Transgenic A ₁ adenosine receptor overexpression increases myocardial resistance to ischemia

Abstract

Activation of myocardial A 1 adenosine receptors (A 1 AR) protects the heart from ischemic injury. In this study transgenic mice were created using the cardiac-specific ␣-myosin heavy chain promoter and rat A 1 AR cDNA. Heart membranes from two transgene positive lines displayed Ϸ1,000-fold overexpression of A 1 AR (6,574 ؎ 965 and 10,691 ؎ 1,002 fmol per mg of protein vs. 8 ؎ 5 fmol per mg of protein in control hearts). Compared with control hearts, transgenic Langendorff-perfused hearts had a significantly lower intrinsic heart rate (248 beats per min vs. 318 beats per min, P < 0.05), lower developed tension (1.2 g vs. 1.6 g, P < 0.05), and similar coronary resistance. The difference in developed tension was eliminated by pacing. Injury of control hearts during global ischemia, indexed by time-to-ischemic contracture, was accelerated by blocking adenosine receptors with 50 M 8-(p-sulfophenyl) theophylline but was unaffected by addition of 20 nM N 6 -cyclopentyladenosine, an A 1 AR agonist. Thus A 1 ARs in ischemic myocardium are presumably saturated by endogenous adenosine. Overexpressing myocardial A 1 ARs increased time-to-ischemic contracture and improved functional recovery during reperfusion. The data indicate that A 1 AR activation by endogenous adenosine affords protection during ischemia, but that the response is limited by A 1 AR number in murine myocardium. Overexpression of A 1 AR affords additional protection. These data support the concept that genetic manipulation of A 1 AR expression may improve myocardial tolerance to ischemia.

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of altered adrenergic responsiveness of Ltype calcium channel current in myocytes isolated from transgenic hearts (unpublished results).…”

“…85-23, revised 1996) and the work was approved by the Institutional Animal Care and Use committee. Transgenic mice overexpressing the rat A1AR cDNA were produced as described previously (12). 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.…”

“…Since the degree of protection is limited by the availability of A 1 ARs, we have developed lines of transgenic mice with 20-to 200-fold overexpression of cardiac A 1 ARs to optimize the cardioprotective effect (12). Transgenic mouse hearts demonstrate better functional tolerance and diminished cell necrosis, compared with wild-type controls, in response to global ischemia in isolated perfused heart studies (13).…”

A1 adenosine receptors play an essential role in protecting the embryo against hypoxia

“…A 1 AR signaling has also been shown to protect cells from damage. Deletion of adenosine deaminase leads to elevated adenosine levels and protects the heart from ischemic/ reperfusion injury (18,19). Overexpression of A 1 AR also helps to protect the heart from ischemic/reperfusion injury and conversely the loss of A 1 AR impairs ischemic tolerance (18,19).…”

The rat adenine receptor: pharmacological characterization and mutagenesis studies to investigate its putative ligand binding site

“…2) [45][46][47]; it also showed somewhat reduced affinity and potency. In contrast, several of the mutants displayed increased potency of adenine up to 14 [48,49].…”