Genetic and immune determinants of E. coli liver abscess formation

Reverse transcriptase inhibitors diminish systemic proinflammatory responses to bacterial pathogens

Bacterial infections can induce exuberant immune responses that can damage host tissues. Previously, we demonstrated that systemic Escherichia coli infection in mice causes tissue damage in the liver. This liver necrosis is associated with the expression of endogenous retroviruses, chromosomally integrated retroviruses that encode a reverse transcriptase. Furthermore, nucleotide/nucleoside reverse transcriptase inhibitors (NRTIs) completely prevent tissue damage and subsequent bacterial growth within necrotic lesions. Since liver necrosis is linked to heightened systemic inflammatory responses, we hypothesized that NRTIs diminish inflammation caused by E. coli infection and may also have broad impacts on the systemic immune response to bacterial pathogens. Here, we tested this hypothesis by characterizing the effects of NRTIs on the innate immune response to bacteria. In the liver, NRTI administration following E. coli inoculation reduced the expression of a large repertoire of proinflammatory transcripts. NRTIs also had systemic anti-inflammatory effects, including reducing proinflammatory cytokine levels in serum in response to E. coli in different mouse strains. The anti-inflammatory effects of NRTIs were also apparent in response to lipopolysaccharide (LPS) and Staphylococcus aureus, suggesting that the molecular mechanisms underlying the immunomodulatory functions of NRTIs are likely conserved across distinct immune signaling pathways. Moreover, in a model of lethal LPS shock, NRTI administration prevented hypothermia and death. Together, our observations reveal that NRTIs can potently impede systemic inflammatory responses during Gram-positive and Gram-negative bacterial infections. Our findings lay the groundwork for further investigation of the therapeutic scope of NRTIs and the mechanisms underlying their anti-inflammatory effects across non-retroviral infectious diseases.IMPORTANCEInflammatory responses are critical for host control of bacterial infection, but excessive inflammation can damage host tissues and lead to sepsis. Understanding how innate immune responses are controlled during infection is important for developing new approaches to dampen excessive inflammation. In previous work, we found that tissue damage caused by excessive inflammatory responses may be driven by endogenous reverse transcriptases. Here we demonstrate that treatment of mice with reverse transcriptase inhibitors leads to broad reductions in systemic proinflammatory responses during bacterial infections and can protect mice from acute death in a lethal model of sepsis. Our findings indicate that uncovering the mechanisms underlying the anti-inflammatory functions of reverse transcriptase inhibitors may lead to new therapeutics for bacterial infectious diseases.

Differential neutrophil responses in murine following intraperitoneal injections of Escherichia coli and Staphylococcus aureus

Objective

This study aimed to investigate the proportion of neutrophils among leukocytes, in various tissues following intraperitoneal injection of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in mice.

Methods

Twelve specific-pathogen free (SPF) male mice, aged eight weeks, were segregated into three groups, each containing four mice. Two of these groups were subjected to intraperitoneal injections of E. coli and S. aureus, both in high concentrations, to establish mouse models of inflammation. The remaining group, which received an intraperitoneal injection of phosphate buffered saline (PBS), served as the control group. Observe the mice every half hour. Then mice were anesthetized, and samples from peripheral blood, liver, and brain tissues were carefully collected nearing death. These samples underwent a digestion process to produce single-cell suspensions. Subsequently, these suspensions were stained with fluorescent antibodies targeting CD45, Ly6G, and CD11b. A flow cytometric analyzer was then employed to enumerate and compare the neutrophil alterations across each group (Fig. 1).

Results

The results indicated a significant variation in the ratio of CD11b+ Ly6G+ neutrophils to CD45+ leukocytes among the groups. In peripheral blood, the control group showed a neutrophil proportion of approximately 1.44 %, while the E. coli and S. aureus groups exhibited increased proportions of 6.53 % and 3.82 %, respectively. In liver tissue, a marked elevation was observed in the experimental groups, with ratios of 19.20 % and 20.40 % for E. coli and S. aureus, respectively, compared to 1.64 % in the control. In brain tissue, the increments were more modest but noticeable, with the experimental groups showing 2.40 % and 1.11 % in contrast to 0.13 % in the control group.

Conclusions

These findings suggest neutrophils are involved in the response after intraperitoneal injection of E. coli and S. aureus, with marked differences in neutrophil responses in different tissues. This study enhances our understanding of the acute inflammatory response to bacterial infection.

Preparation techniques, structural features, and bioactivities of Eucommia ulmoides polysaccharides: A review

Eucommia ulmoides Oliv. (tu-chung), as a famous nature medical and edible plant, has the effect of tonifying liver and kidney, strengthening the function of the muscles and bones, and miscarriage prevention. Accumulating evidence has demonstrated that the polysaccharides from Eucommia ulmoides Oliv. (EUPs) are a kind of vital and representative biologically active macromolecules and have various health-promoting biological activities in vivo and in vitro, such as antioxidant activity, immunomodulatory activity, hypolipidemic and hypoglycemic activities, anti-inflammatory activities, anti-tumor activity, and among others. The review aims to comprehensively and systematically collate the recent research progress on extraction and purification methods, structural characteristics, biological activities, mechanism of action, structural modification, and toxicity of EUPs to support their therapeutic potential and health-care functions. New valuable insights for future research with EUPs were also proposed in the areas of structural characterization and pharmacological activities to promoting the development of therapeutic agents and functional foods.

A Customized Biohybrid Presenting Cascade Responses to Tumor Microenvironment

Intrinsic characteristics of microorganisms, including non-specific metabolism sites, toxic byproducts, and uncontrolled proliferation constrain their exploitation in medical applications such as tumor therapy. Here, the authors report an engineered biohybrid that can efficiently target cancerous sites through a pre-determined metabolic pathway to enable precise tumor ablation. In this system, DH5α Escherichia coli is engineered by the introduction of hypoxia-inducible promoters and lactate oxidase genes, and further surface-armored with iron-doped ZIF-8 nanoparticles. This bioengineered E. coli can produce and secrete lactate oxidase to reduce lactate concentration in response to hypoxic tumor microenvironment, as well as triggering immune activation. The peroxidase-like functionality of the nanoparticles extends the end product of the lactate metabolism, enabling the conversion of hydrogen peroxide (H2O2) into highly cytotoxic hydroxyl radicals. This, coupled with the transformation of tirapazamine loaded on nanoparticles to toxic benzotriazinyl, culminates in severe tumor cell ferroptosis. Intravenous injection of this biohybrid significantly inhibits tumor growth and metastasis.

Emerging Roles of Spatial Transcriptomics in Liver Research

Spatial transcriptomics, leveraging sequencing- and imaging-based techniques, has emerged as a groundbreaking technology for mapping gene expression within the complex architectures of tissues. This approach provides an in-depth understanding of cellular and molecular dynamics across various states of healthy and diseased livers. Through the integration of sophisticated bioinformatics strategies, it enables detailed exploration of cellular heterogeneity, transitions in cell states, and intricate cell-cell interactions with remarkable precision. In liver research, spatial transcriptomics has been particularly revelatory, identifying distinct zonated functions of hepatocytes that are crucial for understanding the metabolic and detoxification processes of the liver. Moreover, this technology has unveiled new insights into the pathogenesis of liver diseases, such as the role of lipid-associated macrophages in steatosis and endothelial cell signals in liver regeneration and repair. In the domain of liver cancer, spatial transcriptomics has proven instrumental in delineating intratumor heterogeneity, identifying supportive microenvironmental niches and revealing the complex interplay between tumor cells and the immune system as well as susceptibility to immune checkpoint inhibitors. In conclusion, spatial transcriptomics represents a significant advance in hepatology, promising to enhance our understanding and treatment of liver diseases.

Temporal and spatial dynamics of Listeria monocytogenes central nervous system infection in mice

Listeria monocytogenes is a bacterial pathogen that can cause life-threatening central nervous system (CNS) infections. While mechanisms by which L. monocytogenes and other pathogens traffic to the brain have been studied, a quantitative understanding of the underlying dynamics of colonization and replication within the brain is still lacking. In this study, we used barcoded L. monocytogenes to quantify the bottlenecks and dissemination patterns that lead to cerebral infection. Following intravenous (IV) inoculation, multiple independent invasion events seeded all parts of the CNS from the blood, however, only one clone usually became dominant in the brain. Sequential IV inoculations and intracranial inoculations suggested that clones that had a temporal advantage (i.e., seeded the CNS first), rather than a spatial advantage (i.e., invaded a particular brain region), were the main drivers of clonal dominance. In a foodborne model of cerebral infection with immunocompromised mice, rare invasion events instead led to a highly infected yet monoclonal CNS. This restrictive bottleneck likely arose from pathogen transit into the blood, rather than directly from the blood to the brain. Collectively, our findings provide a detailed quantitative understanding of the L. monocytogenes population dynamics that lead to CNS infection and a framework for studying the dynamics of other cerebral infections.

Reverse transcriptase inhibitors prevent liver abscess formation during Escherichia coli bloodstream infection

The presence of bacteria in the bloodstream is associated with severe clinical outcomes. In mice, intravenous inoculation of Escherichia coli can lead to the formation of macroscopic abscesses in the liver. Abscesses are regions of severe necrosis and consist of millions of bacteria surrounded by inflammatory immune cells. Liver abscess susceptibility varies widely across strains of mice, but the host factors governing this variation are unknown. Here, we profiled hepatic transcriptomes in mice with varying susceptibility to liver abscess formation. We found that transcripts from endogenous retroviruses (ERVs) are robustly induced in the liver by E. coli infection and ERV expression positively correlates with the frequency of abscess formation. Hypothesizing that ERV-encoded reverse transcriptase may generate cytoplasmic DNA and heighten inflammatory responses, we tested whether nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) influence abscess formation. Strikingly, a single NRTI dose administered immediately following E. coli inoculation prevented abscess formation, leading to a concomitant 100,000-fold reduction in bacterial burden. We provide evidence that NRTIs inhibit abscess formation by preventing the tissue necrosis that facilitates bacterial replication. Together, our findings suggest that endogenous reverse transcriptases drive inflammatory responses during bacterial bloodstream infection to drive abscess formation. The high efficacy of NRTIs in preventing abscess formation suggests that the consequences of reverse transcription on inflammation should be further examined, particularly in infectious diseases where inflammation drives negative clinical outcomes, such as sepsis.