Abstract 19509: Cardiomyocyte-Specific Overexpression of the E3 Ubiquitin Ligase Wwp1 Causes Altered Connexin 43 and 45 Expression Leading to Arrhythmias and Sudden Cardiac Death
Rationale: The electrical coupling between adjacent cardiomyocytes is tightly regulated by gap junctions (GJ) to ensure proper electrical conduction in the myocardium. We have recently shown that the ubiquitin ligase Wwp1 can interact with and ubiquitylate the GJ protein connexin 43 (Cx43) causing its degradation. All mice ubiquitously overexpressing Wwp1 develop left ventricular hypertrophy (LVH), a 90% decrease in Cx43 protein, and die from sudden cardiac death (SCD) around 8 weeks of age.
Hypothesis: We hypothesize that the effects of Wwp1 overexpression are cell autonomous to cardiomyocytes and that some degree of compensation exists until 8 weeks of age in mice.
Methods: Cardiomyocyte-specific overexpression of Wwp1 was achieved using a tamoxifen-inducible cre transgenic mouse line driven by the α-MHC promoter. LVH was assessed in animals overexpressing cardiac Wwp1 (n=8) relative to their wild type littermates (n=8) using echocardiography. Cx43 and Cx45 protein levels and localization within myocardial tissue was determined via Western blotting and multi-immunofluorescence staining in conjunction with laser scanning confocal microscopy. Susceptibility to arrhythmias was ascertained using ventricular burst pacing monitored by ECG.
Results: Induction of cardiomyocyte-specific Wwp1overexpression at 4 weeks of age resulted in decreased Cx43 expression, ECG abnormalities, and inducible ventricular arrhythmias as early as 48h following induction. In contrast, protein levels of Cx45 were unaltered but showed mislocalization. Unpaced Wwp1 overexpressers (n=12) displayed progressive LVH and SCD at 8 weeks of age. Interestingly, induction of cardiac Wwp1 overexpression at 8 weeks of age or later resulted in similar Cx43 and Cx45 changes and associated ECG abnormalities. Spontaneous or induced ventricular arrhythmias were observed as early as 48h following induction with no associated LVH.
Conclusions: Wwp1 exerts its effects on cardiac structure and function in a cell autonomous manner. There is some plasticity in the myocardium which provides protection against spontaneous arrhythmias up until 8 weeks of age in mice. This mechanistic insight highlights the potential for novel anti-arrhythmia therapeutics targeting Wwp1.
- © 2012 by American Heart Association, Inc.