Mechanisms by which African trypanosomes sense and respond to iron availability in the mammalian host

Living organisms have the ability to sense changes in their environment and adapt their gene expression to ensure their survival. The acquisition of nutrients from their environment is particularly important for unicellular organisms, especially for unicellular parasites that must acquire nutrients from their host. Iron is an essential element for the growth of all forms of life, and mammals tightly control the availability of iron to prevent the growth of invasive organisms by binding iron to a protein called transferrin.

The African trypanosomes are unicellular parasites that are transmitted by the bite of an infected tsetse fly in sub-Saharan Africa, and causes a disease in farm animals and humans. The parasite is able to fulfil its requirement for iron by expressing a protein that recognises and uptakes transferrin from its host, and importantly is able to rapidly increase the amount of this protein in response to iron starvation. The way the parasite is able to do this is not clear, but we do know that it is different to the mechanism used by mammals.

This project will investigate the way in which the parasite is able to sense and respond to iron starvation using a combination of experimental techniques that use parasite cells grown in flasks. Studying this mechanism is important as it will help us to understand how these parasites sense and adapt to their host environments, knowledge that will help in the fight against the diseases they cause. Improved fundamental understanding of these mechanisms is also important for our understanding of metabolic diseases and cancers where disregulation occurs.

The ability of the African trypanosomes to sense and respond to their host environment is critical for their survival and virulence, and is achieved despite a near complete lack of transcriptional control that results in a reliance on RNA binding proteins (RBPs). The African trypanosomes Trypanosoma brucei and Trypanosoma congolense are vector borne parasites of domestic cattle and are a major cause of economic hardship in sub-Saharan Africa, with two sub-species of T. brucei also causing fatal infections in humans.

T. brucei acquire the essential nutrient iron by expressing its own transferrin receptor (TbTfR) to uptake transferrin from the mammalian host. Expression of TbTfR is dynamically regulated, with iron starvation inducing a rapid upregulation of the TbTfR (~5-fold in 6 h) equally at the mRNA and protein level by a mechanism distinct from the mammalian iron response protein (IRP)/ iron response element (IRE) system. We have recently shown that the iron starvation response in T. brucei is mediated through the TbTfR 3'UTR, as fusion of the 3'UTR to a reporter gene is sufficient to confer upregulation of reporter mRNA and protein levels upon iron starvation. The TfR receptor is conserved in T. congolense, although it is not currently known if the iron starvation response is maintained.

The iron starvation response pathway will be elucidated in T. brucei using SILAC-based quantitative proteomics to identify proteins and phosphorylation sites that are dynamically regulated under iron starvation conditions. Trans-acting RBPs that bind the TfR-3'UTR under normal and iron starvation conditions will be identified using quantitative proteomic analysis of the proteins affinity purified by immobilised TfR-3'UTR mRNA. We will also establish the extent of conservation of iron uptake, sensing and response in T. congolense.

The project aims to improve our understanding of the fundamental biology of African trypanosome parasites that cause disease in economically important farm animals and humans in sub-Saharan Africa, and is likely to identify novel drug targets. Translation of this work into improved therapies for these diseases has the potential to improve economic performance, health and wellbeing in endemic areas.

Staff associated with the project will develop skills in genetic manipulation and proteomic technologies that are highly desirable in the UK Bioscience industry, and should they choose enter the commercial sphere this will promote knowledge exchange and add to the UK economic competitiveness.

The broad aims and outcomes of this research will be communicated to the public through the 'Parasites in a Box' outreach resource, inspiring the next generation of scientists and enabling members of the public to act as informed citizens.