Abstract 349: Dilated Cardiomyopathy and Progressive Myocardial Failure in Gαq Overexpressing Mice are Associated with Transcriptional and Oxidative Post-Translational Modifications of RyR2 and SERCA2
Background: Cardiac myocytes from Gαq mice have reduced contractile amplitude associated with decreased systolic and prolonged diastolic Ca2+transients. We have shown that cardiac-specific catalase overexpression in Gαq mice prevented progression to failure but not the initial dilated phenotype. We therefore tested the hypothesis that in Gq mice the initial cardiomyopathic phenotype and the subsequent progression to myocardial failure are mediated by distinct mechanisms that are ROS-independent and ROS-dependant, respectively.
Methods and Results: Hearts were isolated from 8 or 20 wk-old wild-type (WT), Gαq-overexpressing (Gq) or Gαq-catalase (GqCat) overexpressing transgenic mice (n =3– 6 in each group). SERCA and NCX protein expression remained unchanged in all groups at both ages. In contrast, RyR2 protein expression was reduced by 63% ± 18 at 8wks and by 61% ± 28 at 20wks in Gq mice compared with WT (p<0.05). Catalase overexpression did not prevent the decrease in RyR2 expression in Gq mice. RyR2 mRNA level, quantified by real-time RT-PCR, was reduced in 20 wk-old Gq and GqCat mice compared with WT mice (0.65 ± 0.02 and 0.67 ± 0.05 units respectively vs 1.12 ± 0.14 units, p<0.05). At 8 weeks, no oxidative modifications, as reflected by decreased labeling with biotinylated iodoacetamide (BIAM), were detected for RyR2, NCX, or SERCA2. At 20 weeks, BIAM labeling was unchanged for NCX and RyR2, whereas SERCA2 BIAM labeling was reduced by 37 ± 5% in Gq mice compared with WT mice (p<0.001). Catalase overexpression reduced SERCA oxidation (−17 ± 8%, p<0.05 vs WT, p>0.05 vs Gq). To further assess SERCA2 oxidation, heart sections were stained with an antibody raised against a peptide containing the sulfonylated Cys674 residue. Compared with WT, staining was increased in Gq mice and was prevented by catalase overexpression.
Conclusion: In Gαq mice, the initial cardiomyopathy is associated with the transcriptional downregulation of RyR2 mRNA expression by a ROS-independent mechanism. In contrast, the subsequent progressive myocardial failure is associated with increased oxidative stress and oxidative post-translational modification of SERCA2 on Cys674 that is mediated by hydrogen peroxide.