Abstract 16420: The E3 Ubiquitin Ligase is Upregulated During Cardiac Hypertrophy

Abstract

Introduction: Cardiomyocyte hypertrophy is observed during normal postnatal cardiac development as well as during disease-related cardiac remodeling. This growth is accompanied by dynamic changes at the intercalated disc, including the redistribution and degradation of the gap junction protein connexin 43 (Cx43). We have shown that the ubiquitin ligase Wwp1 can promote the degradation of Cx43, and that genetic upregulation of Wwp1 stimulates hypertrophy and arrhythmogenesis. Hypothesis: We hypothesized that changes in the expression of Wwp1 would be associated with developmental and pathological hypertrophy programs. Methods: Expression of Wwp1 was analyzed by digital droplet PCR in hearts derived from normally developing mice at 2, 4, 6, and 8 weeks of age (n=6 for each) or from adult mice subjected to transverse aortic constriction (n=5) vs. sham operated animals (n=5). Cardiac structure and function of mice overexpressing or lacking expression of Wwp1 was evaluated by transmission electron microscopy (n=3) and echocardiography (n=6). Results: The expression of Wwp1 during postnatal development was very dynamic, peaking at a concentration of 324 copies/uL in the hearts derived from 4 week old animals. This also corresponded to the timepoint when the gap junction length at the intercalated disc plateaued. Further, a 1.5-fold increase in the expression of Wwp1 in animals subjected to pressure overload was detected as compared to animals subjected to surgery without pressure overload (p<0.007). Interestingly, the concentration of Wwp1 message in pressure overloaded animals (331 copies/uL) was nearly identical to that found in 4 week old wild type animals during normal postnatal development. Consistent with the level of Wwp1 correlating with cardiomyocyte hypertrophy, animals lacking Wwp1 had a 23-42% decrease in left ventricular mass (p<0.01) whereas transgenic animals overexpressing Wwp1 had a 28-50% increase in left ventricular mass (p<0.005) as compared to wild type controls between 4 and 8 weeks of age. Conclusions: This study shows that expression of Wwp1 is upregulated during hypertrophy and this correlates with ultrastructural changes at the intercalated disc.