The role of tyrosine metabolism in tuberculosis pathogenesis

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ABSTRACT Tuberculosis (TB) is a leading cause of death globally. It remains unclear why only a small number of Mycobacterium tuberculosis (Mtb)-infected individuals progress to TB disease. Mtb is known to rewire the immunometabolism of infected monocyte-derived phagocytes following acute infection. Consistently, systemic shifts in metabolism are a hallmark of TB pathogenesis, thus highlighting metabolism as a possible target for intervention. Tyrosine, an aromatic amino acid, is shown to accumulate in the serum of TB patients compared to healthy controls. However, it is unknown whether and how defects in tyrosine metabolism could mediate susceptibility to Mtb infection or risk of TB progression. We found that Mtb infection of primary human myeloid cells downregulates expression of Fumarylacetoacetate hydrolase (FAH); a key enzyme involved in tyrosine catabolism. We also identified a genetic variant associated with lower FAH expression in monocyte-derived dendritic cells (DCs) in Peruvians who progressed to TB. We previously showed accumulation of tyrosine in the plasma of prospectively enrolled African household contacts of TB patients who progress to TB compared to non-progressors, consistently with a role for tyrosine catabolism in protection from TB. Importantly, knocking out FAH in murine macrophages increased their susceptibility to Mtb infection, suggesting that impaired tyrosine metabolism by FAH may drive loss of Mtb control. Mechanistically, tyrosine metabolites may contribute to the altered metabolic states of Mtb-infected cells. We hypothesize that Mtb-mediated interference with tyrosine metabolism has evolved as a mechanism of virulence and could mediate progression to TB disease. We propose a series of in vitro and in vivo experiments to define the requirement for host tyrosine metabolism following Mtb infection. We will target FAH using gene editing of primary human myeloid cells to test whether this key step in tyrosine metabolism is required to contain Mtb infection. We also plan to adoptively transfer fah- deficient fetal liver cells into TB-susceptible mice to test the requirement for tyrosine metabolism in hematopoietic cells to control Mtb infection in vivo. Secondly, we will define the metabolic consequences of FAH deletion in Mtb-infected monocyte-derived DCs and macrophages using metabolic flux experiments, and metabolite complementation of Mtb-infected FAH-deficient cells. Finally, we will leverage samples and datasets from two independent cohorts of different TB disease states. The first is a cross-sectional Peruvian cohort of TB patients and Mtb-infected and uninfected contacts, where we bio-banked plasma samples for targeted analysis of tyrosine metabolites by high resolution mass spectrometry. The second is a previously described longitudinal cohort of African household contacts of TB patients followed for 2 years, where we also obtained genotyping data to explore the impact of polymorphisms in select metabolic genes on expression of tyrosine metabolites. Defining a causal association between impaired tyrosine metabolism and TB risk would motivate for future trials to repurpose existing agents to treat inborn errors of tyrosine metabolism as host-directed treatments against TB.