High glucose promotes mouse embryonic stem cells growth through PGE₂ and PPAR-δ signaling pathways

C8

Peroxisome proliferator-activated receptor is a nuclear receptor that has been implicated in blastocyst implantation, lipid metabolism, cell cycle, and pathogenesis of diabetes. However, the signal cascades underlying this effect are largely unknown in embryonic stem (ES) 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) δ and the growth response to high glucose levels in mouse ES cells. 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 intercellular reactive oxygen species (ROS), phosphorylation of the cytosolic phospholipase A₂ (cPLA₂), and the release of [³H]labeled 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 PPARδ expression directly or through Akt phosphorylation indirectly through the EP receptors. The PPARδ antagonist inhibited the 25 mM glucose-induced DNA synthesis. Moreover, transfection with a pool of PPARδ 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 PPARδ pathways. In conclusion, high glucose in part promotes mouse ES cell growth through the cPLA₂-mediated PGE₂ synthesis and PPARδ pathways.
 KEY WORDS: High glucose (HG), Embryonic stem (ES) cells, Peroxisome proliferators-activated receptor (PPAR) δ, prostaglandin E₂ (PGE₂)