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Prostaglandin biosynthesis in pulmonary macrophages
Abstract:
Cultured rabbit alveolar macrophages, prelabeled with 14C-arachidonic acid (AA), released into the medium a trace amount of labeled prostaglandins (PG) as well as their precursor, AA. Phagocytosis of zymosan, heat-killed Staphylococcus, or bacille Calmette-Guérin (BCG) increased the AA and PG release to 2--2.5 times control values. The released PGs consisted of PGE2, D2, F2 alpha, and 6-keto F1 alpha. Phagocytosis of latex particles had no effect on PG release. Indomethacin inhibited release of PGs but did not affect AA release at low doses. Analysis of the cellular lipids showed that zymosan decreased the radioactive label in phosphatidylcholine (PC), but not in other phospholipids or neutral lipids, suggesting that PC is the main source of AA for PG synthesis in pulmonary macrophages. Cytochalasin B (CB) at phagocytosis-inhibiting doses or below, markedly increased PG synthesis by zymosan-treated macrophages. These data suggest that PG release is not dependent on engulfment of the particles. Phagocytosis of zymosan (but not latex) also resulted in the release of two lysosomal enzymes, acid phosphatase and beta-glucuronidase, which appeared temporally associated with the release of PGs (but not to phagocytosis). Furthermore, CB augmented the zymosan-stimulated release of these enzymes at the same doses stimulating PG synthesis. However, indomethacin, at a dose completely inhibiting PG synthesis, failed to block lysosomal enzyme release. Thus, the coincidental release of PGs and lysosomal enzymes is not the result of a regulatory role of PGs in the release of lysosomal enzymes, but probably is the result of a common pathway of stimulation. (Am J Pathol 97:137--148, 1979).
Insights
Phagocytosis stimulates pulmonary macrophages to release arachidonic acid (AA) and prostaglandins (PGs), primarily from phosphatidylcholine. This release is linked to lysosomal enzyme secretion, suggesting a common activation pathway.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Pulmonary macrophages play a crucial role in immune responses.
- Arachidonic acid (AA) metabolism into prostaglandins (PGs) is a key inflammatory pathway.
- The precise mechanisms regulating PG and lysosomal enzyme release in macrophages are not fully understood.
Purpose of the Study:
- To investigate the release of AA and PGs by rabbit alveolar macrophages upon stimulation.
- To identify the cellular source of AA for PG synthesis.
- To explore the relationship between PG release, phagocytosis, and lysosomal enzyme secretion.
Main Methods:
- Cultured rabbit alveolar macrophages were prelabeled with 14C-arachidonic acid (AA).
- Cells were stimulated with various particles (zymosan, Staphylococcus, BCG, latex) and treated with indomethacin or cytochalasin B (CB).
- Released AA, PGs, and lysosomal enzymes were quantified; cellular lipids were analyzed.
Main Results:
- Phagocytosis of zymosan, Staphylococcus, or BCG increased AA and PG release, while latex particles had no effect.
- Phosphatidylcholine (PC) was identified as the main source of AA for PG synthesis.
- Cytochalasin B (CB) enhanced PG and lysosomal enzyme release, suggesting PG release is not dependent on particle engulfment.
- PG and lysosomal enzyme release were temporally associated, but PGs did not regulate enzyme release.
Conclusions:
- Stimulated macrophages release AA and PGs, with PC being the primary AA source.
- PG release is not strictly dependent on particle engulfment.
- Coincidental release of PGs and lysosomal enzymes suggests a shared stimulation pathway.