Impact of the elderly lung mucosa on <i>Mycobacterium tuberculosis</i> transcriptional adaptation during infection of alveolar epithelial cells

Tuberculosis is one of the leading causes of death due to a single infectious agent. Upon infection, <i>Mycobacterium tuberculosis</i> (<i>M.tb</i>) is deposited in the alveoli and encounters the lung mucosa or alveolar lining fluid (ALF). We previously showed that, as we age, ALF presents a higher degree of oxidation and inflammatory mediators, which favors <i>M.tb</i> replication in human macrophages and alveolar epithelial cells (ATs). Here, we define the transcriptional profile of <i>M.tb</i> when exposed to healthy ALF from adult (A-ALF) or elderly (E-ALF) humans before and during infection of ATs. Prior to infection, <i>M.tb</i> exposure to E-ALF upregulated genes essential for bacterial host adaptation directly involved in <i>M.tb</i> pathogenesis. During infection of ATs, E-ALF exposed <i>M.tb</i> further upregulated genes involved in its ability to escape into the AT cytosol bypassing critical host defense mechanisms, as well as genes associated with defense against oxidative stress. These findings demonstrate how alterations in human ALF during the aging process can impact the metabolic status of <i>M.tb</i>, potentially enabling a greater adaptation and survival within host cells. Importantly, we present the first transcriptomic analysis on the impact of the elderly lung mucosa on <i>M.tb</i> pathogenesis during intracellular replication in ATs.IMPORTANCETuberculosis is one of the leading causes of death due to a single infectious agent. Upon infection, <i>Mycobacterium tuberculosis</i> (<i>M.tb</i>) is deposited in the alveoli and comes in contact with the alveolar lining fluid (ALF). We previously showed that elderly ALF favors <i>M.tb</i> replication in human macrophages and alveolar epithelial cells (ATs). Here we define the transcriptional profile of when exposed to healthy ALF from adult (A-ALF) or elderly (E-ALF) humans before and during infection of ATs. Prior to infection, exposure to E-ALF upregulates genes essential for bacterial host adaptation and pathogenesis. During infection of ATs, E-ALF further upregulates <i>M.tb</i> genes involved in its ability to escape into the AT cytosol, as well as genes for defense against oxidative stress. These findings demonstrate how alterations in human ALF during the aging process can impact the metabolic status of <i>M.tb</i>, potentially enabling a greater adaptation and survival within host cells.