies that extend hypotheses concerning LS gene function in P. 41 berghei to human-infective Plasmodium parasites. 42 43 IMPORTANCE 44The LS of Plasmodium infection is an asymptomatic yet necessary stage for producing 45 blood-infective parasites, the causative agents of malaria. Blocking the liver stage of the life cycle 46 can prevent clinical malaria, but relatively less is known about the parasite's biology at this stage. 47 Using the rodent model P. berghei, we investigated whole-transcriptome changes occurring as 48 early as 2 hpi of hepatocytes. The transcriptional profiles of early time points (2, 4, 12, and 18 hpi) 49have not been accessible before due to the technical challenges associated with liver-stage 50 infections. Our data now provides insights into these early parasite fluxes that may facilitate 51 establishment of infection, transformation and replication in the liver. 52 INTRODUCTION 54Plasmodium spp., the causative agents of malaria, are eukaryotic parasites with a largely 55 conserved and complex life cycle that begins in the mammalian host by invasion of hepatocytes. 56In these host cells, a single parasite, termed a sporozoite, will transform and then replicate 57 asexually to form thousands of merozoites, or blood-infective forms (1). After maturation and 58 release from the liver, parasites replicate within erythrocytes causing the clinical manifestation of 59 malaria. Some parasites differentiate into sexual forms ...