Carbacyclin induces carnitine palmitoyltransferase-1 in cardiornyocytes via peroxisome proliferator-activated receptor (PPAR) δ independent of the IP receptor signaling pathway

Prostacyclin (PG12) and its analogues exert cardioprotective effects via the rhodopsin type membrane PG12 receptor, IP. Peroxisome proliferator-activated receptor (PPAR) delta is a nuclear receptor abundantly expressed in cardionnyocytes and plays a pivotal role in maintaining constitutive mitochondrial fatty acid l beta-oxidation (FAO). Recently, a novel signaling pathway of PG12 via PPAR delta has been demonstrated in non-cardiac tissues. We therefore examined whether carbacyclin (cPG12), a PG12 analogue, up-regulates transcriptional expression of carnitine palmitoyltransferase-1 (CPT-1), the rate-limiting enzyme in mitochondrial FAO, via PPAR delta in cardiomyocytes. Intraperitoneal injection of cPG12 increased CPT-1 mRNA expression in murine hearts. Transcriptional activity was evaluated by PPAR responsive element (PPRE)-luciferase reporter gene assay in cultured neonatal rat cardiomyocytes. CPT-I mRNA expression and PPRE promoter activity were significantly increased by cPG12 in a concentration-dependent manner, where PPRE has been mapped to the promoter region of the CPT-1 gene. Moreover, the elevation of CPT-1 mRNA expression and PPRE promoter activity by cPG12 was not abolished by H-89, a potent protein kinase A inhibitor, but was significantly inhibited in cardiomyocytes over-expressing a dominant-negative type of PPAR delta. Furthermore, electrophoretic mobility shift assays demonstrated that binding of PPAR delta to PPRE in the CPT-1 gene promoter is enhanced in response to cPG12 stimulation. In addition, down-regulation of CPT-] mRNA expression in cardiomyocytes subjected to hypoxia was attenuated by cPG12. These results indicate that cPG12 induces CPT-1 mRNA expression through PPAR delta, independent of the IP receptor signaling pathway, suggesting a possibility that cPG12 modulates cardiac energy metabolism by activating FAO via PPAR delta. (C) 2007 Elsevier Inc. All rights reserved.