Cardiac overexpression of A₁-adenosine receptor protects intact mice against myocardial infarction

Abstract

Previous studies have shown that high-level (300-fold normal) cardiac overexpression of A1-adenosine receptors (A1-ARs) in transgenic (TG) mice protects isolated hearts against ischemiareperfusion injury. However, this high level of overexpression is associated with bradycardia and increased incidence of arrhythmia during ischemia in intact mice, which interfered with studies to determine whether this line of TG mice might also be protected against myocardial infarction (MI) in vivo. For these studies, we therefore selected a line of TG mice that overexpresses the A1-AR at more moderate levels (30-fold normal), which affords cardioprotection in the isolated heart while minimizing bradycardia and arrhythmia during ischemia in intact mice. Wild-type (WT; n ϭ 10) and moderate-level A1-AR TG (n ϭ 10) mice underwent 45 min of left anterior descending coronary artery occlusion, followed by 24-h reperfusion. Infarct size and region at risk were determined by triphenyltetrazolium chloride and phthalo blue staining, respectively. Infarct size (% region at risk) in WT mice was 52 Ϯ 3%, whereas overexpression of A1-ARs in the TG mice markedly reduced infarct size to 31 Ϯ 3% (P Ͻ 0.05). Furthermore, contractile function (left ventricular ejection fraction) as determined by cardiac magnetic resonance imaging 24 h after MI was better preserved in TG vs. WT mice. Cardiac overexpression of A1-ARs reduces infarct size by 40% and preserves cardiac function in intact mice after MI.ischemia-reperfusion; cardioprotection; transgenic mice; magnetic resonance imaging REPETITIVE A 1 -adenosine receptor (A 1 -AR) activation can maintain the heart in a protected state against myocardial ischemia-reperfusion injury (6). However, prolonged activation of A 1 -ARs with pharmacological agents induces a state of tolerance that blunts this cardioprotective effect (25). One possible explanation for this tolerance is the desensitization of A 1 -ARs resulting from continuous stimulation by A 1 -AR agonists. Using transgenic techniques, we showed (11-15, 19, 21) that cardiac A 1 -AR overexpression activates endogenous protective mechanisms that provide the heart with increased resistance to ischemia-reperfusion injury. Unlike transient ischemic preconditioning that occurs in wild-type (WT) animals, the constitutive preconditioning secondary to transgenic overexpression of the A 1 -AR has the potential to provide continuous cardioprotection (21). Although our past work was critical in establishing the long-term cardioprotective potential of A 1 -AR overexpression, these studies were conducted in isolated hearts from a line of mice with a 300-fold level of overexpression. In this study, we sought to determine whether A 1 -AR overexpression could also protect intact mice against ischemiareperfusion injury.Although cardiac-specific 300-fold A 1 -AR overexpression provided cardioprotection in globally ischemic, isolated heart models of ischemia-reperfusion injury, this was associated with adverse side effects such as significant resting bradycardia [h...

Gene expression profile of mouse myocardium with transgenic overexpression of A1adenosine receptors

“…GLUT4 is an important transporter for the entry of glucose into myocardial cells, and NADH dehydrogenase is a mitochondrial enzyme involved in the first step of the electron transport chain. The role of these proteins in cellular ATP production supports the hypothesis that their overexpression could contribute to the preservation of ATP stores during ischemia (7) and possibly the overall tolerance to ischemia-reperfusion injury afforded by A 1 AR overexpression (12,13,25). Another previous finding in transgenic mice is the observation of altered adrenergic responsiveness of Ltype calcium channel current in myocytes isolated from transgenic hearts (unpublished results).…”

“…Furthermore, hearts with overexpression of A 1 ARs show improved cardiac energetics during ischemia, compared with wild-type hearts (7). Finally, we have observed that transgenic animals overexpressing A 1 ARs have reduced infarct size in response to in vivo regional ischemia (25).…”

“…Briefly, the full-length rat A1 cDNA was subcloned into a construct containing the ␣-MHC promoter with a MEF-2 mutation and the human growth hormone polyadenylation signal. The transgenic line used in this study has demonstrated 30-fold overexpression at 20 wk of age (25). Male transgenic (n ϭ 4) and wild-type (n ϭ 6) mice Article published online before print.…”

Cardiac purinergic signalling in health and disease

“…Magnesium reduced infarct size also via enhancement of the action of adenosine in rabbits [625]. Over-expression of A1R protected mice against MI [626]. The use of intravenous adenosine after primary coronary stenting reduced the infarct size [627].…”

Separation of on-target efficacy from adverse effects through rational design of a bitopic adenosine receptor agonist

“…Although all four AR subtypes are expressed in the mammalian heart (11,12), the well-known protective effects of adenosine in this tissue are predominantly mediated by the adenosine A 1 receptor (A 1 AR) subtype, especially under conditions of ischemia and reperfusion injury (13)(14)(15)(16)(17). Unfortunately, the transition of A 1 AR agonists into the clinic has been severely hindered because of high doses causing on-target bradycardia, atrioventricular block, and hypotension (13,18). As a consequence, clinical trials of AR agonists have had limited success because of the suboptimal dose of agonist that can be used (19)(20)(21)(22).…”