Arachidonic acid inhibits osteoblast differentiation through cytosolic phospholipase A2-dependent pathway.
OBJECTIVE
Arachidonic acid, a precursor of prostaglandins (PGs), is released by phospholipase A2 (PLA2) and plays an important role in biological reactions. We examined the roles of arachidonic acid on the pathway of PG synthesis and osteoblast differentiation by using clone MC3T3-E1 cells.


METHODS
The effect of arachidonic acid was evaluated by the measurement of alkaline phosphatase activity, cells shape, production of arachidonic acid and the expression of cyclooxygenase (COX).


RESULTS
Arachidonic acid dose dependently decreased alkaline phosphatase activity and increased PGE2 production in MC3T3-E1 cells. The cell shape changed from polygonal to fibroblastic following treatment with arachidonic acid. These effects were recovered by the treatment of NS-398 and indomethacin. Arachidonic acid increased the expression of COX-2 mRNA and the PGE2 production. The exogenous arachidonic acid induced the release of cellular arachidonic acid in MC3T3-E1 cells. Moreover, methylarachidonyl fluorophosphonate suppressed the arachidonic acid release and the expression of COX-2 mRNA.


CONCLUSIONS
The present results indicate that exogenous arachidonic acid stimulated the activity of PLA2, leading to the new release of membranous arachidonic acid. The amplified arachidonic acid enhanced PGE2 production by COX-2, which inhibits the differentiation of MC3T3-E1 cells. Our results provide a new insight into the molecular mechanisms by which exogenous arachidonic acid plays a role as a paracrine/autocrine amplifier of PGE2 biosynthesis by coupling with PLA2 and COX-2.
Yoshida
K
K
Department of Histology and Oral Histology, Institute of Health Biosciences, The University of Tokushima Graduate School, Kuramoto, Tokushima, Japan. kaya@dent.tokushima-u.ac.jp
Shinohara
H
H
Haneji
T
T
Nagata
T
T
D016475:3T3 Cells; D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D016718:Arachidonic Acid / Q000096:biosynthesis / Q000494:pharmacology*; D001095:Arachidonic Acids / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002999:Clone Cells; D051546:Cyclooxygenase 2 / Q000187:drug effects; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology*; D015232:Dinoprostone / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects; D007213:Indomethacin / Q000494:pharmacology; D051379:Mice; D009578:Nitrobenzenes / Q000494:pharmacology; D063065:Organophosphonates / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000187:drug effects*; D054467:Phospholipases A2; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis; D011453:Prostaglandins / Q000096:biosynthesis; D012333:RNA, Messenger / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology
D001095:Arachidonic Acids; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D009578:Nitrobenzenes; D063065:Organophosphonates; D011453:Prostaglandins; D012333:RNA, Messenger; D013449:Sulfonamides; C104810:methyl arachidonylfluorophosphonate; C080955:N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide; D016718:Arachidonic Acid; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D010741:Phospholipases A; D054467:Phospholipases A2; D000469:Alkaline Phosphatase; D015232:Dinoprostone; D007213:Indomethacin