Elderly lung mucosa impact on Mycobacterium tuberculosis adaptation during infection of alveolar epithelial cells
Tuberculosis (TB) is one of the leading causes of death due to a single infectious agent and is considered a global threat killing over 4,300 people every day. Upon infection, Mycobacterium tuberculosis (M.tb) deposits in the alveoli and encounters the lung mucosa or alveolar lining fluid (ALF), whose primary function is to keep the lung's health intact, dictating host-cell interactions. Age-associated changes to innate soluble components in the ALF lead to increased susceptibility of the elderly population to respiratory infectious diseases such as TB. We previously determined that increased M.tb replication in human macrophages and alveolar epithelial cells (ATs) is mediated by age-associated changes in human ALF. In this study, we determine the transcriptional profile of M.tb when exposed to healthy human ALF from adult (A-ALF) or elderly (E-ALF) individuals prior and during intracellular replication in ATs, using A549 cells as a model. Prior to infection, exposure of M.tb to E-ALF upregulates several genes associated with the ESX-4 secretion system as well as immunomodulatory proteins linked to the ESX-5 secretion system. It additionally increases the expression of genes related to phospholipases, phosphatases, and proteases, which are important virulence factors in the establishment of M.tb infection. Importantly, we present the first transcriptomic analysis of the impact of the elderly lung mucosa on M.tb pathogenesis during intracellular replication in ATs. Interestingly, exposure to E-ALF altered expression of key genes related to the ESX-5 secretion system during infection. Additionally, compared to the A-ALF group, there was enhanced expression of genes associated with PDIMs biosynthesis and translocation to the cell surface. Lastly, E-ALF-exposed M.tb exhibits upregulation of genes linked to ROS defense mechanisms during ATs infection. Overall, these findings demonstrate how altered ALF functions in old age can impact the M.tb metabolic status, enabling greater adaptation and increased survival in the host cells. Overall design: RNAseq data of M.tb Erdman exposed to human alveolar lining fluid (ALF) from adult or elderly individuals before infection and during ATs infection at 72hpi, 3 replicates each (except E-ALF-exposed M.tb with 2 replicates). Control sample is unexposed bacteria prior to infection. Total: 14 samples