Conditional disruption of interactions between Gα(i2) and regulator of G protein signaling (RGS) proteins protects the heart from ischemic injury

BACKGROUND: 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 Gα(i2) is lost (RGS insensitive Gα(i2)(G184S)) exhibit beneficial (protection against ischemic injury) and detrimental (enhanced fibrosis) cardiac phenotypes. This mouse model has revealed the physiological significance of RGS/Gα(i2) interactions. Previous studies of the Gα(i2)(G184S) mutation used mice that express this mutant protein throughout their lives. Thus, it is unclear whether these phenotypes result from chronic or acute Gα(i2)(G184S) expression. We addressed this issue by developing mice that conditionally express Gα(i2)(G184S). METHODS: Mice that conditionally express RGS insensitive Gα(i2)(G184S) were generated using a floxed minigene strategy. Conditional expression of Gα(i2)(G184S) 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 Gα(i2)(G184S) 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. RESULTS: We demonstrate tamoxifen-dependent expression of Gα(i2)(G184S), enhanced inhibition of cAMP production, and cardioprotection from ischemic injury in hearts conditionally expressing Gα(i2)(G184S). Thus the cardioprotective phenotype previously reported in mice expressing Gα(i2)(G184S) does not require embryonic or chronic Gα(i2)(G184S) expression. Rather, cardioprotection occurs following acute (days rather than months) expression of Gα(i2)(G184S). CONCLUSIONS: 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 Gα(i2) and RGS proteins.