DeGeorge Brent R, Gao Erhe, Boucher Matthieu, Vinge Leif E, Martini Jeffrey S, Raake Philip W, Chuprun J Kurt, Harris David M, Kim Gilbert W, Soltys Stephen, Eckhart Andrea D, Koch Walter J
Center for Translational Medicine and George Zallie and Family Laboratory of Cardiovascular Gene Therapy, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Circulation. 2008 Mar 18;117(11):1378-87. doi: 10.1161/CIRCULATIONAHA.107.752618. Epub 2008 Mar 3.
A salient characteristic of dysfunctional myocardium progressing to heart failure is an upregulation of the adenylyl cyclase inhibitory guanine nucleotide (G) protein alpha subunit, G alpha(i2). It has not been determined conclusively whether increased Gi activity in the heart is beneficial or deleterious in vivo. Gi signaling has been implicated in the mechanism of cardioprotective agents; however, no in vivo evidence exists that any of the G alpha subunits are cardioprotective. We have created a novel molecular tool to specifically address the role of Gi proteins in normal and dysfunctional myocardium.
We have developed a class-specific Gi inhibitor peptide, GiCT, composed of the region of G alpha(i2) that interacts specifically with G protein-coupled receptors. GiCT inhibits Gi signals specifically in vitro and in vivo, whereas Gs and Gq signals are not affected. In vivo expression of GiCT in transgenic mice effectively causes a "functional knockout" of cardiac G alpha(i2) signaling. Inducible, cardiac-specific GiCT transgenic mice display a baseline phenotype consistent with nontransgenic mice. However, when subjected to ischemia/reperfusion injury, GiCT transgenic mice demonstrate a significant increase in infarct size compared with nontransgenic mice (from 36.9+/-2.5% to 50.9+/-4.3%). Mechanistically, this post-ischemia/reperfusion phenotype includes increased myocardial apoptosis and resultant decreased contractile performance.
Overall, our results demonstrate the in vivo utility of GiCT to dissect specific mechanisms attributed to Gi signaling in stressed myocardium. Our results with GiCT indicate that upregulation of G alpha(i2) is an adaptive protective response after ischemia to shield myocytes from apoptosis.
进展为心力衰竭的功能失调心肌的一个显著特征是腺苷酸环化酶抑制性鸟嘌呤核苷酸（G）蛋白α亚基Gα（i2）上调。心脏中Gi活性增加在体内是有益还是有害尚未得到最终确定。Gi信号传导与心脏保护剂的机制有关；然而，尚无体内证据表明任何Gα亚基具有心脏保护作用。我们创建了一种新型分子工具，以专门研究Gi蛋白在正常和功能失调心肌中的作用。
我们开发了一种类别特异性Gi抑制剂肽GiCT，它由Gα（i2）中与G蛋白偶联受体特异性相互作用的区域组成。GiCT在体外和体内均能特异性抑制Gi信号，而Gs和Gq信号不受影响。在转基因小鼠中体内表达GiCT可有效导致心脏Gα（i2）信号传导的“功能敲除”。可诱导的、心脏特异性GiCT转基因小鼠表现出与非转基因小鼠一致的基线表型。然而，当遭受缺血/再灌注损伤时，与非转基因小鼠相比，GiCT转基因小鼠的梗死面积显著增加（从36.9±2.5%增至50.9±4.3%）。从机制上讲，这种缺血/再灌注后的表型包括心肌细胞凋亡增加以及由此导致的收缩性能下降。
总体而言，我们的结果证明了GiCT在剖析应激心肌中归因于Gi信号传导的特定机制方面的体内效用。我们使用GiCT的结果表明，Gα（i2）上调是缺血后一种适应性保护反应，可保护心肌细胞免受凋亡。
