Escherichia coli Braun Lipoprotein (BLP) exhibits endotoxemia - like pathology in Swiss albino mice

TLR2 and NLRP3 Orchestrate Regulatory Roles in Escherichia coli Infection-Induced Septicemia in Mouse Models

INTRODUCTION

Escherichia coli (E. coli) is a significant commensal gram-negative bacterium that can give rise to various diseases. The roles of Toll-like receptor 2 (TLR2) and the NOD-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome in sepsis induced by E. coli infection remain unclear.

METHODS

In vivo, we investigated differences in mortality, production of inflammatory mediators, organ damage, neutrophil count, and bacterial load during E. coli infection in C57BL/6J mice, as well as in mice deficient in TLR2 or NLRP3. In vitro, we investigated the impact of E. coli on the activation of TLR2 and NLRP3 in macrophages and the influence of TLR2 and NLRP3 on the activation of inflammatory signaling pathways and the secretion of inflammatory mediators in macrophages induced by E. coli infection.

RESULTS

TLR2-deficient (TLR2-/-) and NLRP3-deficient (NLRP3-/-) mice exhibit significantly increased mortality and organ damage after E. coli infection. These mice also show elevated levels of TNF-α and IL-10 in serum and peritoneal lavage fluid. Additionally, TLR2-/- and NLRP3-/- mice display heightened neutrophil recruitment and increased bacterial load in the blood. Furthermore, macrophages from these mice demonstrate a significant reduction in the activation of the MAPK signaling pathway.

CONCLUSION

TLR2 and NLRP3 play crucial roles in modulating inflammatory mediator expression, immune cell recruitment, and bactericidal activity, thereby preventing excessive tissue damage and reducing mortality in E. coli-induced sepsis.

The roles of Braun Lipoprotein in inducing tolerance of bovine endometrium infected by Escherichia coli

Escherichia coli (E. coli), a Gram-negative bacterium, is the primary pathogen responsible for endometritis in dairy cattle. The outer membrane components of E. coli, namely lipopolysaccharide (LPS) and bacterial lipoprotein, have the capacity to trigger the host's innate immune response through pattern recognition receptors (PRRs). Tolerance to bacterial cell wall components, including LPS, may play a crucial role as an essential regulatory mechanism during bacterial infection. However, the precise role of Braun lipoprotein (BLP) tolerance in E. coli-induced endometritis in dairy cattle remains unclear. In this study, we aimed to investigate the impact of BLP on the regulation of E. coli infection-induced endometritis in dairy cattle. The presence of BLP was found to diminish the expression and release of proinflammatory cytokines (IL-8 and IL-6), while concurrently promoting the expression and release of the anti-inflammatory cytokine IL-10 in endometrial epithelial cells (EECs). Furthermore, BLP demonstrated the ability to impede the activation of MAPK (ERK and p38) and NF-κB (p65) signaling pathways, while simultaneously enhancing signaling through the STAT3 pathway in EECs. Notably, BLP exhibited a dual role, acting both as an activator of TLR2 and as a regulator of TLR2 activation in LPS- and E. coli-treated EECs. In E. coli-infected endometrial explants, the presence of BLP was noted to decrease the release of proinflammatory cytokines and the expression of HMGB1, while simultaneously enhancing the release of anti-inflammatory cytokines. Collectively, our findings provide evidence that the bacterial component BLP plays a protective role in E. coli-induced endometritis in dairy cattle.

Prostaglandin D2 regulates Escherichia coli-induced inflammatory responses through TLR2, TLR4, and NLRP3 in macrophages

Prostaglandin D2 (PGD2) synthesis is closely associated with the innate immune response mediated by pattern recognition receptors (PPRs). We determined PGD2 synthesis whether mediated by Toll-like receptor 2 (TLR2), TLR4 and Nod-like receptor pyrin domain-containing protein 3 (NLRP3) in Escherichia coli (E. coli)-, lipopolysaccharide (LPS)- and Braun lipoprotein (BLP)-stimulated macrophages. Our data demonstrate that TLR2, TLR4, and NLRP3 could regulate the synthesis of PGD2 through cyclo-oxygenase-2 (COX-2) and hematopoietic PGD synthase (H-PGDS) in E. coli-, LPS- or BLP-stimulated macrophages, suggesting that TLR2, TLR4, and NLRP3 are critical in regulating PGD2 secretion by controlling PGD2 synthetase expression in E. coli-, LPS- or BLP-stimulated macrophages. The H-PGDS (a PGD2 specific synthase) inhibitor pre-treatment could down-regulate the secretion of TNF-α, RANTES and IL-10 in LPS- and E. coli-stimulated macrophage. Meanwhile, H-PGDS inhibitor could down-regulate the secretion of TNF-α, while up-regulated RANTES and IL-10 secretion in BLP-stimulated macrophages, suggesting that PGD2 could regulate the secretion of cytokines and chemokines in E. coli-, LPS- or BLP-stimulated macrophages. Furthermore, exogenous PGD2 regulates the secretion of cytokines and chemokines through activation of MAPK and NF-κB signaling pathways after E. coli-, LPS- or BLP stimulation in macrophages. Taken together, PGD2 is found able to regulate E. coli-induced inflammatory responses through TLR2, TLR4, and NLRP3 in macrophages.

Besides TLR2 and TLR4, NLRP3 is also involved in regulating Escherichia coli infection-induced inflammatory responses in mice

The host Toll-like Receptor-2 (TLR2) and Toll-like Receptor-4 (TLR4) play critical roles in defense against Escherichia coli (E. coli) infection is well-known. The NLR pyrin domain-containing 3 (NLRP3) inflammasome is also an important candidate during the host-recognized pathogen, while the roles of NLRP3 in the host inflammatory response to E. coli infection remains unclear. This study aimed to explore the roles of NLRP3 in regulating the inflammatory response in E. coli infection-induced mice. Our result indicated that compared to wild-type mice, the TLR2-deficient (TLR2^-/-), TLR4-deficient (TLR4^-/-), and NLRP3-deficient (NLRP3^-/-) mice had significant decrease in liver damage after stimulation with Lipopolysaccharide (LPS, 1 μg/mL), Braun lipoprotein (BLP, 1 μg/mL), or infected by WT E. coli (1 × 10⁷ CFU, MOI 5:1). Meanwhile, compared with wild-type mice, the TNF-α and IL-1β production in serum decreased in TLR2^-/-, TLR4^-/-, and NLRP3^-/- mice after LPS, BLP treatment, or WT E. coli infection. In macrophages from NLRP3^-/- mice showed significantly reduced secretion of TNF-α and IL-1β in response to stimulation with LPS, BLP, or WT E. coli infection compared with macrophages from wild-type mice. These results indicate that besides TLR2 and TLR4, NLRP3 also plays a critical role in host inflammatory responses to defense against E. coli infection, and might provide a therapeutic target in combating disease with bacterium infection.

Braun Lipoprotein Protects against Escherichia coli-Induced Inflammatory Responses and Lethality in Mice

Escherichia coli (E. coli), a Gram-negative bacterium, is an important pathogen that causes several mammalian diseases. The outer membrane components of E. coli, namely, lipopolysaccharide (LPS) and bacterial lipoprotein, can induce the host innate immune response through pattern recognition receptors (PRRs). However, the detailed roles of the E. coli Braun lipoprotein (BLP) in the regulation of host inflammatory response to E. coli infection remain unclear. In this study, we sought to determine the effects of BLP on E. coli-induced host inflammatory response and lethality using mouse models. Experiments using the E. coli DH5α strain (BLP-positive), E. coli JE5505 strain (BLP-negative), and E. coli JE5505 strain combined with BLP indicated that the presence of BLP could alleviate mortality and organ (liver and lung) damage and decrease proinflammatory cytokine (tumor necrosis factor alpha [TNF-α] and interleukin-1β [IL-1β]) and chemokine (regulated on activation normal T-cell expressed and secreted [RANTES]) production in mouse serum and organs. Conversely, E. coli JE5505, E. coli DH5α strain, and E. coli JE5505 combined with BLP treatment induce enhanced anti-inflammatory cytokine (interleukin 10 [IL-10]) production in mouse serum and organs. In addition, BLP could regulate the secretion of proinflammatory cytokines (TNF-α and IL-1β), chemokines (RANTES), and anti-inflammatory factors (IL-10) through mitogen-activated protein kinase (MAPK) and nuclear factor-kappaB (NF-κB) signaling pathways in macrophages. Altogether, our results demonstrate that the bacterial component BLP plays crucial and protective roles in E. coli-infected mice, which may influence the outcome of inflammation in host response to E. coli infection. IMPORTANCE In this study, we investigated the roles of bacterial outer membrane component BLP in regulating inflammatory responses and lethality in mice that were induced by a ubiquitous and serious pathogen, Escherichia coli. BLP could alleviate the mortality of mice and organ damage, as well as decrease proinflammatory cytokines and chemokine production and enhance anti-inflammatory cytokine production in mouse serum and organs. Overall, our results demonstrate that the bacterial component BLP plays crucial and protective roles in E. coli-infected mice through regulating the production of an inflammatory mediator, which may influence the outcome of inflammation in host response to E. coli infection. Our findings provide new information about the basic biology involved in immune responses to E. coli and host-bacterial interactions, which have the potential to translate into novel approaches for the diagnosis and treatment of E. coli-related medical conditions, such as bacteremia and sepsis.

Reversible cross-tolerance to platelet-activating factor signaling by bacterial toxins

Bacterial toxins signaling through Toll-like receptors (TLRs) are implicated in the pathogenesis of many inflammatory diseases. Among the toxins, lipopolysaccharide (LPS) exerts its action via TLR-4 while lipoteichoic acid (LTA) and bacterial lipoproteins such as Braun lipoprotein (BLP) or its synthetic analogue Pam3CSK4 act through TLR-2. Part of the TLR mediated pathogenicity is believed to stem from endogenously biosynthesized platelet-activating factor (PAF)- a potent inflammatory phospholipid acting through PAF-receptor (PAF-R). However, the role of PAF in inflammatory diseases like endotoxemia is controversial. In order to test the direct contribution of PAF in TLR-mediated pathogenicity, we intraperitoneally injected PAF to Wistar albino mice in the presence or absence of bacterial toxins. Intraperitoneal injection of PAF (5 μg/mouse) causes sudden death of mice, that can be delayed by simultaneously or pre-treating the animals with high doses of bacterial toxins- a phenomenon known as endotoxin cross-tolerance. The bacterial toxins- induced tolerance to PAF can be reversed by increasing the concentration of PAF suggesting the reversibility of cross-tolerance. We did similar experiments using human platelets that express both canonical PAF-R and TLRs. Although bacterial toxins did not induce human platelet aggregation, they inhibited PAF-induced platelet aggregation in a reversible manner. Using rabbit platelets that are ultrasensitive to PAF, we found bacterial toxins (LPS and LTA) and Pam3CSK4 causing rabbit platelet aggregation via PAF-R dependent way. The physical interaction of PAF-R and bacterial toxins is also demonstrated in a human epidermal cell line having stable PAF-R expression. Thus, we suggest the possibility of direct physical interaction of bacterial toxins with PAF-R leading to cross-tolerance.

Bacterial lipoproteins in sepsis

Bacterial lipoproteins are membrane proteins derived from both gram-negative and gram-positive bacteria. They seem to have diverse functions not only on bacterial growth, but also play an important role in host's virulence. Bacterial lipoproteins exert their action on host immune cells via TLR2/1 or TLR2/6. Therefore, bacterial lipoproteins also need to be considered while addressing bacterial pathogenicity besides classical bacterial endotoxin like LPS and other microbial associated molecular patterns such as LTA, and peptidoglycans. In this mini-review, we provide an overview of general bacterial lipoprotein biosynthesis and the need to understand the lipoprotein-mediated pathogenicity in diseases like sepsis.

Protective Effects of Idebenone against Sepsis Induced Acute Lung Damage

BACKGROUND/AIMS

Sepsis is an uncontrolled systemic infection, withcomplex pathophysiology that may result in acute lung organ damage and cause multiple organ failure. Although much research has been conducted to illuminate sepsis's complex pathophysiology, sepsis treatment protocols are limited, and sepsis remains an important cause of mortality andmorbidity in intensive care units.Various studies have shown that idebenone (IDE) possesses strong antioxidant properties, which inhibit lipid peroxidation and protect cells from oxidative damage. The present study aimed to evaluate the protective effects of IDE against lung injury in a cecal ligation and puncture (CLP)-induced sepsis rat model.

METHODS

Male albino Wistar rats were used. The animals were divided into a healthy control (no treatment), CLP, IDE control (200 mg/kg), and CLP + IDE subgroups (50 mg/kg, 100 mg/kg, and 200 mg/kg), with nine rats in each group.IDE was administered 1 h after CLP induction.To evaluate the protective effects of IDE, lung tissues were collected 16 h after sepsis for biochemical, immunohistochemical staining, and histopathological examination.

RESULTS

IDE significantly ameliorated sepsis-induced disturbances in oxidative stress-related factors, with its effects increasing in accordance with the dose.IDE also abolished histopathological changes in lung tissues associated with CLP.Furthermore, interleukin 1 beta (IL-1β)and tumor necrosis factor-alpha (TNF-α) immunopositivity markedly decreased in the septic rats following IDE treatment.

CONCLUSIONS

IDE largely mitigated the inflammatory response in sepsis-induced lung injury by decreasing free radicals and preventing lipid peroxidation. The results suggest that IDE may represent a potential novel therapeutic drug for sepsis treatment.

Different glycoforms of alpha-1-acid glycoprotein contribute to its functional alterations in platelets and neutrophils

Alpha-1-acid glycoprotein (AGP-1) is a positive acute phase glycoprotein with uncertain functions. Serum AGP-1 (sAGP-1) is primarily derived from hepatocytes and circulates as 12-20 different glycoforms. We isolated a glycoform secreted from platelet-activating factor (PAF)-stimulated human neutrophils (nAGP-1). Its peptide sequence was identical to hepatocyte-derived sAGP-1, but nAGP-1 differed from sAGP-1 in its chromatographic behavior, electrophoretic mobility, and pattern of glycosylation. The function of these 2 glycoforms also differed. sAGP-1 activated neutrophil adhesion, migration, and neutrophil extracellular traps (NETosis) involving myeloperoxidase, peptidylarginine deiminase 4, and phosphorylation of ERK in a dose-dependent fashion, whereas nAGP-1 was ineffective as an agonist for these events. Furthermore, sAGP-1, but not nAGP-1, inhibited LPS-stimulated NETosis. Interestingly, nAGP-1 inhibited sAGP-1-stimulated neutrophil NETosis. The discordant effect of the differentially glycosylated AGP-1 glycoforms was also observed in platelets where neither of the AGP-1 glycoforms alone stimulated aggregation of washed human platelets, but sAGP-1, and not nAGP-1, inhibited aggregation induced by PAF or ADP, but not by thrombin. These functional effects of sAGP-1 correlated with intracellular cAMP accumulation and phosphorylation of the protein kinase A substrate vasodilator-stimulated phosphoprotein and reduction of Akt, ERK, and p38 phosphorylation. Thus, the sAGP-1 glycoform limits platelet reactivity, whereas nAGP-1 glycoform also limits proinflammatory actions of sAGP-1. These studies identify new functions for this acute phase glycoprotein and demonstrate that the glycosylation of AGP-1 controls its effects on 2 critical cells of acute inflammation.

Biochemical Research of the Effects of Essential Oil Obtained from the Fruit of Myrtus communis L. on Cell Damage Associated with Lipopolysaccharide-Induced Endotoxemia in a Human Umbilical Cord Vein Endothelial Cells

The aim of this study to investigate the potential effects of essential oils and compounds obtained from MC fruit on sepsis induced endothelial cell damage in human umbilical cord vein endothelial cells (HUVECs) at molecular and cellular levels on in vitro sepsis model. A sepsis model was induced by the application of LPS. The HUVEC treatment groups were as follows: control, LPS, MC, MC plus LPS, 1.8 cineole, 1.8 cineole plus LPS, α-pinene, α-pinene plus LPS, α-terpineol, and α-terpineol plus LPS. Following the treatments, cell proliferation was analyzed using the xCELLigence® system. The mRNA expression of various cytokines [tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), and IL-6] and endothelial nitric oxide (eNOS) were determined by quantitative polymerase chain reaction (qPCR) analysis. The 1.8 cineole and α-pinene treatments at specific doses showed toxic effects on α-terpineine, although it did not result in a change in the cellular index as compared with that of the control group. The application of LPS to HUVECs led to a significant decrease in the cellular index, depending on the treatment time. It did not correct the decreased cell index of MC plus LPS and α-terpineol plus LPS groups as compared with that of the LPS-only group. The 1.8 cineole plus LPS treatment and α-pinene plus LPS treatment significantly increased the cell index as compared with that of the LPS-only treatment, and the cell index in these groups was closer to that of the control. According to the results of the qPCR analysis, neither the MC-only treatment nor the α-terpineol-only treatment significantly reduced cellular damage caused by LPS-induced increases in TNF-α, IL-1β, IL-6, and eNOS mRNA expression. However, both the 1.8 cineole treatment and α-pinene treatments significantly decreased TNF-α, IL-1β, IL-6, and eNOS mRNA expression induced by LPS. Volatile oil obtained from MC fruit and the MC compound α-terpineol had no effect on the decreased cell index and increased cytokine response due to LPS-induced endothelial cell damage. However, 1.8 cineole and α-pinene, other major components of MC fruit, ameliorated LPS-induced damage in HUVECs at cellular and biomolecular levels (TNF-α, IL-1β, IL-6, and eNOS).

Acute phase protein, α - 1- acid glycoprotein (AGP-1), has differential effects on TLR-2 and TLR-4 mediated responses

Alpha-1-acid glycoprotein (AGP-1) is a major positive acute phase glycoprotein with unknown functions that likely play a role in inflammation. We tested its involvement in a variety of inflammatory responses using human AGP-1 purified to apparent homogeneity and confirmed its identity by immunoblotting and mass spectrometry. AGP-1 alone upregulated MAPK signaling in murine peritoneal macrophages. However, when given in combination with TLR ligands, AGP-1 selectively augmented MAPK activation induced by ligands of TLR-2 (Braun lipoprotein) but not TLR-4 (lipopolysaccharide). In vivo treatment of AGP-1 in a murine model of sepsis with or without TLR-2 or TLR-4 ligands, selectively potentiated TLR-2-mediated mortality, but was without significant effect on TLR-4-mediated mortality. Furthermore, in vitro, AGP-1 selectively potentiated TLR-2 mediated adhesion of human primary immune cell, neutrophils. Hence, our studies highlight a new role for the acute phase protein AGP-1 in sepsis via its interaction with TLR-2 signaling mechanisms to selectively promote responsiveness to one of the two major gram-negative endotoxins, contributing to the complicated pathobiology of sepsis.

Caspase-1 inhibitor exerts brain-protective effects against sepsis-associated encephalopathy and cognitive impairments in a mouse model of sepsis

Sepsis-associated encephalopathy (SAE) manifested clinically in acute and long-term cognitive impairments and associated with increased morbidity and mortality worldwide. The potential pathological changes of SAE are complex and remain to be elucidated. Pyroptosis, a novel programmed cell death, is executed by caspase-1-cleaved GSDMD N-terminal (GSDMD-NT) and we investigated it in peripheral blood immunocytes of septic patients previously. Here, a caspase-1 inhibitor VX765 was treated with CLP-induced septic mice. Novel object recognition test indicated that VX765 treatment reversed cognitive dysfunction in septic mice. Elevated plus maze, tail suspension test and open field test revealed that depressive-like behaviors of septic mice were relieved. Inhibited caspase-1 suppressed the expressions of GSDMD and its cleavage form GSDMD-NT, and reduced pyroptosis in brain at day 1 and day 7 after sepsis. Meantime, inhibited caspase-1 mitigated the expressions of IL-1β, MCP-1 and TNF-α in serum and brain, diminished microglia activation in septic mice, and reduced sepsis-induced brain-blood barrier disruption and ultrastructure damages in brain as well. Inhibited caspase-1 protected the synapse plasticity and preserved long-term potential, which may be the possible mechanism of cognitive functions protective effects of septic mice. In conclusion, caspase-1 inhibition exerts brain-protective effects against SAE and cognitive impairments in a mouse model of sepsis.

Modulation of inflammatory platelet-activating factor (PAF) receptor by the acyl analogue of PAF

Platelet-activating factor (PAF) is a potent inflammatory mediator that exerts its actions via the single PAF receptor (PAF-R). Cells that biosynthesize alkyl-PAF also make abundant amounts of the less potent PAF analogue acyl-PAF, which competes for PAF-R. Both PAF species are degraded by the plasma form of PAF acetylhydrolase (PAF-AH). We examined whether cogenerated acyl-PAF protects alkyl-PAF from systemic degradation by acting as a sacrificial substrate to enhance inflammatory stimulation or as an inhibitor to dampen PAF-R signaling. In ex vivo experiments both PAF species are prothrombotic in isolation, but acyl-PAF reduced the alkyl-PAF-induced stimulation of human platelets that express canonical PAF-R. In Swiss albino mice, alkyl-PAF causes sudden death, but this effect can also be suppressed by simultaneously administering boluses of acyl-PAF. When PAF-AH levels were incrementally elevated, the protective effect of acyl-PAF on alkyl-PAF-induced death was serially decreased. We conclude that, although acyl-PAF in isolation is mildly proinflammatory, in a pathophysiological setting abundant acyl-PAF suppresses the action of alkyl-PAF. These studies provide evidence for a previously unrecognized role for acyl-PAF as an inflammatory set-point modulator that regulates both PAF-R signaling and hydrolysis.

Class A CpG Oligonucleotide Priming Rescues Mice from Septic Shock via Activation of Platelet-Activating Factor Acetylhydrolase

Sepsis is a life-threatening, overwhelming immune response to infection with high morbidity and mortality. Inflammatory response and blood clotting are caused by sepsis, which induces serious organ damage and death from shock. As a mechanism of pathogenesis, platelet-activating factor (PAF) induces excessive inflammatory responses and blood clotting. In this study, we demonstrate that a Class A CpG oligodeoxynucleotide (CpG-A₁₅₈₅) strongly induced PAF acetylhydrolase, which generates lyso-PAF. CpG-A₁₅₈₅ rescued mice from acute lethal shock and decreased fibrin deposition, a hallmark of PAF-induced disseminated intravascular coagulation. Furthermore, CpG-A₁₅₈₅ improved endotoxin shock induced by lipopolysaccharide, which comprises the cell wall of Gram-negative bacteria and inhibits inflammatory responses induced by cytokines such as interleukin-6 and tumor necrosis factor-α. These results suggest that CpG-A₁₅₈₅ is a potential therapeutic target to prevent sepsis-related induction of PAF.