Outer membrane vesicles produced by pathogenic strains of Escherichia coli block autophagic flux and exacerbate inflammasome activation

Inhibiting NLRP3 enhances cellular autophagy induced by outer membrane vesicles from Pseudomonas aeruginosa

The bacterium Pseudomonas aeruginosa is able to invade lung epithelial cells and survive intracellularly. During this process, it secretes outer membrane vesicles (OMVs), however, it is currently unclear how OMVs from P. aeruginosa (PA-OMVs) affect lung epithelial cells and their impact on oxidative stress, autophagy, and other physiological activities of lung epithelial cells. In this study, we found that PA-OMVs activated oxidative stress and autophagy in cells. We demonstrated that the NLRP3 (NLR family, pyrin domain containing 3) inhibitor MCC950 can enhance autophagy induced by PA-OMVs. The main function of NLRP3 is related to the body's immune response and inflammation regulation. MCC950 is the most common inhibitor of NLRP3. Additionally, we showed that PA-OMVs not only enhanced the expression of AMP-activated protein kinase, a key regulator of cellular energy homeostasis, and reactive oxygen species, which play a crucial role in cellular signaling and oxidative stress, but also significantly enhanced the expression of NLRP3. Inhibiting the expression of NLRP3 further enhanced the process of PA-OMVs induced autophagy. These results demonstrate that PA-OMVs activate both autophagy and the NLRP3 inflammasome, with NLRP3 suppressing autophagy to a certain extent, hoping to provide broad ideas for the future applications of PA-OMVs.IMPORTANCEThe discovery that lung epithelial cells exposed to outer membrane vesicles from Pseudomonas aeruginosa (PA-OMVs) activate cellular autophagy and induce protective immunity is significant. Specifically, the addition of an NLRP3 inhibitor, MCC950, has been found to decrease NLRP3 targets while simultaneously enhancing the autophagy activity induced by PA-OMVs. This finding unveils a novel theoretical framework for the development of PA-OMVs vaccines, highlighting new targets for enhancing the body's anti-infective responses. By elucidating the mechanisms through which PA-OMVs trigger autophagy and bolster immune defenses, this research opens avenues for innovative vaccine design strategies aimed at combatting infections effectively.

The role of programmed cell death in organ dysfunction induced by opportunistic pathogens

Sepsis is a life-threatening condition resulting from pathogen infection and characterized by organ dysfunction. Programmed cell death (PCD) during sepsis has been associated with the development of multiple organ dysfunction syndrome (MODS), impacting various physiological systems including respiratory, cardiovascular, renal, neurological, hematological, hepatic, and intestinal systems. It is well-established that pathogen infections lead to immune dysregulation, which subsequently contributes to MODS in sepsis. However, recent evidence suggests that sepsis-related opportunistic pathogens can directly induce organ failure by promoting PCD in parenchymal cells of each affected organ. This study provides an overview of PCD in damaged organ and the induction of PCD in host parenchymal cells by opportunistic pathogens, proposing innovative strategies for preventing organ failure in sepsis.

Two birds with one stone: natural polyphenols boosted periodontitis treatment of chlorhexidine via reducing toxicity and regulating microenvironments

Chlorhexidine (CHX) is considered the gold standard for controlling periodontal plaque and has been extensively used as a topical agent in treating periodontitis. Nevertheless, the practical clinical application of CHX is still constrained by the inherent limitations of its properties, including toxicity, inadequate biofilm scavenging capacity, and single biological effect. In this study, polyphenolic epigallocatechin gallate (EGCG) has been employed to integrate with CHX to form an EGCG-CHX nanoplatform via a facile one-pot method. Due to the dynamic bonding between EGCG and CHX, the EGCG-CHX nanoparticles (NPs) show reduced toxicity and excellent response release behavior. Moreover, a series of in vitro and in vivo studies demonstrated that the EGCG-CHX NPs significantly enhanced the antibiofilm, antioxidative, anti-inflammatory, and autophagic flux activation effects of CHX, ultimately achieving an improved therapeutic effect on periodontitis. This study successfully developed a strategy boosting the efficiency of CHX for periodontitis treatment.

Consistency in bacterial extracellular vesicle production: key to their application in human health

Bacterial extracellular vesicles (BEVs) are naturally occurring functional structures that play critical roles in bacterial life processes. These vesicles, commonly known as outer membrane vesicles (OMVs), were first found to be released by Gram-negative bacteria; however, it has since been confirmed that Gram-positive bacteria also secrete BEVs. As research advances, BEVs are increasingly utilized in diverse applications, including vaccine development and drug delivery. Nevertheless, the effective employment of BEVs in these contexts requires the acquisition of vesicles with consistent properties and functions through appropriate culture, isolation, and purification methods. This review examines the advantages and disadvantages of various purification techniques alongside the heterogeneity they may introduce. We utilize the heterogeneity of BEVs as a framework to critically analyze the barriers to their application and the factors influencing their characteristics. Additionally, we constructively propose solutions to enhance the consistency of BEVs, thereby facilitating their further development and application.

Uncovering a new family of conserved virulence factors that promote the production of host-damaging outer membrane vesicles in gram-negative bacteria

CprA is a short-chain dehydrogenase/reductase (SDR) that contributes to resistance against colistin and antimicrobial peptides. The cprA gene is conserved across Pseudomonas aeruginosa clades and its expression is directly regulated by the two-component system PmrAB. We have shown that cprA expression leads to the production of outer membrane vesicles (OMVs) that block autophagic flux and have a greater capacity to activate the non-canonical inflammasome pathway. In a murine model of sepsis, a P. aeruginosa strain deleted for cprA was less virulent than the wild-type (WT) strain. These results demonstrate the important role of CprA in the pathogenicity of P. aeruginosa. It is worth noting that CprA is also a functional ortholog of hemolysin F (HlyF), which is encoded by virulence plasmids of Escherichia coli. We have shown that other cryptic SDRs encoded by mammalian and plant pathogens, such as Yersinia pestis and Ralstonia solanacearum are functional orthologs of CprA and HlyF. These SDRs also induce the production of OMVs which block autophagic flux. This study uncovers a new family of virulence determinants in Gram-negative bacteria, offering potential for innovative therapeutic interventions and deeper insights into bacterial pathogenesis.

The intricate interactions between inflammasomes and bacterial pathogens: Roles, mechanisms, and therapeutic potentials

Inflammasomes are intracellular multiprotein complexes that consist of a sensor, an adaptor, and a caspase enzyme to cleave interleukin (IL)-1β and IL-18 into their mature forms. In addition, caspase-1 and -11 activation results in the cleavage of gasdermin D to form pores, thereby inducing pyroptosis. Activation of the inflammasome and pyroptosis promotes host defense against pathogens, whereas dysregulation of the inflammasome can result in various pathologies. Inflammasomes exhibit versatile microbial signal detection, directly or indirectly, through cellular processes, such as ion fluctuations, reactive oxygen species generation, and the disruption of intracellular organelle function; however, bacteria have adaptive strategies to manipulate the inflammasome by altering microbe-associated molecular patterns, intercepting innate pathways with secreted effectors, and attenuating inflammatory and cell death responses. In this review, we summarize recent advances in the diverse roles of the inflammasome during bacterial infections and discuss how bacteria exploit inflammasome pathways to establish infections or persistence. In addition, we highlight the therapeutic potential of harnessing bacterial immune subversion strategies against acute and chronic bacterial infections. A more comprehensive understanding of the significance of inflammasomes in immunity and their intricate roles in the battle between bacterial pathogens and hosts will lead to the development of innovative strategies to address emerging threats posed by the expansion of drug-resistant bacterial infections.

Azithromycin inhibits the intracellular persistence of Acinetobacter baumannii by inducing host cell autophagy in human bronchial epithelial cells

The invasion of host cells by bacteria, leading to intracellular infections, is a major cause of infection recurrence. Drug-resistant Acinetobacter baumannii (A. baumannii) is one of the most challenging public health issues worldwide, with very limited clinical treatment options available. A. baumannii has been found to be able to invade host cells and proliferate within them in recent studies. In addition to the direct antimicrobial effect of antibiotics, the activation of host autophagic flux also plays an important role in eliminating intracellular pathogens. Herein, this study aimes to evaluate the clearance effect of antibiotics on intracellular A. baumannii both in vivo and in vitro, and explore the relationship between this effect and autophagy. The results showed that intracellular pathogens resulted in a significant increase in the minimum bactericidal concentration, while azithromycin can significantly eliminate intracellular A. baumannii in vitro and in vivo. Notably, 60 μg/mL azithromycin demonstrated intracellular clearance against multidrug-resistant A. baumannii and markedly induced autophagosomes in BEAS-2B cells with a mild stimulation of autophagosomes degradation. These findings indicated that azithromycin can significantly clear intracellular A. baumannii and its ability to clear intracellular A. baumannii may be related to the stimulation of autophagosome formation and the induction of host autophagy, which has important implications for the clinical treatment of A. baumannii infections, especially when intracellular infections are present.

Lipopolysaccharide Imprinted Polymers for Specific Recognition of Bacterial Outer Membrane Vesicles

Outer membrane vesicles (OMVs) secreted by bacteria are emerging diagnostic markers for bacterial infection or disease detection due to their carriage of various signaling molecules. However, actual biological samples of patients are extremely complex, and applying OMVs to clinical diagnosis remains a major challenge. One of the major challenges is that there are still great difficulties in the enrichment of OMVs including tedious steps and lower concentration. And some commonly used exosome enrichment methods, such as ultracentrifugation, still have some shortcomings. Herein, we introduce lipopolysaccharide (LPS) molecularly imprinted polymer (MIP) for efficient capturing and analyzing OMVs, enabling a novel approach to bacterial disease diagnosis based on biorecognition materials. LPS, as a unique structure of Gram-negative bacteria, also widely expressed on the surface of OMVs, which will form cyclic hydrogen bonds with functional monomers of MIP with affinity interactions. The prepared MIP efficiently can isolate OMVs from 100 μL of culture broth via specific affinity LPS in less than 40 min with a recovery rate of over 95%. Moreover, MIP exhibits good reusability, with almost identical enrichment performance after 5 repeated cycles, contributing to reducing experimental costs in both time and economy. The captured OMVs can be detected using Western blotting with target protein antibodies or in combination with proteomic analysis, providing a proteomic biomarker platform for early bacteria disease diagnosis.

Extracellular NCOA4 is a mediator of septic death by activating the AGER-NFKB pathway

Sepsis, a life-threatening condition resulting from a dysregulated response to pathogen infection, poses a significant challenge in clinical management. Here, we report a novel role for the autophagy receptor NCOA4 in the pathogenesis of sepsis. Activated macrophages and monocytes secrete NCOA4, which acts as a mediator of septic death in mice. Mechanistically, lipopolysaccharide, a major component of the outer membrane of Gram-negative bacteria, induces NCOA4 secretion through autophagy-dependent lysosomal exocytosis mediated by ATG5 and MCOLN1. Moreover, bacterial infection with E. coli or S. enterica leads to passive release of NCOA4 during GSDMD-mediated pyroptosis. Upon release, extracellular NCOA4 triggers the activation of the proinflammatory transcription factor NFKB/NF-κB by promoting the degradation of NFKBIA/IκB molecules. This process is dependent on the pattern recognition receptor AGER, rather than TLR4. In vivo studies employing endotoxemia and polymicrobial sepsis mouse models reveal that a monoclonal neutralizing antibody targeting NCOA4 or AGER delays animal death, protects against organ damage, and attenuates systemic inflammation. Furthermore, elevated plasma NCOA4 levels in septic patients, particularly in non-survivors, correlate positively with the sequential organ failure assessment score and concentrations of lactate and proinflammatory mediators, such as TNF, IL1B, IL6, and HMGB1. These findings demonstrate a previously unrecognized role of extracellular NCOA4 in inflammation, suggesting it as a potential therapeutic target for severe infectious diseases. Abbreviation: BMDMs: bone marrow-derived macrophages; BUN: blood urea nitrogen; CLP: cecal ligation and puncture; ELISA: enzyme-linked immunosorbent assay; LPS: lipopolysaccharide; NO: nitric oxide; SOFA: sequential organ failure assessment.

Recent advances in bacterial outer membrane vesicles: Effects on the immune system, mechanisms and their usage for tumor treatment

Tumor treatment remains a significant medical challenge, with many traditional therapies causing notable side effects. Recent research has led to the development of immunotherapy, which offers numerous advantages. Bacteria inherently possess motility, allowing them to preferentially colonize tumors and modulate the tumor immune microenvironment, thus influencing the efficacy of immunotherapy. Bacterial outer membrane vesicles (OMVs) secreted by gram-negative bacteria are nanoscale lipid bilayer structures rich in bacterial antigens, pathogen-associated molecular patterns (PAMPs), various proteins, and vesicle structures. These features allow OMVs to stimulate immune system activation, generate immune responses, and serve as efficient drug delivery vehicles. This dual capability enhances the effectiveness of immunotherapy combined with chemotherapy or phototherapy, thereby improving anticancer drug efficacy. Current research has concentrated on engineering OMVs to enhance production yield, minimize cytotoxicity, and improve the safety and efficacy of treatments. Consequently, OMVs hold great promise for applications in tumor immunotherapy, tumor vaccine development, and drug delivery. This article provides an overview of the structural composition and immune mechanisms of OMVs, details various OMVs modification strategies, and reviews the progress in using OMVs for tumor treatment and their anti-tumor mechanisms. Additionally, it discusses the challenges faced in translating OMV-based anti-tumor therapies into clinical practice, aiming to provide a comprehensive understanding of OMVs' potential for in-depth research and clinical application.

Bacterial membrane vesicles: formation, functions, and roles in bacterial-phage interactions

Outer membrane vesicles (OMVs) are nano-sized vesicles actively released by Gram-negative bacteria, playing a crucial role in bacterial survival and interactions with phages. This review focuses on OMVs and succinctly delineates the stimuli instigating OMV formation, their functional repertoire, and their involvement in bacterial-phage interplays. Initially, the discussion centers on the drivers prompting OMV genesis, encompassing both extrinsic environmental pressures and intrinsic regulatory mechanisms within bacterial systems. Subsequently, a comprehensive examination of OMVs' multifaceted functions in bacterial physiology ensues, spanning signaling cascades, nutrient transport, antibiotic resilience, and evasion of immune surveillance. Particular emphasis is placed on elucidating the paramount significance of OMVs in mediating bacterial-phage dynamics. OMVs function as decoys, providing protection to bacterial hosts against phages, and concurrently promoting the spread of phage receptors, thereby rendering phage-resistant strains susceptible to phage invasion. This comprehensive review deepens our comprehension of membrane vesicles biogenesis in bacteria and their pivotal role in microbial community dynamics.

Material-based treatment strategies against intraosseous implant biofilm infection

Implant-associated infections present a significant clinical obstacle for orthopedic practitioners, with bacterial biofilm formation serving as a pivotal factor in the initiation, progression, and management of such infections. Conventional approaches have proven inadequate in fully eradicating biofilm-related infections. Consequently, novel material-based therapeutic strategies have been developed, encompassing the utilization of antimicrobial agents, delivery vehicles, and synergistic antibacterial systems. In this review, we provide a succinct overview of recent advancements in anti-biofilm strategies, with the aim of offering insights that may aid in the treatment of intraosseous implant infections.

Bacteria extracellular vesicle as nanopharmaceuticals for versatile biomedical potential

Bacteria extracellular vesicles (BEVs), characterized as the lipid bilayer membrane-surrounded nanoparticles filled with molecular cargo from parent cells, play fundamental roles in the bacteria growth and pathogenesis, as well as facilitating essential interaction between bacteria and host systems. Notably, benefiting from their unique biological functions, BEVs hold great promise as novel nanopharmaceuticals for diverse biomedical potential, attracting significant interest from both industry and academia. Typically, BEVs are evaluated as promising drug delivery platforms, on account of their intrinsic cell-targeting capability, ease of versatile cargo engineering, and capability to penetrate physiological barriers. Moreover, attributing to considerable intrinsic immunogenicity, BEVs are able to interact with the host immune system to boost immunotherapy as the novel nanovaccine against a wide range of diseases. Towards these significant directions, in this review, we elucidate the nature of BEVs and their role in activating host immune response for a better understanding of BEV-based nanopharmaceuticals' development. Additionally, we also systematically summarize recent advances in BEVs for achieving the target delivery of genetic material, therapeutic agents, and functional materials. Furthermore, vaccination strategies using BEVs are carefully covered, illustrating their flexible therapeutic potential in combating bacterial infections, viral infections, and cancer. Finally, the current hurdles and further outlook of these BEV-based nanopharmaceuticals will also be provided.

The potential immunological mechanisms of sepsis

Sepsis is described as a life-threatening organ dysfunction and a heterogeneous syndrome that is a leading cause of morbidity and mortality in intensive care settings. Severe sepsis could incite an uncontrollable surge of inflammatory cytokines, and the host immune system's immunosuppression could respond to counter excessive inflammatory responses, characterized by the accumulated anti-inflammatory cytokines, impaired function of immune cells, over-proliferation of myeloid-derived suppressor cells and regulatory T cells, depletion of immune effector cells by different means of death, etc. In this review, we delve into the underlying pathological mechanisms of sepsis, emphasizing both the hyperinflammatory phase and the associated immunosuppression. We offer an in-depth exploration of the critical mechanisms underlying sepsis, spanning from individual immune cells to a holistic organ perspective, and further down to the epigenetic and metabolic reprogramming. Furthermore, we outline the strengths of artificial intelligence in analyzing extensive datasets pertaining to septic patients, showcasing how classifiers trained on various clinical data sources can identify distinct sepsis phenotypes and thus to guide personalized therapy strategies for the management of sepsis. Additionally, we provide a comprehensive summary of recent, reliable biomarkers for hyperinflammatory and immunosuppressive states, facilitating more precise and expedited diagnosis of sepsis.

Streptococcus pneumoniae extracellular vesicles aggravate alveolar epithelial barrier disruption via autophagic degradation of OCLN (occludin)

Streptococcus pneumoniae (S. pneumoniae) represents a major human bacterial pathogen leading to high morbidity and mortality in children and the elderly. Recent research emphasizes the role of extracellular vesicles (EVs) in bacterial pathogenicity. However, the contribution of S. pneumoniae EVs (pEVs) to host-microbe interactions has remained unclear. Here, we observed that S. pneumoniae infections in mice led to severe lung injuries and alveolar epithelial barrier (AEB) dysfunction. Infections of S. pneumoniae reduced the protein expression of tight junction protein OCLN (occludin) and activated macroautophagy/autophagy in lung tissues of mice and A549 cells. Mechanically, S. pneumoniae induced autophagosomal degradation of OCLN leading to AEB impairment in the A549 monolayer. S. pneumoniae released the pEVs that could be internalized by alveolar epithelial cells. Through proteomics, we profiled the cargo proteins inside pEVs and found that these pEVs contained many virulence factors, among which we identified a eukaryotic-like serine-threonine kinase protein StkP. The internalized StkP could induce the phosphorylation of BECN1 (beclin 1) at Ser93 and Ser96 sites, initiating autophagy and resulting in autophagy-dependent OCLN degradation and AEB dysfunction. Finally, the deletion of stkP in S. pneumoniae completely protected infected mice from death, significantly alleviated OCLN degradation in vivo, and largely abolished the AEB disruption caused by pEVs in vitro. Overall, our results suggested that pEVs played a crucial role in the spread of S. pneumoniae virulence factors. The cargo protein StkP in pEVs could communicate with host target proteins and even hijack the BECN1 autophagy initiation pathway, contributing to AEB disruption and bacterial pathogenicity.Abbreviations: AEB: alveolarepithelial barrier; AECs: alveolar epithelial cells; ATG16L1: autophagy related 16 like 1; ATP:adenosine 5'-triphosphate; BafA1: bafilomycin A1; BBB: blood-brain barrier; CFU: colony-forming unit; co-IP: co-immunoprecipitation; CQ:chloroquine; CTRL: control; DiO: 3,3'-dioctadecylox-acarbocyanineperchlorate; DOX: doxycycline; DTT: dithiothreitol; ECIS: electricalcell-substrate impedance sensing; eGFP: enhanced green fluorescentprotein; ermR: erythromycin-resistance expression cassette; Ery: erythromycin; eSTKs: eukaryotic-like serine-threoninekinases; EVs: extracellular vesicles; HA: hemagglutinin; H&E: hematoxylin and eosin; HsLC3B: human LC3B; hpi: hours post-infection; IP: immunoprecipitation; KD: knockdown; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LC/MS: liquid chromatography-mass spectrometry; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MVs: membranevesicles; NC:negative control; NETs:neutrophil extracellular traps; OD: optical density; OMVs: outer membrane vesicles; PBS: phosphate-buffered saline; pEVs: S.pneumoniaeextracellular vesicles; protK: proteinase K; Rapa: rapamycin; RNAi: RNA interference; S.aureus: Staphylococcusaureus; SNF:supernatant fluid; sgRNA: single guide RNA; S.pneumoniae: Streptococcuspneumoniae; S.suis: Streptococcussuis; TEER: trans-epithelium electrical resistance; moi: multiplicity ofinfection; TEM:transmission electron microscope; TJproteins: tight junction proteins; TJP1/ZO-1: tight junction protein1; TSA: tryptic soy agar; WB: western blot; WT: wild-type.

Influences of bacterial extracellular vesicles on macrophage immune functions

Bacterial extracellular vesicles (EVs) are crucial mediators of information transfer between bacteria and host cells. Macrophages, as key effector cells in the innate immune system, have garnered widespread attention for their interactions with bacterial EVs. Increasing evidence indicates that bacterial EVs can be internalized by macrophages through multiple pathways, thereby influencing their immune functions. These functions include inflammatory responses, antimicrobial activity, antigen presentation, and programmed cell death. Therefore, this review summarizes current research on the interactions between bacterial EVs and macrophages. This will aid in the deeper understanding of immune modulation mediated by pathogenic microorganisms and provide a basis for developing novel antibacterial therapeutic strategies.

Milk Extracellular Vesicles: Natural Nanoparticles for Enhancing Oral Drug Delivery against Bacterial Infections

Oral drug delivery is typically preferred as a therapeutic intervention due to the complexities and expenses associated with intravenous administration. However, some drugs are poorly absorbed orally, requiring intravenous administration to bypass the gastrointestinal tract and deliver the drug directly into the bloodstream. Thus, there is an urgent need to develop novel drug delivery platforms to overcome the challenges of oral drug delivery with low solubility, low permeability, oral degradation, and low bioavailability. Advances in extracellular vesicles (EVs) as natural carriers have provided emerging approaches to improve potential therapeutic applications. Milk not only contains traditional nutrients but is also rich in EVs. In this Review, we focus mainly on the purification of milk EVs (mEVs), their safety, and the advantages of mEV-based drug carriers in combatting intestinal infections. Additionally, we summarize several advantages of mEVs over conventional synthetic carriers, such as low immunogenicity, high biocompatibility, and the ability to transfer bioactive molecules between cells. Considering the unmet gaps of mEVs in clinical translation, it is essential to review the cargo loading into mEVs and future perspectives for their use as natural drug carriers for oral delivery. This overview of mEV-based drug carriers for oral delivery sheds light on alternative approaches to treat clinical infections associated with intestinal pathogens and the development of novel oral delivery systems.

Bacterial membrane vesicles: orchestrators of interkingdom interactions in microbial communities for environmental adaptation and pathogenic dynamics

Bacterial membrane vesicles (MVs) have attracted increasing attention due to their significant roles in bacterial physiology and pathogenic processes. In this review, we provide an overview of the importance and current research status of MVs in regulating bacterial physiology and pathogenic processes, as well as their crucial roles in environmental adaptation and pathogenic infections. We describe the formation mechanism, composition, structure, and functions of MVs, and discuss the various roles of MVs in bacterial environmental adaptation and pathogenic infections. Additionally, we analyze the limitations and challenges of MV-related research and prospect the potential applications of MVs in environmental adaptation, pathogenic mechanisms, and novel therapeutic strategies. This review emphasizes the significance of understanding and studying MVs for the development of new insights into bacterial environmental adaptation and pathogenic processes. Overall, this review contributes to our understanding of the intricate interplay between bacteria and their environment and provides valuable insights for the development of novel therapeutic strategies targeting bacterial pathogenicity.

Morphological and biochemical characteristics associated with autophagy in gastrointestinal diseases

Autophagy is a cellular catabolic process characterized by the formation of double-membrane autophagosomes. Transmission electron microscopy is the most rigorous method to clearly visualize autophagic engulfment and degradation. A large number of studies have shown that autophagy is closely related to the digestion, secretion, and regeneration of gastrointestinal (GI) cells. However, the role of autophagy in GI diseases remains controversial. This article focuses on the morphological and biochemical characteristics of autophagy in GI diseases, in order to provide new ideas for their diagnosis and treatment.

Bacteria-derived extracellular vesicles: endogenous roles, therapeutic potentials and their biomimetics for the treatment and prevention of sepsis

Sepsis is one of the medical conditions with a high mortality rate and lacks specific treatment despite several years of extensive research. Bacterial extracellular vesicles (bEVs) are emerging as a focal target in the pathophysiology and treatment of sepsis. Extracellular vesicles (EVs) derived from pathogenic microorganisms carry pathogenic factors such as carbohydrates, proteins, lipids, nucleic acids, and virulence factors and are regarded as "long-range weapons" to trigger an inflammatory response. In particular, the small size of bEVs can cross the blood-brain and placental barriers that are difficult for pathogens to cross, deliver pathogenic agents to host cells, activate the host immune system, and possibly accelerate the bacterial infection process and subsequent sepsis. Over the years, research into host-derived EVs has increased, leading to breakthroughs in cancer and sepsis treatments. However, related approaches to the role and use of bacterial-derived EVs are still rare in the treatment of sepsis. Herein, this review looked at the dual nature of bEVs in sepsis by highlighting their inherent functions and emphasizing their therapeutic characteristics and potential. Various biomimetics of bEVs for the treatment and prevention of sepsis have also been reviewed. Finally, the latest progress and various obstacles in the clinical application of bEVs have been highlighted.

Extracellular vesicles from Fusobacterium nucleatum: roles in the malignant phenotypes of gastric cancer

The increase of the Fusobacterium nucleatum level has been previously identified in various cancers including gastric cancer (GC), but how the F. nucleatum exerts its carcinogenic role in GC remains unclear. Several studies revealed that F. nucleatum contributes to cancer progression via its secretion of extracellular vehicles (EVs). Hence, it's designed to reveal the influence of F. nucleatum-derived EVs (Fn-EVs) in GC progression. The tumor and adjacent tissues were collected from 30 GC patients, and the abundance of F. nucleatum was found to be highly expressed in tumor samples. The ultracentrifugation was employed to isolate EVs from F. nucleatum and Escherischia coli (E. coli), which were labeled Fn-EVs and E. coli-EVs, respectively. After treating GC cells with Fn-EVs and E. coli-EVs, cell counting kit 8, colony formation, wound healing as well as transwell assay were performed, which revealed that Fn-EVs effectively enhanced oxaliplatin resistance, and facilitated cell proliferation, migration, invasion, and stemness in GC cells while E. coli-EVs exert no significant effect on GC cells. Besides, the stemness and DNA repair of GC cells were also enhanced by Fn-EVs, as revealed by the sphere-forming assay and the detection of stemness- and DNA repair-associated proteins by western blotting. In vivo analyses demonstrated that Fn-EVs administration not only promoted GC tumor growth and liver metastasis but also conferred GC tumor resistance to oxaliplatin resistance. This study first revealed the contributive role of F. nucleatum in GC development via Fn-EVs, which provided a better perspective for manipulating F. nucleatum in treating GC patients with malignant phenotypes.

Two-component system RstAB promotes the pathogenicity of adherent-invasive Escherichia coli in response to acidic conditions within macrophages

Adherent-invasive Escherichia coli (AIEC) strain LF82, isolated from patients with Crohn's disease, invades gut epithelial cells, and replicates in macrophages contributing to chronic inflammation. In this study, we found that RstAB contributing to the colonization of LF82 in a mouse model of chronic colitis by promoting bacterial replication in macrophages. By comparing the transcriptomes of rstAB mutant- and wild-type when infected macrophages, 83 significant differentially expressed genes in LF82 were identified. And we identified two possible RstA target genes (csgD and asr) among the differentially expressed genes. The electrophoretic mobility shift assay and quantitative real-time PCR confirmed that RstA binds to the promoters of csgD and asr and activates their expression. csgD deletion attenuated LF82 intracellular biofilm formation, and asr deletion reduced acid tolerance compared with the wild-type. Acidic pH was shown by quantitative real-time PCR to be the signal sensed by RstAB to activate the expression of csgD and asr. We uncovered a signal transduction pathway whereby LF82, in response to the acidic environment within macrophages, activates transcription of the csgD to promote biofilm formation, and activates transcription of the asr to promote acid tolerance, promoting its replication within macrophages and colonization of the intestine. This finding deepens our understanding of the LF82 replication regulation mechanism in macrophages and offers new perspectives for further studies on AIEC virulence mechanisms.

Role of Extracellular Vesicles in Immunity and Host Defense

Extracellular vesicles (EVs) are membrane-bound structures released by cells and have become significant players in immune system functioning, primarily by facilitating cell-to-cell communication. Immune cells like neutrophils and dendritic cells release EVs containing bioactive molecules that modulate chemotaxis, activate immune cells, and induce inflammation. EVs also contribute to antigen presentation, lymphocyte activation, and immune tolerance. Moreover, EVs play pivotal roles in antimicrobial host defense. They deliver microbial antigens to antigen-presenting cells (APCs), triggering immune responses, or act as decoys to neutralize virulence factors and toxins. This review discusses host and microbial EVs' multifaceted roles in innate and adaptive immunity, highlighting their involvement in immune cell development, antigen presentation, and antimicrobial responses.

Pyroptosis in septic lung injury: Interactions with other types of cell death

Sepsis is a life-threatening systemic inflammatory response syndrome caused by the host imbalanced response to infection. Lung injury is the most common complication of sepsis and one of the leading causes of patient death. Pyroptosis is a specific programmed cell death characterized by the release of inflammatory cytokines. Appropriate pyroptosis can reduce tissue damage and exert a protective effect against infection during sepsis. However, overactivated pyroptosis results in massive cell death, leading to septic shock, multiple organ dysfunction syndrome, and even an increased risk of secondary infection. Recent studies suggest that pyroptosis can interact with and cross-regulate other types of cell death programs to establish a complex network of cell death, which participates in the occurrence and development of septic lung injury. This review will focus on the interactions between pyroptosis and other types of cell death, including apoptosis, necroptosis, PANoptosis, NETosis, autophagy, and ferroptosis, to summarize the role of pyroptosis in sepsis-induced lung injury, and will discuss the potential therapeutic strategies of targeting pyroptosis during sepsis treatment.

Novel insights into the regulatory role of N6-methyladenosine methylation modified autophagy in sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. It is characterized by high morbidity and mortality and one of the major diseases that seriously hang over global human health. Autophagy is a crucial regulator in the complicated pathophysiological processes of sepsis. The activation of autophagy is known to be of great significance for protecting sepsis induced organ dysfunction. Recent research has demonstrated that N6-methyladenosine (m6A) methylation is a well-known post-transcriptional RNA modification that controls epigenetic and gene expression as well as a number of biological processes in sepsis. In addition, m6A affects the stability, export, splicing and translation of transcripts involved in the autophagic process. Although it has been suggested that m6A methylation regulates the biological metabolic processes of autophagy and is more frequently seen in the progression of sepsis pathogenesis, the underlying molecular mechanisms of m6A-modified autophagy in sepsis have not been thoroughly elucidated. The present article fills this gap by providing an epigenetic review of the processes of m6A-modified autophagy in sepsis and its potential role in the development of novel therapeutics.

Bacterial extracellular vesicles: an emerging avenue to tackle diseases

A growing body of research, especially in recent years, has shown that bacterial extracellular vesicles (bEVs) are one of the key underlying mechanisms behind the pathogenesis of various diseases like pulmonary fibrosis, sepsis, systemic bone loss, and Alzheimer's disease. Given these new insights, bEVs are proposed as an emerging vehicle that can be used as a diagnostic tool or to tackle diseases when used as a therapeutic target. To further boost the understanding of bEVs in health and disease we thoroughly discuss the contribution of bEVs in disease pathogenesis and the underlying mechanisms. In addition, we speculate on their potential as novel diagnostic biomarkers and how bEV-related mechanisms can be exploited as therapeutic targets.

Agaricus blazei Murrill Polysaccharide Attenuates Periodontitis via H2 S/NRF2 Axis-Boosted Appropriate Level of Autophagy in PDLCs

SCOPE

Periodontitis is one of the most prevalent chronic inflammatory diseases with impaired autophagy. Agaricus blazei Murrill polysaccharide (ABMP) shows beneficial effects in various inflammatory diseases. However, whether ABMP is involved in autophagy regulation and periodontitis attenuation remains to be elucidated.

METHODS AND RESULTS

This study firstly shows the dynamic changes in inflammatory and autophagy levels in silk ligature periodontitis model. Then the positive regulation effect of autophagy on inflammation and its vital role in ABMP inhibiting PDLCs inflammatory response are testified in LPS-treated PDLCs. Secondly, the Micro-CT, quantitative RT-PCR, Western Blot, TRAP, and immunofluorescence staining analysis are performed to assess the effects of ABMP on periodontitis and autophagy. The data show the augmented autophagy and alleviated gingival recession, inflammatory cell infiltration, alveolar bone resorption, and reduced osteoclasts in periodontitis by ABMP treatment. Further experiments using chemical inhibitors demonstrate the vital role of H2 S/NRF2 axis in ABMP-induced appropriate level of autophagy augmentation against periodontitis.

CONCLUSIONS

Collectively, the findings not only reveal the unrecognized capacity and mechanism of ABMP as an effective and potential dietary intake against periodontitis, but also suggest the possibility for ABMP to be used in the treatment of other autophagy-related diseases.

Molecular imaging of bacterial outer membrane vesicles based on bacterial surface display

The important roles of bacterial outer membrane vesicles (OMVs) in various diseases and their emergence as a promising platform for vaccine development and targeted drug delivery necessitates the development of imaging techniques suitable for quantifying their biodistribution with high precision. To address this requirement, we aimed to develop an OMV specific radiolabeling technique for positron emission tomography (PET). A novel bacterial strain (E. coli BL21(DE3) ΔnlpI, ΔlpxM) was created for efficient OMV production, and OMVs were characterized using various methods. SpyCatcher was anchored to the OMV outer membrane using autotransporter-based surface display systems. Synthetic SpyTag-NODAGA conjugates were tested for OMV surface binding and 64Cu labeling efficiency. The final labeling protocol shows a radiochemical purity of 100% with a ~ 29% radiolabeling efficiency and excellent serum stability. The in vivo biodistribution of OMVs labeled with 64Cu was determined in mice using PET/MRI imaging which revealed that the biodistribution of radiolabeled OMVs in mice is characteristic of previously reported data with the highest organ uptakes corresponding to the liver and spleen 3, 6, and 12 h following intravenous administration. This novel method can serve as a basis for a general OMV radiolabeling scheme and could be used in vaccine- and drug-carrier development based on bioengineered OMVs.

Pyroptosis: the dawn of a new era in endometrial cancer treatment

Endometrial cancer (EC) is a malignancy of the inner epithelial lining of the uterus. While early-stage EC is often curable through surgery, the management of advanced, recurrent and metastatic EC poses significant challenges and is associated with a poor prognosis. Pyroptosis, an emerging form of programmed cell death, is characterized by the cleavage of gasdermin proteins, inducing the formation of extensive gasdermin pores in the cell membrane and the leakage of interleukin-1β (IL-1β) and interleukin-18 (IL-18), consequently causing cell swelling, lysis and death. It has been found to be implicated in the occurrence and progression of almost all tumors. Recent studies have demonstrated that regulating tumor cells pyroptosis can exploit synergies function with traditional tumor treatments. This paper provides an overview of the research progress made in molecular mechanisms of pyroptosis. It then discusses the role of pyroptosis and its components in initiation and progression of endometrial cancer, emphasizing recent insights into the underlying mechanisms and highlighting unresolved questions. Furthermore, it explores the potential value of pyroptosis in the treatment of endometrial cancer, considering its current application in tumor radiotherapy, chemotherapy, targeted therapy and immunotherapy.

Extracellular vesicles of the probiotic bacteria E. coli O83 activate innate immunity and prevent allergy in mice

BACKGROUND

E. coli O83 (Colinfant Newborn) is a Gram-negative (G-) probiotic bacterium used in the clinic. When administered orally, it reduces allergic sensitisation but not allergic asthma. Intranasal administration offers a non-invasive and convenient delivery method. This route bypasses the gastrointestinal tract and provides direct access to the airways, which are the target of asthma prevention. G- bacteria such as E. coli O83 release outer membrane vesicles (OMVs) to communicate with the environment. Here we investigate whether intranasally administered E. coli O83 OMVs (EcO83-OMVs) can reduce allergic airway inflammation in mice.

METHODS

EcO83-OMVs were isolated by ultracentrifugation and characterised their number, morphology (shape and size), composition (proteins and lipopolysaccharide; LPS), recognition by innate receptors (using transfected HEK293 cells) and immunomodulatory potential (in naïve splenocytes and bone marrow-derived dendritic cells; BMDCs). Their allergy-preventive effect was investigated in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

EcO83-OMVs are spherical nanoparticles with a size of about 110 nm. They contain LPS and protein cargo. We identified a total of 1120 proteins, 136 of which were enriched in OMVs compared to parent bacteria. Proteins from the flagellum dominated. OMVs activated the pattern recognition receptors TLR2/4/5 as well as NOD1 and NOD2. EcO83-OMVs induced the production of pro- and anti-inflammatory cytokines in splenocytes and BMDCs. Intranasal administration of EcO83-OMVs inhibited airway hyperresponsiveness, and decreased airway eosinophilia, Th2 cytokine production and mucus secretion.

CONCLUSIONS

We demonstrate for the first time that intranasally administered OMVs from probiotic G- bacteria have an anti-allergic effect. Our study highlights the advantages of OMVs as a safe platform for the prophylactic treatment of allergy. Video Abstract.

Modulation of Autophagy and Cell Death by Bacterial Outer-Membrane Vesicles

Bacteria, akin to eukaryotic cells, possess the ability to release extracellular vesicles, lipidic nanostructures that serve diverse functions in host-pathogen interactions during infections. In particular, Gram-negative bacteria produce specific vesicles with a single lipidic layer called OMVs (Outer Membrane Vesicles). These vesicles exhibit remarkable capabilities, such as disseminating throughout the entire organism, transporting toxins, and being internalized by eukaryotic cells. Notably, the cytosolic detection of lipopolysaccharides (LPSs) present at their surface initiates an immune response characterized by non-canonical inflammasome activation, resulting in pyroptotic cell death and the release of pro-inflammatory cytokines. However, the influence of these vesicles extends beyond their well-established roles, as they also profoundly impact host cell viability by directly interfering with essential cellular machinery. This comprehensive review highlights the disruptive effects of these vesicles, particularly on autophagy and associated cell death, and explores their implications for pathogen virulence during infections, as well as their potential in shaping novel therapeutic approaches.

The genetic network underlying the evolution of pathogenicity in avian Escherichia coli

Introduction

Colibacillosis is a worldwide prevalent disease in poultry production linked to Escherichia coli strains that belong to the avian pathogenic E. coli (APEC) pathotype. While many virulence factors have been linked to APEC isolates, no single gene or set of genes has been found to be exclusively associated with the pathotype. Moreover, a comprehensive description of the biological processes linked to APEC pathogenicity is currently lacking.

Methods

In this study, we compiled a dataset of 2015 high-quality avian E. coli genomes from pathogenic and commensal isolates, based on publications from 2000 to 2021. We then conducted a genome-wide association study (GWAS) and integrated candidate gene identification with available protein-protein interaction data to decipher the genetic network underlying the biological processes connected to APEC pathogenicity.

Results

Our GWAS identified variations in gene content for 13 genes and SNPs in 3 different genes associated with APEC isolates, suggesting both gene-level and SNP-level variations contribute to APEC pathogenicity. Integrating protein-protein interaction data, we found that 15 of these genes clustered in the same genetic network, suggesting the pathogenicity of APEC might be due to the interplay of different regulated pathways. We also found novel candidate genes including an uncharacterized multi-pass membrane protein (yciC) and the outer membrane porin (ompD) as linked to APEC isolates.

Discussion

Our findings suggest that convergent pathways related to nutrient uptake from host cells and defense from host immune system play a major role in APEC pathogenicity. In addition, the dataset curated in this study represents a comprehensive historical genomic collection of avian E. coli isolates and constitutes a valuable resource for their comparative genomics investigations.

Bacterial extracellular vesicles and their interplay with the immune system

The mammalian intestinal tract harbors trillions of microorganisms confined within this space by mucosal barriers. Despite these barriers, bacterial components may still be found elsewhere in the body, even in healthy subjects. Bacteria can release small lipid-bound particles, also named bacterial extracellular vesicles (bEV). While bacteria themselves cannot normally penetrate the mucosal defense, bEVs may infiltrate the barrier and disseminate throughout the body. The extremely diverse cargo that bEVs can carry, depending on their parent species, strain, and growth conditions, grant them an equally broad potential to interact with host cells and influence immune functions. Herein, we review the current knowledge of processes underlying the uptake of bEVs by mammalian cells, and their effect on the immune system. Furthermore, we discuss how bEVs could be targeted and manipulated for diverse therapeutic purposes.

Gasdermins assemble; recent developments in bacteriology and pharmacology

The discovery of gasdermin D (GSDMD) as the terminal executioner of pyroptosis provided a large piece of the cell death puzzle, whilst simultaneously and firmly putting the gasdermin family into the limelight. In its purest form, GSDMD provides a connection between the innate alarm systems to an explosive, inflammatory form of cell death to jolt the local environment into immunological action. However, the gasdermin field has moved rapidly and significantly since the original seminal work and novel functions and mechanisms have been recently uncovered, particularly in response to infection. Gasdermins regulate and are regulated by mechanisms such as autophagy, metabolism and NETosis in fighting pathogen and protecting host. Importantly, activators and interactors of the other gasdermins, not just GSDMD, have been recently elucidated and have opened new avenues for gasdermin-based discovery. Key to this is the development of potent and specific tool molecules, so far a challenge for the field. Here we will cover some of these recently discovered areas in relation to bacterial infection before providing an overview of the pharmacological landscape and the challenges associated with targeting gasdermins.

Prototheca bovis induces autophagy in bovine mammary epithelial cells via the HIF-1α and AMPKα/ULK1 pathway

Prototheca bovis, a highly contagious pathogen, causes bovine mastitis, resulting in premature culling of affected cows and severe economic losses. Infection with P. bovis caused oxidative stress and apoptosis in bovine mammary epithelial cells (bMECs); however, mechanisms underlying P. bovis-induced autophagy remain unclear. Therefore, the autophagy flux induced by P. bovis in bMECs was analyzed by Western blot and laser scanning confocal microscopy. Expression levels of proteins in the HIF-1α and AMPKα/ULK1 pathway, including HIF-1α, AMPKα, p-AMPKα, ULK1, p-ULK1, mTOR, and p-mTOR, plus expression of autophagy-related genes including SQSTM1/p62, Atg5, Beclin1, and LC3II/LC3I, were quantified with Western blot. Infection with P. bovis induced autophagosomes and LC3 puncta in bMECs that were detected using transmission electron microscopy and laser scanning confocal microscopy, respectively. In addition, lysosome-associated proteins Rab7 and LAMP2a, and lysosomal activity were measured with Western blot and laser scanning confocal microscopy. Infection with P. bovis induced an unobstructed autophagic flux, increased protein expression of LC3II/LC3I, and decreased SQSTM1/p62 protein expression at 6 hpi. Furthermore, P. bovis upregulated protein expression in the HIF-1α and AMPKα/ULK1 pathway and increased the ratio of LC3II/LC3I, implying autophagy was activated in bMECs. However, deletion of AMPKα or ULK1 decreased LC3II/LC3I expression levels and LC3 puncta numbers, suggesting that autophagy was inhibited in bMECs. Additionally, deficiency of HIF-1α decreased protein expression of AMPKα and ULK1 as well as LC3 puncta numbers, and autophagy induced by P. bovis was also inhibited in bMECs. At 6 hpi, lysosome-associated protein Rab7 was decreased and LAMP2a was increased, indicating normal autophagy. In contrast, at 12 hpi, expression of Rab7 and LAMP2a proteins indicated that autophagy was inhibited in bMECs at that time. Therefore, we confirmed that P. bovis infection induced autophagy in bMECs via the HIF-1α and AMPKα/ULK1 pathway, with involvement of lysosome-associated protein Rab7 and LAMP2a.