טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNagaraja Shruti
SubjectQueuine-Driven Regulation of Entamoeba Histolytica
Virulence and Resistance to Oxidative
Stress
DepartmentDepartment of Medicine
Supervisor ASSOCIATE PROF. Serge Ankri


Abstract

Entamoeba histolytica is a unicellular parasite responsible for causing amebiasis. This parasite infects millions of people all around the globe through the ingestion of contaminated food and water. The parasite resides in the colon and feeds on the colonic microbiota. Although most infected individuals are asymptomatic, however, in 10% of the infected patients the parasite leads to extraintestinal infections. The gut flora is implicated in the onset of symptomatic amebiasis due to alterations in the composition of the bacteria. These bacteria modulate the physiology of the parasite and affect the virulence of the parasite through unknown mechanisms. Thus, it is imperative to understand and identify the potential pathways in order to develop therapeutic targets against amebiasis. In this study, we focus on queuine, which is a micronutrient exclusively produced by the gut bacteria. We have shown that uptake of queuine in E.histolytica leads to the modification of anticodon loop in the tRNA and it provides resistance against oxidative stress. Queuine-induced hypermethylation of tRNAAsp also plays an important role in oxidative stress resistance. Our study shows that on hand, queuine exerts an extensive impact on the transcriptome of the parasite by turning on genes involved in neutralizing the effect of oxidative stress. On the other hand, queuine attenuates the virulence of the parasite in the large intestine of mice with experimentally induced amebiasis by downregulating the expression of virulence-associated genes. Impairing the enzyme incorporating queuine into tRNA leads to a loss in stress resistance and virulence. Our study highlights the importance of bacterially derived products in shaping the physiology of the parasite. tRNAs are the key players of translation and growing evidence suggest that tRNA modifications play major roles in human pathologies. These tRNA modifications lead to the transcripts whose translation is affected by changes occurring in the wobble base of the tRNA. Our study sheds light on the importance of one such tRNA modification and how bacterial products orchestrate this event in the parasite and modulate its behavior. Results from this study may provide important clues to understand the amoeba-bacteria relationship and help us exploit strategies to develop anti-amoebic drugs.