Polymorphic Variants in the GRK5 Gene Promoter Are Associated With Diastolic Dysfunction in Coronary Artery Bypass Graft Surgery Patients
Authors: Fassbender Philipp , Klenke Stefanie , Omer Saed , Komanek Tomas , Ochsenfarth Crista , Frey Ulrich H. , Peters Jürgen 
Published: December 2021

BACKGROUND:
The G-protein–coupled receptor kinase 5 (GRK5) is a mediator of cardiovascular homeostasis and participates in inflammation and cardiac fibrosis, both being involved in the development of diastolic dysfunction (DD). While mechanisms of transcriptional regulation of the GRK5 promoter are unclear, we tested the hypotheses, that (1) GRK5 expression varies depending on functional single nucleotide polymorphisms (SNPs) in the GRK5 promoter and (2) this is associated with DD in patients undergoing coronary artery bypass graft (CABG) surgery.

METHODS:
We amplified and sequenced the GRK5 promoter followed by cloning, reporter assays, and electrophoretic mobility shift assays (EMSA). GRK5 messenger ribonucleic acid (mRNA) expression was determined in right atrial tissue sampled from 50 patients undergoing CABG surgery. In another prospective study, GRK5 genotypes were associated with determinants of diastolic function using transesophageal echocardiography in 255 patients with CABG with normal systolic left ventricular (LV) function. Specifically, we measured ejection fraction (EF), transmitral Doppler early filling velocity (E), tissue Doppler early diastolic lateral mitral annular velocity (E′ lateral), and calculated E/E′, E′ norm and the difference of E′ lateral and E′ norm to account for age-related changes in diastolic function.

RESULTS:
We identified 6 SNPs creating 3 novel haplotypes with the greatest promoter activation in haplotype tagging (ht) SNP T(-678)C T-allele constructs (P < .001). EMSAs showed allele-specific transcription factor binding proving functional activity. GRK5 mRNA expression was greatest in TT genotypes (TT: 131 fg/µg [95% CI, 108–154]; CT: 109 [95% confidence interval {CI}, 93–124]; CC: 83 [95% CI, 54–112]; P = .012). Moreover, GRK5 genotypes were significantly associated with determinants of diastolic function. Grading of DD revealed more grade 3 patients in TT compared to CT and CC genotypes (58% vs 38% vs 4%; P = .023). E´ lateral was lowest in TT genotypes (P = .007) and corresponding E/E′ measurements showed 1.27-fold increased values in TT versus CC genotypes (P = .01), respectively. While E′ norm values were not different between genotypes (P = .182), the difference between E′ lateral and E′ norm was significantly higher in TT genotypes compared to CC and CT genotypes (−1.2 [interquartile range {IQR}, 2.7], −0.5 [IQR, 3.4], and −0.4 [IQR, 4.2; P = .035], respectively).

CONCLUSIONS:
A functional GRK5 SNP results in allele-dependent differences in GRK5 promoter activity and mRNA expression. This is associated with altered echocardiographic determinants of diastolic function. Thus, SNPs in the GRK5 promoter are associated with altered perioperative diastolic cardiac function. In the future, preoperative testing for these and other SNPs might allow to initiate more specific diagnostic and perioperative pathways to benefit patients at risk.