Biology subjects

Murin, L.

Publications and source records attributed to Murin, L..

3 recordsLinked to original sources

bioRxiv2026

Lactate Oxidase (LctO) Acts as a Metabolic Checkpoint Restraining Streptococcus pneumoniae Invasion of Respiratory Epithelial Barriers

Streptococcus pneumoniae rapidly translocates across polarized human bronchial epithelial barriers, with viable bacteria recovered from the basolateral compartment within 1 h post-infection. Disruption of the pyruvate node through combined deletion of pyruvate oxidase (spxB) and lactate oxidase (lctO) markedly enhanced transmigration of S. pneumoniae across polarized Calu-3 monolayers without causing early cytotoxicity or loss of monolayer integrity. This hyper-invasive phenotype was conserved in the TIGR4 and EF3030 background and under air-liquid interface conditions. Importantly, single {Delta}lctO mutants exhibited significantly greater translocation than {Delta}spxB mutants or wild-type strains across bronchial (Calu-3), alveolar (A549), and pharyngeal (Detroit 562) epithelial models. Enhanced translocation correlated with increased bacterial adherence but was independent of capsule expression, extracellular H2O2 production, pneumolysin, or tight junction disruption, as evidenced by stable transepithelial electrical resistance (TEER), lack of caspase-3/7 activation, and minimal IL-18 release at early time points. High-resolution confocal microscopy revealed intracellular {Delta}lctO pneumococci localized within N-acetylglucosamine/sialic acid (GN/SA)-containing compartments as early as 1 h post-infection. In murine macrophages, {Delta}lctO mutants were phagocytosed at rates similar to wild-type bacteria but induced greater pneumolysin-dependent cytotoxicity at 24 h. These findings demonstrate that LctO functions as a metabolic checkpoint that restrains pneumococcal invasion of respiratory epithelia, revealing a previously unrecognized role for lactate oxidase in controlling the transition from colonization to invasive disease. ImportanceThis study identifies lactate oxidase (LctO) as a critical metabolic checkpoint that restrains Streptococcus pneumoniae invasion of respiratory epithelial barriers. By linking pyruvate node metabolism to the control of transmigration, these findings reveal a novel mechanism by which central carbon metabolism regulates pneumococcal virulence and the transition from colonization to invasive disease.

microbiology↗

bioRxiv2023

Oxidation of hemoglobin in the lung parenchyma facilitates the differentiation of pneumococci into encapsulated bacteria

Streptococcus pneumoniae (the pneumococcus) causes cytotoxicity and encapsulates within the lung parenchyma, leading to pneumococcal pneumonia. However, the underlying mechanisms remain unclear and likely involve multiple bacterial and host factors. We investigated the selection process of encapsulated pneumococci, a critical factor in lung damage during pneumococcal pneumonia. Our study revealed that pneumococci initially lack capsules but re-encapsulate upon reaching the alveoli. This process is driven by S. pneumoniae-derived hydrogen peroxide (Spn-H2O2), which oxidizes lung hemoglobin, leading to heme release and polymerized hemoglobin formation. Physiologically relevant levels of heme were found to promote the selection of encapsulated bacteria. Furthermore, encapsulation protects bacteria from intracellular heme toxicity, a defense absent in non-encapsulated strains. Ultrastructural analysis demonstrated interactions between hemoglobin and both encapsulated and non-encapsulated pneumococci in human sputum. These findings reveal a critical connection between oxidative stress-mediated lung damage and the selection of encapsulated pneumococci, suggesting potential therapeutic avenues by targeting these oxidative processes.

microbiology↗

bioRxiv2023

Oxidation of hemoproteins by Streptococcus pneumoniae collapses the cell cytoskeleton and disrupts mitochondrial respiration leading to cytotoxicity of human lung cells

Streptococcus pneumoniae (Spn) causes pneumonia that kills millions through acute toxicity and invasion of the lung parenchyma. During aerobic respiration, Spn releases hydrogen peroxide (Spn-H2O2), as a by-product of enzymes SpxB and LctO, and causes cell death with signs of both apoptosis and pyroptosis by oxidizing unknown cell targets. Hemoproteins are molecules essential for life and prone to oxidation by H2O2. We recently demonstrated that during infection-mimicking conditions, Spn-H2O2 oxidizes the hemoprotein hemoglobin (Hb), releasing toxic heme. In this study, we investigated details of the molecular mechanism(s) by which the oxidation of hemoproteins by Spn-H2O2 causes human lung cell death. Spn strains, but not H2O2-deficient Spn{Delta}spxB{Delta}lctO strains caused time-dependent cell cytotoxicity characterized by the rearrangement of the actin, the loss of the microtubule cytoskeleton and nuclear contraction. Disruption of the cell cytoskeleton correlated with the presence of invasive pneumococci and an increase of intracellular reactive oxygen species. In cell culture, the oxidation of Hb or cytochrome c (Cytc) caused DNA degradation and mitochondrial dysfunction from inhibition of complex I-driven respiration, which was cytotoxic to human alveolar cells. Oxidation of hemoproteins resulted in the creation of a radical, which was identified as a protein derived side chain tyrosyl radical by using electron paramagnetic resonance (EPR). Thus, we demonstrate that Spn invades lung cells, releasing H2O2 that oxidizes hemoproteins, including Cytc, catalyzing the formation of a tyrosyl side chain radical on Hb and causing mitochondrial disruption, that ultimately leads to the collapse of the cell cytoskeleton.

microbiology↗