Relationship between the expression level of genes of Ca(2+)-transporting proteins of the cardiomyocytes' sarcoplasmic reticulum with the severity of heart failure
Authors: Muslimova E , Rebrova T , Akhmedov S , Afanasiev S 
Published: November 2020

Abstract

Introduction
The sarcoplasmic reticulum of cardiomyocytes is the main Ca(2+) ion depot, the main functional proteins of which are Ca(2+)-ATPase SERCA2a, which re-traps ions from myoplasma, calsequestrin CASQ2, which binds most of Ca(2+), and ryanodine receptors RyR2 releasing Ca(2+) from the intracellular depot. A change in their functional activity can determine the progression of contractile myocardial dysfunction. The effectiveness of the Ca(2+)-transporting system and, consequently, the risk of development and progression of heart failure, may depend on the expression of the corresponding genes.

Purpose
To evaluate the association between the level of relative expression of the ATP2A2, CASQ2, RYR2 genes in the myocardium and the clinical parameters of heart failure in patients with coronary heart disease.

Methods
The study was carried out on the material of 90 patients with chronic heart failure developed on the background of coronary heart disease. Myocardial samples (a fragment of the right atrium appendage) obtained by connecting the cardiopulmonary bypass during planned coronary bypass surgery. The level of expression of the Ca(2+)-ATPase ATP2A2 gene, the ryanodine receptor RYR2 gene, and the calsequestrin CASQ2 gene was estimated. Samples were homogenized, RNA was isolated and cDNA was synthesized, and real-time PCR was performed. As reference, the glyceraldehyde-3-phosphate dehydrogenase GAPDH gene, the beta-actin ACTB gene, and the 18S gene were used. The level of gene expression was calculated automatically using the software of the thermocycler. For the analysis of quantitative data, the Kruskel-Wallis test or the Mann-Whitney test was used. The analysis of the strength of the linear relationship was carried out using the Spearman rank correlation coefficient.

Results
ATP2A2 gene expression was reduced in the myocardium of patients with left ventricular (LV) hypertrophy (p=0.027 for ATP2A2/GAPDH, p=0.043 for ATP2A2/ACTB, p=0.039 for ATP2A2/18S). A correlation was observed between an increase in the functional class of heart failure (NYHA) and a decrease in the expression level of the RYR2/GAPDH gene (p=0.023). Among patients with heart failure, there was a weak negative linear relationship between the expression level of CASQ2/18S and the LV ejection fraction (r=−0.288, p=0.047). A significant (p=0.040) increase in CASQ2/ACTB gene expression was also found in patients with diastolic dysfunction compared to individuals without it, as well as a similar tendency for CASQ2/GAPDH (p=0.068) and CASQ2/18S (p=0.090).

Conclusion
In patients with heart failure due to coronary heart disease with LV hypertrophy, there was a decrease in the expression of the Ca (2+)-ATPase ATP2A2 gene. A decrease in the expression of the ryanodine receptor RYR2 gene was found as the heart failure class worsened. However, CASQ2 expression increased with diastolic dysfunction and a decrease in LV ejection fraction.

Funding Acknowledgement
Type of funding source: Public grant(s) – National budget only. Main funding source(s): Russian Foundation for Basic Research