Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance
IntroductionMacrophages 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...
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| Format: | Article |
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Frontiers Media S.A.
2023-01-01
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| Series: | Frontiers in Immunology |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fimmu.2023.1006002/full |
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| author | Anna M. Masyutina Anna M. Masyutina Polina V. Maximchik Georgy Z. Chkadua Mikhail V. Pashenkov |
| author_facet | Anna M. Masyutina Anna M. Masyutina Polina V. Maximchik Georgy Z. Chkadua Mikhail V. Pashenkov |
| author_sort | Anna M. Masyutina |
| collection | DOAJ |
| description | IntroductionMacrophages 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.MethodsTo 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.ResultsWe 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.DiscussionThus, inhibition of specific signaling pathways rather than epigenetic silencing is the dominant mechanism of innate tolerance. |
| first_indexed | 2024-04-10T20:13:33Z |
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| id | doaj.art-7a1f183895084c9ebff95d3efdc4b204 |
| institution | Directory Open Access Journal |
| issn | 1664-3224 |
| language | English |
| last_indexed | 2024-04-10T20:13:33Z |
| publishDate | 2023-01-01 |
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| series | Frontiers in Immunology |
| spelling | doaj.art-7a1f183895084c9ebff95d3efdc4b2042023-01-26T07:52:08ZengFrontiers Media S.A.Frontiers in Immunology1664-32242023-01-011410.3389/fimmu.2023.10060021006002Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate toleranceAnna M. Masyutina0Anna M. Masyutina1Polina V. Maximchik2Georgy Z. Chkadua3Mikhail V. Pashenkov4Laboratory of Clinical Immunology, National Research Center “Institute of Immunology” of the Federal Medical-Biological Agency of Russia, Moscow, RussiaBiological Faculty, Lomonosov Moscow State University, Moscow, RussiaFaculty of Fundamental Medicine, Lomonosov Moscow State University, Moscow, RussiaLaboratory 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, RussiaLaboratory of Clinical Immunology, National Research Center “Institute of Immunology” of the Federal Medical-Biological Agency of Russia, Moscow, RussiaIntroductionMacrophages 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.MethodsTo 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.ResultsWe 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.DiscussionThus, inhibition of specific signaling pathways rather than epigenetic silencing is the dominant mechanism of innate tolerance.https://www.frontiersin.org/articles/10.3389/fimmu.2023.1006002/fullinnate immune responsetolerancelipopolysaccharideTLR4muramyl peptidesNOD1 |
| spellingShingle | Anna M. Masyutina Anna M. Masyutina Polina V. Maximchik Georgy Z. Chkadua Mikhail V. Pashenkov Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance Frontiers in Immunology innate immune response tolerance lipopolysaccharide TLR4 muramyl peptides NOD1 |
| title | Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| title_full | Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| title_fullStr | Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| title_full_unstemmed | Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| title_short | Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| title_sort | inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance |
| topic | innate immune response tolerance lipopolysaccharide TLR4 muramyl peptides NOD1 |
| url | https://www.frontiersin.org/articles/10.3389/fimmu.2023.1006002/full |
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