Carabeo, R. | bioRxiv Science

bioRxiv2025

Chlamydia iron starvation links nutritional immunity to pathogen recognition

Nutritional immunity is an antimicrobial strategy that evolved to starve pathogens of essential nutrients, with death as the desired outcome. Here, we report that transient iron starvation of the obligate intracellular pathogen Chlamydia trachomatis, growing in endocervical epithelial cells, enhances pathogen recognition by the host cell through the dysregulation of a peptidoglycan (PG) remodeling enzyme, resulting in the activation of the nucleotide-binding oligomerization domain 2 (NOD2) pathway that recognizes PG fragments, increased production of tumor necrosis factor alpha (TNF) via increased activation of NF-{kappa}B, which correlated with death of infected cells. Activation of the NOD2/ NF-{kappa}B signaling axis is linked to the dysregulated overexpression of the PG remodeling enzyme AmiA and the subsequent cleavage and mislocalization of D-Ala-D-Ala analog. Inhibiting amiA transcriptional upregulation by CRISPR interference reduced pathogen recognition. We propose that nutritional immunity in general mediate abnormal expression of bacterial genes linked to pathogen-associated molecular patterns. ImportanceLimiting pathogen access to essential nutrients is the central tenet of nutritional immunity, with the outcome being severe starvation and eventual death of the pathogen. However, pathogen starvation induces several physiological changes prior to its death. They include errors in several biological processes, including metabolism and gene expression, which could lead to pathogen death. Here, we demonstrate that iron starvation of the clinically relevant human pathogen Chlamydia trachomatis significantly dysregulates the expression of a peptidoglycan remodeling amidase, AmiA to enhance chlamydial recognition by the host cell and the subsequent increased production of tumor necrosis factor and death of infected cells to the detriment of Chlamydia.

microbiology↗

bioRxiv2024

Chlamydia trachomatis modulates the expression of JAK-STAT signaling components to attenuate the Type II interferon response of epithelial cells

Chlamydia trachomatis has adapted to subvert signaling in epithelial cells to ensure successful intracellular development. Interferon-{gamma} (IFN{gamma}) produced by recruited lymphocytes signals through the JAK/STAT pathway to restrict chlamydial growth in the genital tract. However, during Chlamydia infection in vitro, addition of IFN{gamma} does not fully induce nuclear localization of its transcription factor STAT1 and target gene, IDO1. We hypothesize that this altered interferon response is a result of Chlamydia targeting components of the IFN{gamma}-JAK/STAT pathway. To assess the ability of replicating Chlamydia to dampen interferon signaling, HEp2 human epithelial cells were infected with C. trachomatis serovar L2 for 24 hours prior to exposure to physiologically relevant levels of IFN{gamma} (500 pg/mL). This novel approach enabled us to observe reduced phospho-activation of both STAT1 and its kinase Janus Kinase 2 (JAK2) in infected cells compared to mock-infected cells. Importantly, basal JAK2 and STAT1 transcript and protein levels were dampened by infection even in the absence of interferon, which could have implications for cytokine signaling beyond IFN{gamma}. Additionally, target genes IRF1, GBP1, APOL3, IDO1, and SOCS1 were not fully induced in response to IFN{gamma} exposure. Infection-dependent decreases in transcript, protein, and phosphoprotein were rescued when de novo bacterial protein synthesis was inhibited with chloramphenicol, restoring expression of IFN{gamma}-target genes. Similar Chlamydia-dependent dampening of STAT1 and JAK2 transcript levels were observed in infected END1 endocervical cells and in HEp2s infected with C. trachomatis serovar D, suggesting a conserved mechanism of dampening the interferon response by reducing the availability of key signaling components. ImportanceAs an obligate intracellular pathogen that has evolved to infect the genital epithelium, Chlamydia has developed strategies to prevent detection and antimicrobial signaling in its host to ensure its survival and spread. A major player in clearing Chlamydia infections is the inflammatory cytokine interferon-{gamma} (IFN{gamma}), which is produced by immune cells that are recruited to the site of infection. Reports of IFN{gamma} levels in vaginal and cervical swabs from Chlamydia-infected patients range from 1-350 pg/mL, while most in vitro studies of the effects of IFN{gamma} on chlamydial growth have used 15-85 fold higher concentrations. By using physiologically-relevant concentrations of IFN{gamma} we were able assess Chlamydias ability to modulate its signaling. We found that Chlamydia decreases the expression of multiple components that are required for inducing gene expression by IFN{gamma}, providing a possible mechanism by which C. trachomatis can attenuate the immune response in the female genital tract to cause long-term infections.

microbiology↗