Copyright © 2005, European Society of Cardiology
Enhanced cardiac function in mice overexpressing protein phosphatase Inhibitor-2
aInstitut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität, 48149 Münster, Germany
bInstitut für Pathologie, Universität Essen, 45147 Essen, Germany
cDepartment of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
dInstitut für Pharmakologie und Toxikologie, Martin-Luther-Universität Halle-Wittenberg, 06112 Halle, Germany
* Corresponding authors. Anna DePaoli-Roach is to be contacted at Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA. Tel.: +1 317 274 1585; fax: +1 317 274 4686. Joachim Neumann, Institut für Pharmakologie und Toxikologie, Martin-Luther-Universität Halle-Wittenberg, 06112 Halle, Germany. Tel.: +49 345 5571868; fax: +49 3455571835. Email address: adepaoli{at}iupui.edu neumannjoachim{at}hotmail.com
Objective: Protein phosphatase 1 (PP1) has been implicated in the control of cardiac function. Cardiac specific overexpression of the catalytic subunit, PP1c, results in hypertrophy and depressed contractility.
Methods: To further address the role of PP1, transgenic mice (TG) were generated that overexpress in heart a functional COOH-terminally truncated form (amino acids 1-140) of the PP1 inhibitor-2 (I-2140).
Results: The TG hearts show increased levels of I-2140 mRNA as well as protein and activity. No increase in absolute or relative heart weight was observed, nor any changes in gross pathology or increase in morbidity or mortality in the TG mice. Immunohistochemical and biochemical analyses revealed that expression of the I-2140 protein is confined to cardiomyocytes where it is mainly localized in the cytosol. The total protein phosphatase (PP) activity was reduced by 80% in TG hearts as compared to wild-type littermates (WT). The PP1c mRNA level was the same in TG and WT, while the protein level was increased by
7-fold in TG animals. The maximal rates of contraction (+dP/dt) and of relaxation (–dP/dt) were increased by 32% and 40%, respectively, in the intact catheterized TG mice compared to WT. However, the maximal contractile response to β-adrenergic agonists was comparable in hearts from TG and WT mice. In isolated cardiomyocytes of TG mice, Ca2+transient amplitude was increased by 50% under basal conditions and by 60% upon rapid caffeine application. The phospholamban (PLB) protein level was unchanged whereas the basal phosphorylation of PLB at Ser16 was significantly increased in TG hearts.
Conclusion: These results indicate that I-2140 overexpression results in decreased PP1 activity and enhanced contractility in the heart, underscoring the fundamental role of PP1 in cardiac function.
KEYWORDS Protein phoshatase 1; Inhibitor-2; Heart; transgenic mouse; contractility
1 Equally contributing senior authors.
* This work was supported by a grant from the Deutsche Forschungsgemeinschaft to JN and by National Institute of Health Grant DK36569 to AADPR.
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