Macrophage nuclear receptors, metabolism and immune effectors during health and M. tuberculosis infection - Project Summary/Abstract Resident alveolar macrophages (AMs) possess a unique, highly regulated immune response that remains poorly understood, especially for human AMs (HAMs). Failure to understand the molecular events underlying AM development & biology creates a critical barrier to developing new treatment strategies effective in the lung. The overall goal of this ongoing research program is to identify transcriptional regulators and pathways that dictate AM immunobiology and how these are co-opted by the host-adapted intracellular pathogen Mycobacterium tuberculosis (M.tb) to enable its survival. In the last grant cycle, the lab developed the first HAM model (alveolar macrophage-like cells, AMLs) that possesses many key features of HAMs. Armed with this new model, we aim to continue our studies of nuclear receptor (NR) function in human macrophages. NRs are critical sensors & regulators of immune functions in macrophages and other cell types. Previous grant cycle work has identified MCL-1 as an effector of the NR peroxisome proliferator-activated receptor gamma (PPAR) that is critical for M.tb growth. Combination preclinical MCL-1 & BCL-2 inhibitors robustly inhibits drug-sensitive and - resistant M.tb growth in human macrophages and a human in vitro granuloma model, demonstrating the potential efficacy of a targeted host-directed therapy (HDT) for tuberculosis (TB). Building on this success, we have now identified an emerging NR family (NR4A1,2&3), whose expression, similar to PPAR, swiftly declines after AM removal from the lung, indicating a role for the NR4A family in AM phenotype & function. Thus, the NR4A family and their downstream effectors may represent a new frontier for HDT approaches for TB. Our preliminary data indicate that NR4As are important for control of M.tb in macrophages, epithelial cells, a lung on chip (LoC) model, and in vivo in mice, and therefore may oppose PPARactivity in balancing AM immune responses. Exciting new data show that key macrophage pathways in M.tb pathogenesis regulated by NR4As include Type I interferon (IFN) signaling & apoptosis. We hypothesize that lung-specific activation of NR4A family members dampens Type I IFNs and drives apoptosis to control M.tb growth. The Specific Aims are to: 1) define the roles of NR4A family members in regulating Type I IFN-mediated responses and apoptosis during M.tb infection in vitro, 2) elucidate the protective role of NR4As in vivo using M.tb mouse models, and 3) identify novel compounds that target NR4As as potential HDTs for M.tb. HAMs, AMLs, LoC, human granuloma and mouse models will be used to define the role of NR4As & PPAR during M.tb infection using biochemical, in silico, next generation sequencing and cellular immunology techniques. Since these NRs operate 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, and will aid in developing HDTs for TB, a leading cause of death.
