Chlamydia trachomatis Alters Mitochondrial Protein Composition and Secretes Effector Proteins That Target Mitochondria

Chlamydia psittaci infection induces IFN-I and IL-1β through the cGAS-STING-IRF3/NLRP3 pathway via mitochondrial oxidative stress in human macrophages

Chlamydia psittaci (C. psittaci) is a multi-host pathogen that elicits robust innate immune responses in macrophages. Chlamydiae target host mitochondria to manipulate the cellular fate and metabolic functions. However, the effect of C. psittaci on the host mitochondria remains obscure. This study investigated how C. psittaci, post-infection in human macrophages, induces mitochondrial oxidative stress and damage to activate the cGAS-STING-IRF3/NLRP3 pathway for IFN-I and IL-1β production. Results demonstrate that C. psittaci increased mitochondrial ROS (mtROS) production. This induced the release of oxidized mitochondrial DNA (mtDNA) into the cytoplasm of macrophages. It also augmented IFN-I and IL-1β production dependent on the cGAS-STING pathway. Macrophages pre-treated with mtROS inhibitor mito-TEMPO displayed reduced oxidized mtDNA. This consequently lowered IFN-I and IL-1β production via the cGAS-STING pathway induced by C. psittaci. Additionally, we found that mtROS production may inhibit C. psittaci proliferation through the synergistic action of IFN-I and IL-1β. In conclusion, our study reveals that C. psittaci induces mtROS production leading to mtDNA release. This activates the cGAS-STING-IRF3/NLRP3 pathway to increase IFN-I and IL-1β production. This study elucidates a novel mechanism of bacterial pathogen activation in the cGAS-STING pathway. This reveals the molecular mechanisms underlying the immune response to C. psittaci infection and proposes potential targets for the treatment of C. psittaci related diseases.

Mitochondria as sensors of intracellular pathogens

Mitochondria must sense their environment to enable cells and organisms to adapt to diverse environments and survive during stress. However, during microbial infection, an evolutionary pressure since the inception of the eukaryotic cell, these organelles are traditionally viewed as targets for microbes. In this opinion we consider the perspective that mitochondria are domesticated microbes that sense and guard their 'host' cell against pathogens. We explore potential mechanisms by which mitochondria detect intracellular pathogens and induce mitochondria-autonomous responses that activate cellular defenses.

Contributions of diverse models of the female reproductive tract to the study of Chlamydia trachomatis-host interactions

Chlamydia trachomatis is a common cause of sexually transmitted infections in humans with devastating sequelae. Understanding of disease on all scales, from molecular details to the immunology underlying pathology, is essential for identifying new ways of preventing and treating chlamydia. Infection models of various complexity are essential to understand all aspects of chlamydia pathogenesis. Cell culture systems allow for research into molecular details of infection, including characterization of the unique biphasic Chlamydia developmental cycle and the role of type-III-secreted effectors in modifying the host environment to allow for infection. Multicell type and organoid culture provide means to investigate how cells other than the infected cells contribute to the control of infection. Emerging comprehensive three-dimensional biomimetic systems may fill an important gap in current models to provide information on complex phenotypes that cannot be modeled in simpler in vitro models.

Features and algorithms: facilitating investigation of secreted effectors in Gram-negative bacteria

Gram-negative bacteria deliver effector proteins through type III, IV, or VI secretion systems (T3SSs, T4SSs, and T6SSs) into host cells, causing infections and diseases. In general, effector proteins for each of these distinct secretion systems lack homology and are difficult to identify. Sequence analysis has disclosed many common features, helping us to understand the evolution, function, and secretion mechanisms of the effectors. In combination with various algorithms, the known common features have facilitated accurate prediction of new effectors. Ensemblers or integrated pipelines achieve a better prediction of performance, which combines multiple computational models or modules with multidimensional features. Natural language processing (NLP) models also show the merits, which could enable discovery of novel features and, in turn, facilitate more precise effector prediction, extending our knowledge about each secretion mechanism.

Type III Secretion in Chlamydia

Type III secretion systems (T3SSs) are utilized by Gram-negative pathogens to enhance their pathogenesis. This secretion system is associated with the delivery of effectors through a needle-like structure from the bacterial cytosol directly into a target eukaryotic cell. These effector proteins then manipulate specific eukaryotic cell functions to benefit pathogen survival within the host. The obligate intracellular pathogens of the family Chlamydiaceae have a highly evolutionarily conserved nonflagellar T3SS that is an absolute requirement for their survival and propagation within the host with about one-seventh of the genome dedicated to genes associated with the T3SS apparatus, chaperones, and effectors. Chlamydiae also have a unique biphasic developmental cycle where the organism alternates between an infectious elementary body (EB) and replicative reticulate body (RB). T3SS structures have been visualized on both EBs and RBs. And there are effector proteins that function at each stage of the chlamydial developmental cycle, including entry and egress. This review will discuss the history of the discovery of chlamydial T3SS and the biochemical characterization of components of the T3SS apparatus and associated chaperones in the absence of chlamydial genetic tools. These data will be contextualized into how the T3SS apparatus functions throughout the chlamydial developmental cycle and the utility of heterologous/surrogate models to study chlamydial T3SS. Finally, there will be a targeted discussion on the history of chlamydial effectors and recent advances in the field.

Chlamydia Infection Remodels Host Cell Mitochondria to Alter Energy Metabolism and Subvert Apoptosis

Chlamydia infection represents an important cause for concern for public health worldwide. Chlamydial infection of the genital tract in females is mostly asymptomatic at the early stage, often manifesting as mucopurulent cervicitis, urethritis, and salpingitis at the later stage; it has been associated with female infertility, spontaneous abortion, ectopic pregnancy, and cervical cancer. As an obligate intracellular bacterium, Chlamydia depends heavily on host cells for nutrient acquisition, energy production, and cell propagation. The current review discusses various strategies utilized by Chlamydia in manipulating the cell metabolism to benefit bacterial propagation and survival through close interaction with the host cell mitochondrial and apoptotic pathway molecules.