Exposure ofMycobacterium tuberculosisto human alveolar lining fluid shows temporal and strain-specific adaptation to the lung environment

Abstract

ABSTRACTUpon 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 theM.tbcell envelope, drivingM.tb-host cell interactions. Still, the contribution of ALF duringM.tbinfection is poorly understood. Here, we exposed 4M.tbstrains 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-exposedvs.unexposedM.tbrevealed 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.tbstrain 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 thatM.tb-ALF contact drives initial metabolic and physiologic changes inM.tb, with potential implications in infection outcome.IMPORTANCETuberculosis, caused by airborne pathogenMycobacterium tuberculosis(M.tb), is one of the leading causes of mortality worldwide. Upon infection,M.tbreaches the alveoli and gets in contact with human alveolar lining fluid (ALF), where ALF hydrolases modify theM.tbcell envelope driving subsequentM.tb-host cell interactions. Still, the contributions of ALF during infection are poorly understood. We exposed 4M.tbstrains to ALF for 15-min and 12-h and performed RNA sequencing, demonstrating a temporal and strain-specific adaptation ofM.tbto 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 inM.tbduring 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.