Shedding light on the molecular and regulatory mechanisms of TLR4 signaling in endothelial cells under physiological and inflamed conditions

Heat shock protein family D member 1 mediates lung cancer cell‑induced angiogenesis of endothelial cells

Angiogenesis is a crucial process in lung cancer growth and progression. Heat shock protein family D member 1 (HSPD1 or HSP60) plays a significant role in promoting lung cancer development, but its role in angiogenesis remains largely unexplored. The present study aimed to investigate the involvement of HSPD1 in lung cancer cell-induced angiogenesis using indirect co-culture experiments. Secretomes were collected from stable HSPD1-knockdown A549 lung cancer cells [short hairpin (sh)HSPD1-A549 cells] and scramble control cells (shControl-A549 cells) and used to treat human endothelial EA.hy926 cells. Effects of the secretomes on key steps of angiogenesis, including endothelial cell proliferation, migration, invasion, aggregation and tube formation, were assessed using BrdU incorporation, wound healing, Transwell invasion, hanging-drop and Matrigel tube formation assays, respectively. The amount of vascular endothelial growth factor (VEGF) secreted by EA.hy926 cells was determined using ELISA. The correlation of VEGFA expression with HSPD1 expression and overall survival in patients with lung adenocarcinoma was evaluated using bioinformatics analysis. The results revealed that the shControl-A549 secretome markedly stimulated endothelial cell proliferation, migration, invasion, aggregation, tube formation and VEGF secretion, whereas the shHSPD1-A549 secretome had no significant effects on these processes. VEGFA expression was markedly associated with HSPD1 expression and overall survival in patients with lung adenocarcinoma. In conclusion, the findings highlighted the role of HSPD1 in promoting angiogenesis capability of endothelial cells, potentially through VEGF-mediated pathways. Targeting HSPD1 may represent a promising therapeutic strategy to inhibit angiogenesis and improve clinical outcomes in lung cancer patients.

Anserine reduces mortality in experimental sepsis by preventing methylglyoxal-induced capillary leakage

BACKGROUND

We previously identified methylglyoxal as a biomarker for early identification and outcome prediction in human sepsis. We hypothesised that methylglyoxal causally impacts disease severity, and the methylglyoxal-scavenging dipeptide anserine can attenuate the detrimental effects of methylglyoxal.

METHODS

Using a translational approach, secondary analyses of two observational trials were performed to test the initial hypotheses. Afterwards, these results were re-evaluated in different murine models of experimental sepsis in vivo. The detrimental effects of methylglyoxal as well as the underlying mechanisms were further assessed in vitro using transendothelial electrical resistance measurements, fluorescence-activated cell sorting analyses, cytokine assays, gene expression analyses, and enzyme activity assays, as well as immunofluorescence and immunohistochemistry staining.

FINDINGS

The secondary analyses confirmed methylglyoxal as an independent marker associated with increased mortality within the first 48 h after sepsis onset and high catecholamine and fluid requirements in the first 24 h after sepsis onset. In the sepsis models, methylglyoxal-derived carbonyl stress significantly contributed to the development of capillary leakage by disrupting endothelial barrier-forming proteins. Mechanistically, a pathway involving the receptor of advanced glycation end products and mitogen-activated protein kinase was identified. The methylglyoxal-scavenging dipeptide anserine (β-alanyl-N-methylhistidine) reduced methylglyoxal-induced advanced glycation end-product formation and disruptions of junctional complexes in vitro. Moreover, anserine reduced capillary leakage and mortality in vivo.

INTERPRETATION

Methylglyoxal causally contributes to capillary leak formation and mortality in experimental sepsis, which can be mitigated by anserine. Therefore, anserine represents an innovative therapeutic option for the treatment of septic shock.

FUNDING

German Research Foundation (grant number BR 4144/2-1).

Supplementation with Lentil (Lens culinaris) Hull Soluble Dietary Fiber Ameliorates Sodium Dextran Sulfate-Induced Colitis and Behavioral Deficits via the Gut-Brain Axis

In this study, the impact of lentil hull soluble dietary fibers (SDFs) on colitis and behavioral deficits in mice was assessed. Structural characterizations of SDFs confirmed that cellulase-modified soluble dietary fiber exhibited better physicochemical properties: more porous microstructure; similar polysaccharide structure; more stable particle size distribution; higher crystallinity; better adsorption capacity; and lower viscosity. Additionally, we explored its potential cognitive benefits via the gut-brain axis by behavioral tests, histopathology, 16S rRNA sequencing, gas chromatography and metabolomics analysis. The results showed that SDFs significantly improved inflammatory symptoms in colon and brain and cognitive behaviors. LSDF had better efficacy than HSDF. LSDF intervention decreased the harmful bacteria abundance (Bacteroides, Flexispira and Escherichia, etc.) and increased beneficial bacteria abundance (Aggregatibacter and Helicobacter, etc.). LSDF also affected brain metabolites through the sphingolipid metabolism. Spearman correlation analysis showed that there was a positive correlation between harmful bacteria with inflammatory factors (LPS, IL-1β, IL-6, and TNF-α, etc.) and sphingolipid metabolites, while beneficial bacteria were positively correlated with brain-derived neurotrophic factor (BDNF), IL-10, and cognitive behavior. This study highlights the value of SDFs in future diet-based therapeutic strategies targeting gut-brain interactions.

Discovery of New 4-Aminoquinoline-Thiazolidinone Hybrid Analogs as Antiproliferative Agents Inhibiting TLR4-LPS-Mediated Migration in Triple-Negative Breast Cancer Cells

The Toll-like receptor 4 (TLR4) signaling pathway plays a leading role in triggering proinflammatory responses by targeting lipopolysaccharide (LPS) molecules from different bacteria. Meanwhile, it is also expressed at higher levels in breast cancer cells than in normal breast tissue. After LPS binding, it initiates downstream signaling pathways that promote inflammation and cell apoptosis. Thus, targeting TLR4-LPS presents a promising dual therapeutic strategy for breast cancer treatment by not only inhibiting tumor growth but also reducing inflammation within the tumor microenvironment. To achieve this, the discovery of a new antiinflammatory agent is needed to reduce LPS-mediated cancer cell proliferation and migration. In this study, a series of 4-aminoquinoline-thiazolidinone hybrid analogs (4a-m) have been synthesized to explore their antiinflammatory as well as anticancer activity to find a new lead. Among them, 4e revealed the most promising antiinflammatory (IC50 = 2.38 ± 0.77 μM) as well as anticancer activity (IC50 = 3.26 ± 1.06 μM) in RAW 267.7 cell line and triple-negative breast cancer (TNBC) cell line, respectively. Further structure-activity relationship study followed by MD simulation analysis was carried out to identify probable binding residues of TLR4 which may play a significant role in developing antiinflammatory activity for promoting cell apoptosis in cancer cells.

Innate immune sensors and regulators at the blood brain barrier: focus on toll-like receptors and inflammasomes as mediators of neuro-immune crosstalk and inflammation

Cerebral endothelial cells (CEC) that form the brain capillaries are the principal constituents of the blood brain barrier (BBB), the main active interface between the blood and the brain which plays a protective role by restricting the infiltration of pathogens, harmful substances and immune cells into the brain while allowing the entry of essential nutrients. Aberrant CEC function often leads to increased permeability of the BBB altering the bidirectional communication between the brain and the bloodstream and facilitating the extravasation of immune cells into the brain. In addition to their role as essential gatekeepers of the BBB, CEC exhibit immune cell properties as they can receive and transmit signals between the blood and the brain partly via release of inflammatory effectors in pathological conditions. Cerebral endothelial cells express innate immune receptors, including toll like receptors (TLRs) and inflammasomes which are the first sensors of exogenous or endogenous dangers and initiators of immune and inflammatory responses which drive neural dysfunction and degeneration. Accumulating evidence indicates that activation of TLRs and inflammasomes in CEC compromises BBB integrity, promotes aberrant neuroimmune interactions and modulates both systemic and neuroinflammation, common pathological features of neurodegenerative and psychiatric diseases and central nervous system (CNS) infections and injuries. The goal of the present review is to provide an overview of the pivotal roles played by TLRs and inflammasomes in CEC function and discuss the molecular and cellular mechanisms by which they contribute to BBB disruption and neuroinflammation especially in the context of traumatic and ischemic brain injuries and brain infections. We will especially focus on the most recent advances and literature reports in the field to highlight the knowledge gaps. We will discuss future research directions that can advance our understanding of the central contribution of innate immune receptors to CEC and BBB dysfunction and the potential of innate immune receptors at the BBB as promising therapeutic targets in a wide variety of pathological conditions of the brain.

Structural Diversity and Mutational Challenges of Toll-Like Receptor 4 Antagonists as Inflammatory Pathway Blocker

Toll-like receptor 4 (TLR4) is an important mediator that activates bacterial inflammation through its signaling pathway. It binds lipopolysaccharide (LPS) in the presence of myeloid differentiation protein 2 (MD2) to dimerise the TLR4-MD2-LPS complex. The TLR4 mediated signaling pathway stimulates cytokine production in humans, initiating inflammatory responses. Overactivation of the TLR4 pathway can trigger binding of LPS to the TLR4-MD2 complex, which may lead to the development of several inflammatory disorders. Therefore, the TLR4-MD2 complex is a potential therapeutic target for the identification of new and effective anti-inflammatory agents. Various biologically active TLR4 and MD2 targeting natural and synthetic molecules are explored with anti-inflammatory activity in micromolar ranges. But no FDA-approved drugs are available in the market as of now, and some are discontinued in clinical trials due to drug resistance and severe side effects. In this review, we have assessed recent molecular advancements in TLR4-MD2 antagonists which are showing direct inhibition in lower micro and nanomolar levels. Along with it, protein informatics analysis of the binding pockets of wild type and mutated TLR4-MD2 proteins are also discussed here to give a new insight about the changes in physicochemical properties of the ligand binding area. We have also pointed out several important residues in three different sites of the large LPS binding pocket of TLR4-MD2 complex to understand probable binding affinity of small molecule inhibitors (SMIs). In addition, the present status of clinical trials for TLR4 antagonists is also reviewed. The current assessment will pave a future perspective to design different small molecules as a direct inhibitor of TLR4-MD2 complex for anti-inflammatory activities.

Force Nanoscopy Demonstrates Stress-Activated Adhesion between Staphylococcus aureus Iron-Regulated Surface Determinant Protein B and Host Toll-like Receptor 4

The Staphylococcus aureus iron-regulated surface determinant protein B (IsdB) has recently been shown to bind to toll-like receptor 4 (TLR4), thereby inducing a strong inflammatory response in innate immune cells. Currently, two unsolved questions are (i) What is the molecular mechanism of the IsdB-TLR4 interaction? and (ii) Does it also play a role in nonimmune systems? Here, we use single-molecule experiments to demonstrate that IsdB binds TLR4 with both weak and extremely strong forces and that the mechanostability of the molecular complex is dramatically increased by physical stress, sustaining forces up to 2000 pN, at a loading rate of 105 pN/s. We also show that TLR4 binding by IsdB mediates time-dependent bacterial adhesion to endothelial cells, pointing to the role of this bond in cell invasion. Our findings point to a function for IsdB in pathogen-host interactions, that is, mediating strong bacterial adhesion to host endothelial cells under fluid shear stress, unknown until now. In nanomedicine, this stress-dependent adhesion represents a potential target for innovative therapeutics against S. aureus-resistant strains.

Immunomodulation of exopolysaccharide produced by Lacticaseibacillus rhamnosus ZFM216 in cyclophosphamide-induced immunosuppressed mice by modulating gut microbiota

This study investigated the immunoregulatory activity of exopolysaccharides (EPS) produced by Lacticaseibacillus rhamnosus ZFM216 in immunosuppressed mice induced by cyclophosphamide (CTX). The results showed that EPS treatment effectively improved the body weight, immune organ index and splenic lymphocyte proliferation. EPS also mitigated the damage of immune organs, restored intestinal morphology, and regulated the levels of serum hemolysin and cytokines (e.g. TNF-α, INF-γ and IL-10). EPS promoted the release of NO, TNF-α, IL-1β, and IL-6 in RAW 264.7 cells, however, such effect was inhibited in the presence of inhibitors of TLR4 and MAPKs signaling pathways-related proteins, confirming that EPS achieved the immunomodulation by activating these two signaling pathways. Additionally, EPS, as a prebiotic, effectively improved the diversity of microbial communities, regulated the relative abundance of dominant microbial communities, restored CTX-induced gut microbiota dysbiosis, and promoted the production of short chain fatty acids (SCFAs) in the gut of mice. Thus, immunoregulatory effect of EPS could be attributed to its good ability to modulate the gut microbiota. EPS produced by L. rhamnosus ZFM216 has promising application as an ingredient of functional foods due to its potent probiotic effect.

Machine learning accelerates the discovery of epitope-based dual-bioactive peptides against skin infections

OBJECTIVES

Skin injuries and infections are an inevitable part of daily human life, particularly with chronic wounds, becoming an increasing socioeconomic burden. In treating skin infections and promoting wound healing, bioactive peptides may hold significant potential, particularly those possessing antimicrobial and anti-inflammatory properties. However, obtaining these peptides solely through traditional wet laboratory experiments is costly and time-consuming, and peptides identified by current computer-assisted predictive models largely lack validation of their effects via wet laboratory experiments. Consequently, this study aimed to integrate computer-assisted methods and traditional wet laboratory experiments to identify anti-inflammatory and antimicrobial peptides.

METHODS

We developed a computer-assisted mining pipeline to screen potential peptides from the epitopes of the major histocompatibility complex class II.

RESULTS

The peptide AIMP1 was identified, with the ability to physically damage Escherichia coli by increasing bacterial cell membrane permeability, and with the ability to inhibit inflammation by binding to endotoxin-lipopolysaccharide. Additionally, in an LPS-induced inflammation animal model, AIMP1 slightly increased levels of proinflammatory cytokines (TNF-α, IL-1β, and IL-6), and in a skin wound infection animal model, AIMP1 effectively accelerated healing, reduced levels of these pro-inflammatory cytokines, and showed no acute hepatotoxicity or nephrotoxicity.

CONCLUSIONS

In conclusion, this study not only developed a computer-assisted mining pipeline for identifying anti-inflammatory and antimicrobial peptides but also successfully pinpointed the peptide AIMP1, demonstrating its therapeutic potential for skin injury treatment.

Supersulphides suppress type-I and type-II interferon responses by blocking JAK/STAT signalling in macrophages

Interferons (IFNs) are cytokines produced and secreted by immune cells when viruses, tumour cells, and so forth, invade the body. Their biological effects are diverse, including antiviral, cell growth-inhibiting, and antitumour effects. The main subclasses of IFNs include type-I (e.g. IFN-α and IFN-β) and type-II (IFN-γ), which activate intracellular signals by binding to type-I and type-II IFN receptors, respectively. We have previously shown that when macrophages are treated with supersulphide donors, which have polysulphide structures in which three or more sulphur atoms are linked within the molecules, IFN-β-induced cellular responses, including signal transducer and activator of transcription 1 (STAT1) phosphorylation and inducible nitric oxide synthase (iNOS) expression, were strongly suppressed. However, the subfamily specificity of the suppression of IFN signals by supersulphides and the mechanism of this suppression are unknown. This study demonstrated that supersulphide donor N-acetyl-L-cysteine tetrasulphide (NAC-S2) can inhibit IFN signalling in macrophages stimulated not only with IFN-α/β but also with IFN-γ. Our data suggest that NAC-S2 blocks phosphorylation of Janus kinases (JAKs), thereby contributing to the inhibition of phosphorylation of STAT1. Under the current experimental conditions, the hydrogen sulphide (H2S) donor NaHS failed to inhibit IFN signalling. Similar to NAC-S2, the carbohydrate-based supersulphide donor thioglucose tetrasulphide (TGS4) was capable of strongly inhibiting tumour necrosis factor-α production, iNOS expression, and nitric oxide production from macrophages stimulated with lipopolysaccharide. Further understanding of the molecular mechanisms by which supersulphide donors exhibit their inhibitory actions towards JAK/STAT signalling is a necessary basis for the development of supersulphide-based therapeutic strategy against autoimmune disorders with dysregulated IFN signalling.

Nets in fibrosis: Bridging innate immunity and tissue remodeling

Fibrosis, a complex pathological process characterized by excessive deposition of extracellular matrix components, leads to tissue scarring and dysfunction. Emerging evidence suggests that neutrophil extracellular traps (NETs), composed of DNA, histones, and antimicrobial proteins, significantly contribute to fibrotic diseases pathogenesis. This review summarizes the process of NETs production, molecular mechanisms, and related diseases, and outlines the cellular and molecular mechanisms associated with fibrosis. Subsequently, this review comprehensively summarizes the current understanding of the intricate interplay between NETs and fibrosis across various organs, including the lung, liver, kidney, skin, and heart. The mechanisms by which NETs contribute to fibrogenesis, including their ability to promote inflammation, induce epithelial-mesenchymal transition (EMT), activate fibroblasts, deposit extracellular matrix (ECM) components, and trigger TLR4 signaling were explored. This review aimed to provide insights into the complex relationship between NETs and fibrosis via a comprehensive analysis of existing reports, offering novel perspectives for future research and therapeutic interventions.

Targeting S100A12 to Improve Angiogenesis and Accelerate Diabetic Wound Healing

Long-term inflammation and impaired angiogenesis are thought to be the causes of delayed healing or nonhealing of diabetic wounds. S100A12 is an essential pro-inflammatory factor involved in inflammatory reactions and serves as a biomarker for various inflammatory diseases. However, whether high level of S100A12 exists in and affects the healing of diabetic wounds, as well as the underlying molecular mechanisms, remain unclear. In this study, we found that the serum concentration of S100A12 is significantly elevated in patients with type 2 diabetes. Exposure of stratified epidermal cells to high glucose environment led to increased expression and secretion of S100A12, resulting in impaired endothelial function by binding to the advanced glycation endproducts (RAGE) or Toll-like receptor 4 (TLR4) on endothelial cell. The transcription factor Krüpple-like Factor 5 (KLF5) is highly expressed in the epidermis under high glucose conditions, activating the transcriptional activity of the S100A12 and boost its expression. By establishing diabetic wounds model in alloxan-induced diabetic rabbit, we found that local inhibition of S100A12 significantly accelerated diabetic wound healing by promoting angiogenesis. Our results illustrated the novel endothelial-specific injury function of S100A12 in diabetic wounds and suggest that S100A12 is a potential target for the treatment of diabetic wounds.

The Influence of Metabolic Risk Factors on the Inflammatory Response Triggered by Myocardial Infarction: Bridging Pathophysiology to Treatment

Myocardial infarction (MI) sets off a complex inflammatory cascade that is crucial for effective cardiac healing and scar formation. Yet, if this response becomes excessive or uncontrolled, it can lead to cardiovascular complications. This review aims to provide a comprehensive overview of the tightly regulated local inflammatory response triggered in the early post-MI phase involving cardiomyocytes, (myo)fibroblasts, endothelial cells, and infiltrating immune cells. Next, we explore how the bone marrow and extramedullary hematopoiesis (such as in the spleen) contribute to sustaining immune cell supply at a cardiac level. Lastly, we discuss recent findings on how metabolic cardiovascular risk factors, including hypercholesterolemia, hypertriglyceridemia, diabetes, and hypertension, disrupt this immunological response and explore the potential modulatory effects of lifestyle habits and pharmacological interventions. Understanding how different metabolic risk factors influence the inflammatory response triggered by MI and unraveling the underlying molecular and cellular mechanisms may pave the way for developing personalized therapeutic approaches based on the patient's metabolic profile. Similarly, delving deeper into the impact of lifestyle modifications on the inflammatory response post-MI is crucial. These insights may enable the adoption of more effective strategies to manage post-MI inflammation and improve cardiovascular health outcomes in a holistic manner.

Establishment of a model of LPS-induced inflammatory injury in human aortic endothelial cells

PURPOSE

We aim to establish an LPS-induced human aortic endothelial cells (HAECs) inflammatory injury model and explore the optimal conditions for inducing its injury. We expect to provide modeling references for the related experiments of vascular inflammatory diseases.

METHODS

HAECs were cultured in vitro and treated with different concentrations of lipopolysaccharide (LPS) (0.1, 1, 10, 50, 100 μg/mL) for 6, 12, and 24 h to establish the HAECs inflammatory injury model. The cell viability was determined by CCK-8 assay; the expression levels of inflammatory cytokines in the cells were detected by RT-PCR；the apoptosis rate of the cells was detected by flow cytometry.

RESULTS

① Within 24 h of LPS treatment, the cell viability of the 0.1 and 1 μg/mL groups showed an overall increasing trend with time, while the cell viability of the 10, 50, and 100 μg/mL groups increased first and then decreased with time, and the cell viability of 50 and 100 μg/mL groups was significantly lower than the normal control group at 24 h (P<0.01). ② RT-PCR results showed that after 50 and 100 μg/mL LPS for 24 h, the inflammatory cytokines all showed an apparent upward trend compared with the normal control group (P<0.05), which was more significant in the 100 μg/mL group. ③ After 100 μg/mL LPS for 24 h, the apoptotic necrosis rate of HAECs was higher than the normal control group (P<0.01).

CONCLUSIONS

This experiment successfully established a HAECs injury model, indicating that the optimal conditions for inducing injury are an LPS concentration of 100 μg/mL and a treatment time of 24 h.

TRIM56-mediated production of type I interferon inhibits intracellular replication of Rickettsia rickettsii

Rickettsia rickettsii (R. rickettsii), the causative agent of Rocky Mountain spotted fever (RMSF), is the most pathogenic member among Rickettsia spp. Previous studies have shown that tripartite motif-containing 56 (TRIM56) E3 ligase-induced ubiquitination of STING is important for cytosolic DNA sensing and type I interferon production to induce anti-DNA viral immunity, but whether it affects intracellular replication of R. rickettsii remains uncharacterized. Here, we investigated the effect of TRIM56 on HeLa and THP-1 cells infected with R. rickettsii. We found that the expression of TRIM56 was upregulated in the R. rickettsii-infected cells, and the overexpression of TRIM56 inhibited the intracellular replication of R. rickettsii, while R. rickettsii replication was enhanced in the TRIM56-silenced host cells with the reduced phosphorylation of IRF3 and STING and the increased production of interferon-β. In addition, the mutation of the TRIM56 E3 ligase catalytic site impairs the inhibitory function against R. rickettsii in HeLa cells. Altogether, our study discovers that TRIM56 is a host restriction factor of R. rickettsii by regulating the cGAS-STING-mediated signaling pathway. This study gives new evidence for the role of TRIM56 in the innate immune response against intracellular bacterial infection and provides new therapeutic targets for RMSF.

IMPORTANCE

Given that Rickettsia rickettsii (R. rickettsii) is the most pathogenic member within the Rickettsia genus and serves as the causative agent of Rocky Mountain spotted fever, there is a growing need to explore host targets. In this study, we examined the impact of host TRIM56 on R. rickettsii infection in HeLa and THP-1 cells. We observed a significant upregulation of TRIM56 expression in R. rickettsii-infected cells. Remarkably, the overexpression of TRIM56 inhibited the intracellular replication of R. rickettsii, while silencing TRIM56 enhanced bacterial replication accompanied by reduced phosphorylation of IRF3 and STING, along with increased interferon-β production. Notably, the mutation of the TRIM56's E3 ligase catalytic site did not impede R. rickettsii replication in HeLa cells. Collectively, our findings provide novel insights into the role of TRIM56 as a host restriction factor against R. rickettsii through the modulation of the cGAS-STING signaling pathway.