Abstract 234: Expression of Activated PKCϵ Accelerates the Transition to Heart Failure in Response to Increased Hemodynamic Load
Expression of constitutively active PKCϵ in the myocardium promotes a steady progression to a dilated cardiomyopathy over time. Functional and biochemical studies demonstrate that the myofibrillar proteins are a target of PKCϵ mediated phosphorylation. In this model, changes in myofibrillar protein phosphorylation at 3-months are associated with compensatory mechanisms, whereas at 9 and 12-months are associated with the transition to failure. To test the hypothesis that PKCϵ phosphorylation alters the post-translational modification of the contractile proteins and that these changes predispose the heart to failure, we imposed a hemodynamic load on young mice (3-mice). Both transgenic (TG) and non-transgenic (NTG) mice were banded (AoB) for 10 weeks before assessment of cardiac function in vivo, gene expression and 2-D electrophoresis of myofibrillar extracts. Analysis of heart weight to body weight ratios (3mNTG=4.3±0.4 vs. 3mTG=4.2±0.3 vs. 3mNTG(AoB)= 5.9±0.3* vs. 3mT-G(AoB)=7.4±0.6** *p<0.05), shows hypertrophy in both groups of AoB mice, but to a greater degree in the TG (AoB). Gene expression analysis using quantitative qRT-PCR shows significant increases in both ANF and β-MHC mRNA in AoB mice compared with non-banded groups. Expression was significantly greater in the TG (AoB) along with a decrease in SERCA mRNA. Banding induced both diastolic and systolic dysfunction in TG compared to NTG hearts. Maximal −dP/dt in the TG (AoB) hearts was significantly lower compared to all other groups (3mNTG=9433±1000 vs. 3mTG=9474±857 vs. 3mNTG(AoB)=8620±1264 vs. 3mT-G(AoB)=4911±738* mmHg/sec, *p<0.05). Load-independent measurements revealed a significant decreases the time constant of isovolumic relaxation (3mNTG(AoB)=5.4±0.6 vs. 3mTG(AoB)=8.4±1.5* ms). In addition, maximal +dP/dt-end diastolic volume relation (3mNTG(AoB)=213±64 vs. 3mTG(AoB)=79±20*, p<0.05) was significantly depressed in banded TG compared to banded NTG. 2-D gel analysis of myofibrillar proteins revealed hyper-phosphorylation of troponin I in the PKCϵ TG mice. These data suggest that while the TG hearts have compensated to an initial insult (PKC activation) imposition of a second insult (hemodynamic load) accelerates the transition to failure.