Aims: Cardiac overexpression of the beta-adrenoceptor-coupled G-protein subunit Galphas in mice enhances inotropic responses to sympathetic stimulation, but evokes cardiomyopathy with increasing age. We tested whether functional single nucleotide polymorphisms (SNPs) in the human Galphas (GNAS) gene modulate Galphas expression and assessed functional consequences.
Methods and results: Sequencing the promoter and intron 1 of GNAS revealed 11 SNPs resulting in three common haplotypes. Haplotype *3 constructs exhibited significantly higher promoter activity than haplotypes *1 and *2, resulting in a more than 50% higher Galphas mRNA expression in homozygous *3 carriers (*3/*3) than in heterozygous (*3/-) and negative *3 (-/-) carriers (P = 0.002). Basal, Galphas- (via NaF and GTP) and isoproterenol-stimulated adenylyl cyclase (AC) activities were also significantly higher in *3/*3 than in *3/- and -/- carriers. In contrast, direct AC activation via forskolin was independent of GNAS haplotypes. Furthermore, haemodynamic measurements in 137 coronary artery bypass patients revealed a higher cardiac index in *3/*3 carriers than in *3/- and -/- carriers (P = 0.025) associated with a lower NYHA functional class (P = 0.040) and serum NT-proBNP concentrations (P = 0.002).
Conclusion: SNPs in regulatory regions of GNAS impact upon Galphas expression and stimulated cAMP formation in human hearts in vitro and upon cardiac performance in vivo.