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Autocrine amplification of PAF-acether formation in immunologically activated murine macrophages
Abstract:
When murine macrophages activated in vivo with bacille Calmette-Guérin were triggered with either acetyl-CoA or propionyl-CoA to form PAF-acether (PAF), similar amounts of platelet-aggregating product were recovered. Liquid chromatographic purification and reversed-phase analysis showed that the composition of PAF molecular species formed in the presence of acetyl-CoA was an equimolar mixture of PAF bearing C16:0 alkyl chain (57% +/- 7, mean +/- SD, n = 3) and PAF C18:1. The PAF-like material obtained from the propionyl-CoA-supplemented macrophages was a mixture of the propionyl analogue of PAF (66% +/- 11, n = 3) and native PAF. The rate of lyso-PAF:acetyl-CoA acetyltransferase (EC 2.3.1.67) reaction in a macrophage lysate was similar for either substrate in the presence of an equimolar mixture of propionyl-CoA and acetyl-CoA. We conclude that the exogenously added propionyl-CoA is transferred to lyso-PAF acceptor to form propionyl-PAF by the PAF-forming acetyltransferase. Propionyl-PAF triggers the formation of native PAF probably from the endogenous acetyl-CoA pool. Two specific PAF antagonists, BN 52021 (60 microM) and WEB 2086 (3 microM), did not influence the rate of PAF synthesis in the presence of either acetyl-CoA or propionyl-CoA and did not prevent native PAF formation when propionyl-CoA was added alone, suggesting that the classical PAF receptors are not involved. This is the first description of a possible mechanism of autocrine amplification of PAF biosynthesis in macrophages.
Insights
Propionyl-CoA can trigger macrophages to produce platelet-activating factor (PAF) and its analogue, propionyl-PAF. This suggests a novel autocrine amplification pathway for PAF biosynthesis independent of classical PAF receptors.
Area of Science:
- Immunology
- Biochemistry
Background:
- Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammation and immune responses.
- Macrophages play a crucial role in immune cell signaling and can synthesize PAF.
Purpose of the Study:
- To investigate the role of propionyl-CoA in PAF biosynthesis in activated murine macrophages.
- To elucidate the mechanism of PAF formation and potential autocrine signaling.
Main Methods:
- Murine macrophages were activated with bacille Calmette-Guérin and stimulated with acetyl-CoA or propionyl-CoA.
- PAF molecular species were analyzed using liquid chromatography and reversed-phase analysis.
- The activity of lyso-PAF:acetyl-CoA acetyltransferase was assessed in macrophage lysates.
- The effect of PAF antagonists (BN 52021, WEB 2086) on PAF synthesis was evaluated.
Main Results:
- Both acetyl-CoA and propionyl-CoA stimulated PAF production in activated macrophages.
- Acetyl-CoA led to the formation of PAF with C16:0 and C18:1 alkyl chains.
- Propionyl-CoA resulted in a mixture of propionyl-PAF and native PAF.
- Lyso-PAF:acetyl-CoA acetyltransferase showed similar activity with both substrates.
- PAF antagonists did not inhibit PAF synthesis, suggesting a non-classical receptor mechanism.
Conclusions:
- Exogenous propionyl-CoA is converted to propionyl-PAF by PAF-forming acetyltransferase.
- Propionyl-PAF likely stimulates endogenous PAF production, indicating an autocrine amplification loop.
- This novel mechanism of PAF biosynthesis appears independent of classical PAF receptors.