A Pseudomonas aeruginosa hepta-acylated lipid A variant associated with cystic fibrosis selectively activates human neutrophils

Pseudomonas aeruginosa Lipid A Structural Variants Induce Altered Immune Responses

Pseudomonas aeruginosa causes chronic lung infection in cystic fibrosis (CF), resulting in structural lung damage and progressive pulmonary decline. P. aeruginosa in the CF lung undergoes numerous changes, adapting to host-specific airway pressures while establishing chronic infection. P. aeruginosa undergoes lipid A structural modification during CF chronic infection that is not seen in any other disease state. Lipid A, the membrane anchor of LPS (i.e., endotoxin), comprises the majority of the outer membrane of Gram-negative bacteria and is a potent Toll-like receptor 4 (TLR4) agonist. The structure of P. aeruginosa lipid A is intimately linked with its recognition by TLR4 and subsequent immune response. Prior work has identified P. aeruginosa strains with altered lipid A structures that arise during chronic CF lung infection; however, the impact of the P. aeruginosa lipid A structure on airway disease has not been investigated. Here, we show that P. aeruginosa lipid A lacks PagL-mediated deacylation during human airway infection using a direct-from-sample mass spectrometry approach on human BAL fluid. This structure triggers increased proinflammatory cytokine production by primary human macrophages. Furthermore, alterations in lipid A 2-hydroxylation impact cytokine response in a site-specific manner, independent of CF transmembrane conductance regulator function. It is interesting that there is a CF-specific reduction in IL-8 secretion within the epithelial-cell compartment that only occurs in CF bronchial epithelial cells when infected with CF-adapted P. aeruginosa that lacks PagL-mediated lipid A deacylation. Taken together, we show that P. aeruginosa alters its lipid A structure during acute lung infection and that this lipid A structure induces stronger signaling through TLR4.

The multifaceted role of c-di-AMP signaling in the regulation of Porphyromonas gingivalis lipopolysaccharide structure and function

Background

This study unveils the intricate functional association between cyclic di-3',5'-adenylic acid (c-di-AMP) signaling, cellular bioenergetics, and the regulation of lipopolysaccharide (LPS) profile in Porphyromonas gingivalis, a Gram-negative obligate anaerobe considered as a keystone pathogen involved in the pathogenesis of chronic periodontitis. Previous research has identified variations in P. gingivalis LPS profile as a major virulence factor, yet the underlying mechanism of its modulation has remained elusive.

Methods

We employed a comprehensive methodological approach, combining two mutants exhibiting varying levels of c-di-AMP compared to the wild type, alongside an optimized analytical methodology that combines conventional mass spectrometry techniques with a novel approach known as FLATn.

Results

We demonstrate that c-di-AMP acts as a metabolic nexus, connecting bioenergetic status to nuanced shifts in fatty acid and glycosyl profiles within P. gingivalis LPS. Notably, the predicted regulator gene cdaR, serving as a potent regulator of c-di-AMP synthesis, was found essential for producing N-acetylgalactosamine and an unidentified glycolipid class associated with the LPS profile.

Conclusion

The multifaceted roles of c-di-AMP in bacterial physiology are underscored, emphasizing its significance in orchestrating adaptive responses to stimuli. Furthermore, our findings illuminate the significance of LPS variations and c-di-AMP signaling in determining the biological activities and immunostimulatory potential of P. gingivalis LPS, promoting a pathoadaptive strategy. The study expands the understanding of c-di-AMP pathways in Gram-negative species, laying a foundation for future investigations into the mechanisms governing variations in LPS structure at the molecular level and their implications for host-pathogen interactions.

Role of Host and Bacterial Lipids in Pseudomonas aeruginosa Respiratory Infections

The opportunistic pathogen Pseudomonas aeruginosa is one of the most common agents of respiratory infections and has been associated with high morbidity and mortality rates. The ability of P. aeruginosa to cause severe respiratory infections results from the coordinated action of a variety of virulence factors that promote bacterial persistence in the lungs. Several of these P. aeruginosa virulence mechanisms are mediated by bacterial lipids, mainly lipopolysaccharide, rhamnolipid, and outer membrane vesicles. Other mechanisms arise from the activity of P. aeruginosa enzymes, particularly ExoU, phospholipase C, and lipoxygenase A, which modulate host lipid signaling pathways. Moreover, host phospholipases, such as cPLA2α and sPLA2, are also activated during the infectious process and play important roles in P. aeruginosa pathogenesis. These mechanisms affect key points of the P. aeruginosa-host interaction, such as: i) biofilm formation that contributes to bacterial colonization and survival, ii) invasion of tissue barriers that allows bacterial dissemination, iii) modulation of inflammatory responses, and iv) escape from host defenses. In this mini-review, we present the lipid-based mechanism that interferes with the establishment of P. aeruginosa in the lungs and discuss how bacterial and host lipids can impact the outcome of P. aeruginosa respiratory infections.

Heat stress-induced mucosal barrier dysfunction is potentially associated with gut microbiota dysbiosis in pigs

Heat stress (HS) can be detrimental to the gut health of swine. Many negative outcomes induced by HS are increasingly recognized as including modulation of intestinal microbiota. In turn, the intestinal microbiota is a unique ecosystem playing a critical role in mediating the host stress response. Therefore, we aimed to characterize gut microbiota of pigs’ exposure to short-term HS, to explore a possible link between the intestinal microbiota and HS-related changes, including serum cytokines, oxidation status, and intestinal epithelial barrier function. Our findings showed that HS led to intestinal morphological and integrity changes (villus height, serum diamine oxidase [DAO], serum D-lactate and the relative expressions of tight junction proteins), reduction of serum cytokines (interleukin [IL]-8, IL-12, interferon-gamma [IFN-γ]), and antioxidant activity (higher glutathione [GSH] and malondialdehyde [MDA] content, and lower superoxide dismutase [SOD]). Also, 16S rRNA sequencing analysis revealed that although there was no difference in microbial α-diversity, some HS-associated composition differences were revealed in the ileum and cecum, which partly led to an imbalance in the production of short-chain fatty acids including propionate acid and valerate acid. Relevance networks revealed that HS-derived changes in bacterial genera and microbial metabolites, such as Chlamydia, Lactobacillus, Succinivibrio, Bifidobacterium, Lachnoclostridium, and propionic acid, were correlated with oxidative stress, intestinal barrier dysfunction, and inflammation in pigs. Collectively, our observations suggest that intestinal damage induced by HS is probably partly related to the gut microbiota dysbiosis, though the underlying mechanism remains to be fully elucidated.

Integrated mass spectrometry-based multi-omics for elucidating mechanisms of bacterial virulence

Despite being considered the simplest form of life, bacteria remain enigmatic, particularly in light of pathogenesis and evolving antimicrobial resistance. After three decades of genomics, we remain some way from understanding these organisms, and a substantial proportion of genes remain functionally unknown. Methodological advances, principally mass spectrometry (MS), are paving the way for parallel analysis of the proteome, metabolome and lipidome. Each provides a global, complementary assay, in addition to genomics, and the ability to better comprehend how pathogens respond to changes in their internal (e.g. mutation) and external environments consistent with infection-like conditions. Such responses include accessing necessary nutrients for survival in a hostile environment where co-colonizing bacteria and normal flora are acclimated to the prevailing conditions. Multi-omics can be harnessed across temporal and spatial (sub-cellular) dimensions to understand adaptation at the molecular level. Gene deletion libraries, in conjunction with large-scale approaches and evolving bioinformatics integration, will greatly facilitate next-generation vaccines and antimicrobial interventions by highlighting novel targets and pathogen-specific pathways. MS is also central in phenotypic characterization of surface biomolecules such as lipid A, as well as aiding in the determination of protein interactions and complexes. There is increasing evidence that bacteria are capable of widespread post-translational modification, including phosphorylation, glycosylation and acetylation; with each contributing to virulence. This review focuses on the bacterial genotype to phenotype transition and surveys the recent literature showing how the genome can be validated at the proteome, metabolome and lipidome levels to provide an integrated view of organism response to host conditions.

Recombinant Pseudomonas bio-nanoparticles induce protection against pneumonic Pseudomonas aeruginosa infection

To develop an effective Pseudomonas aeruginosa (PA) outer-membrane-vesicles (OMVs) vaccine, we eliminated multiple virulence factors from a wild-type P. aeruginosa PA103 strain (PA103) to generate a recombinant strain, PA-m14. The PA-m14 strain was tailored with a pSMV83 plasmid encoding the pcrV-hitA_T fusion gene to produce OMVs. The recombinant OMVs enclosed increased amounts of PcrV-HitA_T bivalent antigen (PH) (termed OMV-PH) and exhibited reduced toxicity compared to the OMVs from PA103. Intramuscular vaccination with OMV-PH from PA-m14(pSMV83) afforded 70% protection against intranasal challenge with 6.5 × 10⁶ CFU (∼30 LD₅₀) of PA103, while immunization using OMVs without the PH antigen (termed OMV-NA) or the PH antigen alone failed to offer effective protection against the same challenge. Further immune analysis showed that the OMV-PH immunization significantly stimulated potent antigen-specific humoral and T-cell (Th1/Th17) responses in comparison to the PH or OMV-NA immunization in mice, which can effectively hinder PA infection. Undiluted anti-sera from OMV-PH-immunized mice displayed significant opsonophagocytic killing of WT PA103 compared to antisera from PH antigen- or OMV-NA-immunized mice. Moreover, the OMV-PH immunization afforded significant antibody-indentpednet cross-protection to mice against PAO1 and a clinical isolate AMC-PA10 strains. Collectively, the recombinant PA OMV delivering the PH bivalent antigen exhibits high immunogenicity and would be a promising next-generation vaccine candidate against PA infection.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Lipopolysaccharide from biofilm-forming Pseudomonas aeruginosa PAO1 induces macrophage hyperinflammatory responses

Introduction. Macrophages polarization is essential in infection control. Llipopolysaccharide (LPS) plays an essential role in host innate immune system-pathogen interaction. The LPS structure of Pseudomonas aeruginosa modifies in the adaptation of this pathogen to biofilm-related chronic infection.Gap statement. There have been several studies on LPS induced polarization of human and mouse macrophages with different results. And it was reported that the lipid A structure of the LPS derived from biofilm-forming Pseudomonas aeruginosa strain PAO1 was modified.Aim. This study aimed to investigate the effect and the involved pathway of LPS from biofilm-forming PAO1 on human and murine macrophage polarization.Methodology. LPS was isolated from biofilm-forming and planktonic PAO1 and quantified. Then the LPS was added to PMA-differentiated human macrophage THP-1 cells and Raw264.7 murine macrophage cells. The expression of iNOS, Arg-1, IL4, TNF-α, CCL3, and CCL22 was analysed in the different cell lines. The expression of TICAM-1 and MyD88 in human THP-1 macrophages was quantified by Western blot. PAO1 infected macrophages at different polarization states, and the intracellular bacterial growth in macrophages was evaluated.Results. LPS from biofilm-forming PAO1 induced more marked hyperinflammatory responses in THP-1 and Raw264.7 macrophages than LPS derived from planktonic PAO1, and these responses were related to the up-regulation of MyD88. Intracellular growth of PAO1 was significantly increased in THP-1 macrophages polarized by LPS from biofilm-forming PAO1, but decreased both in THP-1 and Raw264.7 macrophages polarized by LPS from planktonic PAO1.Conclusion. The presented in vitro study indicates that LPS derived from biofilm-forming PAO1 induces enhanced M1 polarization in human and murine macrophage cell lines than LPS from planktonic PAO1.

Pseudomonas aeruginosa: An Audacious Pathogen with an Adaptable Arsenal of Virulence Factors

Pseudomonas aeruginosa is a dominant pathogen in people with cystic fibrosis (CF) contributing to morbidity and mortality. Its tremendous ability to adapt greatly facilitates its capacity to cause chronic infections. The adaptability and flexibility of the pathogen are afforded by the extensive number of virulence factors it has at its disposal, providing P. aeruginosa with the facility to tailor its response against the different stressors in the environment. A deep understanding of these virulence mechanisms is crucial for the design of therapeutic strategies and vaccines against this multi-resistant pathogen. Therefore, this review describes the main virulence factors of P. aeruginosa and the adaptations it undergoes to persist in hostile environments such as the CF respiratory tract. The very large P. aeruginosa genome (5 to 7 MB) contributes considerably to its adaptive capacity; consequently, genomic studies have provided significant insights into elucidating P. aeruginosa evolution and its interactions with the host throughout the course of infection.

Failed eradication therapy of new onset Pseudomonas aeruginosa infections in cystic fibrosis children is associated with bacterial resistance to neutrophil functions

BACKGROUND

Antibiotics, such as inhaled tobramycin are used to eradicate new onset Pseudomonas aeruginosa (PA) infections in cystic fibrosis (CF) patients but frequently fail due to reasons poorly understood. We hypothesized that PA isolates' resistance to neutrophil antibacterial functions was associated with failed eradication in patients harboring those strains.

METHODS

We analyzed all PA isolates from a cohort of 39 CF children with new onset PA infections undergoing tobramycin eradication therapy, where N=30 patients had eradicated and N=9 patients had persistent infection. We characterized several bacterial phenotypes and measured the isolates' susceptibility to neutrophil antibacterial functions using in vitro assays of phagocytosis and intracellular bacterial killing.

RESULTS

PA isolates from persistent infections were more resistant to neutrophil functions, with lower phagocytosis and intracellular bacterial killing compared to those from eradicated infections. In multivariable analyses, in vitro neutrophil responses were positively associated with twitching motility, and negatively with mucoidy. In vitro neutrophil phagocytosis was a predictor of persistent infection following tobramycin even after adjustment for clinical risk factors.

CONCLUSIONS

PA isolates from new onset CF infection show strain-specific susceptibility to neutrophil antibacterial functions, and infection with PA isolates resistant to neutrophil phagocytosis is an independent risk factor for failed tobramycin eradication.

Whole Transcriptome Analysis Reveals That Filifactor alocis Modulates TNFα-Stimulated MAPK Activation in Human Neutrophils

Periodontitis is an irreversible, bacteria-induced, chronic inflammatory disease that compromises the integrity of tooth-supporting tissues and adversely affects systemic health. As the immune system's first line of defense against bacteria, neutrophils use their microbicidal functions in the oral cavity to protect the host against periodontal disease. However, periodontal pathogens have adapted to resist neutrophil microbicidal mechanisms while still propagating inflammation, which provides essential nutrients for the bacteria to proliferate and cause disease. Advances in sequencing technologies have recognized several newly appreciated bacteria associated with periodontal lesions such as the Gram-positive anaerobic rod, Filifactor alocis. With the discovery of these oral bacterial species, there is also a growing need to assess their pathogenic potential and determine their contribution to disease progression. Currently, few studies have addressed the pathogenic mechanisms used by oral bacteria to manipulate the neutrophil functional responses at the level of the transcriptome. Thus, this study aims to characterize the global changes at the gene expression level in human neutrophils during infection with F. alocis. Our results indicate that the challenge of human neutrophils with F. alocis results in the differential expression of genes involved in multiple neutrophil effector functions such as chemotaxis, cytokine and chemokine signaling pathways, and apoptosis. Moreover, F. alocis challenges affected the expression of components from the TNF and MAPK kinase signaling pathways. This resulted in transient, dampened p38 MAPK activation by secondary stimuli TNFα but not by fMLF. Functionally, the F. alocis-mediated inhibition of p38 activation by TNFα resulted in decreased cytokine production but had no effect on the priming of the respiratory burst response or the delay of apoptosis by TNFα. Since the modulatory effect was characteristic of viable F. alocis only, we propose this as one of F. alocis' mechanisms to control neutrophils and their functional responses.

Toll-like Receptor 4-Independent Effects of Lipopolysaccharide Identified Using Longitudinal Serum Proteomics

Sepsis remains one of the most lethal and costly conditions treated in U.S. hospitals, with approximately 50% of cases caused by Gram-negative bacterial infections. Septic shock is induced when lipopolysaccharide (LPS), the main component of Gram-negative outer bacterial membrane, signals through the Toll-like receptor 4 (TLR4) complex. Lethal endotoxemia, a model for septic shock, was induced in WT C57BL6 and TLR4^-/- mice by administration of Escherichia coli LPS. WT LPS treated mice showed high morbidity, while PBS treated LPS and treated TLR4^-/- mice did not. ANOVA analysis of label-free quantification of longitudinal serum proteome revealed 182 out of 324 proteins in LPS injected WT mice that were significantly changed across four time points (0, 6, 12, and 18 h). No significant changes were identified in the two control groups. From the 182 identified proteins, examples of known sepsis biomarkers were validated by ELISA, which showed similar trends as MS proteomics data. Longitudinal analysis within individual mice produced 3-fold more significantly changed proteins than pair-wise comparison. A subsequent global analysis of WT and TLR4^-/- mice identified pathways activated independent of TLR4. These pathways represent possible compensatory mechanisms that allow for control of Gram-negative bacterial infection regardless of host immune status.

Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis

Mycobacterium smegmatis rarely causes disease in the immunocompetent, but reported cases of soft tissue infection describe abscess formation requiring surgical debridement for resolution. Neutrophils are the first innate immune cells to accumulate at sites of bacterial infection, where reactive oxygen species and proteolytic enzymes are used to kill microbial invaders. As these phagocytic cells play central roles in protection from most bacteria, we assessed human neutrophil phagocytosis and granule exocytosis in response to serum opsonized or non-opsonized M. smegmatis mc². Although phagocytosis was enhanced by serum opsonization, M. smegmatis did not induce exocytosis of secretory vesicles or azurophilic granules at any time point tested, with or without serum opsonization. At early time points, opsonized M. smegmatis induced significant gelatinase granule exocytosis compared to non-opsonized bacteria. Differences in granule release between opsonized and non-opsonized M. smegmatis decreased in magnitude over the time course examined, with bacteria also evoking specific granule exocytosis by six hours after addition to cultured primary single-donor human neutrophils. Supernatants from neutrophils challenged with opsonized M. smegmatis were able to digest gelatin, suggesting that complement and gelatinase granule exocytosis can contribute to neutrophil-mediated tissue damage seen in these rare soft tissue infections.

The Role of Pseudomonas aeruginosa Lipopolysaccharide in Bacterial Pathogenesis and Physiology

The major constituent of the outer membrane of Gram-negative bacteria is lipopolysaccharide (LPS), which is comprised of lipid A, core oligosaccharide, and O antigen, which is a long polysaccharide chain extending into the extracellular environment. Due to the localization of LPS, it is a key molecule on the bacterial cell wall that is recognized by the host to deploy an immune defence in order to neutralize invading pathogens. However, LPS also promotes bacterial survival in a host environment by protecting the bacteria from these threats. This review explores the relationship between the different LPS glycoforms of the opportunistic pathogen Pseudomonas aeruginosa and the ability of this organism to cause persistent infections, especially in the genetic disease cystic fibrosis. We also discuss the role of LPS in facilitating biofilm formation, antibiotic resistance, and how LPS may be targeted by new antimicrobial therapies.

Human neutrophils depend on extrinsic factors produced by monocytes for their survival response to TLR4 stimulation

LPS delays neutrophil apoptosis by a process generally assumed to involve cell-intrinsic TLR4 signaling. However, neutrophil survival responses to LPS have been reported to be monocyte-dependent, which would indicate more complexity than is currently appreciated. We compared the survival responses of conventionally purified vs highly purified neutrophils to confirm or refute the need for secondary cell-types and to identify the cellular or molecular mechanisms involved. Direct stimulation of TLR4 failed to extend the survival of highly purified neutrophils, but survival activity was retained in less pure neutrophil preparations containing low numbers of eosinophils, monocytes, platelets and CD3+ lymphocytes. Sequential depletions identified monocytes as the only cell type required. Transfer of culture supernatants after lipid A-conditioning revealed that purified monocytes were sufficient for production of nearly all of the survival activity observed in mixed populations. The survival factors secreted upon TLR4 stimulation remain unidentified, but were not correlated with IL-1β, IL-6 or TNF-α nor could survival activity be inhibited by Ab blockade of IL-8 or of several other candidate factors other than endogenously produced GM-CSF, which was responsible for about one-tenth of the survival activity present in conditioned supernatants. These observations confirm that ex vivo neutrophil survival responses to TLR4 agonists are not cell intrinsic and involve potentially novel factors secreted by TLR4-stimulated monocytes.

Putative Periodontal Pathogens, Filifactor Alocis and Peptoanaerobacter Stomatis, Induce Differential Cytokine and Chemokine Production by Human Neutrophils

Periodontitis is a highly prevalent infectious disease that affects ~ 50% of the adults in the USA alone. Two Gram-positive anaerobic oral bacteria, Filifactor alocis and Peptoanaerobacterstomatis, have emerged as important periodontal pathogens. Neutrophils are a major component of the innate host response in the gingival tissue, and the contribution of neutrophil-derived cytokines and chemokines plays a central role in disease progression. The pattern of cytokines and chemokines released by human neutrophils upon stimulation with newly appreciated periodontal bacteria compared to the keystone oral pathogen Porphyromonas gingivalis was investigated. Our results showed that both F. alocis and P. stomatis triggered TLR2/6 activation. F. alocis induced significant changes in gene expression of cytokines and chemokines in human neutrophils compared to unstimulated cells. However, except for IL-1ra, neutrophils released lower levels of cytokines and chemokines in response to F. alocis compared to P. stomatis. Furthermore, bacteria-free conditioned supernatant collected from neutrophils challenged with P. stomatis, but not from P. gingivalis or F. alocis, was chemotactic towards both neutrophils and monocytes. Elucidating stimuli-specific modulation of human neutrophil effector functions in the context of dysbiotic microbial community constituents provides valuable information for understanding the pathogenesis of periodontal diseases.

Pseudomonas aeruginosa biofilm is a potent inducer of phagocyte hyperinflammation

Objective

Pseudomonas aeruginosa effectively facilitate resistance to phagocyte killing by biofilm formation. However, the cross talk between biofilm components and phagocytes is still unclear. We hypothesize that a biofilm provides a concentrated extracellular source of LPS, DNA and exopolysaccharides (EPS), which polarize neighbouring phagocytes into an adverse hyperinflammatory state of activation.

Methods

We measured the release of a panel of mediators produced in vitro by murine neutrophils and macrophages exposed to various biofilm components of P. aeruginosa cultures.

Results

We found that conditioned media from a high biofilm-producing strain of P. aeruginosa, PAR5, accumulated high concentrations of extracellular bacterial LPS, DNA and EPS by 72 h. These conditioned media induced phagocytes to release a hyperinflammatory pattern of mediators, with enhanced levels of TNF-α, IL-6, IL12p40, PGE₂ and NO. Moreover, the phagocytes also upregulated COX-2 and iNOS with no influence on the expression of arginase-1.

Conclusions

Phagocytes exposed to biofilm microenvironment, called by us biofilm-associated neutrophils/macrophages (BANs/BAMs), display secretory properties similar to that of N1/M1-type phagocytes. These results suggest that in vivo high concentrations of LPS and DNA, trapped in biofilm by EPS, might convert infiltrating phagocytes into cells responsible for tissue injury without direct contact with bacteria and phagocytosis.

Subgingival lipid A profile and endotoxin activity in periodontal health and disease

OBJECTIVES

Regulation of lipopolysaccharide (LPS) chemical composition, particularly its lipid A domain, is an important, naturally occurring mechanism that drives bacteria-host immune system interactions into either a symbiotic or pathogenic relationship. Members of the subgingival oral microbiota can critically modulate host immuno-inflammatory responses by synthesizing different LPS isoforms. The objectives of this study were to analyze subgingival lipid A profiles and endotoxin activities in periodontal health and disease and to evaluate the use of the recombinant factor C assay as a new, lipid A-based biosensor for personalized, point-of-care periodontal therapy.

MATERIALS AND METHODS

Subgingival plaque samples were collected from healthy individuals and chronic periodontitis patients before and after periodontal therapy. Chemical composition of subgingival lipid A moieties was determined by ESI-Mass Spectrometry. Endotoxin activity of subgingival LPS extracts was assessed using the recombinant factor C assay, and their inflammatory potential was examined in THP-1-derived macrophages by measuring TNF-α and IL-8 production.

RESULTS

Characteristic lipid A molecular signatures, corresponding to over-acylated, bi-phosphorylated lipid A isoforms, were observed in diseased samples. Healthy and post-treatment samples were characterized by lower m/z peaks, related to under-acylated, hypo-phosphorylated lipid A structures. Endotoxin activity levels and inflammatory potentials of subgingival LPS extracts from periodontitis patients were significantly higher compared to healthy and post-treatment samples.

CONCLUSIONS

This is the first study to consider structure-function-clinical implications of different lipid A isoforms present in the subgingival niche and sheds new light on molecular pathogenic mechanisms of subgingival biofilm communities.

CLINICAL RELEVANCE

Subgingival endotoxin activity (determined by lipid A chemical composition) could be a reliable, bacterially derived biomarker and a risk assessment tool for personalized periodontal care.

Mass Spectrometry-based Structural Analysis and Systems Immunoproteomics Strategies for Deciphering the Host Response to Endotoxin

One cause of sepsis is systemic maladaptive immune response of the host to bacteria and specifically, to Gram-negative bacterial outer-membrane glycolipid lipopolysaccharide (LPS). On the host myeloid cell surface, proinflammatory LPS activates the innate immune system via Toll-like receptor-4/myeloid differentiation factor-2 complex. Intracellularly, LPS is also sensed by the noncanonical inflammasome through caspase-11 in mice and 4/5 in humans. The minimal functional determinant for innate immune activation is the membrane anchor of LPS called lipid A. Even subtle modifications to the lipid A scaffold can enable, diminish, or abolish immune activation. Bacteria are known to modify their LPS structure during environmental stress and infection of hosts to alter cellular immune phenotypes. In this review, we describe how mass spectrometry-based structural analysis of endotoxin helped uncover major determinations of molecular pathogenesis. Through characterization of LPS modifications, we now better understand resistance to antibiotics and cationic antimicrobial peptides, as well as how the environment impacts overall endotoxin structure. In addition, mass spectrometry-based systems immunoproteomics approaches can assist in elucidating the immune response against LPS. Many regulatory proteins have been characterized through proteomics and global/targeted analysis of protein modifications, enabling the discovery and characterization of novel endotoxin-mediated protein translational modifications.

Comprehensive analysis of clinical Burkholderia pseudomallei isolates demonstrates conservation of unique lipid A structure and TLR4-dependent innate immune activation

Burkholderia pseudomallei is an environmental bacterium that causes melioidosis, a major community-acquired infection in tropical regions. Melioidosis presents with a range of clinical symptoms, is often characterized by a robust inflammatory response, may relapse after treatment, and results in high mortality rates. Lipopolysaccharide (LPS) of B. pseudomallei is a potent immunostimulatory molecule comprised of lipid A, core, and O-polysaccharide (OPS) components. Four B. pseudomallei LPS types have been described based on SDS-PAGE patterns that represent the difference of OPS-type A, type B, type B2 and rough LPS. The majority of B. pseudomallei isolates are type A. We used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) followed by electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QqTOF MS) and gas chromatography to characterize the lipid A of B. pseudomallei within LPS type A isolates. We determined that B. pseudomallei lipid A is represented by penta- and tetra-acylated species modified with 4-amino-4-deoxy-arabinose (Ara4N). The MALDI-TOF profiles from 171 clinical B. pseudomallei isolates, including 68 paired primary and relapse isolates and 35 within-host isolates were similar. We did not observe lipid A structural changes when the bacteria were cultured in different growth conditions. Dose-dependent NF-κB activation in HEK cells expressing TLR4 was observed using multiple heat-killed B. pseudomallei isolates and corresponding purified LPS. We demonstrated that TLR4-dependent NF-κB activation induced by heat-killed bacteria or LPS prepared from OPS deficient mutant was significantly greater than those induced by wild type B. pseudomallei. These findings suggest that the structure of B. pseudomallei lipid A is highly conserved in a wide variety of clinical and environmental circumstances but that the presence of OPS may modulate LPS-driven innate immune responses in melioidosis.

Structure-Activity Relationship of Plesiomonas shigelloides Lipid A to the Production of TNF-α, IL-1β, and IL-6 by Human and Murine Macrophages

Plesiomonas shigelloides is a Gram-negative bacterium that is associated with diarrheal disease in humans. Lipopolysaccharide (LPS) is the main surface antigen and virulence factor of this bacterium. The lipid A (LA) moiety of LPS is the main region recognized by target cells of immune system. Here, we evaluated the biological activities of P. shigelloides LA for their abilities to induce the productions of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) by human and murine macrophages [THP-1 macrophages and immortalized murine bone marrow-derived macrophages (iBMDM)]. Four native P. shigelloides LA preparations differing in their phosphoethanolamine (PEtn) substitution, length, number, and saturation of fatty acids were compared with Escherichia coli O55 LA. The bisphosphorylated, hexaacylated, and asymmetric forms of the P. shigelloides and E. coli LA molecules had similar activities in human and murine macrophages, indicating that shortening of the acyl chains in P. shigelloides LA had no effect on its in vitro activities. The PEtn decoration also had no impact on the interaction with the toll-like receptor 4/MD-2 receptor complex. The heptaacylated form of P. shigelloides LA decorated with 16:0 exhibited strong effect on proinflammatory activity, significantly decreasing the levels of all tested cytokines in both murine and human macrophages. Our results revealed that despite the presence of shorter acyl chains and an unsaturated acyl residue (16:1), the bisphosphorylated, hexaacylated, and asymmetric forms of P. shigelloides LA represent highly immunostimulatory structures.

Microbiota, Immune Subversion, and Chronic Inflammation

Several host-adapted pathogens and commensals have evolved mechanisms to evade the host innate immune system inducing a state of low-grade inflammation. Epidemiological studies have also documented the association of a subset of these microorganisms with chronic inflammatory disorders. In this review, we summarize recent studies demonstrating the role of the microbiota in chronic inflammatory diseases and discuss how specific microorganisms subvert or inhibit protective signaling normally induced by toll-like receptors (TLRs). We highlight our work on the oral pathogen Porphyromonas gingivalis and discuss the role of microbial modulation of lipid A structures in evasion of TLR4 signaling and resulting systemic immunopathology associated with atherosclerosis. P. gingivalis intrinsically expresses underacylated lipid A moieties and can modify the phosphorylation of lipid A, leading to altered TLR4 signaling. Using P. gingivalis mutant strains expressing distinct lipid A moieties, we demonstrated that expression of antagonist lipid A was associated with P. gingivalis-mediated systemic inflammation and immunopathology, whereas strains expressing agonist lipid A exhibited modest systemic inflammation. Likewise, mice deficient in TLR4 were more susceptible to vascular inflammation after oral infection with P. gingivalis wild-type strain compared to mice possessing functional TLR4. Collectively, our studies support a role for P. gingivalis-mediated dysregulation of innate and adaptive responses resulting in immunopathology and systemic inflammation. We propose that anti-TLR4 interventions must be designed with caution, given the balance between the protective and destructive roles of TLR signaling in response to microbiota and associated immunopathologies.