Nrf2 regulation of alveolar macrophage immune responses in vivo to Mycobacterium tuberculosis - PROJECT SUMMARY
Mycobacterium tuberculosis (Mtb) claims nearly 1.5 million lives each year and is one of the leading causes of
death by an infectious agent worldwide. The lack of a protective TB vaccine for adult pulmonary disease, the
length and toxicity of current antibiotic treatment regimens, and the rise in Mtb drug resistance all strongly
motivate the pursuit of new host-directed therapies and strategies for vaccine design. Alveolar macrophages are
the first cells in the lung to be infected with Mtb following aerosol transmission, performing a critical role as Mtb
innate sentinels in the airway. They must initiate the host response that will recruit other innate cells into the lung
and transfer bacteria to cells that can carry it to the draining lymph node for efficient immune priming. As tissue-
resident myeloid cells, alveolar macrophages also perform a critical homeostatic function, clearing debris from
the airway without triggering pulmonary inflammation. It is unknown how alveolar macrophages balance their
innate sensing and tissue maintenance duties, while any delay in the initiation of the host response to Mtb
provides the bacteria with additional time to replicate unchecked. Our previous results showed that Mtb-infected
alveolar macrophages up-regulate a cell-protective signature, dependent on the transcription factor Nrf2. This in
vivo response is distinct from the canonical pro-inflammatory response previously reported for Mtb-infected
macrophages in vitro indicating that new information that can be gained from this in vivo approach. Our results
showed that in the absence of Nrf2, Mtb-infected alveolar macrophages are more activated, less viable, and
demonstrate enhanced control of bacteria within the first 10 days of infection, yet it is unknown how Nrf2
regulation of alveolar macrophage function early during infection impacts the subsequent stages of disease
progression. The goal of this proposal is to develop diverse tools to modulate alveolar macrophage Nrf2
expression in order to define how Nrf2 impacts the timing and quality of the immune events following bacterial
deposition in the airway, which ultimately lead to either disease progression or bacterial containment. First, we
will characterize Nrf2 regulation of alveolar macrophage cell death and bacterial dissemination using myeloid-
specific Nrf2 conditional knock-out strains (Aim 1). Second, we will develop an ex vivo system to study how Nrf2
interferes with alveolar macrophage innate sensing pathways and an shRNA lentiviral oropharyngeal delivery
system to transiently block alveolar macrophage Nrf2 expression in vivo, allowing us to avoid any confounding
effects of Nrf2 during development (Aim 2). The studies are driven by the hypothesis that the induction of a cell-
protective program by Nrf2 prevents alveolar macrophages from mounting a rapid and effective pro-inflammatory
response to Mtb infection, leading to delays in subsequent immune events that impair the host from controlling
infection. By developing new tools and reagents to study the role of alveolar macrophage-specific Nrf2
expression, we will gain a better understanding of the early events of Mtb infection in the lung and evaluate the
potential of Nrf2 as a future target for host-directed therapy.
