Wewers, M. D. | bioRxiv Science

bioRxiv2023

Exposure of Mycobacterium tuberculosis to human alveolar lining fluid shows temporal and strain-specific adaptation to the lung environment

Upon infection, Mycobacterium tuberculosis (M.tb) reaches the alveolar space and comes in close contact with human alveolar lining fluid (ALF) for an uncertain period of time prior to its encounter with alveolar cells. We showed that homeostatic ALF hydrolytic enzymes modify the M.tb cell envelope, driving M.tb-host cell interactions. Still, the contribution of ALF during M.tb infection is poorly understood. Here, we exposed 4 M.tb strains with different levels of virulence, transmissibility, and drug resistance (DR) to physiological concentrations of human ALF for 15-min and 12-h, and performed RNA sequencing. Gene expression analysis showed a temporal and strain-specific adaptation to human ALF. Differential expression (DE) of ALF-exposed vs. unexposed M.tb revealed a total of 397 DE genes associated with lipid metabolism, cell envelope and processes, intermediary metabolism and respiration, and regulatory proteins, among others. Most DE genes were detected at 12-h post-ALF exposure, with DR-M.tb strain W-7642 having the highest number of DE genes. Interestingly, genes from the KstR2 regulon, which controls the degradation of cholesterol C and D rings, were significantly upregulated in all strains post-ALF exposure. These results indicate that M.tb-ALF contact drives initial metabolic and physiologic changes in M.tb, with potential implications in infection outcome. IMPORTANCETuberculosis, caused by airborne pathogen Mycobacterium tuberculosis (M.tb), is one of the leading causes of mortality worldwide. Upon infection, M.tb reaches the alveoli and gets in contact with human alveolar lining fluid (ALF), where ALF hydrolases modify the M.tb cell envelope driving subsequent M.tb-host cell interactions. Still, the contributions of ALF during infection are poorly understood. We exposed 4 M.tb strains to ALF for 15-min and 12-h and performed RNA sequencing, demonstrating a temporal and strain-specific adaptation of M.tb to ALF. Interestingly, genes associated with cholesterol degradation were highly upregulated in all strains. This study shows for the first time that ALF drives global metabolic changes in M.tb during the initial stages of the infection, with potential implications in disease outcome. Biologically relevant networks and common and strain-specific bacterial determinants derived from this study could be further investigated as potential therapeutic candidates.

microbiology↗

bioRxiv2018

Is IκBζ constitutively expressed in mammalian airway epithelium?

I{kappa}B{zeta} is a transcriptional factor induced primarily in immune cells upon Toll-like receptor (TLR) activation that drives important cytokine responses. Recent studies have demonstrated constitutive I{kappa}B{zeta} expression in the epithelial cells of mouse skin and eyes, possibly reflecting the activation of TLRs by pathogen-associated molecular patterns (PAMPs). In this context, another mucosal surface, the lung epithelium, may not be as actively exposed to the external environment as the skin and the conjunctiva, especially since the lower lung airways are typically conceived to be sterile. Whether I{kappa}B{zeta} expression in the lungs is constitutive or induced remains largely unexplored. This is especially important since I{kappa}B{zeta} has been shown to promote the expression of protective cytokine and antimicrobial peptide responses, supporting a role for I{kappa}B{zeta} in lung host defense. We hence evaluated I{kappa}B{zeta} expression in airway epithelia of both humans and mice using immunostaining with antiserum raised against recombinant I{kappa}B{zeta} in our laboratory. We observed positive signal in the nuclei of ciliated epithelial cells lining the central airways. Airway cells of gnotobiotic mice also stained positive, suggesting that I{kappa}B{zeta} expression does not require induction by bacterial PAMPs. Unexpectedly, we also observed staining in the lung epithelia of I{kappa}B{zeta} knockout mice, indicating possible false positive signals from our immunohistochemistry experiments. In this context, 2D gel analysis followed by mass spectrometry revealed that our I{kappa}B{zeta} antiserum also detected a nuclear protein lamin B1. Nevertheless, immunoblotting tissue homogenates from gnotobiotic mouse lungs and primary human airway epithelial cells showed the appropriate 86 kDa band for I{kappa}B{zeta}. Together, these results demonstrate constitutive I{kappa}B{zeta} expression in airway epithelium, suggesting that lung epithelial cells may depend upon I{kappa}B{zeta} expression for airway protection.

immunology↗