Bacterial infection reinforces host metabolic flux from arginine to spermine for NLRP3 inflammasome evasion

Reciprocal regulation between bacterial secretion systems and host metabolism: Enhancing bacterial intracellular survival capability

Secretion systems are intricate nanomachines present on many bacterial cell membranes that deliver various bacterially-encoded effector proteins into eukaryotic or prokaryotic cells. They are pivotal in bacterial invasion, host colonization, and pathogenesis. After infection, bacteria employ these machines to deliver toxic effectors to the cytoplasm of host cells that disrupt their metabolic balance, such as interfering with glucose metabolism, promoting lipid droplets formation, altering amino acid profiles and mitochondrial morphology, and reducing ROS levels, to ensure bacterial intracellular survival. Furthermore, metabolites within host cells can modulate the expression and/or function of bacterial secretion systems. This review summarizes recent advancements in understanding the impact of bacterial secretion systems on host cell metabolism and the feedback regulation of host metabolites on these machines, providing novel perspectives on host-pathogen interactions and mechanisms of bacterial pathogenesis.

The arginine/ornithine binding protein ArgT plays an essential role in Brucella neotomae/Brucella melitensis to prevent intracellular killing and contribute to chronic persistence in the host

Brucella species are facultative intracellular bacterial pathogens that cause the contagious zoonotic disease, brucellosis. Brucella spp. infect a wide range of animals, including livestock, wild animals, and marine mammals. Compared with other invasive bacterial pathogens, partial information is available on the virulence factors of Brucella that enable them to survive in the host. Here, we performed transposon-based random mutagenesis of B. neotomae and identified the arginine/ornithine binding protein, ArgT, as one of the crucial virulence determinants of Brucella. Deleting ArgT from B. neotomae or B. melitensis resulted in its attenuation in macrophages, which was restored upon complementation with an ArgT expression plasmid. We observed that macrophages infected with ΔArgT-B. neotomae produced elevated levels of NO due to the inability of these mutants to deplete the host intracellular arginine through their importer. Furthermore, defective survival of ΔArgT B. neotomae and B. melitensis was observed in the infected mice, which correlated with enhanced NO production in the mice. Our studies revealed that ArgT plays a vital role in preventing intracellular killing and contributes to the chronic persistence of B. neotomae/B. melitensis in the host. This study highlights the essential role of arginine in clearing intracellular infections and the subversion of this host defense mechanism by intracellular pathogens for their chronic persistence.

Acute hypoxia stress mediates HIF-1α-Yki-Cactus axis to facilitate the infection of Vibrio parahaemolyticus in Litopenaeus vannamei

Introduction

Hypoxia stress renders aquatic animals more susceptible to bacterial disease, yet the underlying mechanism remains elusive.

Methods

We conducted an acute hypoxia stress experiment to investigate the impact of stress on the immune response of Litopenaeus vannamei via transcriptome analysis, RT-qPCR and Western blot.

Results

Our results showed that acute hypoxia stress disrupted the tissue architecture, and significantly changed the gene expression profiles in the hepatopancreas of shrimp. More importantly, acute hypoxia stress significantly changed the expression levels of immune-related genes. Ladderlectin, GBP 1, Caspase-1, CLEC4F, MR1 and GBP 2 were significantly down-regulated, but HIF-1α, Cactus, TIPE, Akirin-2, Ivns1abp and TLR3 were significantly up-regulated. We further demonstrated that acute hypoxia activated Yki via HIF-1α to enhance expression level of Cactus, and then Cactus inhibited the phosphorylation of Dorsal and its nuclear translocation, thereby suppressing antibacterial immunity. Subsequently, the challenge experiment following stress revealed that exposure to acute hypoxia stress amplified the infectivity and lethality of Vibrio parahaemolyticus to shrimp. The mechanism of HIF-1α-Yki-Cautus axis provided an explanation for this phenomenon.

Discussion

This study offered new insights into interactions among environmental hypoxia stress, host immunity and pathogens, thereby providing practical guidelines for optimizing shrimp culture practices.

Roles of Critical Amino Acids Metabolism in The Interactions Between Intracellular Bacterial Infection and Macrophage Function

Macrophages, as crucial participants in the innate immune system, respond to pathogenic challenges through their dynamic metabolic adjustments, demonstrating the intimate interplay between cellular metabolism and immune function. Bacterial infection of macrophages causes changes in macrophage metabolism, affecting both macrophage function and bacterial virulence and intracellular survival. This review explores the reprogramming of amino acid metabolism in macrophages in response to bacterial infection, with a particular focus on the influence of critical amino acids such as serine, glutamine, and arginine on the immune functions of macrophages; highlights the roles of these metabolic pathways in macrophage functions such as phagocytosis, inflammatory response, immune regulation, and pathogen clearance; reveals how pathogens exploit and manipulate the amino acid metabolism within macrophages to support their own growth and replication, thereby showcasing the intricate interplay between macrophages and pathogens. It provides a foundation for understanding the interactions between macrophages amino acid metabolism and pathogens, offering potential strategies and therapeutic targets for the development of novel anti-infection therapies.

Salmonella Enteritidis antitoxin DinJ inhibits NLRP3-dependent canonical inflammasome activation in macrophages

The inflammasome is a pivotal component of the innate immune system, acting as a multiprotein complex that plays an essential role in detecting and responding to microbial infections. Salmonella Enteritidis have evolved multiple mechanisms to regulate inflammasome activation and evade host immune system clearance. Through screening S. Enteritidis C50336ΔfliC transposon mutant library, we found that the insertion mutant of dinJ increased inflammasome activation. In this study, we demonstrated the genetic connection between the antitoxin DinJ and the toxin YafQ in S. Enteritidis, confirming their co-transcription. The deletion mutant ΔfliCΔdinJ increased cell death and IL-1β secretion in J774A.1 cells. Western blotting analysis further showed elevated cleaved Caspase-1 product (p10 subunits) and IL-1β secretion in cells infected with ΔfliCΔdinJ compared to cells infected with ΔfliC. DinJ was found to inhibit canonical inflammasome activation using primary bone marrow-derived macrophages (BMDMs) from Casp-/- C57BL/6 mice. Furthermore, DinJ specifically inhibited NLRP3 inflammasome activation, as demonstrated in BMDMs from Nlrp3-/- and Nlrc4-/- mice. Fluorescence resonance energy transfer (FRET) experiments confirmed the translocation of DinJ into host cells during infection. Finally, we revealed that DinJ could inhibit the secretion of IL-1β and IL-18 in vivo, contributing to S. Enteritidis evading host immune clearance. In summary, our findings provide insights into the role of DinJ in modulating the inflammasome response during S. Enteritidis infection, highlighting its impact on inhibiting inflammasome activation and immune evasion.

Lysine acetylation regulates the AT-rich DNA possession ability of H-NS

H-NS, the histone-like nucleoid-structuring protein in bacteria, regulates the stability of the bacterial genome by inhibiting the transcription of horizontally transferred genes, such as the type III and type VI secretion systems (T3/T6SS). While eukaryotic histone posttranslational modifications (PTMs) have been extensively studied, little is known about prokaryotic H-NS PTMs. Here, we report that the acetylation of H-NS attenuates its ability to silence horizontally transferred genes in response to amino acid nutrition and immune metabolites. Moreover, LC-MS/MS profiling showed that the acetyllysine sites of H-NS and K120 are indispensable for its DNA-binding ability. Acetylation of K120 leads to a low binding affinity for DNA and enhances T3/T6SS expression. Furthermore, acetylation of K120 impairs the AT-rich DNA recognition ability of H-NS. In addition, lysine acetylation in H-NS modulates in vivo bacterial virulence. These findings reveal the mechanism underlying H-NS PTMs and propose a novel mechanism by which bacteria counteract the xenogeneic silencing of H-NS.

Micro-RNA expression profile of BALB/c mouse glandular stomach in the early phase of Cryptosporidium muris infection

Cryptosporidiosis is a zoonotic disease in humans and animals that is caused by infection with the oocysts of Cryptosporidium. MicroRNAs (miRNAs) are important players in regulating the innate immune response against parasitic infection. Public miRNAs data for studying pathogenic mechanisms of cryptosporidiosis, particularly in natural hosts, are scarce. Here, we compared miRNA profiles of the glandular stomach of C. muris-infected and uninfected BALB/c mice using microarray sequencing. A total of 10 miRNAs (including 3 upregulated and 7 downregulated miRNAs) with significant differential expression (|FC| ≥ 2 and P value < 0.05) were identified in the glandular stomach of BALB/c mice 8 h after infection with C. muris. MiRWalk and miRDB online bioinformatics tools were used to predict the target genes of differentially expressed miRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to annotate the target genes. GO analysis indicate that gene transcription-related and ion transport-related GO terms were significantly enriched. In addition, the KEGG analyses showed that the target genes were strongly related to diverse types of tumor disease progression and anti-pathogen immunity pathways. In the current study, we firstly report changes in miRNA expression profiles in the glandular stomach of BALB/c mice at the early phase of C. muris invasion. This dysregulation in miRNA expression may contribute to our understanding of cryptosporidiosis pathology. This study provides a new perspective on the miRNA regulatory mechanisms of cryptosporidiosis, which may help in the development of effective control strategies against this pathogen.

Europium- and Black Phosphorus-Functionalized Porphyrin as an l-Arginine Sensor and l-Arginine-Activated PDT/PTT Agent for Bacterial Treatment

The attenuation of bacterial metabolism provides an adjunct to the treatment of bacterial infections. To develop a bacterial eradication agent, a bioactivatable material (BP@Eu-TCPP) was designed and synthesized by coordination and reduction of europium(III) with thin-layer black phosphorus (BP) and tetrakis (4-carboxyphenyl) porphyrin (TCPP). The existence of the P-Eu bond and Eu2+ 3d5/2 in X-ray photoelectron spectroscopy confirmed the successful synthesis of BP@Eu-TCPP. This material showed high fluorescence sensitivity to l-Arginine (l-Arg) and the main binding ratio of BP@Eu-TCPP to l-Arg was ca. 1:2 or 1:3, with the limit of detection of 4.0 μM. The material also showed good photothermal properties and stability, with a photothermal conversion efficiency of 37.3%. Although metal coordination has blocked the generation of 1O2, the addition of l-Arg to BP@Eu-TCPP can restore 1O2 generation upon red light-emitting diode (LED) light irradiation due to the formation of water-soluble Arg-TCPP species. Additionally, BP@Eu-TCPP was enabled to change the bacterial membrane and interfered with the bacterial iron absorption that effectively contributes to bacterial eradication. Such BP@Eu-TCPP is promised to be a novel material for the detection of l-Arg and l-Arg-activated photodynamic therapy.

Edwardsiella piscicida infection reshapes the intestinal microbiome and metabolome of big-belly seahorses: mechanistic insights of synergistic actions of virulence factors

Uncovering the mechanism underlying the pathogenesis of Edwardsiella piscicida-induced enteritis is essential for global aquaculture. In the present study, we identified E. piscicida as a lethal pathogen of the big-belly seahorse (Hippocampus abdominalis) and revealed its pathogenic pattern and characteristics by updating our established bacterial enteritis model and evaluation system. Conjoint analysis of metagenomic and metabolomic data showed that 15 core virulence factors could mutually coordinate the remodeling of intestinal microorganisms and host metabolism and induce enteritis in the big-belly seahorse. Specifically, the Flagella, Type IV pili, and Lap could significantly increase the activities of the representative functional pathways of both flagella assembly and bacterial chemotaxis in the intestinal microbiota (P < 0.01) to promote pathogen motility, adherence, and invasion. Legiobactin, IraAB, and Hpt could increase ABC transporter activity (P < 0.01) to compete for host nutrition and promote self-replication. Capsule1, HP-NAP, and FarAB could help the pathogen to avoid phagocytosis. Upon entering epithelial cells and phagocytes, Bsa T3SS and Dot/Icm could significantly increase bacterial secretion system activity (P < 0.01) to promote the intracellular survival and replication of the pathogen and the subsequent invasion of the neighboring tissues. Finally, LPS3 could significantly increase lipopolysaccharide biosynthesis (P < 0.01) to release toxins and kill the host. Throughout the pathogenic process, BopD, PhoP, and BfmRS significantly activated the two-component system (P < 0.01) to coordinate with other VFs to promote deep invasion. In addition, the levels of seven key metabolic biomarkers, Taurine, L-Proline, Uridine, L-Glutamate, Glutathione, Xanthosine, and L-Malic acid, significantly decreased (P < 0.01), and they can be used for characterizing E. piscicida infection. Overall, the present study systematically revealed how a combination of virulence factors mediate E. piscicida-induced enteritis in fish for the first time, providing a theoretical reference for preventing and controlling this disease in the aquaculture of seahorses and other fishes.

Overexpression of SMS in the tumor microenvironment is associated with immunosuppression in hepatocellular carcinoma

Disorders of polyamine metabolism may contribute to the development of hepatocellular carcinoma (HCC), but the precise mechanism remains unknown. This study reports that spermine synthase (SMS), an enzyme involved in polyamine biosynthesis, is overexpressed in HCC and not associated with hepatitis virus infection in HCC patients. The results of analyzing the clinical data of HCC patients showed that SMS level as a categorical dependent variable was related to clinicopathological features of poor prognosis. Furthermore, the Kaplan-Meier survival analysis and ROC curve indicated that increased SMS level is associated with poor survival rate in HCC and may be a potential biomarker to discriminate HCC tissues. However, SMS overexpression limited the therapeutic effect of immune checkpoint blockade (ICB), which seemed to be related to the immunosuppressive effect of the HCC immune microenvironment formed by higher mRNA transcript levels of immune checkpoints and higher infiltration levels of immunosuppressive cells. In samples with high and low SMS expression, functional enrichment analysis of the differentially expressed genes (DEGs) showed that SMS may be linked to the occurrence and development of HCC by affecting a variety of immune-related pathways, such as Intestinal immune network for IgA production, Fc gamma R-mediated phagocytosis, Antigen processing and presentation, Th1 and Th2 cell differentiation. Subsequently, analysis of the co-expression network of SMS in the liver hepatocellular carcinoma (LIHC) cohort revealed that SMS has a broad impact on multiple important immune- and metabolic-related processes in HCC. In summary, SMS is a promising biomarker to differentiate the prognosis, immune characteristics, and holds promise as a potential target for ICB therapy to improve HCC.

Bacterial subversion of NLR-mediated immune responses

Members of the mammalian Nod-like receptor (NLR) protein family are important intracellular sensors for bacteria. Bacteria have evolved under the pressure of detection by host immune sensing systems, leading to adaptive subversion strategies to dampen immune responses for their benefits. These include modification of microbe-associated molecular patterns (MAMPs), interception of innate immune pathways by secreted effector proteins and sophisticated instruction of anti-inflammatory adaptive immune responses. Here, we summarise our current understanding of subversion strategies used by bacterial pathogens to manipulate NLR-mediated responses, focusing on the well-studied members NOD1/2, and the inflammasome forming NLRs NLRC4, and NLRP3. We discuss how bacterial pathogens and their products activate these NLRs to promote inflammation and disease and the range of mechanisms used by bacterial pathogens to evade detection by NLRs and to block or dampen NLR activation to ultimately interfere with the generation of host immunity. Moreover, we discuss how bacteria utilise NLRs to facilitate immunotolerance and persistence in the host and outline how various mechanisms used to attenuate innate immune responses towards bacterial pathogens can also aid the host by reducing immunopathologies. Finally, we describe the therapeutic potential of harnessing immune subversion strategies used by bacteria to treat chronic inflammatory conditions.

Dysregulation of Cytosolic c-di-GMP in Edwardsiella piscicida Promotes Cellular Non-Canonical Ferroptosis

Programmed cell death plays an important role in modulating host immune defense and pathogen infection. Ferroptosis is a type of inflammatory cell death induced by intracellular iron-dependent accumulation of toxic lipid peroxides. Although ferroptosis has been associated with cancer and other sterile diseases, very little is known about the role of ferroptosis in modulating host-pathogen interactions. We show that accumulation of the secondary messenger bis-(3′,5′)-cyclic dimeric GMP (c-di-GMP) in the pathogenic bacterium Edwardsiella piscicida (E. piscicida) triggers a non-canonical ferroptosis pathway in infected HeLa cells. Moreover, we observed that the dysregulation of c-di-GMP in E. piscicida promotes iron accumulation, mitochondrial dysfunction, and production of reactive oxygen species, all of which that can be blocked by iron chelator. Importantly, unlike classical ferroptosis that is executed via excess lipid peroxidation, no lipid peroxidation was detected in the infected cells. Furthermore, lipoxygenases inhibitors and lipophilic antioxidants are not able to suppress morphological changes and cell death induced by E. piscicida mutant producing excess c-di-GMP, and this c-di-GMP dysregulation attenuates bacterial virulence in vivo. Collectively, our results reveal a novel non-canonical ferroptosis pathway mediated by bacterial c-di-GMP and provide evidence for a role of ferroptosis in the regulation of pathogen infection.

Development and Validation of a Pyroptosis-Related Long Non-coding RNA Signature for Hepatocellular Carcinoma

Background: Hepatocellular carcinoma (HCC) is a highly aggressive malignant disease, and numerous studies have demonstrated that an inflammatory environment can induce normal cells to transform into cancerous.

Methods: We integrated genomic data to comprehensively assess the association between pyroptosis and tumor microenvironment (TME) cell-infiltrating characteristics in HCC, as well as the potential molecular function and clinical significance of lncRNA.

Results: The analysis of CNV alteration frequency displayed that CNV changes were common in 33 PRGs, and most were focused on copy number amplification. As a result of lasso regression analysis, nine differentially expressed lncRNAs (AL031985.3, NRAV, OSMR-AS1, AC073611.1, MKLN1-AS, AL137186.2, AL049840.4, MIR4435-2HG, and AL118511.1) were selected as independent prognosis factors of HCC patients. Patients at high risk have poorer survival than those in the low-risk group in training and testing cohorts. A low-risk score was significantly associated with an IC50 of chemotherapeutics such as bortezomib (p < 0.001), but a high-risk score was significantly linked to docetaxel (p < 0.001), implying that signature served as a prospective predictor for chemosensitivity.

Conclusion: This work suggests pyroptosis-related lncRNAs features and their potential mechanisms on tumor microenvironment. The exploration may assist in identifying novel biomarkers and assist patients in predicting their prognosis, clinical diagnosis, and management.