CYCLOOXYGENASE-2 DERIVED PGE₂ PROTECTS MOUSE EMBRYONIC STEM CELLS FROM APOPTOSIS

¹ Division of Hematology, The University of Texas Health Science Center at Houston, Houston, Texas; Vascular Biology Research Center, The University of Texas Health Science Center at Houston, Houston, Texas
² Division of Hematology, The University of Texas Health Science Center at Houston, Houston, Texas; Vascular Biology Research Center, The University of Texas Health Science Center at Houston, Houston, ; Department of Obstetrics and Gynecology, The University of Texas Health Science Center at Houston, Houston, Texas
³ Department of Obstetrics and Gynecology, The University of Texas Health Science Center at Houston, Houston, Texas
⁴ Division of Hematology, The University of Texas Health Science Center at Houston, Houston, Texas; Vascular Biology Research Center, The University of Texas Health Science Center at Houston, Houston, ; Stem Cell research Center, National health research Institutes, Zhunan, Miaoli, Taiwan

^* To whom correspondence should be addressed. E-mail: Kenneth.K.Wu{at}uth.tmc.edu.

	Abstract

Little is known about prostaglandin synthesis and function in embryonic stem cells. We postulated that mouse embryonic stem (mES) cells possess enzymes to synthesize protective prostaglandins. Compared to differentiated adult cells, mES cells were less susceptible to H₂O₂-induced apoptosis. However, their apoptosis was enhanced by indomethacin or SC-236, a selective inhibitor of cyclooxygenase-2 (COX-2). Analysis of COX pathway enzymes by Western blotting revealed expression of COX-2, cytosolic and microsomal PGE synthases. COX-1 and PGI synthase were undetectable. mES cells produced PGE₂ but not PGI₂. Importantly, PGE₂ rescued mES cells from apoptosis. To elucidate the signaling mechanism by which PGE₂ inhibits apoptosis, we analyzed PGE receptors (EP) by Western blots. All EP isoforms were detected except EP4. Butaprost, a specific EP2 agonist rescued mES cells from apoptosis while sulprostone, an EP1/EP3 agonist, had no effect, suggesting selective interaction of PGE₂ with EP2. The anti-apoptotic effect of PGE₂ was abrogated by Ly-294002 or wortmannin but not H-89 or a specific inhibitor of protein kinase A, suggesting signaling via phosphatidylinositol-3 kinase (PI-3K). Akt was constitutively active in mES cells, which was inhibited by indomethacin and rescued by PGE₂. The rescuing effect of PGE₂ was abrogated by Ly-294002. These results indicate that mES cells constitutively express COX-2 and PGE synthases and produce PGE₂ which confers resistance to apoptosis via EP2-mediated activation of PI-3K to Akt pathway.

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