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Biosynthesis of paf-acether. XIV. Paf-acether output in murine peritoneal macrophages is regulated by the level of
R Palmantier1, A Dulioust, H Maiza
1INSERM U.200, Université Paris-Sud, Clamart, France.
Abstract:
Paf-acether (paf) synthesis was previously shown to be impaired in 24 hr-adherent and Bacillus Calmette-Guérin-activated murine peritoneal macrophages as compared to resident macrophages. We report here that the induction of acetylhydrolase was responsible for the decreased paf output in 24 hr-adherent macrophages. The kinetic analysis of the enzymes derived from 2 hr-, 24 hr- and BCG-activated adherent macrophages and from plasma revealed that the Km for paf was similar whatever the source of the acetylhydrolase whereas the Vmax was five-fold increased in 24 hr-cultured macrophages. The acetylhydrolase activity was Ca2+-independent and was not inhibited by addition of alkyl-acyl (long chain)-glycero-phosphocholine suggesting that the enzyme was not a phospholipase A2.
Insights
Platelet-activating factor (PAF) synthesis is reduced in activated macrophages due to increased acetylhydrolase activity. This enzyme
Area of Science:
- Immunology
- Biochemistry
Background:
- Platelet-activating factor (PAF) synthesis is impaired in activated murine peritoneal macrophages.
- Resident macrophages exhibit higher PAF synthesis compared to 24-hour adherent and BCG-activated macrophages.
Purpose of the Study:
- To investigate the mechanism behind decreased PAF synthesis in 24-hour adherent macrophages.
- To characterize the acetylhydrolase enzyme involved in PAF metabolism.
Main Methods:
- Kinetic analysis of acetylhydrolase from macrophages (2 hr, 24 hr, BCG-activated) and plasma.
- Enzyme activity assays, including Ca2+ dependence and inhibition studies.
Main Results:
- Increased Vmax of acetylhydrolase in 24-hour cultured macrophages, indicating enhanced activity.
- Similar Km for acetylhydrolase across different macrophage sources and plasma.
- Acetylhydrolase activity was Ca2+-independent and not inhibited by phospholipase A2 inhibitors.
Conclusions:
- Elevated acetylhydrolase activity is responsible for reduced PAF output in 24-hour adherent macrophages.
- The characterized acetylhydrolase is distinct from phospholipase A2.
- Understanding this enzyme's role is crucial for modulating inflammatory responses.