Kuroda Tadashi, Hirota Hisao, Fujio Yasushi, Sugiyama Shoko, Masaki Mitsuru, Hiramoto Yoshimune, Shioyama Wataru, Okamoto Kitaro, Hori Masatsugu, Yamauchi-Takihara Keiko
Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Mol Cell Cardiol. 2007 Jul;43(1):54-62. doi: 10.1016/j.yjmcc.2007.04.003. Epub 2007 Apr 12.
Prostacyclin (PGI2) and its analogues exert cardioprotective effects via the rhodopsin type membrane PGI2 receptor, IP. Peroxisome proliferator-activated receptor (PPAR) delta is a nuclear receptor abundantly expressed in cardiomyocytes and plays a pivotal role in maintaining constitutive mitochondrial fatty acid beta-oxidation (FAO). Recently, a novel signaling pathway of PGI2 via PPARdelta has been demonstrated in non-cardiac tissues. We therefore examined whether carbacyclin (cPGI2), a PGI2 analogue, up-regulates transcriptional expression of carnitine palmitoyltransferase-1 (CPT-1), the rate-limiting enzyme in mitochondrial FAO, via PPARdelta in cardiomyocytes. Intraperitoneal injection of cPGI2 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-1 mRNA expression and PPRE promoter activity were significantly increased by cPGI2 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 cPGI2 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 PPARdelta. Furthermore, electrophoretic mobility shift assays demonstrated that binding of PPARdelta to PPRE in the CPT-1 gene promoter is enhanced in response to cPGI2 stimulation. In addition, down-regulation of CPT-1 mRNA expression in cardiomyocytes subjected to hypoxia was attenuated by cPGI2. These results indicate that cPGI2 induces CPT-1 mRNA expression through PPARdelta, independent of the IP receptor signaling pathway, suggesting a possibility that cPGI2 modulates cardiac energy metabolism by activating FAO via PPARdelta.
前列环素（PGI2）及其类似物通过视紫红质型膜PGI2受体IP发挥心脏保护作用。过氧化物酶体增殖物激活受体（PPAR）δ是一种在心肌细胞中大量表达的核受体，在维持组成型线粒体脂肪酸β氧化（FAO）中起关键作用。最近，在非心脏组织中已证明PGI2通过PPARδ的一种新信号通路。因此，我们研究了PGI2类似物卡前列环素（cPGI2）是否通过心肌细胞中的PPARδ上调线粒体FAO的限速酶肉碱棕榈酰转移酶-1（CPT-1）的转录表达。腹腔注射cPGI2可增加小鼠心脏中CPT-1 mRNA的表达。通过PPAR反应元件（PPRE）-荧光素酶报告基因测定法在培养的新生大鼠心肌细胞中评估转录活性。cPGI2以浓度依赖性方式显著增加CPT-1 mRNA表达和PPRE启动子活性，其中PPRE已定位到CPT-1基因的启动子区域。此外，cPGI2对CPT-1 mRNA表达和PPRE启动子活性的升高并未被强效蛋白激酶A抑制剂H-89消除，但在过表达显性负型PPARδ的心肌细胞中受到显著抑制。此外，电泳迁移率变动分析表明，响应cPGI2刺激，PPARδ与CPT-1基因启动子中PPRE的结合增强。此外，cPGI2减弱了缺氧心肌细胞中CPT-1 mRNA表达的下调。这些结果表明，cPGI2通过PPARδ诱导CPT-1 mRNA表达，独立于IP受体信号通路，提示cPGI2可能通过PPARδ激活FAO来调节心脏能量代谢。
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