Chlamydia trachomatis development requires both host glycolysis and oxidative phosphorylation but has only minor effects on these pathways

Neospora caninum hijacks host PFKFB3-driven glycolysis to facilitate intracellular propagation of parasites

Infection with Neospora caninum leads to reproductive failure in ruminants, such as cattle and goats; however, no effective vaccines or treatments are currently available to control this infection. Carefully regulating the glycolysis of host cells is essential for the intracellular survival of pathogens. Nonetheless, the impact of N. caninum infection on host cell glycolysis and the effects and mechanisms of host cell glycolysis on the intracellular survival of this parasite remains unclear. In this study, the analysis of metabolomics and transcriptomics revealed that N. caninum infection increases the expression of glycolysis-related enzymes and lactate production in caprine endometrial epithelial cells (EECs). The study's findings demonstrate that the inhibition of host cell glycolysis using 2-DG or sodium oxamate (an LDH-A inhibitor) inhibits host cell glycolysis and the intracellular propagation of N. caninum tachyzoites. Moreover, the addition of lactate further promotes the replication of N. caninum tachyzoites both in vivo and in vitro. Further investigation found that N. caninum infection induces host cell glycolysis via up-regulating 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) expression, while knockdown of PFKFB3 with small-interfering RNA or 3-PO significantly inhibits host cell glycolysis and the propagation of N. caninum tachyzoites both in vivo and in vitro. Additionally, a mechanistic study showed that N. caninum infection activates the JNK signalling pathway and inhibits the ubiquitination degradation of HIF-1α. Chromatin immunoprecipitation and dual-luciferase reporter assays revealed that N. caninum infection induces the expression of HIF-1α, which binds to the promoter region of pfkfb3. Our findings indicate that cellular glycolysis may serve as a potential therapeutic target for neosporosis, offering a novel insight for further investigating the intracellular survival mechanisms of N. caninum.

Study Models for Chlamydia trachomatis Infection of the Female Reproductive Tract

Chlamydia trachomatis (Ct) is a leading cause of sexually transmitted infections globally, often resulting in inflammatory disorders, ectopic pregnancies, and infertility. Studying Ct's pathogenesis remains challenging due to its unique life cycle and host-specific interactions, which require diverse experimental models. Animal studies using mouse, guinea pig, pig, and non-human primate models provide valuable insights into immune responses, hormonal influences, and disease progression. However, they face limitations in terms of translational relevance due to physiological differences, as well as ethical concerns. Complementing these, in vitro systems, ranging from simple monolayer to advanced three-dimensional models, exhibit improved physiological relevance by replicating the human tissue architecture. This includes the detailed investigation of epithelial barrier disruptions, epithelium-stroma interactions, and immune responses at a cellular level. Nonetheless, in vitro models fall short in mimicking the intricate tissue structures found in vivo and, therefore, cannot faithfully replicate the host-pathogen interactions or infection dynamics observed in living organisms. This review presents a comprehensive overview of the in vivo and in vitro models employed over the past few decades to investigate Ct and its pathogenesis, addressing their strengths and limitations. Furthermore, we explore emerging technologies, including organ-on-chip and in silico models, as promising tools to overcome the existing challenges and refine our understanding of Ct infections.

Hypoxia-inducible factor-driven glycolytic adaptations in host-microbe interactions

Mammalian cells utilize glucose as a primary carbon source to produce energy for most cellular functions. However, the bioenergetic homeostasis of cells can be perturbed by environmental alterations, such as changes in oxygen levels which can be associated with bacterial infection. Reduction in oxygen availability leads to a state of hypoxia, inducing numerous cellular responses that aim to combat this stress. Importantly, hypoxia strongly augments cellular glycolysis in most cell types to compensate for the loss of aerobic respiration. Understanding how this host cell metabolic adaptation to hypoxia impacts the course of bacterial infection will identify new anti-microbial targets. This review will highlight developments in our understanding of glycolytic substrate channeling and spatiotemporal enzymatic organization in response to hypoxia, shedding light on the integral role of the hypoxia-inducible factor (HIF) during host-pathogen interactions. Furthermore, the ability of intracellular and extracellular bacteria (pathogens and commensals alike) to modulate host cellular glucose metabolism will be discussed.

Insights into innate immune cell evasion by Chlamydia trachomatis

Chlamydia trachomatis, is a kind of obligate intracellular pathogen. The removal of C. trachomatis relies primarily on specific cellular immunity. It is currently considered that CD4+ Th1 cytokine responses are the major protective immunity against C. trachomatis infection and reinfection rather than CD8+ T cells. The non-specific immunity (innate immunity) also plays an important role in the infection process. To survive inside the cells, the first process that C. trachomatis faces is the innate immune response. As the "sentry" of the body, mast cells attempt to engulf and remove C. trachomatis. Dendritic cells present antigen of C. trachomatis to the "commanders" (T cells) through MHC-I and MHC-II. IFN-γ produced by activated T cells and natural killer cells (NK) further activates macrophages. They form the body's "combat troops" and produce immunity against C. trachomatis in the tissues and blood. In addition, the role of eosinophils, basophils, innate lymphoid cells (ILCs), natural killer T (NKT) cells, γδT cells and B-1 cells should not be underestimated in the infection of C. trachomatis. The protective role of innate immunity is insufficient, and sexually transmitted diseases (STDs) caused by C. trachomatis infections tend to be insidious and recalcitrant. As a consequence, C. trachomatis has developed a unique evasion mechanism that triggers inflammatory immunopathology and acts as a bridge to protective to pathological adaptive immunity. This review focuses on the recent advances in how C. trachomatis evades various innate immune cells, which contributes to vaccine development and our understanding of the pathophysiologic consequences of C. trachomatis infection.