Ixodes scapularis Tick Cells Control Anaplasma phagocytophilum Infection by Increasing the Synthesis of Phosphoenolpyruvate from Tyrosine

Abstract

The obligate intracellular pathogen, Anaplasma phagocytophilum, is the causative agent of life-threatening diseases in humans and animals. A. phagocytophilum is an emerging tick-borne pathogen in the United States, Europe, Africa and Asia, with increasing numbers of infected people and animals every year. It is increasingly recognized that intracellular pathogens modify host cell metabolic pathways to increase infection and transmission in both vertebrate and invertebrate hosts. Recent reports have shown that amino acids are central to the host–pathogen metabolic interaction. In this study, a genome-wide search for components of amino acid metabolic pathways was performed in Ixodes scapularis, the main tick vector of A. phagocytophilum in the United States, for which the genome was recently published. The enzymes involved in the synthesis and degradation pathways of the twenty amino acids were identified. Then, the available transcriptomics and proteomics data was used to characterize the mRNA and protein levels of I. scapularis amino acid metabolic pathway components in response to A. phagocytophilum infection of tick tissues and ISE6 tick cells. Our analysis was focused on the interplay between carbohydrate and amino acid metabolism during A. phagocytophilum infection in ISE6 cells. The results showed that tick cells increase the synthesis of phosphoenolpyruvate (PEP) from tyrosine to control A. phagocytophilum infection. Metabolic pathway analysis suggested that this is achieved by (i) increasing the transcript and protein levels of mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M), (ii) shunting tyrosine into the tricarboxylic acid (TCA) cycle to increase fumarate and oxaloacetate which will be converted into PEP by PEPCK-M, and (iii) blocking all the pathways that use PEP downstream gluconeogenesis (i.e., de novo serine synthesis pathway (SSP), glyceroneogenesis and gluconeogenesis). While sequestering host PEP may be critical for this bacterium because it cannot actively carry out glycolysis to produce PEP, excess of this metabolite may be toxic for A. phagocytophilum. The present work provides a more comprehensive view of the major amino acid metabolic pathways involved in the response to pathogen infection in ticks, and provides the basis for further studies to develop novel strategies for the control of granulocytic anaplasmosis.

Rickettsial pathogen uses arthropod tryptophan pathway metabolites to evade reactive oxygen species in tick cells

“…Genome analysis of many rickettsial pathogens has reported absence of alanine and glutamate synthesis pathways (Dunning Hotopp et al, 2006). However, in I. scapularis, all genes required for the synthesis of glutamate and alanine from alpha-ketoglutarate and pyruvate, respectively, are present (Cabezas-Cruz, Espinosa, et al, 2017). Studies have shown that A. phagocytophilum decreases glutamate and alanine levels upon infection in ticks (Cabezas-Cruz, Espinosa, et al, 2017;Villar et al, 2018).…”

Quantitative Proteomics Identifies Metabolic Pathways Affected by Babesia Infection and Blood Feeding in the Sialoproteome of the Vector Rhipicephalus bursa

“…In our proteomics analysis, this 69.5 kDa protein was found over-represented in response to feeding stimulus alone (Proteomics: NIF/NINF = 0.30; Western blot: NIF/NINF = 99915.597/ND) and also in response to infection (Proteomics: INF/NINF = 0.38; Western blot: INF/NINF = 9234.421/ND) (Supplementary Table S1, Figure 6A). This positive regulation suggests a role of PCCA enzyme as a key for energy supply, maybe through the formation of building blocks or nutrients that ultimately contributes to tick and parasite growth [21]. Moreover, previous studies reported that bacteria and fungi metabolize and detoxify propionyl-CoA by the 2-methylcitrate cycle [87] to overcome its toxicity and growth inhibition properties [88].…”

“…According to the defined criteria for target selection for RNA interference studies, in silico analysis were performed revealing characteristics such as the putative function, subcellular localization, and immunogenicity of these proteins. STRING analysis showed that those targets and their network are linked to ubiquitination and metabolic pathways (Supplementary Figure S4), essential for tick fitness [21,74] and described as drug targets in other contexts [75,76]. CELLO, TMHMM, and SignalP servers predicted the cytoplasmatic localization and absence of transmembrane helices or signal peptides in both proteins, that alongside with their antigenic propensity (UB2N: 1.0357, with 8 antigenic determinants; PCCA: 1.0357, with 28 antigenic determinants) indicate that those proteins could be tested to evaluate their potential as protective antigens.…”

“…Biotin-dependent carboxylases, which includes a major group that uses as substrate coenzyme A (CoA), e.g., acetyl-CoA carboxylase (ACCA), propionyl-CoA carboxylase (PCCA), and 3-methylcrotonyl-CoA carboxylase (MCCA) [84], are key molecules in several metabolic pathways influenced during tick-pathogen interplay including fatty acid, amino acid, and carbohydrate metabolisms [21,22]. Such enzymes are considered attractive targets for drug discovery against several diseases, including bacterial and fungal infections [85,86].…”

“…Pathogens have co-evolved and adapted to survive within the tick vector cells by regulating host processes such as the acquisition of nutrients, modification of the host environment, and meddling with immune responses [18][19][20][21][22][23] that could be targeted for the identification of protective antigens [24,25]. After entering the vector, pathogens need to disseminate through tick tissues, infect and multiply within salivary gland (SG) cells to be successfully transmitted to susceptible hosts during tick blood meal [23].…”