β-Adrenergic Receptor Subtypes Differentially Affect Apoptosis in Adult Rat Ventricular Myocytes

Abstract

BACKGROUND-Catecholamine-induced apoptosis is mediated by activation of the beta-adrenergic signaling pathway. We tested the hypothesis that beta(1)- and beta(2)-adrenergic receptor (AR) subtypes differentially affect apoptosis in adult rat ventricular myocytes in vitro. METHODS AND RESULTS-Myocytes were first exposed to norepinephrine (NE) alone (10 mcmol/L) or NE+atenolol (AT) (10 mcmol/L) for 12 hours. AT, a beta(1)-selective AR antagonist, abolished the NE-induced increase in nick end-labeling (TUNEL)-positive cells compared with control (NE, 33+/-3% versus control, 3+/-1%, P<0.0001; NE+AT, 4+/-2% versus control, 3+/-1%, P=0. 98). Annexin V staining, DNA laddering, and caspase activity determinations corroborated these results. Subsequent experiments under prazosin treatment established the apoptosis dose-response curves for the increasingly beta(2)-selective AR agonists isoproterenol (ISO) (beta(1) approximately beta(2)) and albuterol (ALB) (beta(2)>beta(1)). ISO and ALB induced significantly less apoptosis than NE (beta(1)>beta(2)) at equimolar concentrations as assessed by TUNEL staining [1 mcmol/L: NE (8+/-2%) approximately ISO (7+/-1%)>ALB (2+/-1%); 10 mcmol/L: NE (35+/-2%)>ISO (23+/-1%)>ALB (3+/-1%); 100 mcmol/L: NE (50+/-2%)>ISO (29+/-2%)>ALB (14+/-1%), P<0.0001 except for NE versus ISO at 1 mcmol/L with P=0.62]. ALB-induced apoptosis at 100 mcmol/L was abolished by AT (10 mcmol/L), indicating a beta(1)AR-mediated effect. Importantly, ICI 118551 (0.1 mcmol/L), a highly selective beta(2)AR antagonist, did not decrease the percentage of NE-, ISO-, and ALB-induced apoptosis. Reverse transcription-polymerase chain reaction studies revealed that AT completely reversed the beta-adrenergic signaling-induced changes in the Bcl-2-to-Bax ratio. CONCLUSIONS-These observations provide evidence that beta AR-mediated apoptotic death signaling is largely dissociated from beta(2)ARs and selectively mediated by beta(1)ARs in adult rat ventricular myocytes.

Is overall blockade superior to selective blockade of adrenergic receptor subtypes in suppressing left ventricular remodeling in spontaneously hypertensive rats?

“…Both pathways have been shown to mediate hypertrophy in myocardial cells. 43,44 In this study, after AR-a 1 blockade with carvedilol, the expression of Gqa protein, PKC-a and PKC-d was decreased significantly in the carvedilol-treated group, which suggested that Gqa, PKC-a and PKC-d were the main molecules linked to AR-a 1 in the signal transduction pathway. In contrast, the expression of AR-b 1 and AR-b 2 was increased after treatment, followed by a normalized Gsa protein expression and decreased PKA level, and these effects were the most significant in the carvediloltreated group.…”

G-proteins in growth and apoptosis: lessons from the heart

“…In a subsequent study apoptosis was shown to be mediated through the b 1 -AdrR, via e ects on cyclic AMP (Communal et al, 1999). Zaugg et al (2000) also demonstrated that it is the b 1 -AdrR which mediates the apoptotic response to NE. This ®nding is particularly relevant in light of the observation that transgenic animals expressing b 1 -AdrR, even at relatively low levels, develop heart failure associated with apoptosis (Engelhardt et al, 1999;Bisognano et al, 2000).…”

Neurohumoral activation in heart failure: the role of adrenergic receptors

“…However, substantial evidence from the literature points to significant differences between β 1 and β 2 -adrenergic receptor subtypes and their ability to stimulate apoptosis, or programmed cell death, in isolated cardiac myocytes and in vivo experiments performed in knockout mice lacking β 1 , β 2 or both subtypes (Patterson et al 2004). β 1 -adrenergic receptor stimulation results in an increased cardiac myocyte apoptosis via cAMP-dependent mechanism (Communal et al 1998(Communal et al , 1999, whereas stimulation of β 2 -subtype inhibits apoptosis via a Gi-coupled pathway involving PI3K and Akt-PKD (Chesley et al 2000, Zaugg et al 2000, Zhu et al 2001. These findings have interesting clinical implications for heart failure therapy, since they provide cellular and molecular mechanisms that underline the beneficial therapeutic effects of some β-adrenergicreceptor antagonists, and provide the rationale for combining β 1 -subtype specific blockade with β 2 -subtype activation.…”