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Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist.

ABSTRACT: RATIONALE:Gq signaling in cardiac myocytes is classically considered toxic. Targeting Gq directly to test this is problematic, because cardiac myocytes have many Gq-coupled receptors. OBJECTIVE:Test whether Gq coupling is required for the cardioprotective effects of an alpha-1A-AR (adrenergic receptor) agonist. METHODS AND RESULTS:In recombinant cells, a mouse alpha-1A-AR with a 6-residue substitution in the third intracellular loop does not couple to Gq signaling. Here we studied a knockin mouse with this alpha-1A-AR mutation. Heart alpha-1A receptor levels and antagonist affinity in the knockin were identical to wild-type. In wild-type cardiac myocytes, the selective alpha-1A agonist A61603-stimulated phosphoinositide-phospholipase C and myocyte contraction. In myocytes with the alpha-1A knockin, both A61603 effects were absent, indicating that Gq coupling was absent. Surprisingly, A61603 activation of cardioprotective ERK (extracellular signal-regulated kinase) was markedly impaired in the KI mutant myocytes, and A61603 did not protect mutant myocytes from doxorubicin toxicity in vitro. Similarly, mice with the ?1A KI mutation had increased mortality after transverse aortic constriction, and A61603 did not rescue cardiac function in mice with the Gq coupling-defective alpha-1A receptor. CONCLUSIONS:Gq coupling is required for cardioprotection by an alpha-1A-AR agonist. Gq signaling can be adaptive.

SUBMITTER: Myagmar BE

PROVIDER: S-EPMC6742539 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist.

Myagmar Bat-Erdene BE Ismaili Taylor T Swigart Philip M PM Raghunathan Anaha A Baker Anthony J AJ Sahdeo Sunil S Blevitt Jonathan M JM Milla Marcos E ME Simpson Paul C PC

Circulation research 20190820 7

<h4>Rationale</h4>Gq signaling in cardiac myocytes is classically considered toxic. Targeting Gq directly to test this is problematic, because cardiac myocytes have many Gq-coupled receptors.<h4>Objective</h4>Test whether Gq coupling is required for the cardioprotective effects of an alpha-1A-AR (adrenergic receptor) agonist.<h4>Methods and results</h4>In recombinant cells, a mouse alpha-1A-AR with a 6-residue substitution in the third intracellular loop does not couple to Gq signaling. Here we ...[more]

PMID: 31426700

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Project description:Reperfusion as a therapeutic intervention for acute myocardial infarction-induced cardiac injury itself induces further cardiomyocyte death. ?-arrestin (?arr)-biased ?-adrenergic receptor (?AR) activation promotes survival signaling responses in vitro; thus, we hypothesize that this pathway can mitigate cardiomyocyte death at the time of reperfusion to better preserve function. However, a lack of efficacious ?arr-biased orthosteric small molecules has prevented investigation into whether this pathway relays protection against ischemic injury in vivo. We recently demonstrated that the pepducin ICL1-9, a small lipidated peptide fragment designed from the first intracellular loop of ?2AR, allosterically engaged pro-survival signaling cascades in a ?arr-dependent manner in vitro. Thus, in this study we tested whether ICL1-9 relays cardioprotection against ischemia/reperfusion (I/R)-induced injury in vivo. Methods: Wild-type (WT) C57BL/6, ?2AR knockout (KO), ?arr1KO and ?arr2KO mice received intracardiac injections of either ICL1-9 or a scrambled control pepducin (Scr) at the time of ischemia (30 min) followed by reperfusion for either 24 h, to assess infarct size and cardiomyocyte death, or 4 weeks, to monitor the impact of ICL1-9 on long-term cardiac structure and function. Neonatal rat ventricular myocytes (NRVM) were used to assess the impact of ICL1-9 versus Scr pepducin on cardiomyocyte survival and mitochondrial superoxide formation in response to either serum deprivation or hypoxia/reoxygenation (H/R) in vitro and to investigate the associated mechanism(s). Results: Intramyocardial injection of ICL1-9 at the time of I/R reduced infarct size, cardiomyocyte death and improved cardiac function in a ?2AR- and ?arr-dependent manner, which led to improved contractile function early and less fibrotic remodeling over time. Mechanistically, ICL1-9 attenuated mitochondrial superoxide production and promoted cardiomyocyte survival in a RhoA/ROCK-dependent manner. RhoA activation could be detected in cardiomyocytes and whole heart up to 24 h post-treatment, demonstrating the stability of ICL1-9 effects on ?arr-dependent ?2AR signaling. Conclusion: Pepducin-based allosteric modulation of ?arr-dependent ?2AR signaling represents a novel therapeutic approach to reduce reperfusion-induced cardiac injury and relay long-term cardiac remodeling benefits.

Project description:AimsTo determine the mechanisms by which the ?1A-adrenergic receptor (AR) regulates cardiac contractility.BackgroundWe reported previously that transgenic mice with cardiac-restricted ?1A-AR overexpression (?1A-TG) exhibit enhanced contractility but not hypertrophy, despite evidence implicating this G?q/11-coupled receptor in hypertrophy.MethodsContractility, calcium (Ca(2+)) kinetics and sensitivity, and contractile proteins were examined in cardiomyocytes, isolated hearts and skinned fibers from ?1A-TG mice (170-fold overexpression) and their non-TG littermates (NTL) before and after ?1A-AR agonist stimulation and blockade, angiotensin II (AngII), and Rho kinase (ROCK) inhibition.ResultsHypercontractility without hypertrophy with ?1A-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, ?1A-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 G?q/11-coupled receptor, was unaltered. Rather, the hypocontractility is a pleiotropic signaling effect of the ?1A-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 ?1A-AR blockade. Critically, ROCK inhibition in normal hearts of NTLs without ?1A-AR overexpression caused hypophosphorylation of both MYPT1 and cMLC2, and rapidly reduced basal contractility.ConclusionsWe report for the first time pleiotropic ?1A-AR signaling and the physiological role of RhoA/ROCK signaling in maintaining contractility in the normal heart.

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Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist.

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Coupling to Gq Signaling Is Required for Cardioprotection by an Alpha-1A-Adrenergic Receptor Agonist.

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