RhoA/ROCK signaling and pleiotropic α1A-adrenergic receptor regulation of cardiac contractility

• Published in: PloS one 2014-06, Vol.9 (6), p.e99024-e99024
• Main Authors: Yu, Ze-Yan, Tan, Ju-Chiat, McMahon, Aisling C, Iismaa, Siiri E, Xiao, Xiao-Hui, Kesteven, Scott H, Reichelt, Melissa E, Mohl, Marion C, Smith, Nicola J, Fatkin, Diane, Allen, David, Head, Stewart I, Graham, Robert M, Feneley, Michael P
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Agonists - pharmacology; Adrenergic receptors; Angiotensin; Angiotensin II; Animals; Biology and Life Sciences; Calcium; Calcium (intracellular); Calcium - metabolism; Cardiology; Cardiomyocytes; Desensitization; Heart; Heart attacks; Heart diseases; Heart failure; Hypertrophy; Inhibition; Intracellular; Kinases; Kinetics; Ligands; Machinery; Machinery and equipment; Medicine; Medicine and Health Sciences; Mice; Mice, Transgenic; Muscle contraction; Myocardial Contraction - physiology; Myosin; Phosphatase; Phosphorylation; Physiology; Proteins; Receptors, Adrenergic, alpha-1 - physiology; Rho-associated kinase; rho-Associated Kinases - metabolism; rhoA GTP-Binding Protein - metabolism; RhoA protein; Rodents; Sensitivity; Signal Transduction; Signaling; Skin; Transgenic animals; Transgenic mice
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0099024

To determine the mechanisms by which the α1A-adrenergic receptor (AR) regulates cardiac contractility. We reported previously that transgenic mice with cardiac-restricted α1A-AR overexpression (α1A-TG) exhibit enhanced contractility but not hypertrophy, despite evidence implicating this Gαq/11-coupled receptor in hypertrophy. Contractility, calcium (Ca(2+)) kinetics and sensitivity, and contractile proteins were examined in cardiomyocytes, isolated hearts and skinned fibers from α1A-TG mice (170-fold overexpression) and their non-TG littermates (NTL) before and after α1A-AR agonist stimulation and blockade, angiotensin II (AngII), and Rho kinase (ROCK) inhibition. Hypercontractility without hypertrophy with α1A-AR overexpression is shown to result from increased intracellular Ca(2+) release in response to agonist, augmenting the systolic amplitude of the intracellular Ca(2+) concentration [Ca(2+)]i transient without changing resting [Ca(2+)]i. In the absence of agonist, however, α1A-AR overexpression reduced contractility despite unchanged [Ca(2+)]i. This hypocontractility is not due to heterologous desensitization: the contractile response to AngII, acting via its Gαq/11-coupled receptor, was unaltered. Rather, the hypocontractility is a pleiotropic signaling effect of the α1A-AR in the absence of agonist, inhibiting RhoA/ROCK activity, resulting in hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), reducing the Ca(2+) sensitivity of the contractile machinery: all these effects were rapidly reversed by selective α1A-AR blockade. Critically, ROCK inhibition in normal hearts of NTLs without α1A-AR overexpression caused hypophosphorylation of both MYPT1 and cMLC2, and rapidly reduced basal contractility. We report for the first time pleiotropic α1A-AR signaling and the physiological role of RhoA/ROCK signaling in maintaining contractility in the normal heart.