High Glucose-Induced Prostaglandin E₂ and Peroxisome Proliferator-Activated Receptor Promotes Mouse Embryonic Stem Cells Proliferation

¹ Department of Veterinary Physiology, Biotherapy Human Resources Center (BK 21), College of Veterinary Medicine, Chonnam National University, Gwangju 500-757, Korea

^* To whom correspondence should be addressed. E-mail: hjhan{at}chonnam.ac.kr.

	Abstract

Peroxisome proliferator-activated receptor is a nuclear receptor that has been implicated in blastocyst implantation, cell cycle, and pathogenesis of diabetes. However, the signal cascades underlying this effect are largely unknown in embryo stem cells. This study examined whether or not there is an association between the reactive oxygen species-mediated prostaglandin E₂ (PGE₂)/peroxisome proliferator-activated receptor (PPAR) and the growth response to high glucose levels in mouse ESCs. A high glucose (25 mM) significantly increased the level of [³H]thymidine incorporation, BrdU incorporation, and the number of cells. Moreover, 25 mM glucose increased the intracellular reactive oxygen species (ROS), phosphorylation of the cytosolic phospholipase A₂ (cPLA₂), and the release of [³H]arachidonic acid (AA). In addition, 25 mM glucose also increased the level of cyclooxygenase-2 (COX-2) protein expression, which stimulated the synthesis of PGE₂. Subsequently, the increase in PGE₂ production stimulated PPAR expression directly or through Akt phosphorylation indirectly through the EP receptors. The PPAR antagonist inhibited the 25 mM glucose-induced DNA synthesis. Moreover, transfection with a pool of PPAR specific siRNA inhibited the 25 mM glucose-induced DNA synthesis and G1/S phase progression. Twenty five mM glucose also increased the level of the cell cycle regulatory proteins [cyclin E/cyclin-dependent kinase (CDK) 2, cyclin D1/CDK 4] and decreased p21^WAF1/Cip1 and p27^Kip1, which were blocked by the inhibition of the cPLA₂, COX-2 or PPAR pathways. In conclusion, high glucose in part promotes mouse ESC growth through the cPLA₂-mediated PGE₂ synthesis and PPAR pathways.

Key Words. High glucose, Embryonic stem cells (ESCs), Peroxisome proliferators-activated receptor (PPAR), prostaglandin E₂(PGE₂)