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Prostaglandin E2 affects differently the release of inflammatory mediators from resident macrophages by LPS and
P Dieter1, U Hempel, S Kamionka
1Institute of Physiological Chemistry, Medical Faculty, Dresden University of Technology, Germany. dieter@rcs.urz.tu-dresden.de
Abstract:
LPS and MTP-PE (liposome-encapsulated N-acetyl-muramyl-L-alanyl-D-isoglutaminyl-L-alanine-2-:[1',2'dipalmitoyl -sni-glycero-3-(hydroxy-phosphoryl-oxyl)] etylamide) induce in liver macrophages a synthesis and release of TNF-alpha, nitric oxide and prostanoids. Both agents induce an expression of mRNA's encoding TNF-alpha, inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, and of corresponding proteins. LPS and MTP-PE induce a rapid activation of the extracellular regulated kinase (ERK) isoenzymes-1 and -2. Inhibition of map kinase isoenzymes leads to a decreased release of TNF-alpha, nitric oxide and prostaglandin (PG) E2 after both agents. The transcription factors NF-kappaB and AP-1 are strongly activated by LPS within 30 minutes. MTP-PE induces a weak activation of both transcription factors only after 5 hours. Inhibition of NF-kappaB inhibits the LPS- but not the MTP-PE-induced release of TNF-alpha, nitric oxide and PGE2. PGE2 release after LPS is higher than after MTP-PE. Exogenously added PGE2 inhibits the activation of map kinase and TNF-alpha release by LPS, but not by MTP-PE. Release of nitric oxide after LPS and MTP-PE is enhanced after prior addition of PGE2. PGD2 is without any effect. MTP-PE, but not LPS, induces a cytotoxicity of Kupffer cells against P815 tumor target cells. The MTP-PE-induced cytotoxicity is reduced by TNF-alpha neutralizing antibodies, indicating the involvement of TNF-alpha. Thus our results suggest that the different potencies of LPS and MTP-PE as immunomodulators probably result from different actions on Kupffer cells, resulting in differences in the amounts and kinetics of released TNF-alpha and PGE2, and that PGE2 plays an important regulatory role in the action of LPS, but not in the actions of MTP-PE.
Insights
Lipopolysaccharide (LPS) and MTP-PE activate liver macrophages, releasing TNF-alpha and nitric oxide. Prostaglandin E2 (PGE2) differentially regulates these responses, impacting immunomodulation potency.
Area of Science:
- Immunology and Molecular Biology
- Macrophage Activation and Signaling
Background:
- Lipopolysaccharide (LPS) and MTP-PE are potent immunomodulators that activate liver macrophages (Kupffer cells).
- These agents induce the release of key inflammatory mediators, including TNF-alpha, nitric oxide, and prostanoids.
Purpose of the Study:
- To investigate the distinct molecular mechanisms underlying the immunomodulatory effects of LPS and MTP-PE in liver macrophages.
- To elucidate the role of prostaglandin E2 (PGE2) in modulating the cellular responses to LPS and MTP-PE.
Main Methods:
- Analysis of mRNA and protein expression for TNF-alpha, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2).
- Assessment of extracellular regulated kinase (ERK) pathway activation and transcription factor activity (NF-kappaB, AP-1).
- Evaluation of Kupffer cell cytotoxicity and the impact of PGE2 on mediator release and signaling pathways.
Main Results:
- Both LPS and MTP-PE induced TNF-alpha, nitric oxide, and prostanoid release, with differential kinetics and potency.
- LPS triggered rapid NF-kappaB and AP-1 activation, while MTP-PE showed weak activation later. PGE2 differentially regulated LPS and MTP-PE effects.
- MTP-PE induced Kupffer cell cytotoxicity, dependent on TNF-alpha, unlike LPS.
Conclusions:
- Differential activation of Kupffer cells by LPS and MTP-PE, particularly regarding TNF-alpha and PGE2 release kinetics, underlies their distinct immunomodulatory potencies.
- PGE2 plays a critical regulatory role in LPS-mediated responses but not in MTP-PE actions.
- MTP-PE's cytotoxicity is mediated by TNF-alpha, highlighting its specific immunomodulatory profile.