Ubiquitin-independent degradation of Bim blocks macrophage pyroptosis in sepsis-related tissue injury.

Pyroptosis, a typical inflammatory cell death mode, has been increasingly demonstrated to have therapeutic value in inflammatory diseases such as sepsis. However, the mechanisms and therapeutic targets of sepsis remain elusive. Here, we reported that REGγ inhibition promoted pyroptosis by regulating members of the gasdermin family in macrophages. Mechanistically, REGγ directly degraded Bim, a factor of the Bcl-2 family that can inhibit the cleavage of GSDMD/E, ultimately preventing the occurrence of pyroptosis. Furthermore, cecal ligation and puncture (CLP)-induced sepsis model mice showed downregulation of REGγ at both the RNA and protein levels. Gasdermin-mediated pyroptosis was augmented in REGγ-knockout mice, and these mice exhibited more severe sepsis-related tissue injury. More importantly, we found that REGγ expression was downregulated in clinical sepsis samples, such as those from patients with Pseudomonas aeruginosa (PA) infection. Finally, PA-infected mice showed decreased REGγ levels in the lung. In summary, our study reveals that the REGγ-Bim-GSDMD/E pathway is a novel regulatory mechanism of pyroptosis in sepsis-related tissue injury.

Pseudomonas aeruginosa Infection and Inflammation in Cystic Fibrosis: A Pilot Study With Lung Explants and a Novel Histopathology Scoring System.

PURPOSE: Pseudomonas aeruginosa is the predominant bacterial pathogen colonizing the cystic fibrosis (CF) lung. Mixed populations of nonmucoid and mucoid variants of P. aeruginosa have been isolated from the CF airway. While the association between mucoid variants and pulmonary function decline is well-established, their impact on inflammation and tissue damage in advanced CF lung disease remains unclear. METHODS: This pilot study utilized 1 non-CF and 3 CF lung explants to examine lobar distribution, inflammation, and histopathology related to nonmucoid and mucoid P. aeruginosa infection. To study tissue damage, we developed a novel lung histopathology scoring system, the first applied to human CF lung biopsies, which is comprised of five indicators: bronchiolar epithelial infiltrate, luminal inflammation, peribronchial/bronchiolar infiltrate, peribronchiolar fibrosis, and alveolar involvement. RESULTS: Mucoid P. aeruginosa variants were distributed throughout the CF lung but associated with greater concentrations of proinflammatory cytokines, IL-1ß, TNF-α, IL-6, IL-8, and IFN-γ, and one anti-inflammatory cytokine, IL-10, compared to nonmucoid variants. CF lung explants exhibited higher histopathology scores compared to a non-CF lung control. In mixed-variant infection, nonmucoid constituents associated with increased bronchiolar epithelial infiltration, one indicator of histopathology. CONCLUSION: This pilot study suggests ongoing interplay between host and bacterial elements in late-stage CF pulmonary disease. Mucoid P. aeruginosa infection correlates with inflammation regardless of lung lobe, whereas nonmucoid P. aeruginosa is associated with increased inflammatory cell infiltration. The development of a novel lung histopathology scoring system lays the groundwork for future large-cohort investigations.

cUMP elicits interendothelial gap formation during Pseudomonas aeruginosa infection.

Pseudomonas aeruginosa utilizes a type 3 secretion system to intoxicate host cells with the nucleotidyl cyclase ExoY. After activation by its host cell cofactor, filamentous actin, ExoY produces purine and pyrimidine cyclic nucleotides, including cAMP, cGMP, and cUMP. ExoY-generated cyclic nucleotides promote interendothelial gap formation, impair motility, and arrest cell growth. The disruptive activities of cAMP and cGMP during the P. aeruginosa infection are established; however, little is known about the function of cUMP. Here, we tested the hypothesis that cUMP contributes to endothelial cell barrier disruption during P. aeruginosa infection. Using a membrane permeable cUMP analog, cUMP-AM, we revealed that during infection with catalytically inactive ExoY, cUMP promotes interendothelial gap formation in cultured pulmonary microvascular endothelial cells (PMVECs) and contributes to increased filtration coefficient in the isolated perfused lung. These findings indicate that cUMP contributes to endothelial permeability during P. aeruginosa lung infection.NEW & NOTEWORTHY During pneumonia, bacteria utilize a virulence arsenal to communicate with host cells. The Pseudomonas aeruginosa T3SS directly introduces virulence molecules into the host cell cytoplasm. These molecules are enzymes that trigger interkingdom communication. One of the exoenzymes is a nucleotidyl cyclase that produces noncanonical cyclic nucleotides like cUMP. Little is known about how cUMP acts in the cell. Here we found that cUMP instigates pulmonary edema during Pseudomonas aeruginosa infection of the lung.

Biofilm exopolysaccharides alter sensory-neuron-mediated sickness during lung infection.

Infections of the lung cause observable sickness thought to be secondary to inflammation. Signs of sickness are crucial to alert others via behavioral-immune responses to limit contact with contagious individuals. Gram-negative bacteria produce exopolysaccharide (EPS) that provides microbial protection; however, the impact of EPS on sickness remains uncertain. Using genome-engineered Pseudomonas aeruginosa (P. aeruginosa) strains, we compared EPS-producers versus non-producers and a virulent Escherichia coli (E. coli) lung infection model in male and female mice. EPS-negative P. aeruginosa and virulent E. coli infection caused severe sickness, behavioral alterations, inflammation, and hypothermia mediated by TLR4 detection of the exposed lipopolysaccharide (LPS) in lung TRPV1+ sensory neurons. However, inflammation did not account for sickness. Stimulation of lung nociceptors induced acute stress responses in the paraventricular hypothalamic nuclei by activating corticotropin-releasing hormone neurons responsible for sickness behavior and hypothermia. Thus, EPS-producing biofilm pathogens evade initiating a lung-brain sensory neuronal response that results in sickness.

P. aeruginosa tRNA-fMet halves secreted in outer membrane vesicles suppress lung inflammation in cystic fibrosis.

Although tobramycin increases lung function in people with cystic fibrosis (pwCF), the density of Pseudomonas aeruginosa (P. aeruginosa) in the lungs is only modestly reduced by tobramycin; hence, the mechanism whereby tobramycin improves lung function is not completely understood. Here, we demonstrate that tobramycin increases 5' tRNA-fMet halves in outer membrane vesicles (OMVs) secreted by laboratory and CF clinical isolates of P. aeruginosa. The 5' tRNA-fMet halves are transferred from OMVs into primary CF human bronchial epithelial cells (CF-HBEC), decreasing OMV-induced IL-8 and IP-10 secretion. In mouse lungs, increased expression of the 5' tRNA-fMet halves in OMVs attenuated KC (murine homolog of IL-8) secretion and neutrophil recruitment. Furthermore, there was less IL-8 and neutrophils in bronchoalveolar lavage fluid isolated from pwCF during the period of exposure to tobramycin versus the period off tobramycin. In conclusion, we have shown in mice and in vitro studies on CF-HBEC that tobramycin reduces inflammation by increasing 5' tRNA-fMet halves in OMVs that are delivered to CF-HBEC and reduce IL-8 and neutrophilic airway inflammation. This effect is predicted to improve lung function in pwCF receiving tobramycin for P. aeruginosa infection.NEW & NOTEWORTHY The experiments in this report identify a novel mechanism, whereby tobramycin reduces inflammation in two models of CF. Tobramycin increased the secretion of tRNA-fMet halves in OMVs secreted by P. aeruginosa, which reduced the OMV-LPS-induced inflammatory response in primary cultures of CF-HBEC and in mouse lung, an effect predicted to reduce lung damage in pwCF.

Anti-inflammatory roles of type I interferon signaling in the lung.

Excessive or persistent inflammation may have detrimental effects on lung structure and function. Currently, our understanding of conserved host mechanisms that control the inflammatory response remains incompletely understood. In this study, we investigated the role of type I interferon signaling in the inflammatory response against diverse clinically relevant stimuli. Using mice deficient in type I interferon signaling (IFNAR1-/-), we demonstrate that the absence of interferon signaling resulted in a robust and persistent inflammatory response against Pseudomonas aeruginosa, lipopolysaccharide, and chemotherapeutic agent bleomycin. The elevated inflammatory response in IFNAR1-/- mice was manifested as elevated myeloid cells, such as macrophages and neutrophils, in the bronchoalveolar lavage. The inflammatory cell response in the IFNAR1-/- mice persisted to 14 days and there is impaired recovery and fibrotic remodeling of the lung in IFNAR1-/- mice after bleomycin injury. In the Pseudomonas infection model, the elevated inflammatory cell response led to improved bacterial clearance in IFNAR1-/- mice, although there was similar lung injury and survival. We performed RNA sequencing of lung tissue in wild-type and IFNAR1-/- mice after LPS and bleomycin injury. Our unbiased analysis identified differentially expressed genes between IFNAR1-/- and wild-type mice, including previously unknown regulation of nucleotide-binding oligomerization domain (NOD)-like receptor signaling, retinoic acid-inducible gene-I (RIG-I) signaling, and necroptosis pathway by type I interferon signaling in both models. These data provide novel insights into the conserved anti-inflammatory mechanisms of the type I interferon signaling.NEW & NOTEWORTHY Type I interferons are known for their antiviral activities. In this study, we demonstrate a conserved anti-inflammatory role of type I interferon signaling against diverse stimuli in the lung. We show that exacerbated inflammatory response in the absence of type I interferon signaling has both acute and chronic consequences in the lung including structural changes.

Clinicopathologic features of ecthyma gangrenosum: a single integrated health system cohort.

Ecthyma gangrenosum is an uncommon cutaneous eruption that can initially present with painless macules, which rapidly evolve into necrotic ulcers. This study sought to characterize clinicopathologic features of ecthyma gangrenosum from a single integrated health system. Our cohort consisted of 82 individuals diagnosed with ecthyma gangrenosum. Lesions were most commonly found in the lower extremities (55%) and the truncal region (20%). A wide variety of fungal and bacterial etiologies were found among our cohort. The majority of patients with EG were immunocompromised (79%) and 38% of patients also experienced sepsis. The mortality rate seen in our cohort was approximately 34%. No statistical differences in mortality outcome due to EG related complications were seen between pathogen etiology, and distribution or location of lesions. Patients who were septic or immunocompromised died more frequently than non-septic or immunocompetent patients, suggesting poorer prognosis.

A Pseudomonas aeruginosa small RNA regulates chronic and acute infection.

The ability to switch between different lifestyles allows bacterial pathogens to thrive in diverse ecological niches1,2. However, a molecular understanding of their lifestyle changes within the human host is lacking. Here, by directly examining bacterial gene expression in human-derived samples, we discover a gene that orchestrates the transition between chronic and acute infection in the opportunistic pathogen Pseudomonas aeruginosa. The expression level of this gene, here named sicX, is the highest of the P. aeruginosa genes expressed in human chronic wound and cystic fibrosis infections, but it is expressed at extremely low levels during standard laboratory growth. We show that sicX encodes a small RNA that is strongly induced by low-oxygen conditions and post-transcriptionally regulates anaerobic ubiquinone biosynthesis. Deletion of sicX causes P. aeruginosa to switch from a chronic to an acute lifestyle in multiple mammalian models of infection. Notably, sicX is also a biomarker for this chronic-to-acute transition, as it is the most downregulated gene when a chronic infection is dispersed to cause acute septicaemia. This work solves a decades-old question regarding the molecular basis underlying the chronic-to-acute switch in P. aeruginosa and suggests oxygen as a primary environmental driver of acute lethality.

Luteolin, a promising quorum quencher mitigates virulence factors production in Pseudomonas aeruginosa - In vitro and In vivoapproach.

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes healthcare-associated infection and high mortality in immunocompromised patients. It produces several virulence factors through quorum sensing (QS) mechanisms that is essential for subverting host immune system. Even front-line antibiotics are unable to control PA pathogenicity due to the emergence of antibiotic resistance. Luteolin is a naturally derived compound that has proven to be the effective drug to annihilate pathogens through quorum quenching mechanism. In this study, the protective effect of luteolin against the PA-mediated inflammation was demonstrated using zebrafish model. Luteolin protects zebrafish from PA infection and increases their survival rate. It was found that PA-mediated ROS, lipid peroxidation, and apoptosis were also significantly reduced in luteolin-treated zebrafish larvae. Open field test (OFT) reveals that luteolin rescued PA-infected zebrafish from retarded swimming behavior. Furthermore, luteolin increases SOD and CAT levels and decreases LDH and NO levels in PA-infected zebrafish compare to control group. Histological and gene expression analysis reveals that luteolin protects PA-infected zebrafish by decreasing gut inflammation and altering the expression of inflammatory (TNF-α, IL-1ß, IL-6) and antioxidant markers (iNOS, SOD, CAT). Thus, luteolin was found to have dual effect in protecting PA-infected zebrafish by decreasing virulence factors production in PA and stimulating host immune system. This is the first study demonstrating the protective effect of luteolin using animal model. Hence, luteolin could be used as a future therapeutic drug to control multi-drug resistant PA.

Histological assessment, anti-quorum sensing, and anti-biofilm activities of Dioon spinulosum extract: in vitro and in vivo approach.

Pseudomonas aeruginosa is an opportunistic bacterium causing several health problems and having many virulence factors like biofilm formation on different surfaces. There is a significant need to develop new antimicrobials due to the spreading resistance to the commonly used antibiotics, partly attributed to biofilm formation. Consequently, this study aimed to investigate the anti-biofilm and anti-quorum sensing activities of Dioon spinulosum, Dyer Ex Eichler extract (DSE), against Pseudomonas aeruginosa clinical isolates. DSE exhibited a reduction in the biofilm formation by P. aeruginosa isolates both in vitro and in vivo rat models. It also resulted in a decrease in cell surface hydrophobicity and exopolysaccharide quantity of P. aeruginosa isolates. Both bright field and scanning electron microscopes provided evidence for the inhibiting ability of DSE on biofilm formation. Moreover, it reduced violacein production by Chromobacterium violaceum (ATCC 12,472). It decreased the relative expression of 4 quorum sensing genes (lasI, lasR, rhlI, rhlR) and the biofilm gene (ndvB) using qRT-PCR. Furthermore, DSE presented a cytotoxic activity with IC50 of 4.36 ± 0.52 µg/ml against human skin fibroblast cell lines. For the first time, this study reports that DSE is a promising resource of anti-biofilm and anti-quorum sensing agents.

Pseudomonas aeruginosa associated pulmonary infections and in vitro amplification virulent rhamnolipid (rhlR) gene / Infecções pulmonares associadas a Pseudomonas aeruginosa e gene ramnolipídeo virulento (rhlR) da amplificação in vitro

Background: Pseudomonas aeruginosa is a common opportunistic pathogenic bacterium with the ability to develop a strong communication pathway by quorum sensing system and different virulent factors. Among the various important secretions of P. aeruginosa rhamnolipid is important biological detergent, believed to be involved in the development of the biofilm and intercellular communication. It readily dissolves the lung surfactants that are then easily catalyzed by the phospholipases and in this way is involved in the acute pulmonary infection. Objective: research work was designed to investigate virulence and gene associated with virulence in P. aeruginosa responsible for pulmonary infections. Methods: In current study polymerase chain reaction (PCR) was used for the detection of the rhlR (rhamnolipid encoding) gene of isolated strains. A number of assays were performed that ensured its virulent behavior. Disc diffusion method was used to check its antibiotic resistance. Isolated strains were resistant to a number of antibiotics applied. Result: It was found that males are more prone to respiratory infections as compared to females. Male members with age of 44-58 and 59-73 are at a higher risk, while females with age of 44-58 are also at a risk of pulmonary infections. Antibiotic resistance was observed by measuringzone of inhibition in strains GCU-SG-M4, GCU-SG-M3, GCU-SG-M5, GCU-SG-M2, GCU-SG-M1 and GCU-SG-M6. GCU-SG-M2 was resistant to fluconazole (FLU), clarithromycin (CLR), cefixime (CFM) and Penicillin (P10). No zone of inhibition was observed. But it showed unusual diffused zone around the Ak and MEM antibiotic discs. rhl R gene and 16s rRNA gene were characterized and analyzed. Conclusion: Findings from current study would help[...].

Antecedentes: Pseudomonas aeruginosa é uma bactéria patogênica oportunista comum, com a capacidade de desenvolver uma forte via de comunicação pelo sistema de detecção de quorum e diferentes fatores virulentos. Entre as várias secreções importantes de P. aeruginosa rhamnolipid, há um importante detergente biológico, que se acredita estar envolvido no desenvolvimento do biofilme e na comunicação intercelular. Dissolve rapidamente os surfactantes pulmonares que são facilmente catalisados pelas fosfolipases e, dessa maneira, estão envolvidos na infecção pulmonar aguda. Objetivo: O trabalho de pesquisa foi desenhado para investigar a virulência e o gene associado à virulência em P. aeruginosa responsável por infecções pulmonares. Métodos: No presente estudo, a reação em cadeia da polimerase (PCR) foi utilizada para a detecção do gene rhlR (codificação ramnolipídeo) de cepas isoladas. Foram realizados vários ensaios que garantiram seu comportamento virulento. O método de difusão em disco foi utilizado para verificar sua resistência a antibióticos. As estirpes isoladas foram resistentes a vários antibióticos aplicados. Resultado: Verificou-se que os homens são mais propensos a infecções respiratórias em comparação às mulheres. Membros do sexo masculino com idade entre 44 e 58 e 59 e 73 anos correm maior risco, enquanto mulheres com idade entre 44 e 58 anos também correm risco de infecções pulmonares. A resistência aos antibióticos foi observada medindo a zona de inibição nas cepas GCU-SG-M4, GCU-SG-M3, GCU-SG-M5, GCU-SG-M2, GCU-SG-M1 e GCU-SG-M6. O GCU-SG-M2 foi resistente ao fluconazol (FLU), claritromicina (CLR), cefixima (CFM) e penicilina (P10). Nenhuma zona de inibição foi observada. Mas se notou uma zona difusa incomum ao redor dos discos antibióticos Ak e MEM. Os genes rhl R e 16s rRNA foram caracterizados e analisados. Conclusão: As conclusões do presente estudo ajudariam a aumentar a conscientização sobre a resistência a antibióticos de, [...].

Inhibition of Virulence Factors and Biofilm Formation by Wogonin Attenuates Pathogenicity of Pseudomonas aeruginosa PAO1 via Targeting pqs Quorum-Sensing System.

Pseudomonas aeruginosa, an important opportunistic pathogen, is capable of producing various virulence factors and forming biofilm that are regulated by quorum sensing (QS). It is known that targeting virulence factor production and biofilm formation instead of exerting selective pressure on growth such as conventional antibiotics can reduce multidrug resistance in bacteria. Therefore, many quorum-sensing inhibitors (QSIs) have been developed to prevent or treat this bacterial infection. In this study, wogonin, as an active ingredient from Agrimonia pilosa, was found to be able to inhibit QS system of P. aeruginosa PAO1. Wogonin downregulated the expression of QS-related genes and reduced the production of many virulence factors, such as elastase, pyocyanin, and proteolytic enzyme. In addition, wogonin decreased the extracellular polysaccharide synthesis and inhibited twitching, swimming, and swarming motilities and biofilm formation. The attenuation of pathogenicity in P. aeruginosa PAO1 by wogonin application was further validated in vivo by cabbage infection and fruit fly and nematode survival experiments. Further molecular docking analysis, pathogenicity examination of various QS-related mutants, and PQS signal molecule detection revealed that wogonin could interfere with PQS signal molecular synthesis by affecting pqsA and pqsR. Taken together, the results indicated that wogonin might be used as an anti-QS candidate drug to attenuate the infection caused by P. aeruginosa.

Adjunctive Thymosin Beta-4 Treatment Influences PMN Effector Cell Function during Pseudomonas aeruginosa-Induced Corneal Infection.

Previous work examining the therapeutic efficacy of adjunct thymosin beta 4 (Tß4) to ciprofloxacin for ocular infectious disease has revealed markedly reduced inflammation (inflammatory mediators and innate immune cells) with increased activation of wound healing pathways. Understanding the therapeutic mechanisms of action have further revealed a synergistic effect with ciprofloxacin to enhance bacterial killing along with a regulatory influence over macrophage effector cell function. As a natural extension of the aforementioned work, the current study uses an experimental model of P. aeruginosa-induced keratitis to examine the influence of Tß4 regarding polymorphonuclear leukocyte (PMN/neutrophil) cellular function, contributing to improved disease response. Flow cytometry was utilized to phenotypically profile infiltrating PMNs after infection. The generation of reactive oxygen species (ROS), neutrophil extracellular traps (NETs), and PMN apoptosis were investigated to assess the functional activities of PMNs in response to Tß4 therapy. In vitro work using peritoneal-derived PMNs was similarly carried out to verify and extend our in vivo findings. The results indicate that the numbers of infiltrated PMNs into infected corneas were significantly reduced with adjunctive Tß4 treatment. This was paired with the downregulated expression of proinflammatory markers on these cells, as well. Data generated from PMN functional studies suggested that the corneas of adjunctive Tß4 treated B6 mice exhibit a well-regulated production of ROS, NETs, and limited PMN apoptosis. In addition to confirming the in vivo results, the in vitro findings also demonstrated that neutrophil elastase (NE) was unnecessary for NETosis. Collectively, these data provide additional evidence that adjunctive Tß4 + ciprofloxacin treatment is a promising option for bacterial keratitis that addresses both the infectious pathogen and cellular-mediated immune response, as revealed by the current study.

Esc peptides as novel potentiators of defective cystic fibrosis transmembrane conductance regulator: an unprecedented property of antimicrobial peptides.

Mutations in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein lead to persistent lung bacterial infections, mainly due to Pseudomonas aeruginosa, causing loss of respiratory function and finally death of people affected by CF. Unfortunately, even in the era of CFTR modulation therapies, management of pulmonary infections in CF remains highly challenging especially for patients with advanced stages of lung disease. Recently, we identified antimicrobial peptides (AMPs), namely Esc peptides, with potent antipseudomonal activity. In this study, by means of electrophysiological techniques and computational studies we discovered their ability to increase the CFTR-controlled ion currents, by direct interaction with the F508del-CFTR mutant. Remarkably, this property was not explored previously with any AMPs or peptides in general. More interestingly, in contrast with clinically used CFTR modulators, Esc peptides would give particular benefit to CF patients by combining their capability to eradicate lung infections and to act as promoters of airway wound repair with their ability to ameliorate the activity of the channel with conductance defects. Overall, our findings not only highlighted Esc peptides as the first characterized AMPs with a novel property, that is the potentiator activity of CFTR, but also paved the avenue to investigate the functions of AMPs and/or other peptide molecules, for a new up-and-coming pharmacological approach to address CF lung disease.

Effect of Disinfectants with Different Active Ingredients on Biofilm Formation in Pseudomonas aeruginosa.

We compared the effects of disinfectants on biofilms of 10 Pseudomonas aeruginosa strains isolated from different loci of patients with purulent-septic infections. Identification was carried out by standard bacteriological methods. To substantiate the prospects of using in hospitals and to assess the effect of disinfectants on P. aeruginosa biofilms, the following disinfectants were used in various concentrations: Sekusept Aktiv, A-DEZ, and Monitor Oxy. All clinical strains of P. aeruginosa showed the ability to form biofilms. Both oxygen-containing and quaternary ammonium compounds effectively inhibited the formation of biofilms. In more than 50% cases, disinfectants with different active ingredients did not destroy pre-formed of P. aeruginosa biofilms.

P. aeruginosa Induced Lipid Peroxidation Causes Ferroptotic Cell Death in Airways.

BACKGROUND/AIMS: Oxidative stress and infections by Pseudomonas aeruginosa (P. aeruginosa) are prominent in lungs of patients suffering from cystic fibrosis (CF). METHODS: The present study examines effects of P. aeruginosa on lipid peroxidation in human and mouse lungs, and cell death induced by P. aeruginosa in human airway epithelial cells. The role of the Ca2+ activated Cl- channel TMEM16A, the phospholipid scramblase TMEM16F, and the CFTR Cl- channel for ferroptotic cell death is examined. RESULTS: Lipid peroxidation was detected in human CF lungs, which correlated with bacterial infection. In vivo inoculation with P. aeruginosa or Staphylococcus aureus (S. aureus) induced lipid peroxidation in lungs of mice lacking expression of CFTR, and in lungs of wild type animals. Incubation of CFBE human airway epithelial cells with P. aeruginosa induced an increase in reactive oxygen species (ROS), causing lipid peroxidation and cell death independent of expression of wt-CFTR or F508del-CFTR. Knockdown of TMEM16A attenuated P. aeruginosa induced cell death. Antioxidants such as coenzyme Q10 and idebenone as well as the inhibitor of ferroptosis, ferrostatin-1, inhibited P. aeruginosa-induced cell death. CFBE cells expressing wtCFTR, but not F508del-CFTR, activated a basal Cl- conductance upon exposure to P. aeruginosa, which was caused by an increase in intracellular basal Ca2+ concentrations and activation of Ca2+-dependent adenylate cyclase. CONCLUSION: The data suggest an intrinsic pro-inflammatory phenotype in CF epithelial cells, while ferroptosis is observed in both non-CF and CF epithelial cells upon infection with P. aeruginosa. CF cells fail to activate fluid secretion in response to infection with P. aeruginosa. The use of antioxidants and inhibitors of ferroptosis is proposed as a treatment of pneumonia caused by infection with P. aeruginosa.

Host phospholipid peroxidation fuels ExoU-dependent cell necrosis and supports Pseudomonas aeruginosa-driven pathology.

Regulated cell necrosis supports immune and anti-infectious strategies of the body; however, dysregulation of these processes drives pathological organ damage. Pseudomonas aeruginosa expresses a phospholipase, ExoU that triggers pathological host cell necrosis through a poorly characterized pathway. Here, we investigated the molecular and cellular mechanisms of ExoU-mediated necrosis. We show that cellular peroxidised phospholipids enhance ExoU phospholipase activity, which drives necrosis of immune and non-immune cells. Conversely, both the endogenous lipid peroxidation regulator GPX4 and the pharmacological inhibition of lipid peroxidation delay ExoU-dependent cell necrosis and improve bacterial elimination in vitro and in vivo. Our findings also pertain to the ExoU-related phospholipase from the bacterial pathogen Burkholderia thailandensis, suggesting that exploitation of peroxidised phospholipids might be a conserved virulence mechanism among various microbial phospholipases. Overall, our results identify an original lipid peroxidation-based virulence mechanism as a strong contributor of microbial phospholipase-driven pathology.

Label-free quantitative proteomics identifies unique proteomes of clinical isolates of the Liverpool Epidemic Strain of Pseudomonas aeruginosa and laboratory strain PAO1.

PURPOSE: Comparative genomics and phenotypic assays have shown that antibiotic resistance profiles differ among clinical isolates of Pseudomonas aeruginosa and that genotype-phenotype associations are difficult to establish for resistance phenotypes based on these comparisons alone. EXPERIMENTAL DESIGN: Here, we used label-free quantitative proteomics to compare two isolates of the Liverpool Epidemic Strain (LES) of P. aeruginosa, LESlike1 and LESB58, and the common laboratory strain P. aeruginosa PAO1 to more accurately predict functional differences between strains. RESULTS: Our results show that the proteomes of the LES isolates are more similar to each other than to PAO1; however, a number of differences were observed in the abundance of proteins involved in quorum sensing, virulence, and antibiotic resistance, including in the comparison of LESlike1 and LESB58. Additionally, the proteomic data revealed a higher abundance of proteins involved in polymyxin and aminoglycoside resistance in LESlike1. Minimum inhibitory concentration assays showed that LESlike1 had up to 128-fold higher resistance to antibiotics from these classes. CONCLUSIONS: These findings provide an example of the ability of proteomic data to complement genotypic and phenotypic studies to understand resistance in clinical isolates. CLINICAL RELEVANCE: P. aeruginosa is a predominant pathogen in chronic lung infections in individuals with cystic fibrosis (CF). LES isolates are capable of transferring between CF patients and have been associated with increased hospital visits and antibiotic treatments.

Oxygen-Induced Conformational Changes in the PAS-Heme Domain of the Pseudomonas aeruginosa Aer2 Receptor.

The Aer2 receptor from Pseudomonas aeruginosa has an O2-binding PAS-heme domain that stabilizes O2 via a Trp residue in the distal heme pocket. Trp rotates ∼90° to bond with the ligand and initiate signaling. Although the isolated PAS domain is monomeric, both in solution and in a cyanide-bound crystal structure, an unliganded structure forms a dimer. An overlay of the two structures suggests possible signaling motions but also predicts implausible clashes at the dimer interface when the ligand is bound. Moreover, in a full-length Aer2 dimer, PAS is sandwiched between multiple N- and C-terminal HAMP domains, which would feasibly restrict PAS motions. To explore the PAS dimer interface and signal-induced motions in full-length Aer2, we introduced Cys substitutions and used thiol-reactive probes to examine in vivo accessibility and residue proximities under both aerobic and anaerobic conditions. In vivo, PAS dimers were retained in full-length Aer2 in the presence and absence of O2, and the dimer interface was consistent with the isolated PAS dimer structure. O2-mediated changes were also consistent with structural predictions in which the PAS N-terminal caps move apart and the C-terminal DxT region moves closer together. The DxT motif links PAS to the C-terminal HAMP domains and was critical for PAS-HAMP signaling. Removing the N-terminal HAMP domains altered the distal PAS dimer interface and prevented signaling, even after signal-on lesions were introduced into PAS. The N-terminal HAMP domains thus facilitate the O2-dependent shift of PAS to the signal-on conformation, clarifying their role upstream of the PAS-sensing domain.