Functional evaluation of GUCY1A3 mutations associated with myocardial infarction risk

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 [1]. GUCY1A3 encodes for the α₁-subunit of the soluble guanylyl cyclase (sGC) which consists of α₁- and β₁-subunits and catalyzes the production of cGMP upon stimulation with nitric oxide (NO). cGMP acts a second messenger that mediates diverse cellular functions, e.g. smooth muscle relaxation and inhibition of platelet aggregation. Using whole-exome sequencing, our group also identified nine rare variants in the coding sequence of GUCY1A3 [2]. Two of these variants were found in two extended families with a high prevalence of premature CAD/MI. Seven further rare variants were found in 252 young MI patients. In this study, we aimed to investigate the functional implication of these rare variants found in CAD/MI patients (Table 1) regarding protein level, dimerization capability and enzymatic activity.

Table 1 Rare variants of sGC α1 subunit found in MI patients:

Two of the investigated α₁ variants exhibited significantly decreased protein levels compared to wild type α₁. The amount of β₁ correlated with those of α₁ in all cases. All α₁ variants, except for p.Leu163Phefs*24, still dimerized with the β₁ subunit, as shown by co-immunoprecipitation. Using radioimmunoassay three of the rare variants demonstrated significantly decreased cGMP amounts at every time point tested (0.5/1/2 min). The activity only in part correlated with the observed protein levels pointing to an effect of the tested variants on enzymatic activity. As we have shown that loss of function-mutations in GUCY1A3 may lead to CAD/MI [2], decreased enzymatic activity might also increase risk. Future studies focus on mRNA abundance and protein degradation to uncover the reason for attenuated activity of the respective variants.