title: Overexpression of protein phosphatase 2A in a murine model of chronic myocardial infarction leads to increased adverse remodeling but restores the regulation of β-catenin by glycogen synthase kinase 3β.
abstract: OBJECTIVE
  Increased activity of cardiac protein phosphatases is an important feature in human heart failure. Several different protein phosphatases (PP) are involved in the regulation of excitation-contraction-coupling of the myocardium. Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase consisting of a dimeric core enzyme and tissue-specific subunits. In this study we used transgenic mice overexpressing PP2A to further investigate the role of PP2A in cardiac remodeling after myocardial infarction.
  
  
  RESULTS
  Adult male CD-1 mice overexpressing the catalytic subunit α of PP2A (αMHC-PP2A; TG) underwent chronic LAD-ligation or sham surgery, respectively; wildtype littermates (WT) were used as controls. Cardiac function was determined by echocardiography before and 28 days after LAD-ligation. 28 days after MI, the animals were sacrificed and cardiac remodeling was analyzed in histological sections and by Western blots. PP2A overexpression leads to dilated cardiomyopathy in mice, and increased cardiomyocyte hypertrophy and fibrosis of the remote myocardium can be seen after myocardial infarction. However, we found an improved survival of TG in the subacute phase after MI in comparison to WT. On the molecular level, TG shows reduced expression of SERCA and CaMKII alpha both under basal condition as well 28 days after MI. Additionally, the regulation of the Akt/GSK3β/β-catenin pathway is severely disturbed in TG at baseline where a significant activation of Akt is found that coincides with the typical phosphorylation of GSK3β. However, this does not lead to the accumulation of β-catenin - on the contrary: phosphorylation-induced degradation of β-catenin is significantly enhanced.
  
  
  CONCLUSIONS
  Transgenic overexpression of myocardial PP2A causes adverse remodeling which coincides with a disruption of the classical Akt/GSK3/β-catenin pathway under baseline conditions that is restored to normal values in chronic myocardial infarction. Even so overall survival of TG after myocardial infarction was not constrained and survival after day 2 post MI was improved.
authors: Martin Luther University of Halle-Wittenberg, Department of Medicine III, Halle, Germany.
authors: M
authors: M
authors: Hoehn
authors: Martin Luther University of Halle-Wittenberg, Department of Medicine III, Halle, Germany.
authors: Y
authors: Y
authors: Zhang
authors: Martin Luther University of Halle-Wittenberg, Department of Medicine III, Halle, Germany.
authors: J
authors: J
authors: Xu
authors: Martin Luther University of Halle-Wittenberg, Institute of Pharmacology and Toxicology, Halle, Germany.
authors: U
authors: U
authors: Gergs
authors: Institute of Pharmacology and Toxicology, University Hospital, Münster, Germany.
authors: Peter
authors: P
authors: Boknik
authors: Martin Luther University of Halle-Wittenberg, Department of Medicine III, Halle, Germany.
authors: K
authors: K
authors: Werdan
authors: Martin Luther University of Halle-Wittenberg, Institute of Pharmacology and Toxicology, Halle, Germany.
authors: J
authors: J
authors: Neumann
authors: Martin Luther University of Halle-Wittenberg, Department of Medicine III, Halle, Germany. Electronic address: henningebelt@web.de.
authors: H
authors: H
authors: Ebelt
mesh_terms: D000818:Animals; D064752:Atrial Remodeling / Q000502:physiology; D015153:Blotting, Western; D002311:Cardiomyopathy, Dilated / Q000378:metabolism; D002312:Cardiomyopathy, Hypertrophic / Q000378:metabolism; D004562:Electrocardiography; D015870:Gene Expression / Q000502:physiology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D009203:Myocardial Infarction / Q000378:metabolism* / Q000401:mortality; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D054648:Protein Phosphatase 2
keywords: Akt/GSK3β/β-catenin pathway; Cardiomyocyte hypertrophy; Dilated cardiomyopathy; Excitation–contraction-coupling; Myocardial infarction; Protein phosphatase 2A