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

Abstract

Interactions between pattern-recognition receptors shape innate immune responses to pathogens. NOD1 and TLR4 are synergistically interacting receptors playing a pivotal role in the recognition of Gram-negative bacteria. However, mechanisms of their cooperation are poorly understood. It is unclear whether synergy is produced at the level of signaling pathways downstream of NOD1 and TLR4 or at more distal levels such as gene transcription. We analyzed sequential stages of human macrophage activation by a combination of NOD1 and TLR4 agonists (N-acetyl-d-muramyl-l-alanyl-d-isoglutamyl-meso-diaminopimelic acid [M-triDAP] and LPS, respectively). We show that events preceding or not requiring activation of transcription, such as activation of signaling kinases, rapid boost of glycolysis, and most importantly, nuclear translocation of NF-κB, are regulated nonsynergistically. However, at the output of the nucleus, the combination of M-triDAP and LPS synergistically induces expression of a subset of M-triDAP– and LPS-inducible genes, particularly those encoding proinflammatory cytokines (TNF, IL1B, IL6, IL12B, and IL23A). This synergistic response develops between 1 and 4 h of agonist treatment and requires continuous signaling through NOD1. The synergistically regulated genes have a lower basal expression and higher inducibility at 4 h than those regulated nonsynergistically. Both gene subsets include NF-κB–inducible genes. Therefore, activation of the NF-κB pathway does not explain synergistic gene induction, implying involvement of other transcription factors. Inhibition of IKKβ or p38 MAPK lowers agonist-induced TNF mRNA expression but does not abolish synergy. Thus, nonsynergistic activation of NOD1- and TLR4-dependent signaling pathways results in the synergistic induction of a proinflammatory transcriptional program.

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

“…Similarly, we demonstrated that co-stimulation of PBMCs with NOD1 agonists and LPS brought about a substantial increase in cytokine production (Jakopin et al, 2013). It is worth noting that NOD1/TLR4 synergy extends across different cell types and has also been observed in macrophages (Budikhina et al, 2021), bone-marrow derived DCs (BMDCs) (Masumoto et al, 2006;Xu and Daicoli, 2010), DCs (Tada et al, 2005), invariant natural killer T cells (Selvanantham et al, 2013) and mesothelial cells (Park et al, 2007).…”

Differential adaptation of metabolic inflammation between primiparous and multiparous Zebu cows during transition period

“…Studies from same animals revealed that TLR-4 is an important innate immune molecule to regulate postpartum performance during transition period (Manimaran et al 2021). TLR-4 mediated synthesis of pro-inflammatory cytokines such as TNF-α, IL-β and IL-6 is an important innate immune regulation mechanism (Bronzo et al 2020, Budikhina et al 2021) and same could be the reason for higher levels of cytokines and Hp in multiparous cows. IL-8 is an important inflammatory cytokine and primary chemoattractant for immune cells at the site of infections.…”

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

“…Different ligands, receptors, enzymes, transcription factors and other molecules closely cooperate to enable macrophages to exert more precise regulatory ability ( 133 ), and different concentrations of the same cytokines can trigger and activate different signaling pathways ( 134 ). Key receptors for the polarization of M1-type macrophages include NOD1 and TLR4, which can individually or synergistically activate NF-κB, MAPK and other signaling pathways, triggering the activation and expression of M1 ( 135 ). Different SPMs can inhibit M1 polarization or promote M2 polarization to promote the elimination of inflammation through NF-κB, PPAR-γ and other signaling pathways ( 108 , 136 ).…”