Effect of L-HSL on biofilm and motility of Pseudomonas aeruginosa and its mechanism.

Pseudomonas aeruginosa (P. aeruginosa) biofilm formation is a crucial cause of enhanced antibiotic resistance. Quorum sensing (QS) is involved in regulating biofilm formation; QS inhibitors block the QS signaling pathway as a new strategy to address bacterial resistance. This study investigated the potential and mechanism of L-HSL (N-(3-cyclic butyrolactone)-4-trifluorophenylacetamide) as a QS inhibitor for P. aeruginosa. The results showed that L-HSL effectively inhibited the biofilm formation and dispersed the pre-formed biofilm of P. aeruginosa. The production of extracellular polysaccharides and the motility ability of P. aeruginosa were suppressed by L-HSL. C. elegans infection experiment showed that L-HSL was non-toxic and provided protection to C. elegans against P. aeruginosa infection. Transcriptomic analysis revealed that L-HSL downregulated genes related to QS pathways and biofilm formation. L-HSL exhibits a promising potential as a therapeutic drug for P. aeruginosa infection. KEY POINTS: • Chemical synthesis of N-(3-cyclic butyrolactone)-4-trifluorophenylacetamide, named L-HSL. • L-HSL does not generate survival pressure on the growth of P. aeruginosa and can inhibit the QS system. • KEGG enrichment analysis found that after L-HSL treatment, QS-related genes were downregulated.

Exogenous autoinducer-2 alleviates intestinal damage in necrotizing enterocolitis via PAR2/MMP3 signaling pathway.

BACKGROUND: Imbalanced intestinal microbiota and damage to the intestinal barrier contribute to the development of necrotizing enterocolitis (NEC). Autoinducer-2 (AI-2) plays a crucial role in repairing intestinal damage and reducing inflammation. OBJECTIVE: This study aimed to investigate the impact of AI-2 on the expression of intestinal zonula occludens-1 (ZO-1) and occludin proteins in NEC. We evaluated its effects in vivo using NEC mice and in vitro using lipopolysaccharide (LPS)-stimulated intestinal cells. METHODS: Pathological changes in the intestines of neonatal mice were assessed using histological staining and scoring. Cell proliferation was measured using the cell counting kit-8 (CCK-8) assay to determine the optimal conditions for LPS and AI-2 interventions. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to analyze the mRNA levels of matrix metalloproteinase-3 (MMP3), protease activated receptor-2 (PAR2), interleukin-1ß (IL-1ß), and IL-6. Protein levels of MMP3, PAR2, ZO-1, and occludin were evaluated using western blot, immunohistochemistry, or immunofluorescence. RESULTS: AI-2 alleviated NEC-induced intestinal damage (P < 0.05) and enhanced the proliferation of damaged IEC-6 cells (P < 0.05). AI-2 intervention reduced the mRNA and protein expressions of MMP3 and PAR2 in intestinal tissue and cells (P < 0.05). Additionally, it increased the protein levels of ZO-1 and occludin (P < 0.05), while reducing IL-1ß and IL-6 mRNA expression (P < 0.05). CONCLUSION: AI-2 intervention enhances the expression of tight junction proteins (ZO-1 and occludin), mitigates intestinal damage in NEC neonatal mice and IEC-6 cells, potentially by modulating PAR2 and MMP3 signaling. AI-2 holds promise as a protective intervention for NEC. AI-2 plays a crucial role in repairing intestinal damage and reducing inflammation.

Pseudomonas aeruginosa N-3-Oxododecanoyl Homoserine Lactone Disrupts Endothelial Integrity by Activating the Angiopoietin-Tie System.

The activation of the angiopoietin (Angpt)-Tie system is linked to endothelial dysfunction during sepsis. Bacterial quorum-sensing molecules function as pathogen-associated molecular patterns. However, their impact on the endothelium and the Angpt-Tie system remains unclear. Therefore, this study investigated whether treatment with N-3-oxododecanoyl homoserine lactone (3OC12-HSL), a quorum-sensing molecule derived from Pseudomonas aeruginosa, impaired endothelial function in human umbilical vein endothelial cells. 3OC12-HSL treatment impaired tube formation even at sublethal concentrations, and immunocytochemistry analysis revealed that it seemed to reduce vascular endothelial-cadherin expression at the cell-cell interface. Upon assessing the mRNA expression patterns of genes associated with the Angpt-Tie axis, the expressions of Angpt2, Forkhead box protein O1, Tie1, and vascular endothelial growth factor 2 were found to be upregulated in the 3OC12-HSL-treated cells. Moreover, western blot analysis revealed that 3OC12-HSL treatment increased Angpt2 expression. A co-immunoprecipitation assay was conducted to assess the effect of 3OC12-HSL on the IQ motif containing GTPase activating protein 1 (IQGAP1) and Rac1 complex and the interaction between these proteins was consistently maintained regardless of 3OC12-HSL treatment. Next, recombinant human (rh)-Angpt1 was added to assess whether it modulated the effects of 3OC12-HSL treatment. rh-Angpt1 addition increased cellular viability, improved endothelial function, and reversed the overall patterns of mRNA and protein expression in endothelial cells treated with 3OC12-HSL. Additionally, it was related to the increased expression of phospho-Akt and the IQGAP1 and Rac1 complex. Collectively, our findings indicated that 3OC12-HSL from Pseudomonas aeruginosa can impair endothelial integrity via the activation of the Angpt-Tie axis, which appeared to be reversed by rh-Angpt1 treatment.

Regulation of Bacterial Biofilm Formation by Ultrasound: Role of Autoinducer-2 and Finite-Element Analysis of Acoustic Streaming.

OBJECTIVE: The formation of bacterial biofilm regulated by quorum sensing (QS) is a critical factor that contributes to infections of indwelling medical devices. Autoinducer-2 (AI-2), as a signal molecule in QS, plays a crucial role in mediating bacterial signaling and regulating their biological behavior. This study investigated the impact of ultrasonic vibration at varying frequencies on biofilm formation in a mixture of Staphylococcus aureus and Escherichia coli. METHODS: By exciting ultrasound at different frequencies (20, 100 and 200 kHz), a vibration with an amplitude of 100 nm was generated on the material surface located at the bottom of the petri dish containing mixed bacteria. We measured the content of AI-2 and bacteria in the mixed bacterial solution and bioburden on material surfaces at different time points during culture. In addition, the relationships among AI-2 content, bacterial concentration and distribution were assessed through finite-element analysis of acoustic streaming under ultrasonic vibration. RESULTS: The AI-2 gradient is influenced by the diversity of acoustic streaming patterns on the material surface and in the mixed bacterial solution caused by ultrasonic vibration at different frequencies, thereby regulating biofilm formation. The experimental results showed that the optimal inhibition effect on AI-2 and minimal bacterial adhesion degree was achieved when applying an ultrasonic frequency of 100 kHz with a power intensity of 46.1 mW/cm2 under an amplitude of 100 nm. CONCLUSION: Ultrasound can affect the QS system of bacteria, leading to alterations in their biological behavior. Different species of bacteria exhibit varying degrees of chemotaxis toward different frequencies.

Acyl Homoserine Lactone Sensitised Streptococcus Pyogenes Differentially Regulates the Transcriptional Expression of Early Growth Response 1 (EGR1) in Epithelial and Macrophage Cells.

The host transcriptional activator Early growth response 1 (EGR1) plays a vital role in cell cycle and differentiation, cell proliferation, and regulation of cytokines and several growth factors. It is an immediate-early gene that is expressed as an initial response to various environmental stimuli. Bacterial infection is one such factor that can trigger the expression of EGR1 in host. Therefore, it is imperative to understand expression of EGR1 during early stages of host-pathogen interaction. Streptococcus pyogenes is an opportunistic bacteria causing skin and respiratory tract infections in humans. The quorum-sensing molecule, N-(3-oxododecanoyl)-l-homoserine lactone (Oxo-C12), not synthesised by S. pyogenes, can be sensed by S. pyogenes leading to molecular changes in the pathogen. In this study, we investigated the role of Oxo-C12 on EGR1 regulation in lung epithelial and murine macrophage cell line upon S. pyogenes infection. We report that Oxo-C12 sensitised S. pyogenes upregulates the transcriptional expression of EGR1 through ERK1/2 pathway. It was observed that EGR1 was not involved in the intial attachment of S. pyogenes to A549 cells. However, inhibition of EGR1 in macrophage cell line, J774A.1, through the ERK1/2 pathway resulted in decreased adhesion of S. pyogenes. The EGR1 upregulation by Oxo-C12 sensitised S. pyogenes plays a vital role in enhancing the survival of S. pyogenes in murine macrophages, leading to persistent infection. Thus, understanding the molecular modulation in the host during bacterial infection will further help develop therapeutics to target specific sites.

Repurposing host-guest chemistry to sequester virulence and eradicate biofilms in multidrug resistant Pseudomonas aeruginosa and Acinetobacter baumannii.

The limited diversity in targets of available antibiotic therapies has put tremendous pressure on the treatment of bacterial pathogens, where numerous resistance mechanisms that counteract their function are becoming increasingly prevalent. Here, we utilize an unconventional anti-virulence screen of host-guest interacting macrocycles, and identify a water-soluble synthetic macrocycle, Pillar[5]arene, that is non-bactericidal/bacteriostatic and has a mechanism of action that involves binding to both homoserine lactones and lipopolysaccharides, key virulence factors in Gram-negative pathogens. Pillar[5]arene is active against Top Priority carbapenem- and third/fourth-generation cephalosporin-resistant Pseudomonas aeruginosa and Acinetobacter baumannii, suppressing toxins and biofilms and increasing the penetration and efficacy of standard-of-care antibiotics in combined administrations. The binding of homoserine lactones and lipopolysaccharides also sequesters their direct effects as toxins on eukaryotic membranes, neutralizing key tools that promote bacterial colonization and impede immune defenses, both in vitro and in vivo. Pillar[5]arene evades both existing antibiotic resistance mechanisms, as well as the build-up of rapid tolerance/resistance. The versatility of macrocyclic host-guest chemistry provides ample strategies for tailored targeting of virulence in a wide range of Gram-negative infectious diseases.

Unusual enantiomeric D,L-N-acyl homoserine lactones in Pectobacterium atrosepticum and Pseudomonas aeruginosa.

Quorum Sensing allows bacteria to sense their population density via diffusible N-acyl homoserine lactone (N-HL) signaling molecules. Upon reaching a high enough cell density, bacteria will collectively exhibit a phenotype. Until recently, methods used for detection of N-HLs have not considered the chirality of these molecules and it was assumed that only the L-enantiomer was produced by bacteria. The production and effects of D-N-HLs have rarely been studied. In this work, the temporal production of D-N-HLs by the plant pathogen Pectobacterium atrosepticum and the human pathogen Pseudomonas aeruginosa are reported. Both bacteria produced D-N-HLs in significant amounts and in some cases their concentrations were higher than other low abundance L-N-HLs. Previously unreported D-enantiomers of N-3-oxoacyl and N-3-hydroxyacyl homoserine lactones were detected in P. atrosepticum. Interestingly, L-N-HLs produced in the lowest concentrations had relatively higher amounts of their corresponding D-enantiomers. Potential sources of D-N-HLs and their significance are considered.

Inhibitory Effect of Monoterpenoid Glycosides Extracts from Peony Seed Meal on Streptococcus suis LuxS/AI-2 Quorum Sensing System and Biofilm.

Streptococcus suis LuxS/AI-2 quorum sensing system regulates biofilm formation, resulting in increased pathogenicity and drug resistance, and diminished efficacy of antibiotic treatment. The remaining peony seed cake after oil extraction is rich in monoterpenoid glycosides, which can inhibit the formation of bacterial biofilm. In this study, we investigated the effect of seven major monocomponents (suffruticosol A, suffruticosol B, suffruticosol C, paeonifloin, albiflorin, trans-ε-viniferin, gnetin H) of peony seed meal on minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of S. suis. The results showed that the MICs of the seven single components were all greater than 200 µg/mL, with no significant bacteriostatic and bactericidal advantages. Crystal violet staining and scanning electron microscope observation showed that the seven single components had a certain inhibitory effect on the biofilm formation ability of S. suis at sub-MIC concentration. Among them, the ability of paeoniflorin to inhibit biofilm was significantly higher than that of the other six single components. AI-2 signaling molecules were detected by bioreporter strain Vibrio harvey BB170. The detection results of AI-2 signal molecules found that at 1/2 MIC concentration, paeoniflorin significantly inhibited the production of S. suis AI-2 signal, and the inhibitory effect was better than that of the other six single components. In addition, molecular docking analysis revealed that paeoniflorin had a significant binding activity with LuxS protein compared with the other six single components. The present study provides evidence that paeoniflorin plays a key role in the regulation of the inhibition of S. suis LuxS/AI-2 system and biofilm formation in peony seed meal.

PON2 mediates mitochondrial dysfunction in tracheal epithelial cells in response to a quorum sensing molecule N-(-3-oxododecanoyl)-l-homoserine lactone.

The opportunistic bacterium Pseudomonas aeruginosa secretes the quorum-sensing molecule N-(3-oxododecanoyl)-l-homoserine lactone (C12) to co-ordinate gene expression profiles favorable for infection. Recent studies have demonstrated that high concentrations of C12 impair many aspects of host cell physiology, including mitochondrial function and cell viability. The cytotoxic effects of C12 are mediated by the lactonase enzyme, Paraoxonase 2 (PON2), which hydrolyzes C12 to a reactive metabolite. However, the influence of C12 on host cell physiology at concentrations observed in patients infected with P. aeruginosa is largely unknown. Since the primary site of P. aeruginosa infections is the mammalian airway, we sought to investigate how PON2 modulates the effects of C12 at subtoxic concentrations using immortalized murine tracheal epithelial cells (TECs) isolated from wild-type (WT) or PON2-knockout (PON2-KO) mice. Our data reveal that C12 at subtoxic concentrations disrupts mitochondrial bioenergetics to hinder cellular proliferation in TECs expressing PON2. Subtoxic concentrations of C12 disrupt normal mitochondrial network morphology in a PON2-dependent manner without affecting mitochondrial membrane potential. In contrast, higher concentrations of C12 depolarize mitochondrial membrane potential and subsequently trigger caspase signaling and apoptotic cell death. These findings demonstrate that different concentrations of C12 impact distinct aspects of host airway epithelial cell physiology through PON2 activity in mitochondria.

Identification of small molecules targeting homoserine acetyl transferase from Mycobacterium tuberculosis and Staphylococcus aureus.

There is an urgent need to validate new drug targets and identify small molecules that possess activity against both drug-resistant and drug-sensitive bacteria. The enzymes belonging to amino acid biosynthesis have been shown to be essential for growth in vitro, in vivo and have not been exploited much for the development of anti-tubercular agents. Here, we have identified small molecule inhibitors targeting homoserine acetyl transferase (HSAT, MetX, Rv3341) from M. tuberculosis. MetX catalyses the first committed step in L-methionine and S-adenosyl methionine biosynthesis resulting in the formation of O-acetyl-homoserine. Using CRISPRi approach, we demonstrate that conditional repression of metX resulted in inhibition of M. tuberculosis growth in vitro. We have determined steady state kinetic parameters for the acetylation of L-homoserine by Rv3341. We show that the recombinant enzyme followed Michaelis-Menten kinetics and utilizes both acetyl-CoA and propionyl-CoA as acyl-donors. High-throughput screening of a 2443 compound library resulted in identification of small molecule inhibitors against MetX enzyme from M. tuberculosis. The identified lead compounds inhibited Rv3341 enzymatic activity in a dose dependent manner and were also active against HSAT homolog from S. aureus. Molecular docking of the identified primary hits predicted residues that are essential for their binding in HSAT homologs from M. tuberculosis and S. aureus. ThermoFluor assay demonstrated direct binding of the identified primary hits with HSAT proteins. Few of the identified small molecules were able to inhibit growth of M. tuberculosis and S. aureus in liquid cultures. Taken together, our findings validated HSAT as an attractive target for development of new broad-spectrum anti-bacterial agents that should be effective against drug-resistant bacteria.

Boron Derivatives Accelerate Biofilm Formation of Recombinant Escherichia coli via Increasing Quorum Sensing System Autoinducer-2 Activity.

Boron is an essential element for autoinducer-2 (AI-2) synthesis of quorum sensing (QS) system, which affects bacterial collective behavior. As a living biocatalyst, biofilms can stably catalyze the activity of intracellular enzymes. However, it is unclear how boron affects biofilm formation in E. coli, particularly recombinant E. coli with intracellular enzymes. This study screened different boron derivatives to explore their effect on biofilm formation. The stress response of biofilm formation to boron was illuminated by analyzing AI-2 activity, extracellular polymeric substances (EPS) composition, gene expression levels, etc. Results showed that boron derivatives promote AI-2 activity in QS system. After treatment with H3BO3 (0.6 mM), the AI-2 activity increased by 65.99%, while boron derivatives increased the biomass biofilms in the order H3BO3 > NaBO2 > Na2B4O7 > NaBO3. Moreover, treatment with H3BO3 (0.6 mM) increased biomass by 88.54%. Meanwhile, AI-2 activity had a linear correlation with polysaccharides and protein of EPS at 0−0.6 mM H3BO3 and NaBO2 (R2 > 0.8). Furthermore, H3BO3 upregulated the expression levels of biofilm formation genes, quorum sensing genes, and flagellar movement genes. These findings demonstrated that boron promoted biofilm formation by upregulating the expression levels of biofilm-related genes, improving the QS system AI-2 activity, and increasing EPS secretion in E. coli.

Study of the Dynamics of Biofilm Formation and Elastase Activity of Pseudomonas aeruginosa in the Presence of Dodecanoyl-Homoserine Lactone.

We studied the effect of early accumulation of N-3-oxo-dodecanoyl-homoserine lactone on the suppression of Pseudomonas aeruginosa reproduction, biofilm formation, and elastase activity. N-3-oxo-dodecanoyl-homoserine lactone in various concentrations was added to the P. aeruginosa culture, and changes in the concentration of bacteria and the formation of biofilms were studied in dynamics. N-3-oxo-dodecanoyl-homoserine lactone in a concentration of 25 µM, decelerated proliferation of bacterial cells during the first 6 h of culturing (p<0.05) and stimulated biofilm formation after 18 h of culturing. Elastase activity of P. aeruginosa increased significantly after addition of N-3-oxo-dodecanoyl-homoserine lactone in a concentration of 0.75 µM.

N-3-(oxododecanoyl)-L-homoserine lactone suppresses dendritic cell maturation by upregulating the long noncoding RNA NRIR.

N-3-(oxododecanoyl)-L-homoserine lactone (3-O-C12-HSL), a small bacterial signaling molecule secreted by Pseudomonas aeruginosa (P. aeruginosa), can block dendritic cell (DC) maturation and participate in immune escape, but the underlying mechanism is unclear. We speculate that regulation of DC maturation and function by lncRNAs may be the mechanism by which 3-O-C12-HSL inhibits the immune response. We found that 3-O-C12-HSL increased the expression level of the lncRNA NRIR, impeding monocyte-derived dendritic cell (Mo-DC) maturation. In addition, we observed the effect of NRIR on the expression of CD40, CD80, HLA-DR and IL-6. NRIR overexpression significantly reduced the expression of Mo-DC surface markers, while 3-OC12-HSL did not significantly reduce the expression of Mo-DC surface markers after NRIR knockdown. These results indicate that 3-O-C12-HSL indeed affects the differentiation and maturation of Mo-DCs through NRIR. IL-6 stimulates T cell proliferation and activation, and we found that high NRIR expression reduced IL6 levels. However, under NRIR knockdown, 3-O-C12-HSL did not decrease IL-6 expression, suggesting that 3-O-C12-HSL may affect T cell activation through NRIR. This study is the first to elucidate the important role of a lncRNA in the mechanism of 3-O-C12-HSL activity. It also provides new ideas regarding P. aeruginosa infection pathogenesis.

N-3-Hydroxy Dodecanoyl-DL-homoserine Lactone (OH-dDHL) Triggers Apoptosis of Bone Marrow-Derived Macrophages through the ER- and Mitochondria-Mediated Pathways.

Quorum sensing of Acinetobacter nosocomialis for cell-to-cell communication produces N-3-hydroxy dodecanoyl-DL-homoserine lactone (OH-dDHL) by an AnoR/I two-component system. However, OH-dDHL-driven apoptotic mechanisms in hosts have not been clearly defined. Here, we investigated the induction of apoptosis signaling pathways in bone marrow-derived macrophages treated with synthetic OH-dDHL. Moreover, the quorum-sensing system for virulence regulation was evaluated in vivo using wild-type and anoI-deletion mutant strains. OH-dDHL decreased the viability of macrophage and epithelial cells in dose- and time-dependent manners. OH-dDHL induced Ca2+ efflux and caspase-12 activation by ER stress transmembrane protein (IRE1 and ATF6a p50) aggregation and induced mitochondrial dysfunction through reactive oxygen species (ROS) production, which caused cytochrome c to leak. Pretreatment with a pan-caspase inhibitor reduced caspase-3, -8, and -9, which were activated by OH-dDHL. Pro-inflammatory cytokine and paraoxonase-2 (PON2) gene expression were increased by OH-dDHL. We showed that the anoI-deletion mutant strains have less intracellular invasion compared to the wild-type strain, and their virulence, such as colonization and dissemination, was decreased in vivo. Consequently, these findings revealed that OH-dDHL, as a virulence factor, contributes to bacterial infection and survival as well as the modification of host responses in the early stages of infection.

Exogenous autoinducer-2 inhibits biofilm development of Desulfovibrio sp. Huiquan2017.

Sulfate-reducing bacteria (SRB) are culprits for microbiologically influenced corrosion, and biofilms are believed to play essential roles in the corrosion induced by SRB. However, little is known about the regulation of SRB biofilms. Quorum sensing signal molecules acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2) regulate biofilm formation of many bacteria. In this study, the production of AHLs and AI-2 by one SRB strain, Desulfovibrio sp. Huiquan2017, was detected, and the effect of exogenous AI-2 on bacterial biofilm formation was discussed. It was found that the cell-free supernatants of Desulfovibrio sp. Huiquan2017 induced luminescence in a ∆luxS mutant strain Vibrio harveyi BB170, indicating the production of functional AI-2 by the bacterium. In the presence of exogenous AI-2, the growth of Desulfovibrio sp. Huiquan2017 and early biofilm formation were not affected, but the later stage of biofilm development was inhibited significantly. The biofilms became looser, smaller, and thinner, and contained less bacteria and extracellular polymeric substances (EPS). The inhibition effect of AI-2 on the biofilm development of Desulfovibrio sp. Huiquan2017 was mainly achieved through reducing the amount of EPS in biofilms. These findings shed light on the biofilm regulation of SRB.

The Quorum Sensing Auto-Inducer 2 (AI-2) Stimulates Nitrogen Fixation and Favors Ethanol Production over Biomass Accumulation in Zymomonas mobilis.

Autoinducer 2 (or AI-2) is one of the molecules used by bacteria to trigger the Quorum Sensing (QS) response, which activates expression of genes involved in a series of alternative mechanisms, when cells reach high population densities (including bioluminescence, motility, biofilm formation, stress resistance, and production of public goods, or pathogenicity factors, among others). Contrary to most autoinducers, AI-2 can induce QS responses in both Gram-negative and Gram-positive bacteria, and has been suggested to constitute a trans-specific system of bacterial communication, capable of affecting even bacteria that cannot produce this autoinducer. In this work, we demonstrate that the ethanologenic Gram-negative bacterium Zymomonas mobilis (a non-AI-2 producer) responds to exogenous AI-2 by modulating expression of genes involved in mechanisms typically associated with QS in other bacteria, such as motility, DNA repair, and nitrogen fixation. Interestingly, the metabolism of AI-2-induced Z. mobilis cells seems to favor ethanol production over biomass accumulation, probably as an adaptation to the high-energy demand of N2 fixation. This opens the possibility of employing AI-2 during the industrial production of second-generation ethanol, as a way to boost N2 fixation by these bacteria, which could reduce costs associated with the use of nitrogen-based fertilizers, without compromising ethanol production in industrial plants.

Bitter receptor TAS2R138 facilitates lipid droplet degradation in neutrophils during Pseudomonas aeruginosa infection.

Bitter receptors function primarily in sensing taste, but may also have other functions, such as detecting pathogenic organisms due to their agile response to foreign objects. The mouse taste receptor type-2 member 138 (TAS2R138) is a member of the G-protein-coupled bitter receptor family, which is not only found in the tongue and nasal cavity, but also widely distributed in other organs, such as the respiratory tract, gut, and lungs. Despite its diverse functions, the role of TAS2R138 in host defense against bacterial infection is largely unknown. Here, we show that TAS2R138 facilitates the degradation of lipid droplets (LDs) in neutrophils during Pseudomonas aeruginosa infection through competitive binding with PPARG (peroxisome proliferator-activated receptor gamma) antagonist: N-(3-oxododecanoyl)-L-homoserine lactone (AHL-12), which coincidently is a virulence-bound signal produced by this bacterium (P. aeruginosa). The released PPARG then migrates from nuclei to the cytoplasm to accelerate the degradation of LDs by binding PLIN2 (perilipin-2). Subsequently, the TAS2R138-AHL-12 complex targets LDs to augment their degradation, and thereby facilitating the clearance of AHL-12 in neutrophils to maintain homeostasis in the local environment. These findings reveal a crucial role for TAS2R138 in neutrophil-mediated host immunity against P. aeruginosa infection.

An Efficient Synthesis of Optically Active [4-13C] Labelled Quorum Sensing Signal Autoinducer-2.

A new synthetic route for the quorum sensing signal Autoinducer-2 (AI-2) is described and used for the preparation of [4-13C]-AI-2 starting from [1-13C]-bromoacetic acid. The key step in this process was the enantioselective reduction of an intermediate ketone. This synthesis provides, selectively, both enantiomers of the labelled or unlabelled parent compound, (R) or (S)-4,5-dihydroxypentane-2,3-dione (DPD) and was used for an improved synthesis of [1-13C]-AI-2.

N-(3-oxododecanoyl)-l-homoserine lactone disrupts intestinal epithelial barrier through triggering apoptosis and collapsing extracellular matrix and tight junction.

Microbes employ autoinducers of quorum sensing (QS) for population communication. Although the autoinducer of Pseudomonas aeruginosa LasI-LasR system, N-(3-oxododecanoyl)- l-homoserine lactone (3OC12), has been reported with deleterious effects on host cells, its biological effects on integrity of the intestinal epithelium and epithelial barrier are still unclear and need further investigation. In the present study, flow cytometry, transcriptome analysis and western blot technology have been adopted to investigate the potential molecular mechanisms of 3OC12 and its structurally similar analogs damage to intestinal epithelial cells. Our results indicated that 3OC12 and 3OC14 trigger apoptosis rather than necrosis and ferroptosis in intestinal epithelial cells. RNA-sequencing combined with bioinformatics analysis showed that 3OC12 and 3OC14 reduced the expression of genes from extracellular matrix (ECM)-receptor interaction pathway. Consistently, protein expressions from ECM and tight junction-associated pathway were significantly reduced after 3OC12 and 3OC14 challenge. In addition, 3OC12 and 3OC14 led to blocked cell cycle, decreased mitochondrial membrane potential, increased reactive oxygen species level and elevated Ca2+ concentration. Reversely, the antioxidant NAC could effectively mitigate the reduced expression of ECM and tight junction proteins caused by 3OC12 and 3OC14 challenge. Collectively, this study demonstrated that QS autoinducer exposure to intestinal epithelial cells ablates the ECM and tight junctions by triggering oxidative stress and apoptosis, and finally disrupts the intestinal epithelial barrier. These findings provide a rationale for defensing QS-dependent bacterial infections and potential role of NAC for alleviating the syndrome.

Influence of Pseudomonas autoinducer N-3-oxododecanoyl homoserine lactone on human corneal epithelial cells.

The quorum-sensing (QS) signaling-dependent extracellular virulence factors of Pseudomonas aeruginosa can cause infections such as P. aeruginosa keratitis. P. aeruginosa communicates by secreting and sensing small chemical molecules called autoinducers in QS system. The key QS signal molecule, N-3-oxododecanoyl-homoserine lactone (3OC12HSL), can affect the behavior of host cells and initiate immune response. In this report we investigated the influence of 3OC12HSL on human corneal epithelial cells (HCECs) and the mechanisms of 3OC12HSL on activated toll-like receptor 2 (TLR2)-dependent interleukin-8 (IL-8) secretion in HCECs. Cells were cultured under different concentrations of 3OC12HSL. Cell viability was assessed using Crystal violet staining and the cell counting kit-8 assay. We demonstrated the administration of 3OC12HSL decreased HCEC viability and survival in a concentration- and time-dependent manner. At high concentrations, 3OC12HSL rapidly promoted a time-dependent increase in the expressions of TLR2 and TLR4. It was found that the nuclear translocation and expression of nuclear factor-κB (NF-κB) were also increased in response to 3OC12HSL treatment. The significantly elevated expressions of TLR2, TLR4, and NF-κB, encouraged us to further test their mechanisms that cause inflammatory response. Among the inflammatory factors examined (IL-6, IL-8, IL-10, and TNF-α), we found that IL-8 was significantly increased after treatment with 3OC12HSL and its expression was inhibited when TLR2 was specifically blocked or silenced. These results indicated that the QS signaling molecule 3OC12HSL could be recognized by the host innate immune system in HCECs. This recognition then triggered an immune inflammatory response involving the activation of TLR2 and an increase in expression of IL-8. This crosstalk between 3OC12HSL and host immunity in HCECs contributes to the development and progression of P. aeruginosa keratitis.