Simultaneous stimulation of EP2 and EP4 is essential to the effect of prostaglandin E2 in chondrocyte differentiation.
OBJECTIVE
Prostaglandin E(2)(PGE(2)) has been reported to stimulate chondrocyte differentiation. However, the precise actions and signal transduction pathways of PGE(2)in cartilage are largely unknown. Our purpose is to identify which of the four PGE(2)receptor subtype(s), EP1-4, mediates the action of PGE(2)on chondrocyte differentiation.


METHODS
We used primary chondrocytes derived from the resting zone of rat rib cartilage. The effects on chondrocyte differentiation were assessed by measuring the Alcian blue-stainable proteoglycan content and the expression levels of type II collagen mRNA by Northern blot analysis. The expression of the four PGE(2)receptor subtypes in rat primary chondrocytes was examined by reverse transcription-polymerase chain reaction.


RESULTS
PGE(2)stimulated the accumulation of proteoglycan and up-regulated the expression of type II collagen mRNA in primary chondrocytes. Dibutyryl cAMP, a cell-permeable analog of cAMP, an important intracellular mediator of PGE(2)signaling, also enhanced the expression of type II collagen mRNA and proteoglycan accumulation in chondrocytes. No EP agonist alone induced the expression of type II collagen mRNA. However, simultaneous administration of EP2 and EP4 agonists at high concentrations cooperatively induced the expression of type II collagen mRNA, mimicking the PGE(2)effect. The simultaneous stimulation of EP2 and EP4 also cooperatively enhanced proteoglycan accumulation and intracellular cAMP production. Moreover, an EP4 antagonist partially blocked the stimulatory actions of PGE(2)on the expression of type II collagen mRNA.


CONCLUSIONS
These results suggest that simultaneous stimulation of EP2 and EP4 is necessary and sufficient to elicit the effect of PGE(2)on rat primary chondrocyte differentiation.
Miyamoto
M
M
Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Sakyo, Kyoto 606-8507, Japan.
Ito
H
H
Mukai
S
S
Kobayashi
T
T
Yamamoto
H
H
Kobayashi
M
M
Maruyama
T
T
Akiyama
H
H
Nakamura
T
T
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects* / Q000378:metabolism; D024043:Collagen Type II / Q000096:biosynthesis / Q000235:genetics; D000242:Cyclic AMP / Q000096:biosynthesis; D015232:Dinoprostone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D011509:Proteoglycans / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000378:metabolism*; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058309:Receptors, Prostaglandin E, EP4 Subtype; D015854:Up-Regulation
D024043:Collagen Type II; D011509:Proteoglycans; C545646:Ptger2 protein, rat; C545652:Ptger4 protein, rat; D012333:RNA, Messenger; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D058309:Receptors, Prostaglandin E, EP4 Subtype; D000242:Cyclic AMP; D015232:Dinoprostone