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Molecular mechanism of LPS-induced TNF-α biosynthesis in polarized human macrophages
Erik Schilling1, Ronald Weiss1, Anja Grahnert1
1Institute of Clinical Immunology, Medical Faculty, University of Leipzig, Johannisallee 30, 04103 Leipzig, Germany.
Abstract:
In response to environmental stimuli such as granulocyte-macrophage or macrophage colony stimulating factor (GM-CSF/M-CSF), macrophages (MΦ) can acquire distinct functional phenotypes that control inflammatory processes on the one hand and contribute to a broad spectrum of pathologies on the other. Potential intervention strategies will require an understanding of the signalling processes that are associated with macrophage polarization. In the present study, we show that M-MΦ produce more IFN-β and IL-10 and a lot less TNF-α than do GM-MΦ in response to LPS. To define the molecular mechanisms that underlie the biosynthesis of TNF-α we carried out a detailed investigation of the LPS-induced activation of the canonical and non-canonical myeloid differentiation primary response 88 (MyD88)-dependent signal transduction pathways as well as the TIR-domain-containing adapter-inducing interferon-β (TRIF)-dependent pathway. Our results show that all three pathways are activated in both cell types and that the activation is more pronounced in M-MΦ. While IL-10 was found to interfere with TNF-α production in M-MΦ, we exclude a decisive role for IFN-β in this respect. Furthermore, we demonstrate that TNF-α mRNA is markedly destabilized in M-MΦ and that expression of the mRNA destabilizing protein tristetraprolin is greatly enhanced in these cells. Collectively, our study suggests that differential effects of LPS on TNF-α mRNA turnover and on signal transduction pathways influence the amount of TNF-α finally produced by GM-MΦ and M-MΦ.
Insights
Macrophages polarized by M-CSF (M-MΦ) produce less TNF-α than GM-CSF-polarized macrophages (GM-MΦ) due to enhanced mRNA destabilization, despite increased signaling pathway activation. This impacts inflammatory responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages exhibit diverse functional phenotypes influencing inflammation and disease.
- Macrophage polarization is regulated by signaling pathways, crucial for understanding inflammatory processes.
- Intervention strategies require detailed knowledge of macrophage signaling.
Purpose of the Study:
- To investigate the molecular mechanisms behind differential TNF-α production in M-CSF- vs. GM-CSF-polarized macrophages.
- To analyze the roles of MyD88-dependent and TRIF-dependent pathways in LPS-induced signaling.
- To elucidate the regulation of TNF-α biosynthesis and mRNA stability.
Main Methods:
- Stimulation of macrophages with M-CSF and GM-CSF.
- Analysis of LPS-induced signaling pathways (MyD88, TRIF).
- Quantification of cytokine production (IFN-β, IL-10, TNF-α).
- Investigation of TNF-α mRNA stability and tristetraprolin expression.
Main Results:
- M-MΦ produced significantly less TNF-α but more IFN-β and IL-10 than GM-MΦ upon LPS stimulation.
- All investigated signaling pathways were activated in both macrophage types, with greater activation in M-MΦ.
- IL-10 partially inhibited TNF-α production in M-MΦ, while IFN-β had no decisive role.
- TNF-α mRNA was destabilized in M-MΦ, correlated with increased tristetraprolin expression.
Conclusions:
- Differential TNF-α production by GM-MΦ and M-MΦ is influenced by LPS-induced signaling and mRNA turnover.
- Enhanced TNF-α mRNA destabilization, mediated by tristetraprolin, is a key factor in reduced TNF-α levels in M-MΦ.
- Understanding these mechanisms is vital for targeting macrophage function in inflammatory diseases.
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