Conditional disruption of interactions between Gαi2 and regulator of G protein signaling (RGS) proteins protects the heart from ischemic injury.

Regulator of G protein signaling (RGS) proteins suppress G protein coupled receptor signaling by catalyzing the hydrolysis of Gα-bound guanine nucleotide triphosphate. Transgenic mice in which RGS-mediated regulation of Gαi2 is lost (RGS insensitive Gαi2G184S) exhibit beneficial (protection against ischemic injury) and detrimental (enhanced fibrosis) cardiac phenotypes. This mouse model has revealed the physiological significance of RGS/Gαi2 interactions. Previous studies of the Gαi2G184S mutation used mice that express this mutant protein throughout their lives. Thus, it is unclear whether these phenotypes result from chronic or acute Gαi2G184S expression. We addressed this issue by developing mice that conditionally express Gαi2G184S. Mice that conditionally express RGS insensitive Gαi2G184S were generated using a floxed minigene strategy. Conditional expression of Gαi2G184S was characterized by reverse transcription polymerase chain reaction and by enhancement of agonist-induced inhibition of cAMP production in isolated cardiac fibroblasts. The impact of conditional RGS insensitive Gαi2G184S expression on ischemic injury was assessed by measuring contractile recovery and infarct sizes in isolated hearts subjected to 30 min ischemia and 2 hours reperfusion. We demonstrate tamoxifen-dependent expression of Gαi2G184S, enhanced inhibition of cAMP production, and cardioprotection from ischemic injury in hearts conditionally expressing Gαi2G184S. Thus the cardioprotective phenotype previously reported in mice expressing Gαi2G184S does not require embryonic or chronic Gαi2G184S expression. Rather, cardioprotection occurs following acute (days rather than months) expression of Gαi2G184S. These data suggest that RGS proteins might provide new therapeutic targets to protect the heart from ischemic injury. We anticipate that this model will be valuable for understanding the time course (chronic versus acute) and mechanisms of other phenotypic changes that occur following disruption of interactions between Gαi2 and RGS proteins.