title: Differential cardioprotective/cardiotoxic effects mediated by beta-adrenergic receptor subtypes.
abstract: Recent data suggest that beta-adrenergic receptor subtypes couple differentially to signaling pathways regulating cardiac function vs. cardiac remodeling. To dissect the roles of beta1- vs. beta2-receptors in the pathogenesis of cardiomyopathy, doxorubicin was administered to beta1, beta2, and beta1/beta2 knockout (-/-) and wild-type mice. Expression and activation of MAPKs were measured. Wild-type and beta1-/- mice showed no acute cardiovascular effects, whereas beta2-/- mice all died within 30 min. The additional deletion of the beta1-receptor (beta1/beta2-/-) totally rescued this toxicity. beta2-/- mice developed decreased contractile function, hypotension, QTc prolongation, and ST segment changes and a 20-fold increase in p38 MAPK activity not seen in the other genotypes. The MAPK inhibitor SB-203580 rescued beta2-/- mice from this acute toxicity. The enhanced toxicity in beta2-/- mice was also recapitulated in wild-type mice with the beta2-selective antagonist ICI-118,551, although the rescue effect of the beta1-deletion was not recapitulated using the beta1-selective antagonist metoprolol or the nonselective beta-antagonist propranolol. These data suggest that beta2-adrenergic receptors play a cardioprotective role in the pathogenesis of cardiomyopathy, whereas beta1-adrenergic receptors mediate at least some of the acute cardiotoxicity of anthracyclines. Differential activation of MAPK isoforms, previously shown in vitro to regulate beta-agonist as well as doxorubicin cardiotoxicity, appears to play a role in mediating the differential effects of these beta-adrenergic receptor subtypes in vivo.
authors.affiliation: Dept. of Pediatrics, 750 Welch Rd., Suite 305, Palo Alto, CA 94304, USA. danb@stanford.edu
authors.forename: Daniel
authors.initials: D
authors.lastname: Bernstein
authors.forename: Giovanni
authors.initials: G
authors.lastname: Fajardo
authors.forename: Mingming
authors.initials: M
authors.lastname: Zhao
authors.forename: Takashi
authors.initials: T
authors.lastname: Urashima
authors.forename: Jennifer
authors.initials: J
authors.lastname: Powers
authors.forename: Gerald
authors.initials: G
authors.lastname: Berry
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002311:Cardiomyopathy, Dilated / Q000503:physiopathology*; D002316:Cardiotonic Agents; D006339:Heart Rate; D051379:Mice; D018345:Mice, Knockout; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015996:Survival Rate
chemical_list: D002316:Cardiotonic Agents; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2