Sirtuins and Host Metabolism in TB Pathogenesis and Treatment

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PROJECT SUMMARY Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is the leading cause of death due to infection and many TB survivors are left with permanent lung impairment due to immune-mediated cavitation and fibrotic healing. Sirtuins (SIRTs) are a family of energy-sensing NAD+-dependent deacetylases that modify histones, transcription factors, metabolic enzymes, and other targets to defend starvation, restore homeostasis during stress, support mitochondrial integrity, and promote the resolution of inflammation. In published and unpublished preliminary studies, we found that levels of SIRT1 (the major cytosolic SIRT) and SIRT3 (the major mitochondrial SIRT) are downregulated in macrophages (MΦ) infected with Mycobacterium tuberculosis (Mtb). Preliminary data support a model in which SIRT1/3 axis suppression by Mtb in MΦ alters the expression levels of genes in the tricarboxylic acid cycle, electron transport chain, and glycolytic pathway. This causes a shift from oxidative phosphorylation to glycolysis, increases production of mitochondrial reactive oxygen species (ROS), and impairs ROS scavenging. The result is increased mitochondrial stress and MΦ cell death. The glycolytic shift (Warburg effect) rapidly enhances MΦ antimicrobial performance but at the expense of perturbing multiple SIRT1/3 regulated processes that lead to increased inflammation and TB disease severity with chronic infection. Studies in Aim 1 build on and fill gaps in our preliminary data, with in vitro experiments investigating the mechanism of SIRT1/3 downregulation by Mtb and the downstream effects on metabolic and epigenetic reprogramming. Aim 2 uses existing strains of SIRT1 and SIRT3 null mice, and other strains in development, for aerosol TB studies that will relate in vitro data from Aim1 to host defense at the systemic level in vivo. The project culminates with testing of several SIRT agonists for host-directed therapy of TB. We predict that these agents will restore mitochondrial homeostasis, hasten lesion sterilization, and reduce pulmonary TB immune pathology. The effects of these agents on immunometabolic pathways in vivo will be interpreted in the context of in vitro data produced in Aim 1. Our project addresses an important gap in understanding the upstream triggers and downstream consequences of the Warburg effect in TB while at the same time producing new knowledge about potential adjunctive treatments to improve TB treatment outcomes and reduce the burden of pulmonary impairment in TB survivors.