Interplay between NOD1 and TLR4 Receptors in Macrophages: Nonsynergistic Activation of Signaling Pathways Results in Synergistic Induction of Proinflammatory Gene Expression

A Bibliometric Analysis of Macrophage Research Associated with Periodontitis Over the Past Two Decades

Macrophages are vital for regulating periodontal health, and numerous studies have extensively investigated their role in periodontitis progression. This study employs bibliometric analysis to identify research trends and hotspots related to macrophages in periodontitis from 2004 to 2024, thereby guiding future investigations and exploring potential clinical applications. Literature retrieval and dataset export were conducted via the Web of Science Core Collection database. Subsequently, bibliometric analysis was performed and the results were visualized using Microsoft Office Excel, VOSviewer, CiteSpace, and GraphPad Prism. A total of 1542 papers from 2004 to 2024 on the macrophages associated with periodontitis were identified. The annual number of publications and citations has steadily increased. China and the United States were the primary collaborators and drivers of research. Sichuan University had the largest number of published studies. The Journal of Periodontal Research published the most papers, while the Journal of Periodontology had the most citations. Daniel Grenier was the most prolific author and George Hajishengallis was the most frequently co-cited author. Co-citation analysis indicated that researchers primarily investigate the mechanisms of macrophages in periodontitis through both in vivo and in vitro experiments. Emerging research hotspots encompass keywords such as "macrophage polarization," "extracellular vesicles," and "regeneration." Research on macrophages in periodontitis is progressing quickly, and their strategic targeting offers a new and promising direction for future studies on regenerating periodontal tissues. The utilization of extracellular vesicles derived from diverse sources to regulate M1/M2 macrophage polarization presents a promising strategy for the treatment of periodontitis.

NOD1 and NOD2: Essential Monitoring Partners in the Innate Immune System

Nucleotide-binding oligomerization domain containing 1 (NOD1) and NOD2 are pivotal cytoplasmic pattern-recognition receptors (PRRs) that exhibit remarkable evolutionary conservation. They possess the ability to discern specific peptidoglycan (PGN) motifs, thereby orchestrating innate immunity and contributing significantly to immune homeostasis maintenance. The comprehensive understanding of both the structure and function of NOD1 and NOD2 has been extensively elucidated. These receptors proficiently recognize an array of damage-associated molecular patterns (DAMPs) as well as pathogen-associated molecular patterns (PAMPs), subsequently mediating inflammatory responses and autophagy. In recent years, emerging evidence has highlighted the crucial roles played by NOD1 and NOD2 in regulating infectious diseases, metabolic disorders, cancer, and autoimmune conditions, among others. Perturbation in either their loss or excessive activation can detrimentally impact immune homeostasis. This review offers a comprehensive overview of the structural characteristics, subcellular localization, activation mechanisms, and significant roles of NOD1 and NOD2 in innate immunity and related disease.

IL-4-induced SOX9 confers lineage plasticity to aged adult lung stem cells

Wound healing in response to acute injury is mediated by the coordinated and transient activation of parenchymal, stromal, and immune cells that resolves to homeostasis. Environmental, genetic, and epigenetic factors associated with inflammation and aging can lead to persistent activation of the microenvironment and fibrosis. Here, we identify opposing roles of interleukin-4 (IL-4) cytokine signaling in interstitial macrophages and type II alveolar epithelial cells (ATIIs). We show that IL4Ra signaling in macrophages promotes regeneration of the alveolar epithelium after bleomycin-induced lung injury. Using organoids and mouse models, we show that IL-4 directly acts on a subset of ATIIs to induce the expression of the transcription factor SOX9 and reprograms them toward a progenitor-like state with both airway and alveolar lineage potential. In the contexts of aging and bleomycin-induced lung injury, this leads to aberrant epithelial cell differentiation and bronchiolization, consistent with cellular and histological changes observed in interstitial lung disease.

The adjuvant effect of polymuramil, a NOD1 and NOD2 agonist, differs when immunizing mice of different inbred lines with nonstructural hepatitis C virus (Flaviviridae: Hepacivirus)proteins and is synergistically enhanced in combination with pyrogenalum, a TLR4 agonist

INTRODUCTION

Hepatitis C is a liver disease with high chronicity, the cause of cirrhosis and hepatocarcinoma. The main obstacle to controlling hepatitis C is the lack of vaccines. The aim of the work was to compare the immunogenic activity of nonstructural recombinant proteins NS3, NS4 and NS5B of hepatitis C virus (HCV) as components of a subunit candidate vaccine and to analyze the adjuvant properties of two available commercial drugs, polymuramil and pyrogenalum.

MATERIALS AND METHODS

BALB/c, DBA/2J and C57BL/6 mice were immunized with nonstructural proteins without adjuvants or with polymuramyl (NOD1 and NOD2 agonist) and pyrogenalum (TLR-4 agonist). The activity of antibodies was determined in ELISA, the cellular response - by antigen-specific lymphocyte proliferation and by production of IFN-γ in vitro.

RESULTS

Recombinant proteins showed different immunogenicity. NS4 induced antibodies more efficiently than NS3 and NS5B. Significant differences were found in the immune response of three inbred lines mice: the level of IFN-γ in BALB/c and DBA/2J mice induced by NS5B protein was 30 times higher than in C57Bl/6 mice. In contrast, the induction of antibodies in BALB/c mice was lower than in C57Bl/6 and DBA/2J. Polymuramil did not increase the humoral response to NS5B and enhanced the cellular response only in C57BL/6 mice. The combined use of polymuramil with pyrogenalum significantly increased both the humoral and cellular response of mice to all recombinant HCV proteins.

CONCLUSION

Different immunogenic properties and different functions of recombinant non-structural HCV proteins indicate the feasibility of their combined inclusion in subunit vaccines. It was established for the first time that immunization with HCV proteins with a complex adjuvant (polymuramyl + pyrogenalum) has a synergistic effect, significantly exceeding the effect of each of them separately.

Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance

Introduction

Macrophages activated through a pattern-recognition receptor (PRR) enter a transient state of tolerance characterized by diminished responsiveness to restimulation of the same receptor. Signaling-based and epigenetic mechanisms are invoked to explain this innate tolerance. However, these two groups of mechanisms should result in different outcomes. The epigenetic scenario (silencing of effector genes) predicts that activation of a PRR should broadly cross-tolerize to agonists of unrelated PRRs, whereas in the signaling-based scenario (inhibition of signaling pathways downstream of specific PRRs), cross-tolerization should occur only between agonists utilizing the same PRR and/or signaling pathway. Also, the so-called non-tolerizeable genes have been described, which acquire distinct epigenetic marks and increased responsiveness to rechallenge with the same agonist. The existence of such genes is well explained by epigenetic mechanisms but difficult to explain solely by signaling mechanisms.

Methods

To evaluate contribution of signaling and epigenetic mechanisms to innate tolerance, we tolerized human macrophages with agonists of TLR4 or NOD1 receptors, which signal via distinct pathways, and assessed responses of tolerized cells to homologous restimulation and to cross-stimulation using different signaling, metabolic and transcriptomic read-outs. We developed a transcriptomics-based approach to distinguish responses to secondary stimulation from continuing responses to primary stimulation.

Results

We found that macrophages tolerized with a NOD1 agonist lack responses to homologous restimulation, whereas LPS-tolerized macrophages partially retain the ability to activate NF-κB pathway upon LPS rechallenge, which allows to sustain low-level expression of a subset of pro-inflammatory genes. Contributing to LPS tolerance is blockade of signaling pathways required for IFN-β production, resulting in 'pseudo-tolerization' of IFN-regulated genes. Many genes in NOD1- or TLR4-tolerized macrophages are upregulated as the result of primary stimulation (due to continuing transcription and/or high mRNA stability), but do not respond to homologous restimulation. Hyperresponsiveness of genes to homologous rechallenge is a rare and inconsistent phenomenon. However, most genes that have become unresponsive to homologous stimuli show unchanged or elevated responses to agonists of PRRs signaling via distinct pathways.

Discussion

Thus, inhibition of specific signaling pathways rather than epigenetic silencing is the dominant mechanism of innate tolerance.

miR-146 Relieves Acute Asthma via Decreasing Epidermal Growth Factor Receptor/Toll-Like Receptor 4 (EGFR/TLR4) and Enhancing Autophagy

There is a close relationship between acute asthma and autophagy. In addition, some studies claim that miR-146 can regulate autophagy and participate in acute asthma. This study further explores the role of miR-146 in acute asthma and underlying mechanism. Twenty BALB/c mice were selected and randomly divided into two groups, the model group and the control group, each with 10 mice. Lung tissues, peripheral blood, alveolar lavage fluid, and primary lymphocytes were separated into miR-146 over expression group (miR-146 mimic), miR-146 low expression group (miR-146 inhibitor), negative control group (NC), blank group, or SBI-0206965 group. Acute asthma was established and the expression levels of miR-146, EGFR, TLR4, LC3, beclin1, and ATG5 in each group was measured. The targeting relationship and correlation between miR-146 and EGFR were also investigated. The expression of IL-4 in model group was increased compared to control arm while the expression of IFN-γ was opposite (P < 0.05). The expressions of miR-146, LC3, beclin1, and the expression of ATG5 were decreased (P < 0.05). The expressions of miR-146 gene and LC3, beclin1, ATG5 mRNA and protein in the miR-146 mimic group were the highest, while the expressions of EGFR and TLR4 were the lowest. The SBI-0206965 group and the miR-146 inhibitor group are opposite to the miR-146 mimic group, the SBI-0206965 group and the miR-146 inhibitor group have significant differences (P < 0.05). miR-146 has a directly targeted EGFR and TLR4, and both showed a negative correlation (rEGFR=−0.397, P = 0.013; rTLR4=−0.402, P = 0.021). During the onset of asthma, miR-146 was abnormally decreased. miR-146 directly targets and negatively regulates EGFR. In addition, miR-146 down-regulates TLR4 gene to increase CD4+ lymphocytes’ aphagocytosis-related markers (LC3, beclin1, ATG5) which further promotes the autophagy process and ultimately alleviates the degree of acute asthma. Its main mechanism is related to the down-regulation of the EGFR/TLR4 through regulated the expression of autophagy. Our study provided a scientific reference for further understanding of acute pathogenesis of asthma.

Modifiable Innate Biology within the Gut–Brain Axis for Alzheimer’s Disease

Alzheimer’s disease (AD) is a prototypical inflammation-associated loss of cognitive function, with approximately 90% of the AD burden associated with invading myeloid cells controlling the function of the resident microglia. This indicates that the immune microenvironment has a pivotal role in the pathogenesis of the disease. Multiple peripheral stimuli, conditioned by complex and varied interactions between signals that stem at the intestinal level and neuroimmune processes, are involved in the progression and severity of AD. Conceivably, the targeting of critical innate immune signals and cells is achievable, influencing immune and metabolic health within the gut–brain axis. Considerable progress has been made, modulating many different metabolic and immune alterations that can drive AD development. However, non-pharmacological strategies targeting immunometabolic processes affecting neuroinflammation in AD treatment remain general and, at this point, are applied to all patients regardless of disease features. Despite these possibilities, improved knowledge of the relative contribution of the different innate immune cells and molecules comprising the chronically inflamed brain network to AD pathogenesis, and elucidation of the network hierarchy, are needed for planning potent preventive and/or therapeutic interventions. Moreover, an integrative perspective addressing transdisciplinary fields can significantly contribute to molecular pathological epidemiology, improving the health and quality of life of AD patients. This review is intended to gather modifiable immunometabolic processes based on their importance in the prevention and management of AD.

Nucleotide-Binding Oligomerization Domain 1/Toll-Like Receptor 4 Co-Engagement Promotes Non-Specific Immune Response Against K562 Cancer Cells

Nucleotide-binding oligomerization domain 1 (NOD1) receptor and Toll-like receptor 4 (TLR4) belong to the family of pattern recognition receptors. Interactions between these receptors profoundly shape the innate immune responses. We previously demonstrated that co-stimulation of peripheral blood mononuclear cells (PBMCs) with D-glutamyl-meso-diaminopimelic acid (iE-DAP)-based NOD1 agonists and lipopolysaccharide (LPS), a TLR4 agonist, synergistically increased the cytokine production. Herein, we postulate that stimulation of NOD1 alone or a combined stimulation of NOD1 and TLR4 could also strengthen PBMC-mediated cytotoxicity against cancer cells. Initially, an in-house library of iE-DAP analogs was screened for NOD1 agonist activity to establish their potency in HEK-Blue NOD1 cells. Next, we showed that our most potent NOD1 agonist SZZ-38 markedly enhanced the LPS-induced cytokine secretion from PBMCs, in addition to PBMC- and natural killer (NK) cell-mediated killing of K562 cancer cells. Activation marker analysis revealed that the frequencies of CD69⁺, CD107a⁺, and IFN-γ⁺ NK cells are significantly upregulated following NOD1/TLR4 co-stimulation. Of note, SZZ-38 also enhanced the IFN-γ-induced PBMC cytotoxicity. Overall, our findings provide further insight into how co-engagement of two pathways boosts the non-specific immune response and attest to the importance of such interplay between NOD1 and TLR4.

NOD1 splenic activation confers ferroptosis protection and reduces macrophage recruitment under pro-atherogenic conditions

The bioavailability and regulation of iron is essential for central biological functions in mammals. The role of this element in ferroptosis and the dysregulation of its metabolism contribute to diseases, ranging from anemia to infections, alterations in the immune system, inflammation and atherosclerosis. In this sense, monocytes and macrophages modulate iron metabolism and splenic function, while at the same time they can worsen the atherosclerotic process in pathological conditions. Since the nucleotide-binding oligomerization domain 1 (NOD1) has been linked to numerous disorders, including inflammatory and cardiovascular diseases, we investigated its role in iron homeostasis. The iron content was measured in various tissues of Apoe-/- and Apoe-/-Nod1-/- mice fed a high-fat diet (HFD) for 4 weeks, under normal or reduced splenic function after ligation of the splenic artery. In the absence of NOD1 the iron levels decreased in spleen, heart and liver regardless the splenic function. This iron decrease was accompanied by an increase in the recruitment of F4/80+-macrophages in the spleen through a CXCR2-dependent signaling, as deduced by the reduced recruitment after administration of a CXCR2 inhibitor. CXCR2 mediates monocyte/macrophage chemotaxis to areas of inflammation and accumulation of leukocytes in the atherosclerotic plaque. Moreover, in the absence of NOD1, inhibition of CXCR2 enhanced atheroma progression. NOD1 activation increased the levels of GPX4 and other iron and ferroptosis regulatory proteins in macrophages. Our findings highlight the preeminent role of NOD1 in iron homeostasis and ferroptosis. These results suggest promising avenues of investigation for the diagnosis and treatment of iron-related diseases directed by NOD1.

Polarized Macrophages in Periodontitis: Characteristics, Function, and Molecular Signaling

Periodontitis (PD) is a common chronic infectious disease. The local inflammatory response in the host may cause the destruction of supporting periodontal tissue. Macrophages play a variety of roles in PD, including regulatory and phagocytosis. Moreover, under the induction of different factors, macrophages polarize and form different functional phenotypes. Among them, M1-type macrophages with proinflammatory functions and M2-type macrophages with anti-inflammatory functions are the most representative, and both of them can regulate the tendency of the immune system to exert proinflammatory or anti-inflammatory functions. M1 and M2 macrophages are involved in the destructive and reparative stages of PD. Due to the complex microenvironment of PD, the dynamic development of PD, and various local mediators, increasing attention has been given to the study of macrophage polarization in PD. This review summarizes the role of macrophage polarization in the development of PD and its research progress.

Peripheral blood concentration of toll-like receptor-4 and its accuracy for prediction of postpartum performances of transition zebu (Bos indicus) cows

In this study, we evaluated the peripheral concentrations of Toll-like receptors (TLR)-4 during transition period in relation to postpartum productive and reproductive performances of Deoni (zebu) cattle. Accuracy and threshold values of TLR-4 to predict the postpartum performance, were also estimated using receiver operating characteristics (ROC) analysis. Blood samples were collected at weekly intervals during transition period (from 21 days before to 21 days after calving) and TLR-4 concentration was estimated using bovine specific ELISA kits. Plasma TLR-4 concentration was significantly higher on third day of postpartum in cows that became pregnant within breeding period than the cows that remained non-pregnant (4.48 vs 1.80 ng/mL). ROC analysis revealed that the accuracy of TLR-4 for predication of ability to become pregnant within breeding period was acceptable (AUC: 0.75) with a threshold value of 2.13 ng/mL. It is concluded that concentrations of TLR-4, during transition period, could be used for predicting the possibilities of Deoni cows getting pregnant within the breeding period with moderate accuracy.