Mal (MyD88-adapter-like) is required for Toll-like receptor-4 signal transduction

From periphery to center stage: 50 years of advancements in innate immunity

Over the past 50 years in the field of immunology, something of a Copernican revolution has happened. For a long time, immunologists were mainly concerned with what is termed adaptive immunity, which involves the exquisitely specific activities of lymphocytes. But the other arm of immunity, so-called "innate immunity," had been neglected. To celebrate Cell's 50th anniversary, we have put together a review of the processes and components of innate immunity and trace the seminal contributions leading to the modern state of this field. Innate immunity has joined adaptive immunity in the center of interest for all those who study the body's defenses, as well as homeostasis and pathology. We are now entering the era where therapeutic targeting of innate immune receptors and downstream signals hold substantial promise for infectious and inflammatory diseases and cancer.

Flotillins affect LPS-induced TLR4 signaling by modulating the trafficking and abundance of CD14

Lipopolysaccharide (LPS) induces a strong pro-inflammatory reaction of macrophages upon activation of Toll-like receptor 4 (TLR4) with the assistance of CD14 protein. Considering a key role of plasma membrane rafts in CD14 and TLR4 activity and the significant impact exerted on that activity by endocytosis and intracellular trafficking of the both LPS acceptors, it seemed likely that the pro-inflammatory reaction could be modulated by flotillins. Flotillin-1 and -2 are scaffolding proteins associated with the plasma membrane and also with endo-membranes, affecting both the plasma membrane dynamics and intracellular protein trafficking. To verify the above hypothesis, a set of shRNA was used to down-regulate flotillin-2 in Raw264 cells, which were found to also become deficient in flotillin-1. The flotillin deficiency inhibited strongly the TRIF-dependent endosomal signaling of LPS-activated TLR4, and to a lower extent also the MyD88-dependent one, without affecting the cellular level of TLR4. The flotillin depletion also inhibited the pro-inflammatory activity of TLR2/TLR1 and TLR2/TLR6 but not TLR3. In agreement with those effects, the depletion of flotillins down-regulated the CD14 mRNA level and the cellular content of CD14 protein, and also inhibited constitutive CD14 endocytosis thereby facilitating its shedding. Ultimately, the cell-surface level of CD14 was markedly diminished. Concomitantly, CD14 recycling was enhanced via EEA1-positive early endosomes and golgin-97-positive trans-Golgi network, likely to compensate for the depletion of the cell-surface CD14. We propose that the paucity of surface CD14 is the reason for the down-regulated signaling of TLR4 and the other TLRs depending on CD14 for ligand binding.

Decoding Toll-like receptors: Recent insights and perspectives in innate immunity

Toll-like receptors (TLRs) are an evolutionarily conserved family in the innate immune system and are the first line of host defense against microbial pathogens by recognizing pathogen-associated molecular patterns (PAMPs). TLRs, categorized into cell surface and endosomal subfamilies, recognize diverse PAMPs, and structural elucidation of TLRs and PAMP complexes has revealed their intricate mechanisms. TLRs activate common and specific signaling pathways to shape immune responses. Recent studies have shown the importance of post-transcriptional regulation in TLR-mediated inflammatory responses. Despite their protective functions, aberrant responses of TLRs contribute to inflammatory and autoimmune disorders. Understanding the delicate balance between TLR activation and regulatory mechanisms is crucial for deciphering their dual role in immune defense and disease pathogenesis. This review provides an overview of recent insights into the history of TLR discovery, elucidation of TLR ligands and signaling pathways, and their relevance to various diseases.

Pyroptosis-related gene signature for predicting gastric cancer prognosis

Gastric cancer (GC) is a prevalent form of malignancy characterized by significant heterogeneity. The development of a specific prediction model is of utmost importance to improve therapy alternatives. The presence of H. pylori can elicit pyroptosis, a notable carcinogenic process. Furthermore, the administration of chemotherapeutic drugs is often employed as a therapeutic approach to addressing this condition. In the present investigation, it was observed that there were variations in the production of 17 pyroptosis-regulating proteins between stomach tissue with tumor development and GC cells. The predictive relevance of each gene associated with pyroptosis was assessed using the cohort from the cancer genome atlas (TCGA). The least absolute shrinkage and selection operator (LASSO) was utilized to enhance the outcomes of the regression approach. Patients with gastric cancer GC in the cohort from the TCGA were categorized into low-risk or high-risk groups based on their gene expression profiles. Patients with a low risk of gastric cancer had a higher likelihood of survival compared to persons classified as high risk (P<0.0001). A subset of patients diagnosed with GC from a Genes Expression Omnibus (GEO) cohort was stratified according to their overall survival (OS) duration. The statistical analysis revealed a higher significance level (P=0.0063) regarding OS time among low-risk individuals. The study revealed that the GC risk score emerged as a significant independent prognostic factor for OS in patients diagnosed with GC. The results of Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) research revealed that genes associated with a high-risk group had significantly elevated levels of immune system-related activity. Furthermore, it was found that the state of immunity was diminished within this particular group. The relationship between the immune response to cancer and pyroptosis genes is highly interconnected, suggesting that these genes have the potential to serve as prognostic indicators for GC.

The critical role of toll-like receptor 4 in bone remodeling of osteoporosis: from inflammation recognition to immunity

Osteoporosis is a common chronic metabolic bone disorder. Recently, increasing numbers of studies have demonstrated that Toll-like receptor 4 (TLR4, a receptor located on the surface of osteoclasts and osteoblasts) plays a pivotal role in the development of osteoporosis. Herein, we performed a comprehensive review to summarize the findings from the relevant studies within this topic. Clinical data showed that TLR4 polymorphisms and aberrant TLR4 expression have been associated with the clinical significance of osteoporosis. Mechanistically, dysregulation of osteoblasts and osteoclasts induced by abnormal expression of TLR4 is the main molecular mechanism underlying the pathological processes of osteoporosis, which may be associated with the interactions between TLR4 and NF-κB pathway, proinflammatory effects, ncRNAs, and RUNX2. In vivo and in vitro studies demonstrate that many promising substances or agents (i.e., methionine, dioscin, miR-1906 mimic, artesunate, AEG-1 deletion, patchouli alcohol, and Bacteroides vulgatus) have been able to improve bone metabolism (i.e., inhibits bone resorption and promotes bone formation), which may partially attribute to the inhibition of TLR4 expression. The present review highlights the important role of TLR4 in the clinical significance and the pathogenesis of osteoporosis from the aspects of inflammation and immunity. Future therapeutic strategies targeting TLR4 may provide a new insight for osteoporosis treatment.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

MyD88 in myofibroblasts enhances nonalcoholic fatty liver disease-related hepatocarcinogenesis via promoting macrophage M2 polarization

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a major cause of chronic liver diseases and has emerged as the leading factor in the pathogenesis of hepatocellular carcinoma (HCC). MyD88 contributes to the development of HCC. However, the underlying mechanism by which MyD88 in myofibroblasts regulates NAFLD-associated liver cancer development remains unknown.

RESULTS

Myofibroblast MyD88-deficient (SMAMyD88-/-) mice were protected from diet-induced obesity and developed fewer and smaller liver tumors. MyD88 deficiency in myofibroblasts attenuated macrophage M2 polarization and fat accumulation in HCC tissues. Mechanistically, MyD88 signaling in myofibroblasts enhanced CCL9 secretion, thereby promoting macrophage M2 polarization. This process may depend on the CCR1 receptor and STAT6/ PPARβ pathway. Furthermore, liver tumor growth was attenuated in mice treated with a CCR1 inhibitor. CCLl5 (homologous protein CCL9 in humans) expression was increased in myofibroblasts of HCC and was associated with shorter survival of patients with HCC. Thus, our results indicate that MyD88 in myofibroblasts promotes NAFLD-related HCC progression and may be a promising therapeutic target for HCC treatment.

CONCLUSION

This study demonstrates that MyD88 in myofibroblasts can promote nonalcoholic fatty liver disease-related hepatocarcinogenesis by enhancing macrophage M2 polarization, which might provide a potential molecular therapeutic target for HCC.

POU5F1 promotes the proliferation, migration, and invasion of gastric cancer cells by reducing the ubiquitination level of TRAF6

POU5F1 plays an important role in maintaining the cancer stem cell (CSC) -like properties of gastric cancer (GC) cells. The impact of POU5F1 on the proliferation and metastasis of GC was examined, along with the potential of ATRA as a specific therapeutic agent for GC. The dysregulation of POU5F1 expression in GC tissues was analyzed using public databases and bioinformatics techniques, and the disparity in POU5F1 expression between normal gastric tissues and GC tissues was further assessed through western blot, RT-qPCR, and immunohistochemistry. The present study aimed to investigate the impact of POU5F1 on the proliferation, migration, and invasion of GC cells through both in vivo and in vitro experiments. Additionally, the effects of ATRA on the proliferation, migration, and invasion of GC cells were examined using in vivo and in vitro approaches. Our findings revealed a significant upregulation of POU5F1 in GC tissues, which was found to be associated with a poorer prognosis in patients with GC. Moreover, POU5F1 was observed to enhance the proliferation, migration, and invasion of GC cells in vitro, as well as promote subcutaneous tumor growth and lung metastasis of GC cells in vivo. The overexpression of POU5F1 mechanistically triggers the process of Epithelial-mesenchymal transition (EMT) by down-regulating E-Cadherin and up-regulating N-Cadherin and VIM. POU5F1 hinders the ubiquitination of TRAF6 through negative regulation of TRIM59, thereby facilitating the activation of the NF-κB pathway. Furthermore, the administration of ATRA effectively impedes the proliferation, migration, and invasion of GC cells by suppressing the expression of POU5F1. The upregulation of POU5F1 elicits EMT, fosters the initiation of the NF-κB signaling pathway in GC cells, and stimulates the proliferation, invasion, and metastasis of GC cells. All-trans retinoic acid (ATRA) can impede these POU5F1-induced effects, thereby potentially serving as an adjunctive therapeutic approach for GC.

Vasoactive Intestinal Polypeptide Plays a Key Role in the Microbial-Neuroimmune Control of Intestinal Motility

BACKGROUND & AIMS

Although chronic diarrhea and constipation are common, the treatment is symptomatic because their pathophysiology is poorly understood. Accumulating evidence suggests that the microbiota modulates gut function, but the underlying mechanisms are unknown. We therefore investigated the pathways by which microbiota modulates gastrointestinal motility in different sections of the alimentary tract.

METHODS

Gastric emptying, intestinal transit, muscle contractility, acetylcholine release, gene expression, and vasoactive intestinal polypeptide (VIP) immunoreactivity were assessed in wild-type and Myd88-/-Trif-/- mice in germ-free, gnotobiotic, and specific pathogen-free conditions. Effects of transient colonization and antimicrobials as well as immune cell blockade were investigated. VIP levels were assessed in human full-thickness biopsies by Western blot.

RESULTS

Germ-free mice had similar gastric emptying but slower intestinal transit compared with specific pathogen-free mice or mice monocolonized with Lactobacillus rhamnosus or Escherichia coli, the latter having stronger effects. Although muscle contractility was unaffected, its neural control was modulated by microbiota by up-regulating jejunal VIP, which co-localized with and controlled cholinergic nerve function. This process was responsive to changes in the microbial composition and load and mediated through toll-like receptor signaling, with enteric glia cells playing a key role. Jejunal VIP was lower in patients with chronic intestinal pseudo-obstruction compared with control subjects.

CONCLUSIONS

Microbial control of gastrointestinal motility is both region- and bacteria-specific; it reacts to environmental changes and is mediated by innate immunity-neural system interactions. By regulating cholinergic nerves, small intestinal VIP plays a key role in this process, thus providing a new therapeutic target for patients with motility disorders.

Incomplete Knockdown of MyD88 Inhibits LPS-Induced Lung Injury and Lung Fibrosis in a Mouse Model

Acute lung injury (ALI) is a life-threatening disorder stemmed mainly from an uncontrolled inflammatory response. Lipopolysaccharide (LPS) is commonly used to induce ALI animal models. Toll-like receptor 4 (TLR4) is the main receptor for LPS, and myeloid differentiation factor 88 (MyD88) is a key adaptor protein molecule in the Toll-like receptor (TLR) signaling pathway. Thus, MyD88 knockdown heterozygous mice (MyD88+/-) were used to investigate the effect of incomplete knockout of the MyD88 gene on indirect LPS-induced ALI through intraperitoneal injection of LPS. The LPS-induced ALI significantly upregulated MyD88 expression, and heterozygous mice with incomplete knockout of the MyD88 gene (MyD88+/-) ameliorated LPS-induced histopathological injury and collagen fiber deposition. Heterozygous mice with incomplete knockout of the MyD88 gene (MyD88+/-) inhibited LPS-induced nuclear factor-κB (NF-κB) pathway activation, but TLR-4 expression tended to be upregulated. Incomplete knockdown of the MyD88 gene also downregulated LPS-induced expression of IL1-β, IL-6, TNF-α, TGF-β, SMAD2, and α-SMA. The transcriptome sequencing also revealed significant changes in LPS-regulated genes (such as IL-17 signaling pathway genes) after the incomplete knockdown of MyD88. In conclusion, this paper clarified that LPS activates the downstream NF-κB pathway depending on the MyD88 signaling pathway, which induces the secretion of inflammatory cytokines such as IL-1β/IL-6/TNF-α and ultimately triggers ALI. Incomplete knockdown of the MyD88 reverses LPS-induced lung fibrosis, which confirmed the vital role of MyD88 in LPS-induced ALI.

Ex Vivo Endotoxin Stimulation of Blood for Predicting Survival in Patients With Sepsis: A Systematic Review

BACKGROUND

Sepsis is a syndrome characterized by host immune dysfunction, with the extent of immunoparalysis differing among patients. Lipopolysaccharide (LPS) is used commonly to assess the immune function of critically ill patients with sepsis. However, the reliability of this ex vivo diagnostic test in predicting clinical outcomes remains uncertain.

RESEARCH QUESTION

Does LPS-induced tumor necrosis factor (TNF) production from the blood of patients with sepsis predict mortality? Secondary outcomes included ICU and hospital stay durations, nosocomial infection rate, and organ recovery rate.

STUDY DESIGN AND METHODS

Human sepsis studies from various databases through April 2023 were evaluated. Inclusion criteria encompassed LPS-stimulated blood assays, English language, and reported clinical outcomes. Bias risk was evaluated using the Newcastle-Ottawa scale (NOS). Relationships between TNF production and mortality were analyzed at sepsis onset and during established sepsis, alongside secondary outcomes.

RESULTS

Of 11,580 studies, 17 studies (14 adult and three pediatric) were selected for analysis. Although 15 studies were evaluated as moderate to high quality using the NOS, it is important to note that some of these studies also had identifiable biases, such as unclear methods of participant recruitment. Nine studies detailed survival outcomes associated with LPS-induced TNF production at sepsis onset, whereas five studies explored TNF production's relationship with mortality during established sepsis. Trends suggested that lower LPS-induced TNF production correlated with higher mortality. However, heterogeneity in methodologies, especially the LPS assay protocol, hindered definitive conclusions. Publication bias was highlighted using funnel plot analysis. Concerning secondary outcomes, diminished TNF production might signify worsening organ dysfunction, although the link between cytokine production and nosocomial infection varied among studies.

INTERPRETATION

For functional immune profiling in sepsis, streamlined research methodologies are essential. This entails organizing cohorts based on microbial sources of sepsis, establishing standardized definitions of immunoparalysis, using consistent types and dosages of immune stimulants, adhering to uniform blood incubation conditions, and adopting consistent clinical outcomes.

A Bacterial Quorum Sensing Regulated Protease Inhibits Host Immune Responses by Cleaving Death Domains of Innate Immune Adaptors

Innate immune adaptor proteins are critical components of the innate immune system that propagate pro-inflammatory responses from their upstream receptors, and lead to pathogen clearance from the host. Bacterial pathogens have developed strategies to survive inside host cells without triggering the innate immune surveillance in ways that are still not fully understood. Here, it is reported that Pseudomonas aeruginosa induces its quorum sensing mechanism after macrophage engulfment. Further investigation of its secretome identified a quorum sensing regulated product, LasB, is responsible for innate immune suppression depending on the MyD88-mediated signaling. Moreover, it is showed that this specific type of pathogen-mediated innate immune suppression is due to the enzymatic digestion of the death domains of the innate immune adaptors, mainly MyD88, and attributed to LasB's large substrate binding groove. Lastly, it is demonstrated that the secretion of LasB from P. aeruginosa directly contributed to MyD88 degradation within macrophages. Hence, it is discovered an example of bacterial quorum sensing-regulated cellular innate immune suppression by direct cleavage of immune adaptors.

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

Toll-like receptor 4 (TLR4) are part of the innate immune system. They are capable of recognizing pathogen-associated molecular patterns (PAMPS) of microbes, and damage-associated molecular patterns (DAMPs) of damaged tissues. Activation of TLR4 initiates downstream signaling pathways that trigger the secretion of cytokines, type I interferons, and other pro-inflammatory mediators that are necessary for an immediate immune response. However, the systemic release of pro-inflammatory proteins is a powerful driver of acute and chronic inflammatory responses. Over the past decades, immense progress has been made in clarifying the molecular and regulatory mechanisms of TLR4 signaling in inflammation. However, the most common strategies used to study TLR4 signaling rely on genetic manipulation of the TLR4 or the treatment with agonists such as lipopolysaccharide (LPS) derived from the outer membrane of Gram-negative bacteria, which are often associated with the generation of irreversible phenotypes in the target cells or unintended cytotoxicity and signaling crosstalk due to off-target or pleiotropic effects. Here, optogenetics offers an alternative strategy to control and monitor cellular signaling in an unprecedented spatiotemporally precise, dose-dependent, and non-invasive manner. This review provides an overview of the structure, function and signaling pathways of the TLR4 and its fundamental role in endothelial cells under physiological and inflammatory conditions, as well as the advances in TLR4 modulation strategies.

Infection and inflammation stimulate expansion of a CD74+ Paneth cell subset to regulate disease progression

Paneth cells (PCs), a specialized secretory cell type in the small intestine, are increasingly recognized as having an essential role in host responses to microbiome and environmental stresses. Whether and how commensal and pathogenic microbes modify PC composition to modulate inflammation remain unclear. Using newly developed PC-reporter mice under conventional and gnotobiotic conditions, we determined PC transcriptomic heterogeneity in response to commensal and invasive microbes at single cell level. Infection expands the pool of CD74+ PCs, whose number correlates with auto or allogeneic inflammatory disease progressions in mice. Similar correlation was found in human inflammatory disease tissues. Infection-stimulated cytokines increase production of reactive oxygen species (ROS) and expression of a PC-specific mucosal pentraxin (Mptx2) in activated PCs. A PC-specific ablation of MyD88 reduced CD74+ PC population, thus ameliorating pathogen-induced systemic disease. A similar phenotype was also observed in mice lacking Mptx2. Thus, infection stimulates expansion of a PC subset that influences disease progression.

Anti-inflammatory effects of yeast-derived vacuoles on LPS-induced murine macrophage activation

Saccharomyces cerevisiae is a single-celled fungal microorganism. S. cerevisiae-derived vacuoles are closely related to mammalian lysosomes, which play a role in the degradation of macromolecules by various hydrolytic enzymes. This study evaluated the anti-inflammatory efficacy of S. cerevisiae-vacuoles by inhibiting inflammatory mediators induced by lipopolysaccharide (LPS). The results showed that treatment with 5, 10, and 20 µg/mL of S. cerevisiae-derived vacuoles almost completely inhibited the LPS-induced expression of iNOS protein and mRNA. Moreover, vacuoles significantly reduced the mRNA expression of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6) in LPS-stimulated macrophages compared to the control cells. The immunofluorescence analysis confirmed that S. cerevisiae-derived vacuoles inhibited the translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in LPS-stimulated cells. Taken together, the treatment with S. cerevisiae-derived vacuoles alone activated macrophages, but LPS-activated macrophages modulated pro-inflammatory mediators by downregulating the NF-κB pathway. These results suggest that S. cerevisiae-derived vacuoles may have therapeutic potential in the treatment of inflammatory diseases. In conclusion, our study provides new insights into the immunomodulatory effects of S. cerevisiae-derived vacuoles and their potential as a novel anti-inflammatory agent. IMPORTANCE This study investigates the potential of using vacuoles derived from the yeast Saccharomyces cerevisiae as a new anti-inflammatory therapy. Inflammation is a natural response of the immune system to invading pathogens, but when it is dysregulated, it can lead to chronic diseases. The researchers found that treating macrophages with vacuoles significantly reduced the production of pro-inflammatory cytokines and iNOS, markers of inflammation when they were stimulated with lipopolysaccharide. The study also showed that vacuoles inhibited the NF-κB signaling pathway, which is involved in the induction of pro-inflammatory cytokines in macrophages. These findings suggest that S. cerevisiae-derived vacuoles may have potential as a new therapeutic agent for regulating the inflammatory response in various diseases. Further studies are needed to evaluate the efficacy and safety of vacuoles in vivo and to elucidate the underlying mechanisms of their anti-inflammatory effects.

Human inborn errors of immunity associated with IRF4

The transcription factor interferon regulatory factor 4 (IRF4) belongs to the IRF family and has several important functions for the adaptive immune response. Mutations affecting IRF family members IRF1, IRF3, IRF7, IRF8, or IRF9 have been described in patients presenting with inborn errors of immunity (IEI) highlighting the importance of these factors for the cellular host defense against mycobacterial and/or viral infections. IRF4 deficiency and haploinsufficiency have been associated with IEI. More recently, two novel IRF4 disease-causing mechanisms have been described due to the characterization of IEI patients presenting with cellular immunodeficiency associated with agammaglobulinemia. Here, we review the phenotypes and physiopathological mechanisms underlying IEI of IRF family members and, in particular, IRF4.

Adolescent nonpharmacological interventions for early-life stress and their mechanisms

Those with a negative experience of psychosocial stress during the early stage of life not only have a high susceptibility of the psychiatric disorder in all phases of their life span, but they also demonstrate more severe symptoms and poorer response to treatment compared to those without a history of early-life stress. The interventions targeted to early-life stress may improve the effectiveness of treating and preventing psychiatric disorders. Brain regions associated with mood and cognition develop rapidly and own heightened plasticity during adolescence. So, manipulating nonpharmacological interventions in fewer side effects and higher acceptance during adolescence, which is a probable window of opportunity, may ameliorate or even reverse the constantly deteriorating impact of early-life stress. The present article reviews animal and people studies about adolescent nonpharmacological interventions for early-life stress. We aim to discuss whether those adolescent nonpharmacological interventions can promote individuals' psychological health who expose to early-life stress.

Protective effects of paeoniflorin on cardiovascular diseases: A pharmacological and mechanistic overview

Background and ethnopharmacological relevance: The morbidity and mortality of cardiovascular diseases (CVDs) are among the highest of all diseases, necessitating the search for effective drugs and the improvement of prognosis for CVD patients. Paeoniflorin (5beta-[(Benzoyloxy)methyl] tetrahydro-5-hydroxy-2-methyl-2,5-methano-1H-3,4-dioxacyclobuta [cd] pentalen-1alpha (2H)-yl-beta-D-glucopyranoside, C₂₃H₂₈O₁₁) is mostly derived from the plants of the family Paeoniaceae (a single genus family) and is known to possess multiple pharmacological properties in the treatment of CVDs, making it a promising agent for the protection of the cardiovascular system. Aim of the study: This review evaluates the pharmacological effects and potential mechanisms of paeoniflorin in the treatment of CVDs, with the aim of advancing its further development and application. Methods: Various relevant literatures were searched in PubMed, ScienceDirect, Google Scholar and Web of Science. All eligible studies were analyzed and summarized in this review. Results: Paeoniflorin is a natural drug with great potential for development, which can protect the cardiovascular system by regulating glucose and lipid metabolism, exerting anti-inflammatory, anti-oxidative stress, and anti-arteriosclerotic activities, improving cardiac function, and inhibiting cardiac remodeling. However, paeoniflorin was found to have low bioavailability, and its toxicology and safety must be further studied and analyzed, and clinical studies related to it must be carried out. Conclusion: Before paeoniflorin can be used as an effective therapeutic drug for CVDs, further in-depth experimental research, clinical trials, and structural modifications or development of new preparations are required.

Dorzolamide suppresses PKCδ -TIRAP-p38 MAPK signaling axis to dampen the inflammatory response

Background: Sepsis is a syndrome due to microbial infection causing impaired multiorgan function. Its underlying cause is immune dysfunction and macrophages play an essential role. Methods: TIRAP interaction with PKCδ in macrophage was studied, revealing downstream signaling by Western blot and quantitative reverse transcriptase PCR. Dorzolamide (DZD) disrupting TIRAP-PKCδ interaction was identified by virtual screening and validated in vitro and in septic mice. Results: The study highlights the indispensable role of TIRAP-PKCδ in p38 MAPK-activation, NF-κB- and AP-1-mediated proinflammatory cytokines expression, whereas DZD significantly attenuated the signaling. Conclusion: Targeting TIRAP-PKCδ interaction by DZD is a novel therapeutic approach for treating sepsis.

Enhanced B Cell Receptor Signaling Partially Compensates for Impaired Toll-like Receptor 4 Responses in LPS-Stimulated IκBNS-Deficient B Cells

Lipopolysaccharide (LPS) stimulates dual receptor signaling by bridging the B cell receptor and Toll-like receptor 4 (BCR/TLR4). B cells from IκBNS-deficient bumble mice treated with LPS display reduced proliferative capacity and impaired plasma cell differentiation. To improve our understanding of the regulatory role of IκBNS in B cell activation and differentiation, we investigated the BCR and TLR4 signaling pathways separately by using dimeric anti-IgM Fab (F(ab')₂) or lipid A, respectively. IκBNS-deficient B cells exhibited reduced survival and defective proliferative capacity in response to lipid A compared to B cells from wildtype (wt) control mice. In contrast, anti-IgM stimulation of bumble B cells resulted in enhanced viability and increased differentiation into CD138⁺ cells compared to control B cells. Anti-IgM-stimulated IκBNS-deficient B cells also showed enhanced cycle progression with increased levels of c-Myc and cyclin D2, and augmented levels of pCD79a, pSyk, and pERK compared to control B cells. These results suggest that IκBNS acts as a negative regulator of BCR signaling and a positive regulator of TLR4 signaling in mouse B cells.

SLAMF7 regulates the inflammatory response in macrophages during polymicrobial sepsis

Uncontrolled inflammation occurred in sepsis results in multiple organ injuries and shock, which contributes to the death of patients with sepsis. However, the regulatory mechanisms that restrict excessive inflammation are still elusive. Here, we identified an Ig-like receptor called signaling lymphocyte activation molecular family 7 (SLAMF7) as a key suppressor of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes/macrophages was significantly elevated in patients with sepsis and in septic mice. SLAMF7 attenuated TLR-dependent MAPK and NF-κB signaling activation in macrophages by cooperating with Src homology 2-containing inositol-5'‑phosphatase 1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor-associated factor 6 (TRAF6) to inhibit K63 ubiquitination of TRAF6. In addition, we found that tyrosine phosphorylation sites within the intracellular domain of SLAMF7 and the phosphatase domain of SHIP1 were indispensable for the interaction between SLAMF7, SHIP1, and TRAF6 and SLAMF7-mediated modulation of cytokine production. Finally, we demonstrated that SLAMF7 protected against lethal sepsis and endotoxemia by downregulating macrophage proinflammatory cytokines and suppressing inflammation-induced organ damage. Taken together, our findings reveal a negative regulatory role of SLAMF7 in polymicrobial sepsis, thus providing sights into the treatment of sepsis.

Comparative and Temporal Characterization of LPS and Blue-Light-Induced TLR4 Signal Transduction and Gene Expression in Optogenetically Manipulated Endothelial Cells

In endothelial cells (ECs), stimulation of Toll-like receptor 4 (TLR4) by the endotoxin lipopolysaccharide (LPS) induces the release of diverse pro-inflammatory mediators, beneficial in controlling bacterial infections. However, their systemic secretion is a main driver of sepsis and chronic inflammatory diseases. Since distinct and rapid induction of TLR4 signaling is difficult to achieve with LPS due to the specific and non-specific affinity to other surface molecules and receptors, we engineered new light-oxygen-voltage-sensing (LOV)-domain-based optogenetic endothelial cell lines (opto-TLR4-LOV LECs and opto-TLR4-LOV HUVECs) that allow fast, precise temporal, and reversible activation of TLR4 signaling pathways. Using quantitative mass-spectrometry, RT-qPCR, and Western blot analysis, we show that pro-inflammatory proteins were not only expressed differently, but also had a different time course when the cells were stimulated with light or LPS. Additional functional assays demonstrated that light induction promoted chemotaxis of THP-1 cells, disruption of the EC monolayer and transmigration. In contrast, ECs incorporating a truncated version of the TLR4 extracellular domain (opto-TLR4 ΔECD2-LOV LECs) revealed high basal activity with fast depletion of the cell signaling system upon illumination. We conclude that the established optogenetic cell lines are well suited to induce rapid and precise photoactivation of TLR4, allowing receptor-specific studies.

Regulation of innate immune signaling by IRAK proteins

The Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1R) families are of paramount importance in coordinating the early immune response to pathogens. Signaling via most TLRs and IL-1Rs is mediated by the protein myeloid differentiation primary-response protein 88 (MyD88). This signaling adaptor forms the scaffold of the myddosome, a molecular platform that employs IL-1R-associated kinase (IRAK) proteins as main players for transducing signals. These kinases are essential in controlling gene transcription by regulating myddosome assembly, stability, activity and disassembly. Additionally, IRAKs play key roles in other biologically relevant responses such as inflammasome formation and immunometabolism. Here, we summarize some of the key aspects of IRAK biology in innate immunity.

The first identification of three AdIRAK2 genes from an evolutionarily important amphibian Andrias davidianus and their involvement in NF-κB activation and inflammatory responses

Interleukin-1 receptor associated kinases (IRAK) is the most important downstream kinases of TLRs/IL-1R signaling pathway for signal transduction and activation of inflammatory response against pathogen infections. However, the molecular identification and function characterization of IRAK2 homologs in lower vertebrate remains obscure. In this study, three IRAK2 genes (AdIRAK2a, AdIRAKb and AdIRAK2c) and their respective transcripts were identified from the Chinese giant salamander Andrias davidianus. This is the first evidence that three different IRAK2 genes exist in an ancient amphibian species, which has never been reported in other vertebrates. The complete open reading frames (ORFs) of AdIRAK2a, AdIRAK2b and AdIRAK2c were 2112 bp, 1917 bp and 816 bp encoding deduced proteins of 703 amino acids (aa), 628 aa and 271 aa, respectively. All three AdIRAK2 proteins contained two predicted conserved functional domains, including a death domain (DD) and a serine/threonine protein kinases domain (KD). Phylogenetic analysis showed that the three AdIRAK2s clustered together with other known IRAK2 of vertebrates. The three AdIRAK2s were ubiquitously expressed in all tested tissues with a similar tissues distribution pattern. After challenge of Aeromonas hydrophila (A. hydrophila), Staphylococcus aureus (S.aureus), giant salamander iridovirus (GSIV, belonging to the genus Ranavirus in the family Iridoviridae) and polyinosinic:polycytidylic acid (poly(I:C)), the expression levels of all AdIRAK2s in blood were significantly altered, however, they exhibited distinct response patterns. Moreover, the results of over-expression and RNAi of AdIRAK2s implied the involvement of AdIRAK2s in triggering NF-κB-mediated signaling pathways and inflammatory responses. This study might provide a better understanding of the presence and immune regulation function of IRAK2 in amphibians and even in vertebrates.

Characterization of a novel Toll-like receptor 13 homologue from a marine fish Nibea albiflora, revealing its immunologic function as PRRs

Congenital immunity mediated by Toll-like receptor (TLR) family is the first line of defense for disease-resistant immunity of fish and plays a vital role as a bridge between innate immunity and acquired immunity. As a less known member of the TLR family TLR13 can participate in the immune and inflammatory reactions of the body for recognizing the conserved sequence of 23S rRNA in bacteria and induce immune response. In this study, the full-length cDNA of TLR13 from Nibea albiflora (named as NaTLR13) was cloned and was functionally characterized. It was 4210bp (GenBank accession no. MT701899) including an open reading frame (ORF) of 2886bp to encode 962 amino acids with molecular weight of 110.37 kDa and the theoretical isoelectric point of 9.08. There were several conservative structures in NaTLR13 such as 15 leucine-rich repeat sequences (LRRs), a Toll-IL-1 receptor domain (TIR), an LRR-CT terminal domain, two LRR-TYP structures and two transmembrane domains. The multiple sequence alignment and phylogenetic analysis manifested that NaTLR13 had high similarity with Larimichthys crocea and Collichthys lucidus (88.79% and 87.02%, respectively) and they fell into the same branch. The Real-time PCR showed that NaTLR13 was expressed in all selected tissues, with the highest in the spleen, followed by the liver, kidney, gill, heart and muscle. After being challenged by Vibrio alginolyticus, Vibrio parahaemolyticus or Poly (I:C), the expression of NaTLR13 increased firstly, then decreased and finally stabilized with time for its immune defense function. Subcellular localization analysis revealed that NaTLR13 was unevenly distributed in the cytoplasm with green fluorescence and MyD88 was evenly spread in the cytoplasm with red signals. When NaTLR13 and MyD88 were co-transfected, they obviously overlapped and displayed orange-yellow color, which showed that the homologous TLR13 might interact with MyD88 for NFκB signaling pathway transmission. The functional domains of NaTLR13 (named NaTLR13-TIR and NaTLR13-LRR) were expressed in E.coli BL21 (DE3) and purified by Ni-NAT Superflow Resin conforming to the expected molecular weights, and the recombinant proteins could bind to three Vibrios (V.alginolyticus, V.parahaemolyticus and Vibrio harveyi), indicating that NaTLR13 could be bounden to bacteria through its functional domain. These results suggested that NaTLR13 might play an important role in the defense of N.albiflora against bacteria or viral infection and the data would provide some information for further understanding the regulatory mechanism of the innate immune system in fish.

A Review on COVID-19: Primary Receptor, Endothelial Dysfunction, Related Comorbidities, and Therapeutics

Since December 2019, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a global pandemic named coronavirus disease-19 (COVID-19) and resulted in a worldwide economic crisis. Utilizing the spike-like protein on its surface, the SARS-CoV-2 binds to the receptor angiotensin-converting enzyme 2 (ACE2), which highly expresses on the surface of many cell types. Given the crucial role of ACE2 in the renin–angiotensin system, its engagement by SARS-CoV-2 could potentially result in endothelial cell perturbation. This is supported by the observation that one of the most common consequences of COVID-19 infection is endothelial dysfunction and subsequent vascular damage. Furthermore, endothelial dysfunction is the shared denominator among previous comorbidities, including hypertension, kidney disease, cardiovascular diseases, etc., which are associated with an increased risk of severe disease and mortality in COVID-19 patients. Several vaccines and therapeutics have been developed and suggested for COVID-19 therapy. The present review summarizes the relationship between ACE2 and endothelial dysfunction and COVID-19, also reviews the most common comorbidities associated with COVID-19, and finally reviews several categories of potential therapies against COVID-19.

TIRAP, TRAM, and Toll-Like Receptors: The Untold Story

Toll-like receptors (TLRs) are the most studied receptors among the pattern recognition receptors (PRRs). They act as microbial sensors, playing major roles in the regulation of the innate immune system. TLRs mediate their cellular functions through the activation of MyD88-dependent or MyD88-independent signaling pathways. Myd88, or myeloid differentiation primary response 88, is a cytosolic adaptor protein essential for the induction of proinflammatory cytokines by all TLRs except TLR3. While the crucial role of Myd88 is well described, the contribution of other adaptors in mediating TLR signaling and function has been underestimated. In this review, we highlight important results demonstrating that TIRAP and TRAM adaptors are also required for full signaling activity and responses induced by most TLRs.

Activated cholesterol metabolism is integral for innate macrophage responses by amplifying Myd88 signaling

Recent studies have shown that cellular metabolism is tightly linked to the regulation of immune cells. Here, we show that activation of cholesterol metabolism, involving cholesterol uptake, synthesis, and autophagy/lipophagy, is integral to innate immune responses in macrophages. In particular, cholesterol accumulation within endosomes and lysosomes is a hallmark of the cellular cholesterol dynamics elicited by Toll-like receptor 4 activation and is required for amplification of myeloid differentiation primary response 88 (Myd88) signaling. Mechanistically, Myd88 binds cholesterol via its CLR recognition/interaction amino acid consensus domain, which promotes the protein's self-oligomerization. Moreover, a novel supramolecular compound, polyrotaxane (PRX), inhibited Myd88‑dependent inflammatory macrophage activation by decreasing endolysosomal cholesterol via promotion of cholesterol trafficking and efflux. PRX activated liver X receptor, which led to upregulation of ATP binding cassette transporter A1, thereby promoting cholesterol efflux. PRX also inhibited atherogenesis in Ldlr-/- mice. In humans, cholesterol levels in circulating monocytes correlated positively with the severity of atherosclerosis. These findings demonstrate that dynamic changes in cholesterol metabolism are mechanistically linked to Myd88‑dependent inflammatory programs in macrophages and support the notion that cellular cholesterol metabolism is integral to innate activation of macrophages and is a potential therapeutic and diagnostic target for inflammatory diseases.

Flow cytometric reporter assays provide robust functional analysis of signaling complexes

Conventional assays to probe signaling protein interactions and function involve measurement of luciferase reporter expression within the bulk cell population, with lack of control over target-protein expression level. To address this issue, we have developed a rapid and robust flow cytometric assay for analysis of signaling protein function. A fluorescent reporter and fluorescent tagging of the target protein enables simultaneous assessment of protein expression and signaling within individual cells. We have applied our technique to the analysis of variants of the lipopolysaccharide receptor Toll-like receptor 4 (TLR4) and its adapter protein MyD88, using a NF-кB-responsive promoter driving mScarlet-I expression. The assay enables exclusion of nontransfected cells and overexpressing cells that signal spontaneously. Additionally, our assay allows the identification of protein variants that fail to express. We found that the assays were highly sensitive, with cells expressing an appropriate level of GFP-MyD88 showing approximately 200-fold induction of mScarlet-I by lipopolysaccharide, and we can detect subtle protein concentration-dependent effects of mutations. Importantly, the assay is adaptable to various signaling pathways.

The Focus on Core Genetic Factors That Regulate Hepatic Injury in Cattle Seems to be Important for the Dairy Sector’s Long-Term Development

The cattle during the perinatal period, as well as malnutrition, generate oxidative stress which leads to high culling rates of calves after calving across the world. Although metabolic diseases have such a negative impact on the welfare and economic value of dairy cattle, that becomes a serious industrial concern across the world. According to research, genetic factors have a role or controlling fat deposition in the liver by influencing the biological processes of hepatic lipid metabolism, insulin resistance, gluconeogenesis, oxidative stress, endoplasmic reticulum stress, and inflammation, all of which contribute to hepatic damage. This review focuses on the critical regulatory mechanisms of VEGF, mTOR/AKT/p53, TNF-alpha, Nf-kb, interleukin, and antioxidants that regulate lipid peroxidation in the liver via direct or indirect pathways, suggesting that they could be a potential critical therapeutic target for hepatic disease.

Of Flies and Men—The Discovery of TLRs

In 2011, the Nobel Prize in Physiology or Medicine was awarded to three immunologists: Bruce A. Beutler, Jules A. Hoffmann, and Ralph M. Steinman. While Steinman was honored for his work on dendritic cells and adaptive immunity, Beutler and Hoffman received the prize for their contributions to discoveries in innate immunity. In 1996, Hoffmann found the toll gene to be crucial for mounting antimicrobial responses in fruit flies, first implicating this developmental gene in immune signaling. Two years later, Beutler built on this observation by describing a Toll-like gene, tlr4, as the receptor for the bacterial product LPS, representing a crucial step in innate immune activation and protection from bacterial infections in mammals. These publications spearheaded research in innate immune sensing and sparked a huge interest regarding innate defense mechanisms in the following years and decades. Today, Beutler and Hoffmann’s research has not only resulted in the discovery of the role of multiple TLRs in innate immunity but also in a much broader understanding of the molecular components of the innate immune system. In this review, we aim to collect the discoveries leading up to the publications of Beutler and Hoffmann, taking a close look at how early advances in both developmental biology and immunology converged into the research awarded with the Nobel Prize. We will also discuss how these discoveries influenced future research and highlight the importance they hold today.

Macrophage-specific MyD88 deletion and pharmacological inhibition prevents liver damage in non-alcoholic fatty liver disease via reducing inflammatory response

Activation of the innate immune system through toll-like receptors (TLRs) has been repeatedly demonstrated in non-alcoholic fatty liver disease (NAFLD) and several TLRs have been shown to contribute. Myeloid differentiation primary response 88 (MyD88) is as an adapter protein for the activation of TLRs and bridges TLRs to NF-κB-mediated inflammation in macrophages. However, whether myeloid cell MyD88 contributes to NAFLD are largely unknown. To test this approach, we generated macrophage-specific MyD88 knockout mice and show that these mice are protected against high-fat diet (HFD)-induced hepatic injury, lipid accumulation, and fibrosis. These protective effects were associated with reduced macrophage numbers in liver tissues and surpassed inflammatory responses. In cultured macrophages, saturated fatty acid palmitate utilizes MyD88 to activate NF-κB and induce inflammatory and fibrogenic factors. In hepatocytes, these factors may cause lipid accumulation and a further elaboration of inflammatory cytokines. In hepatic stellate cells, macrophage-derived factors, especially TGF-β, cause activation and hepatic fibrosis. We further show that pharmacological inhibition of MyD88 is also able to reduce NAFLD injury in HFD-fed mice. Therefore, our study has provided empirical evidence that macrophage MyD88 participates in HFD-induced NAFLD and could be targeted to prevent the development and progression of NAFLD/NASH.

Bifurcation of signalling in human innate immune pathways to NF-kB and IRF family activation

The human innate immune response can be activated through a wide range of stimuli. This multi-faceted system can be triggered by a range of immunostimulants including pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). These stimuli drive intracellular signalling pathways that branch off downstream to activate several distinct transcription factors. The two most impactful of which in innate immune outcomes are the NF-κB and the IRF family members. Both transcription factor families play defining roles in driving inflammation as well as the antiviral response. Pathways leading to their simultaneous activation share common upstream components but eventually distinct regulators which directly facilitate their activation. This review will discuss the current state of knowledge about what is known about how these pathways bifurcate to activate NF-κB and IRF family members.

The IRAK4 scaffold integrates TLR4-driven TRIF and MYD88 signaling pathways

Interleukin-1 receptor-associated kinases (IRAKs) -4, -2, and -1 are involved in transducing signals from Toll-like receptors (TLRs) via the adaptor myeloid differentiation primary-response protein 88 (MYD88). How MYD88/IRAK4/2/1 complexes are formed, their redundancies, and potential non-enzymatic roles are subjects of debate. Here, we examine the hierarchical requirements for IRAK proteins in the context of TLR4 activation and confirmed that the kinase activity of IRAK4 is essential for MYD88 signaling. Surprisingly, the IRAK4 scaffold is required for activation of the E3 ubiquitin ligase TNF receptor-associated factor 6 (TRAF6) by both MYD88 and TIR domain-containing adaptor protein inducing IFN-β (TRIF), a unique adaptation in the TLR4 response. IRAK4 scaffold is, therefore, essential in integrating MYD88 and TRIF in TLR4 signaling.

Molecular Characterization of MyD88 in Anodonta woodiana and Its Involvement in the Innate Immune Response to Bacterial Infection

Myeloid differentiation factor 88 (MyD88) is a key adapter molecule in Toll-like receptor signal transduction that triggers downstream immune cascades involved in the host defense response to exogenous pathogens. However, the function of MyD88s in mollusks, especially in freshwater shellfish, remains poorly understood. In this study, a novel freshwater shellfish MyD88 (denoted AwMyD88) was characterized from Anodonta woodiana. The present AwMyD88 protein consists of 474 amino acids and contains a conserved a typical death domain (DD) and a conservative Toll/IL-1R (TIR) domain with three typical boxes. Quantitative real-time PCR (qRT-PCR) analysis showed that AwMyD88 was broadly expressed in all the examined tissues, and the highest expression level was observed in hemocytes of A. woodiana. When challenged with Aeromonas hydrophila and lipopolysaccharide (LPS), the mRNA expression levels of AwMyD88 were significantly induced in hemocytes of A. woodiana in vivo and in vitro. In addition, in vivo injection experiments revealed that MyD88 signaling pathway genes showed strong responsiveness to A. hydrophila challenge, and their expression levels were significantly upregulated in hemocytes. Knockdown of AwMyD88 reduced the transcript levels of immune related transcription factors (AwNF-κB and AwAP-1) and effectors (AwTNF, AwLYZ, AwDefense and AwAIF) during A. hydrophila infection. Moreover, subcellular localization analysis indicated that AwMyD88 was mainly localized to the cytoplasm in HEK293T cells. Finally, luciferase reporter assays revealed that AwMyD88 associates with AwTLR to activate the NF-κB and AP-1 signaling pathways in HEK293T cells. These results suggested that AwMyD88 might be involved in the host defense response to bacterial challenge, providing new insight into the immune function of the MyD88 signaling pathway in freshwater shellfish.

Innate Immune Response to Dengue Virus: Toll-like Receptors and Antiviral Response

Dengue is a mosquito-borne viral disease caused by the dengue virus (DENV1-4). The clinical manifestations range from asymptomatic to life-threatening dengue hemorrhagic fever (DHF) and/or Dengue Shock Syndrome (DSS). Viral and host factors are related to the clinical outcome of dengue, although the disease pathogenesis remains uncertain. The innate antiviral response to DENV is implemented by a variety of immune cells and inflammatory mediators. Blood monocytes, dendritic cells (DCs) and tissue macrophages are the main target cells of DENV infection. These cells recognize pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs). Pathogen recognition is a critical step in eliciting the innate immune response. Toll-like receptors (TLRs) are responsible for the innate recognition of pathogens and represent an essential component of the innate and adaptive immune response. Ten different TLRs are described in humans, which are expressed in many different immune cells. The engagement of TLRs with viral PAMPs triggers downstream signaling pathways leading to the production of inflammatory cytokines, interferons (IFNs) and other molecules essential for the prevention of viral replication. Here, we summarize the crucial TLRs’ roles in the antiviral innate immune response to DENV and their association with viral pathogenesis.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Melatonin Attenuates LPS-Induced Proinflammatory Cytokine Response and Lipogenesis in Human Meibomian Gland Epithelial Cells via MAPK/NF-κB Pathway

Purpose

Inflammation contributes to the development of meibomian gland dysfunction (MGD) under specific disease conditions, but the underlying mechanisms remain elusive. We examined whether lipopolysaccharide (LPS) induced a proinflammatory cytokine response and lipogenesis in human meibomian gland epithelial cells (HMGECs) and whether melatonin (MLT), a powerful anti-inflammatory regent in the eyes, could protect against LPS-induced disorders.

Methods

Human meibomian gland (MG) tissues and immortalized HMGECs were stained to identify Toll-like receptor (TLR) 4 and MLT receptors (MT₁ and MT₂). HMGECs were pretreated with or without MLT and then stimulated with LPS. Then, TLR4 activation, cytokine levels, lipid synthesis, apoptosis, autophagy, and MAPK/NF-κB factor phosphorylation in HMGECs were analyzed.

Results

TLR4, MT₁, and MT₂ were expressed in human MG acini and HMGECs. Pretreatment with MLT inhibited the TLR4/MyD88 signaling and attenuated proinflammatory cytokine response and lipogenesis in LPS-stimulated HMGECs, which manifested as decreased production of cytokines (IL-1β, IL-6, IL-8, and TNF-α), reduced lipid droplet formation, and downregulated expression of meibum lipogenic proteins (ADFP, ELOVL4, and SREBP-1). Phospho-histone H2A.X foci, lysosome accumulation, and cytoplasmic cleaved caspase 3/LC3B-II staining were increased in LPS-stimulated HMGECs, indicating enhanced cell death mediated by apoptosis and autophagy during LPS-induced lipogenesis. MLT downregulated cleaved caspase 3 levels and the Bax/Bcl-2 ratio to alleviate apoptosis and ameliorated the expression of Beclin 1 and LC3B-II to inhibit autophagy. The protective mechanisms of MLT include the inhibition of MAPK and NF-κB phosphorylation.

Conclusions

MLT attenuated lipogenesis, apoptosis, and autophagy in HMGECs induced by proinflammatory stimuli, indicating the protective potential of MLT in MGD.

MyD88 in hepatic stellate cells enhances liver fibrosis via promoting macrophage M1 polarization

During liver fibrosis, quiescent HSCs (qHSCs) are activated to become activated HSCs (aHSCs)/myofibroblasts. The signal adapter MyD88, an essential component of TLR signaling, plays an important role in liver fibrosis. However, far less is known about the specific effects of MyD88 signaling in both qHSCs and aHSCs in the progress of liver fibrosis. Here, we used a CCl₄-induced mouse fibrosis model in which MyD88 was selectively depleted in qHSCs (GFAP^MyD88−/− mice) or aHSCs (α-SMA^MyD88−/− mice). MyD88 deficiency in qHSCs or aHSCs attenuated liver fibrosis in mice and inhibited α-SMA-positive cell activation. Inhibition of MyD88 in HSCs decreased α-SMA and collagen I levels, inflammatory cell infiltration, and pro-inflammatory gene expression. Furthermore, MyD88 signaling in HSCs increased the secretion of CXCL10, which promoted macrophage M1 polarization through CXCR3, leading to activation of the JAK/STAT1 pathway. Inhibition of CXCL10 attenuated macrophage M1 polarization and reduced liver fibrosis. Thus, MyD88 signaling in HSCs crucially contributes to liver fibrosis and provides a promising therapeutic target for the prevention and treatment of liver fibrosis.

CD14 recycling modulates LPS-induced inflammatory responses of murine macrophages

TLR4 is activated by the bacterial endotoxin lipopolysaccharide (LPS) and triggers two pro-inflammatory signaling cascades: a MyD88-dependent one in the plasma membrane, and the following TRIF-dependent one in endosomes. An inadequate inflammatory reaction can be detrimental for the organism by leading to sepsis. Therefore, novel approaches to therapeutic modulation of TLR4 signaling are being sought after. The TLR4 activity is tightly connected with the presence of CD14, a GPI-anchored protein that transfers LPS monomers to the receptor and controls its endocytosis. In this study we focused on CD14 trafficking as a still poorly understood factor affecting TLR4 activity. Two independent assays were used to show that after endocytosis CD14 can recycle back to the plasma membrane in both unstimulated and stimulated cells. This route of CD14 trafficking can be controlled by sorting nexins (SNX) 1, 2, and 6, and is important for maintaining the surface level and the total level of CD14, but can also affect the amount of TLR4. Silencing of these SNXs attenuated especially the CD14-dependent endosomal signaling of TLR4, making them a new target for therapeutic regulation of the inflammatory response of macrophages to LPS.

TLR4 Signaling and Heme Oxygenase-1/Carbon Monoxide Pathway Crosstalk Induces Resiliency of Myeloma Plasma Cells to Bortezomib Treatment

Relapse in multiple myeloma (MM) decreases therapy efficiency through unclear mechanisms of chemoresistance. Since our group previously demonstrated that heme oxygenase-1 (HO-1) and Toll-like receptor 4 (TLR4) are two signaling pathways protecting MM cells from the proteasome inhibitor bortezomib (BTZ), we here evaluated their cross-regulation by a pharmacological approach. We found that cell toxicity and mitochondrial depolarization by BTZ were increased upon inhibition of HO-1 and TLR4 by using tin protoporphyrin IX (SnPP) and TAK-242, respectively. Furthermore, the combination of TAK-242 and BTZ activated mitophagy and decreased the unfolded protein response (UPR) survival pathway in association with a downregulation in HO-1 expression. Notably, BTZ in combination with SnPP induced effects mirroring the treatment with TAK-242/BTZ, resulting in a blockade of TLR4 upregulation. Interestingly, treatment of cells with either hemin, an HO-1 inducer, or supplementation with carbon monoxide (CO), a by-product of HO-1 enzymatic activity, increased TLR4 expression. In conclusion, we showed that treatment of MM cells with BTZ triggers the TLR4/HO-1/CO axis, serving as a stress-responsive signal that leads to increased cell survival while protecting mitochondria against BTZ and ultimately promoting drug resistance.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

An alternative downstream translation start site in the non-TIR adaptor Scimp enables selective amplification of CpG DNA responses in mouse macrophages

Toll-like receptor (TLR) signaling relies on Toll/interleukin-1 receptor homology (TIR) domain-containing adaptor proteins that recruit downstream signaling molecules to generate tailored immune responses. In addition, the palmitoylated transmembrane adaptor protein family member Scimp acts as a non-TIR-containing adaptor protein in macrophages, scaffolding the Src family kinase Lyn to enable TLR phosphorylation and proinflammatory signaling responses. Here we report the existence of a smaller, naturally occurring translational variant of Scimp (Scimp TV1), which is generated through leaky scanning and translation at a downstream methionine. Scimp TV1 also scaffolds Lyn, but in contrast to full-length Scimp, it is basally rather than lipopolysaccharide (LPS)-inducibly phosphorylated. Macrophages from mice that selectively express Scimp TV1, but not full-length Scimp, have impaired sustained LPS-inducible cytokine responses. Furthermore, in granulocyte macrophage colony-stimulating factor-derived myeloid cells that express high levels of Scimp, selective overexpression of Scimp TV1 enhances CpG DNA-inducible cytokine production. Unlike full-length Scimp that localizes to the cell surface and filopodia, Scimp TV1 accumulates in intracellular compartments, particularly the Golgi. Moreover, this variant of Scimp is not inducibly phosphorylated in response to CpG DNA, suggesting that it may act via an indirect mechanism to enhance TLR9 responses. Our findings thus reveal the use of alternative translation start sites as a previously unrecognized mechanism for diversifying TLR responses in the innate immune system.

Network Pharmacology- and Molecular Docking-Based Identification of Potential Phytocompounds from Argyreia capitiformis in the Treatment of Inflammation

The methanolic extract of Argyreia capitiformis stem was examined for anti-inflammatory activities following network pharmacology analysis and molecular docking study. Based on gas chromatography-mass spectrometry (GC-MS) analysis, 49 compounds were identified from the methanolic extract of A. capitiformis stem. A network pharmacology analysis was conducted against the identified compounds, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and Gene Ontology analysis of biological processes and molecular functions were performed. Six proteins (IL1R1, IRAK4, MYD88, TIRAP, TLR4, and TRAF6) were identified from the KEGG pathway analysis and subjected to molecular docking study. Additionally, six best ligand efficiency compounds and positive control (aspirin) from each protein were evaluated for their stability using the molecular dynamics simulation study. Our study suggested that IL1R1, IRAK4, MYD88, TIRAP, TLR4, and TRAF6 proteins may be targeted by compounds in the methanolic extract of A. capitiformis stem to provide anti-inflammatory effects.

miR-182 targeting reprograms tumor-associated macrophages and limits breast cancer progression

Breast cancer is a major threat of women’s health worldwide. Nontumor cell components play crucial roles in cancer. Macrophages, the cells of the innate immune system that normally exert antitumor activities, can be educated by tumors to an alternatively activated phenotype that is known to promote tumor progression. Understanding the mechanism of macrophage education by tumor cells will help the design of new therapeutic approaches. We find that breast tumor cells induce the expression of a microRNA, miR-182, in macrophages, and miR-182 promotes macrophage alternative activation to drive tumor development. Importantly, using cationized mannan-modified extracellular vesicles to load miR-182 inhibitors and deliver the inhibitors specifically into macrophages can effectively inhibit alternative activation of macrophages and suppress breast tumor development.

The protumor roles of alternatively activated (M2) tumor-associated macrophages (TAMs) have been well established, and macrophage reprogramming is an important therapeutic goal. However, the mechanisms of TAM polarization remain incompletely understood, and effective strategies for macrophage targeting are lacking. Here, we show that miR-182 in macrophages mediates tumor-induced M2 polarization and can be targeted for therapeutic macrophage reprogramming. Constitutive miR-182 knockout in host mice and conditional knockout in macrophages impair M2-like TAMs and breast tumor development. Targeted depletion of macrophages in mice blocks the effect of miR-182 deficiency in tumor progression while reconstitution of miR-182-expressing macrophages promotes tumor growth. Mechanistically, cancer cells induce miR-182 expression in macrophages by TGFβ signaling, and miR-182 directly suppresses TLR4, leading to NFκb inactivation and M2 polarization of TAMs. Importantly, therapeutic delivery of antagomiR-182 with cationized mannan-modified extracellular vesicles effectively targets macrophages, leading to miR-182 inhibition, macrophage reprogramming, and tumor suppression in multiple breast cancer models of mice. Overall, our findings reveal a crucial TGFβ/miR-182/TLR4 axis for TAM polarization and provide rationale for RNA-based therapeutics of TAM targeting in cancer.

A Levee to the Flood: Pre-injury Neuroinflammation and Immune Stress Influence Traumatic Brain Injury Outcome

Increasing evidence demonstrates that aging influences the brain's response to traumatic brain injury (TBI), setting the stage for neurodegenerative pathology like Alzheimer's disease (AD). This topic is often dominated by discussions of post-injury aging and inflammation, which can diminish the consideration of those same factors before TBI. In fact, pre-TBI aging and inflammation may be just as critical in mediating outcomes. For example, elderly individuals suffer from the highest rates of TBI of all severities. Additionally, pre-injury immune challenges or stressors may alter pathology and outcome independent of age. The inflammatory response to TBI is malleable and influenced by previous, coincident, and subsequent immune insults. Therefore, pre-existing conditions that elicit or include an inflammatory response could substantially influence the brain's ability to respond to traumatic injury and ultimately affect chronic outcome. The purpose of this review is to detail how age-related cellular and molecular changes, as well as genetic risk variants for AD affect the neuroinflammatory response to TBI. First, we will review the sources and pathology of neuroinflammation following TBI. Then, we will highlight the significance of age-related, endogenous sources of inflammation, including changes in cytokine expression, reactive oxygen species processing, and mitochondrial function. Heightened focus is placed on the mitochondria as an integral link between inflammation and various genetic risk factors for AD. Together, this review will compile current clinical and experimental research to highlight how pre-existing inflammatory changes associated with infection and stress, aging, and genetic risk factors can alter response to TBI.