Targeted inhibition of cardiomyocyte Gi signaling enhances susceptibility to apoptotic cell death in response to ischemic stress.
BACKGROUND
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.


RESULTS
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.


CONCLUSIONS
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.
DeGeorge
Brent R
BR
Center for Translational Medicine and George Zallie and Family Laboratory of Cardiovascular Gene Therapy, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Gao
Erhe
E
Boucher
Matthieu
M
Vinge
Leif E
LE
Martini
Jeffrey S
JS
Raake
Philip W
PW
Chuprun
J Kurt
JK
Harris
David M
DM
Kim
Gilbert W
GW
Soltys
Stephen
S
Eckhart
Andrea D
AD
Koch
Walter J
WJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006333:Heart Failure / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D008929:Mitochondria, Heart / Q000502:physiology*; D009203:Myocardial Infarction / Q000473:pathology / Q000503:physiopathology; D017202:Myocardial Ischemia / Q000473:pathology / Q000503:physiopathology*; D015428:Myocardial Reperfusion Injury / Q000473:pathology / Q000503:physiopathology; D032383:Myocytes, Cardiac / Q000502:physiology*; D018384:Oxidative Stress; D010446:Peptide Fragments / Q000235:genetics; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014161:Transduction, Genetic
D000318:Adrenergic beta-Agonists; D010446:Peptide Fragments; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; C498015:GNAI2 protein, human; D051960:GTP-Binding Protein alpha Subunit, Gi2; C498016:Gnai2 protein, mouse; C498017:Gnai2 protein, rat; D007545:Isoproterenol