PGE2 signal through EP2 promotes the growth of articular chondrocytes.
EP2 was identified as the major PGE2 receptor expressed in articular cartilage. An EP2 agonist increased intracellular cAMP in articular chondrocytes, stimulating DNA synthesis in both monolayer and 3D cultures. Hence, the EP2 agonist may be a potent therapeutic agent for degenerative cartilage diseases.


BACKGROUND
Prostaglandin E2 (PGE2) exhibits pleiotropic effects in various types of tissue through four types of receptors, EP1-4. We examined the expression of EPs and effects of agonists for each EP on articular chondrocytes.


METHODS
The expression of each EP in articular chondrocytes was examined by immunohistochemistry and RT-PCR. A chondrocyte cell line, MMA2, was established from articular cartilage of p53(-/-) mice and used to analyze the effects of agonists for each EP. A search for molecules downstream of the PGE2 signal through the EP2 agonist was made by cDNA microarray analysis. The growth-promoting effect of the EP2 agonist on chondrocytes surrounded by cartilage matrix was examined in an organ culture of rat femora.


CONCLUSIONS
EP2 was identified as the major EP expressed in articular cartilage. Treatment of MMA2 cells with specific agonists for each EP showed that only the EP2 agonist significantly increased intracellular cAMP levels in a dose-dependent manner. Gene expression profiling of MMA2 revealed a set of genes upregulated by the EP2 agonist, including several growth-promoting and apoptosis-protecting genes such as the cyclin D1, fibronectin, integrin alpha5, AP2alpha, and 14-3-3gamma genes. The upregulation of these genes by the EP2 agonist was confirmed in human articular chondrocytes by quantitative mRNA analysis. On treatment with the EP2 agonist, human articular chondrocytes showed an increase in the incorporation of 5-bromo-2-deoxyuracil (BrdU), and the organ culture of rat femora showed an increase of proliferating cell nuclear antigen (PCNA) staining in articular chondrocytes surrounded by cartilage matrix, suggesting growth-promoting effects of the PGE2 signal through EP2 in articular cartilage. These results suggested that the PGE2 signal through EP2 enhances the growth of articular chondrocytes, and the EP2 agonist is a candidate for a new therapeutic compound for the treatment of degenerative cartilage diseases.
Aoyama
Tomoki
T
Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan.
Liang
Bojian
B
Okamoto
Takeshi
T
Matsusaki
Takashi
T
Nishijo
Koichi
K
Ishibe
Tatsuya
T
Yasura
Ko
K
Nagayama
Satoshi
S
Nakayama
Tomitaka
T
Nakamura
Takashi
T
Toguchida
Junya
J
D000328:Adult; D000368:Aged; D000818:Animals; D002358:Cartilage, Articular / Q000166:cytology / Q000502:physiology*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002648:Child; D019902:Chondrocytes / Q000502:physiology*; D015232:Dinoprostone / Q000494:pharmacology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D051379:Mice; D010120:Oxytocics / Q000494:pharmacology*; D051381:Rats; D018078:Receptors, Prostaglandin E / Q000378:metabolism*; D058307:Receptors, Prostaglandin E, EP2 Subtype; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology
D010120:Oxytocics; C545644:PTGER2 protein, human; C545645:Ptger2 protein, mouse; C545646:Ptger2 protein, rat; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D015232:Dinoprostone