Description:
Introduction: Myocardial infarction (MI) is the main complication of coronary artery disease (CAD). Recently, a locus tagging the GUCY1A3 gene has been shown to be genome-wide significantly associated with CAD. GUCY1A3 encodes the α1 subunit of the soluble guanylyl cyclase (sGC), a heterodimer composed of α1 and β1 subunits. Activated by nitric oxide (NO) the sGC produces cGMP. cGMP mediates various cellular functions including vasodilatation and inhibition of platelet aggregation. Besides this common variant, our group also identified rare variants in the coding sequence of GUCY1A3 associated with CAD/MI. Aim: We aimed to investigate the functional implication of rare variants found in CAD/MI patients regarding expression level, dimerization capability and enzymatic activity. Methods and Results: Employing whole-exome sequencing our group identified two rare GUCY1A3 variants in two extended families with a high prevalence of premature CAD/MI (Erdmann et al Nature 2013). Sequencing the respective exons in further 252 young MI patients led to the identification of seven additional rare variants. Effects on protein level were investigated by Western blotting after overexpression in HEK cells. Except for one of the variants, all dimerized with β1 shown by co-immunoprecipitation. One of the α1 variants exhibited significantly decreased protein levels compared to wild type α1 while another showed significantly increased protein levels. The amounts of β1 subunits correlated with those of α1 in all cases. sGC enzymatic activity was assessed by measuring cGMP by radioimmunoassay after stimulating overexpressed HEK cells with NO. Three of the variants demonstrated significantly decreased cGMP production at every time point tested. cGMP levels only correlated in part with the observed protein levels. Conclusion and Outlook: We identified nine rare variants in the coding sequence of GUCY1A3 and demonstrated some of them leading to altered protein levels as well as diminished activity. As both mechanisms in the end influence the capacity of cGMP formation, this appears to be a possible mechanism for GUCY1A3 leading to atherosclerosis and MI. Future studies will focus on mRNA abundance and protein degradation to uncover the reason for altered protein levels.