Investigation Of Contractile Responses, SERCA2a, Phospholamban and SIRT Enzymes Relationship In Atrial Tissues In Heart Failure With Different Ejection Fractions

Project no. 24009 · Status: Kapanmış (Yayın bekleniyor) · 2022

Summary

Backgrounds: Heart failure is a complex clinical syndrome characterized by structural and/or functional abnormalities of the heart, which impair its ability to pump blood effectively. The diagnosis and management of heart failure present significant clinical challenges due to its heterogeneous presentation and overlapping symptoms with other conditions. As a result, the disease is associated with high rates of hospitalization and mortality. Globally, heart failure has emerged as a major public health concern, affecting an estimated 60 million individuals.Objectives: In this study, it was aimed to evaluate the functional responses mediated by Beta-1 receptors using isoproterenol and to examine the roles of SERCA2a, phospholamban and SIRT enzymes in atrial tissue samples obtained from patients diagnosed with heart failure who underwent cardiopulmonary bypass surgery at Ege University Faculty of Medicine, Department of Cardiovascular Surgery.Materials and methods: The patients were categorized into three groups: Group I – patients with heart failure with reduced ejection fraction (HFrEF); Group II – patients with heart failure with preserved ejection fraction (HFpEF); and Group III – patients with heart failure with mildly reduced ejection fraction (HFmrEF). Atrial appendage tissues were obtained intraoperatively from patients undergoing open-heart surgery with cardiopulmonary bypass. Immediately after excision, the tissues were placed in Tyrode’s solution and transported to the laboratory under suitable physiological conditions. Trabeculae within the atrial tissue were carefully isolated and attached in isolated organ bath systems for functional analyses. During the isolated organ bath experiments, the trabeculae were suspended in baths containing Tyrode’s solution, continuously aerated with a gas mixture of 95% O₂ and 5% CO₂, and maintained at appropriate physiological temperature. Following an equilibration period, cumulative concentration–response curves to isoproterenol were generated. Contractile responses were recorded, and parameters such as maximum contraction amplitüde were calculated. Subsequently, the tissues were homogenized, and protein concentrations were quantified using the bicinchoninic acid (BCA) assay. The expression levels of SERCA2a, phospholamban, and sirtuin enzymes were analyzed via Western blotting, employing specific primary and appropriate secondary antibodies. The experimental data were subjected to statistical analysis to determine significance.Results: Isolated organ bath experiments have shown that the contractile response to isoproterenol increases statistically significantly in the group of patients with heart failure with reduced ejection fraction (HFrEF) compared to the group with preserved ejection fraction heart failure (HFpEF) (Emax respectively, 0,86±0,17 vs 0,16±0,23 p<0,01). Statistical analyses revealed that SIRT-1 protein expression levels were significantly reduced in the EF <40% (HFpEF) patient group compared to the EF >50% (HFrEF) patient group. Similarly, it was determined that SIRT-6 protein expression levels were also statistically significantly reduced in the KYdEF group compared to the KYkEF group. No significant difference was detected between the two groups in terms of SERCA2a protein expression levels. In contrast, phospholamban protein expression levels were found to be significantly reduced in the KYdEF group compared to the KYkEF group.Conclusions: The findings of this study demonstrate significant differences in contractile responses and regulatory mechanisms among heart failure groups classified according to ejection fraction. In particular, the marked reduction of SIRT-1 and SIRT-6 expression levels in the reduced ejection fraction group suggests that these enzymes may play critical roles in energy metabolism, oxidative stress, and cellular aging processes in heart failure. Similarly, the decrease in phospholamban expression may contribute to impaired calcium homeostasis, thereby exacerbating contractile dysfunction. In contrast, the absence of significant changes in SERCA2a protein expression implies that its functional activity or interaction with regulatory proteins, rather than expression levels alone, may be more determinant in disease progression. Furthermore, the distinct contractile responses to isoproterenol observed in the reduced ejection fraction group indicate that adrenergic responsiveness could represent an important parameter influencing the course of heart failure. Overall, these results highlight that reduced and preserved ejection fraction heart failure subtypes may be characterized by different pathophysiological mechanisms. In this context, sirtuin enzymes and phospholamban may serve as potential biomarkers or therapeutic targets in the management of heart failure.

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