Myocardial signaling defects and impaired cardiac function of a human beta 2-adrenergic receptor polymorphism expressed in transgenic mice.

Abstract

A threonine to isoleucine polymorphism at amino acid 164 in the fourth transmembrane spanning domain of the 182-adrenergic receptor (,B2AR) is known to occur in the human population. The The human heart expresses both the ,i3AR and f32AR subtypes (6). Each receptor mediates positive inotropic and chronotropic responses to endogenous catecholamines and exogenously administered agonists (7). Most forms of congestive heart failure, including the "idiopathic" forms, are characterized by a diminished responsiveness to 13-agonists (8). As a probable consequence of elevated catecholamines (and perhaps of other factors as well), J31AR expression has been noted to be markedly reduced in patients with idiopathic dilated cardiomyopathy, a finding that has not been observed for the 32AR (8). The 132AR, then, may take on an even greater role in providing for cardiac responses to increased sympathetic drive or exogenous agonists under these circumstances. We have considered that if the Ile-164 variant is in fact dysfunctional in the heart, individuals harboring this receptor with heart failure may exhibit marked decompensation.The current study was undertaken to explore the relevance of the Ile-164 receptor in cardiac myocyte signaling at both the cellular and the whole organ levels. The strategy was to express in transgenic mice the human wild-type (32AR (wt 832AR) or the Ile-164 variant in a cardiac specific manner using the murine a myosin heavy chain (aMHC) promoter. In vitro and in vivo assessments of receptor function were then undertaken that revealed a substantial impairment imposed by this polymorphism in cellular as well as intact heart function. METHODSTransgenic Mice. Cardiac-specific expression of the 32AR in transgenic mice was achieved using the murine aMHC promoter (9). Briefly, the coding block of human wt 132AR cDNA was blunt-end ligated into an aMHC promoter construct (9) at the Sall site. To generate the Ile-164 polymorphism, oligonucleotide-directed site-specific mutagenesis was carried out on the wild-type template, substituting thymidine for cytidine at nucleic acid 491 as described (4). This mutated cDNA was also cloned into the aMHC SailI site, and the integrity of the two constructs was verified by dideoxy sequencing. Each was then digested by NotI and the liberated fragment was then isolated, purified, and used for injection into male pronuclei of embryos

Neurohumoral activation in heart failure: the role of adrenergic receptors

“…One rare and never homozygous Thr 164 Ile variant was associated with reduced survival and depressed exercise capacity in patients with heart failure , Wagoner et al 2000, Brodde et al 2001. These results are consistent with findings in transgenic mice with Thr 164 Ile polymorphism targeted to the heart (Turki et al 1996).…”

Treatment of Chronic Heart Failure With β-Adrenergic Receptor Antagonists

“…116,163 Using this starting material Steve Liggett, whose laboratory had by this time characterized the majority of the common genetic variation in human adrenergic receptors, and colleagues conducted an investigation of six candidate adrenergic receptor polymorphisms on ␤-blocker (bucindolol) clinical responses. As expected, the allele frequency of the ␤ 2 164Ile variant 161 was too small (0.01) in the sample size of 1040 to generate enough clinical events for analysis, but the ␤ 1 389 Arg/Gly allele frequencies of 0.69/0.31 provided ample numbers of clinical events to test the prespecified hypothesis that the 389Arg variant would be associated with a greater therapeutic effect than the counterpart Gly polymorphism. 163 The amino acid position 389 Arg version of the human ␤ 1 -AR is markedly different pharmacologically from the Gly version, with the former having 3 to 4 times the signal transduction capacity, 162,163 a higher affinity for ␤-agonists 162 including NE, 117,164 and a higher probability of being constitutively active 101 and sensitive to the effects of inverse agonists.…”

Adenovirus-mediated gene transfer of the β2-adrenergic receptor to donor hearts enhances cardiac function

“…11 Importantly, a recent report has demonstrated that lower levels of ␤ 2 -AR overexpression in the hearts of transgenic mice leads to a similar in vivo cardiac phenotype. 22 In both of these transgenic mouse models with varying amounts of ␤ 2 -AR overexpression, cardiac function was increased under basal conditions which is significant in the transplant setting due to denervation and the lack of sympathetic stimulation. Thus, the goal of the current study was to determine whether overexpression of the ␤ 2 -AR in transplanted rat myocardium could lead to global alteration of contractility, even in the absence of added inotropic agents.…”