Cellular, molecular and functional characterization of quiescence in Leishmania donovani, the etiological agent of visceral leishmaniasis

Quiescence is a survival strategy adopted by several pathogens in response to prolonged periods of stress, such as drug treatment or host’s immune response. It is characterized by an overall downregulated metabolism, decreased biosynthetic capability and lower level of energy together with a slow or no proliferation. Quiescence of pathogens can represent a major health implication, as it renders them less susceptible to chemotherapy and allows them to survive for years unnoticed in the host organism and be the source of relapses. This is most extensively studied in bacteria, but recent reports described this phenomenon in several protozoan parasites. Leishmania are unicellular eukaryotic parasites causing leishmaniasis, a neglected tropical disease. The most severe form of the disease is visceral leishmaniasis which is caused by L. donovani and is lethal if it is left untreated. It shows several (sub-)clinical features where quiescence could play a major role, complicating clinical management and jeopardizing elimination programs. Studying the biology of quiescence in L. donovani is thus important. Here, we hypothesize that quiescence in L. donovani constitutes a common adaptive strategy to different types of stress, including drug exposure. Quiescent parasites display slow or no proliferation and they are characterized by low activity and down-regulated metabolism where upregulated expression for some genes control the entry, maintenance and exit of the quiescent stage. In the particular case of Leishmania where a lot is still not understood, we aim to characterize in vitro quiescence in L. donovani, in order to understand the mechanisms associated with its emergence, its heterogeneity, its dynamics and its role in parasite adaptation to stress, including drug treatment. Major findings will be validated in vivo on experimental animals and will provide knowledge and tools paving the way for future clinical studies. Our initial focus is on in vitro models and three types of stress: starvation, intracellular lifestyle and drug pressure. In vivo validation of our major findings in experimental animals is foreseen at the end of the project. Our plan is based on 4 work packages: In WP1, we will characterize populations of quiescent and replicative cells under stress conditions, by untargeted bulk analyses. In WP2, cell-to-cell functional heterogeneity in a population of parasites undergoing quiescence under different stress conditions will be studied by single cell transcriptomics. In WP3, we will functionally validate candidate drivers of quiescence. In WP4, we will validate our major findings in vivo, using animal model.

Project type:PhD project