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Masyutina AM, Maximchik PV, Chkadua GZ, Pashenkov MV. Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance. Front Immunol 2023; 14:1006002. [PMID: 36776861 PMCID: PMC9909295 DOI: 10.3389/fimmu.2023.1006002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 01/09/2023] [Indexed: 01/27/2023] Open
Abstract
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.
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Affiliation(s)
- Anna M. Masyutina
- Laboratory of Clinical Immunology, National Research Center “Institute of Immunology” of the Federal Medical-Biological Agency of Russia, Moscow, Russia,Biological Faculty, Lomonosov Moscow State University, Moscow, Russia
| | - Polina V. Maximchik
- Faculty of Fundamental Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Georgy Z. Chkadua
- Laboratory of experimental diagnostics and biotherapy of tumors, N.N.Blokhin National Medical Research Center of Oncology of the Ministry of Health of the Russian Federation, Moscow, Russia
| | - Mikhail V. Pashenkov
- Laboratory of Clinical Immunology, National Research Center “Institute of Immunology” of the Federal Medical-Biological Agency of Russia, Moscow, Russia,*Correspondence: Mikhail V. Pashenkov,
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Budikhina AS, Murugina NE, Maximchik PV, Dagil YA, Nikolaeva AM, Balyasova LS, Murugin VV, Selezneva EM, Pashchenkova YG, Chkadua GZ, Pinegin BV, Pashenkov MV. Interplay between NOD1 and TLR4 Receptors in Macrophages: Nonsynergistic Activation of Signaling Pathways Results in Synergistic Induction of Proinflammatory Gene Expression. THE JOURNAL OF IMMUNOLOGY 2021; 206:2206-2220. [PMID: 33846227 DOI: 10.4049/jimmunol.2000692] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 02/21/2021] [Indexed: 11/19/2022]
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.
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Affiliation(s)
- Anna S Budikhina
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Nina E Murugina
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Polina V Maximchik
- Faculty of Fundamental Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Yulia A Dagil
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Anna M Nikolaeva
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia.,Biological Faculty, Lomonosov Moscow State University, Moscow, Russia; and
| | - Lyudmila S Balyasova
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Vladimir V Murugin
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | | | - Yulia G Pashchenkova
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Georgy Z Chkadua
- Laboratory of Experimental Diagnostics and Biotherapy of Tumors, N.N. Blokhin National Medical Research Center of Oncology of the Ministry of Health of the Russian Federation, Moscow, Russia
| | - Boris V Pinegin
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia
| | - Mikhail V Pashenkov
- Laboratory of Clinical Immunology, National Research Center Institute of Immunology of the Federal Medical-Biological Agency of Russia, Moscow, Russia;
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