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A lung-on-chip model of early Mycobacterium tuberculosis infection reveals an essential role for alveolar epithelial cells in controlling bacterial growth.

ABSTRACT: We establish a murine lung-on-chip infection model and use time-lapse imaging to reveal the dynamics of host-Mycobacterium tuberculosis interactions at an air-liquid interface with a spatiotemporal resolution unattainable in animal models and to probe the direct role of pulmonary surfactant in early infection. Surfactant deficiency results in rapid and uncontrolled bacterial growth in both macrophages and alveolar epithelial cells. In contrast, under normal surfactant levels, a significant fraction of intracellular bacteria are non-growing. The surfactant-deficient phenotype is rescued by exogenous addition of surfactant replacement formulations, which have no effect on bacterial viability in the absence of host cells. Surfactant partially removes virulence-associated lipids and proteins from the bacterial cell surface. Consistent with this mechanism, the attenuation of bacteria lacking the ESX-1 secretion system is independent of surfactant levels. These findings may partly explain why smokers and elderly persons with compromised surfactant function are at increased risk of developing active tuberculosis.

SUBMITTER: Thacker VV

PROVIDER: S-EPMC7735758 | biostudies-literature | 2020 Nov

REPOSITORIES: biostudies-literature

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A lung-on-chip model of early <i>Mycobacterium tuberculosis</i> infection reveals an essential role for alveolar epithelial cells in controlling bacterial growth.

Thacker Vivek V VV Dhar Neeraj N Sharma Kunal K Barrile Riccardo R Karalis Katia K McKinney John D JD

eLife 20201124

We establish a murine lung-on-chip infection model and use time-lapse imaging to reveal the dynamics of host-<i>Mycobacterium tuberculosis</i> interactions at an air-liquid interface with a spatiotemporal resolution unattainable in animal models and to probe the direct role of pulmonary surfactant in early infection. Surfactant deficiency results in rapid and uncontrolled bacterial growth in both macrophages and alveolar epithelial cells. In contrast, under normal surfactant levels, a significan ...[more]

PMID: 33228849

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Project description:Mycobacterium tuberculosis (M. tb) infection is initiated by the few bacilli inhaled into the alveolus. Studies in lungs of aerosol-infected mice provided evidence for extensive replication of M. tb in non-migrating, non-antigen-presenting cells in the alveoli during the first 2-3 weeks post-infection. Alveoli are lined by type II and type I alveolar epithelial cells (AEC) which outnumber alveolar macrophages by several hundred-fold. M. tb DNA and viable M. tb have been demonstrated in AEC and other non-macrophage cells of the kidney, liver, and spleen in autopsied tissues from latently-infected subjects from TB-endemic regions indicating systemic bacterial dissemination during primary infection. M. tb have also been demonstrated to replicate rapidly in A549 cells (type II AEC line) and acquire increased invasiveness for endothelial cells. Together, these results suggest that AEC could provide an important niche for bacterial expansion and development of a phenotype that promotes dissemination during primary infection. In the current studies, we have compared the transcriptional profile of M. tb replicating intracellularly in A549 cells to that of M. tb replicating in laboratory broth, by microarray analysis. Genes significantly upregulated during intracellular residence were consistent with an active, replicative, metabolic, and aerobic state, as were genes for tryptophan synthesis and for increased virulence (ESAT-6, and ESAT-6-like genes, esxH, esxJ, esxK, esxP, and esxW). In contrast, significant downregulation of the DevR (DosR) regulon and several hypoxia-induced genes was observed. Stress response genes were either not differentially expressed or were downregulated with the exception of the heat shock response and those induced by low pH. The intra-type II AEC M. tb transcriptome strongly suggests that AEC could provide a safe haven in which M. tb can expand dramatically and disseminate from the lung prior to the elicitation of adaptive immune responses.

Project description: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.

Project description:Lung alveolar macrophages (AMs) are in the first line of immune defense against respiratory pathogens and play key roles in the pathogenesis of Mycobacterium tuberculosis (Mtb) in humans. Nevertheless, AMs are available only in limited amounts for in vitro studies, which hamper the detailed molecular understanding of host-Mtb interactions in these macrophages. The recent establishment of the self-renewing and primary Max Planck Institute (MPI) cells, functionally very close to lung AMs, opens unique opportunities for in vitro studies of host-pathogen interactions in respiratory diseases. Here, we investigated the suitability of MPI cells as a host cell system for Mtb infection. Bacterial, cellular, and innate immune features of MPI cells infected with Mtb were characterized. Live bacteria were readily internalized and efficiently replicated in MPI cells, similarly to primary murine macrophages and other cell lines. MPI cells were also suitable for the determination of anti-tuberculosis (TB) drug activity. The primary innate immune response of MPI cells to live Mtb showed significantly higher and earlier induction of the pro-inflammatory cytokines TNF?, interleukin 6 (IL-6), IL-1?, and IL-1?, as compared to stimulation with heat-killed (HK) bacteria. MPI cells previously showed a lack of induction of the anti-inflammatory cytokine IL-10 to a wide range of stimuli, including HK Mtb. By contrast, we show here that live Mtb is able to induce significant amounts of IL-10 in MPI cells. Autophagy experiments using light chain 3B immunostaining, as well as LysoTracker labeling of acidic vacuoles, demonstrated that MPI cells efficiently control killed Mtb by elimination through phagolysosomes. MPI cells were also able to accumulate lipid droplets in their cytoplasm following exposure to lipoproteins. Collectively, this study establishes the MPI cells as a relevant, versatile host cell model for TB research, allowing a deeper understanding of AMs functions in this pathology.

Dataset Information

A lung-on-chip model of early Mycobacterium tuberculosis infection reveals an essential role for alveolar epithelial cells in controlling bacterial growth.

Publications

A lung-on-chip model of early <i>Mycobacterium tuberculosis</i> infection reveals an essential role for alveolar epithelial cells in controlling bacterial growth.

Similar Datasets

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