Human lungs, while mediating air exchange in the alveoli, are constantly exposed to pollutants, allergens, and microbes. Resident alveolar macrophages (AMs) must clear insults without damaging the alveoli. Thus, AMs possess a unique, highly regulated immune response that results in inefficient clearance of some airborne microbes, especially host-adapted pathogens like Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis (TB), a top 10 cause of death worldwide. AM development, maintenance and biology are poorly understood, especially for human macrophages and in regards to the effect of the local environment, e.g. surfactant, which lines the alveoli, and locally produced cytokines such as TGF?. Failure to completely understand the molecular events underlying AM development and biology creates a critical barrier to developing new treatment strategies that target the lung. The long-term objective of this ongoing research program is to identify signaling pathways associated with transcriptional regulators and inflammatory metabolites that dictate AM biology and how these are co-opted by the host-adapted intracellular pathogen M.tb, to enhance its growth. New data in the laboratory indicate that M.tb, surfactant proteins and TGF? regulate expression of the nuclear receptors (NRs) peroxisome proliferator-activated receptor gamma (PPAR?), Rev-erb?, Nur77, and Nurr1. NRs are a large family of structurally conserved, ligand activated transcription factors, which enable macrophages to sense their local environment and shape immune responses. In this regard, NRs sit at the interface of metabolism (particularly lipid and eicosanoid) and immunity, and are increasingly recognized as relevant to M.tb pathogenesis, yet are unexplored in the context of the lung and M.tb. It is critical to understand if/how NRs cooperate to regulate AM biology in ways that impact responses to M.tb. Expression and function of NRs are tightly regulated to provide a balanced immune response. The hypothesis for this proposal is that NRs modify eicosanoid metabolism and protective immune responses, thereby making AMs more susceptible to M.tb and that M.tb augments select endogenous pathways to further dampen the AM immune response to enhance its survival.
The Specific Aims are to: 1) determine the effect of surfactant and local cytokines on human macrophage NR expression and activity and how this is modulated by M.tb, 2) characterize newly discovered PPAR? effectors and their regulation of lipid metabolism during M.tb infection, and 3) determine whether PPAR?, Rev-erb?, Nur77 and Nurr1, as well as PPAR? effectors, are viable host-directed therapeutic targets for TB. Human AMs and the tractable model of human blood monocyte-derived macrophages (MDMs), biochemical and genetic techniques, and mouse models will be used to study the role of NRs, and their effectors, in TB. Since NRs regulate metabolism and inflammation in a tissue, gene and signal-specific manner, these findings open the door to a completely new set of biological pathways likely to be critical to host responses in the lung, during health and M.tb infection.
M. tuberculosis, which causes the worldwide global health problem tuberculosis (TB), is transmitted human to human via the airborne route into lung alveoli, which sit at a crucial interface between the environment and the immune system. We seek to understand how alveolar macrophages (AMs) respond metabolically to lung components and infection by M. tuberculosis. Increased understanding of why AMs are susceptible to M. tuberculosis is expected to aid in the development of host-directed therapies for TB.
