Phenotyping of Mice with Heart Specific Overexpression of A2A-Adenosine Receptors: Evidence for Cardioprotective Effects of A2A-Adenosine Receptors

Abstract

Background: Adenosine can be produced in the heart and acts on cardiac adenosine receptors. One of these receptors is the A2A-adenosine receptor (A2A-AR).Methods and Results: To better understand its role in cardiac function, we generated and characterized mice (A2A-TG) which overexpress the human A2A-AR in cardiomyocytes. In isolated atrial preparations from A2A-TG but not from WT, CGS 21680, an A2A-AR agonist, exerted positive inotropic and chronotropic effects. In ventricular preparations from A2A-TG but not WT, CGS 21680 increased the cAMP content and the phosphorylation state of phospholamban and of the inhibitory subunit of troponin in A2A-TG but not WT. Protein expression of phospholamban, SERCA, triadin, and junctin was unchanged in A2A-TG compared to WT. Protein expression of the α-subunit of the stimulatory G-protein was lower in A2A-TG than in WT but expression of the α-subunit of the inhibitory G-protein was higher in A2A-TG than in WT. While basal hemodynamic parameters like left intraventricular pressure and echocardiographic parameters like the systolic diameter of the interventricular septum were higher in A2A-TG than in WT, after β-adrenergic stimulation these differences disappeared. Interestingly, A2A-TG hearts sustained global ischemia better than WT.Conclusion: We have successfully generated transgenic mice with cardiospecific overexpression of a functional A2A-AR. This receptor is able to increase cardiac function per se and after receptor stimulation. It is speculated that this receptor may be useful to sustain contractility in failing human hearts and upon ischemia and reperfusion.

Evidence for Arrhythmogenic Effects of A2A-Adenosine Receptors

“…The generation of transgenic mice has been recently described (Boknik et al, 2018). The investigation conforms to the Guide for the Care and Use of Laboratory Animals published by the National Research Council (2011).…”

“…Contractile function was studied as reported (Boknik et al, 2018; Gergs et al, 2018). In brief, mice were anesthetized by i.p.…”

“…Pentobarbital was used here in order to provide direct comparability with our previous work (e.g. Boknik et al, 2018) and followed the suggestions of our animal protection committee. Right and left atria (about 3 mm of length) were dissected from isolated hearts and mounted in an organ bath.…”

“…Left atrial preparations were continuously electrically stimulated (field stimulation was used for comparability with all our previous work: e.g. Kirchhefer et al, 2001; Gergs et al, 2013; Boknik et al, 2018) with each impulse consisting of 1 Hz, with a voltage of 10–15% above threshold and 5 ms duration. Right atrial preparations were allowed to contract spontaneously.…”

“…In the present study, we tested the hypothesis that overexpression of A 2A -ARs increases the susceptibility to arrhythmias in our recently described model of human A 2A -AR overexpressing mice (Boknik et al, 2018) under basal or stimulated conditions. Furthermore, we studied the functional role of A 2A -AR stimulation in isolated paced right atrial preparations from diseased human hearts in order to ascertain that A 2A -ARs are functional in the human heart.…”