Protein kinase B (AKT) isoforms AKT-1 and AKT-2 are of central importance for cardiac functionality. Tamoxifen-inducible, cardiac myocyte specific AKT-1/2 double knockout (iCMAKT1/2KO) mice exhibited progressive cardiomyocyte atrophy, heart failure, energetic depletion, and reduced survival of 24.4 ±2 days after KO induction. Despite its function in homeostasis of cellular energy status, an inhibitory phosphorylation of AMPK on serine 485/491 was increased during advanced stages of metabolic depression (day 14 and day 21 after knockout induction). Thus, activation of AMPK appears to be depressed despite lack of energy. Here we examined the influence of reduced AMPK activity on cardiac phenotype of iCMAKT1/2KO mice.

Four weeks before knockout induction, iCMAKT1/2KO mice (type: α-MHC-mer-Cre-mer-AKT-1/2-flox) were intraveneously infected with adeno-associated virus of serotype 9 to express a non-inactivatable, c-Myc tagged AMPK-α2-S491A mutant (AMPK-S491A-AAV9). Echocardiographic examination of cardiac left ventricular functional parameters under inhaled 2 % isoflurane anaesthesia was carried out before and 2 weeks after virus application. Upon induction of the knockout 4 weeks after virus application, echocardiography was performed weekly for 3 weeks. AMPK-S491A-AAV9 treated mice were compared to non-infected iCMAKT1/2KO mice. Furthermore, survival of both groups was investigated. Post mortem, heart extracts were examined by Western Blot analysis.

Successful cardiac infection was demonstrated by detection of c-Myc tagged, transgenic AMPK-α. Furthermore, an increase in T-172 phosphorylated AMPK-α suggested that transgenic AMPKα was activatable. Functional analysis by echocardiography indicated that AMPK-S491A-AAV9 infected mice showed a significantly slower decline of the cardiac parameters ejection fraction, fraction area change, fractional shortening, and end-systolic and end-diastolic volume between day 0 to day 14 after KO induction. In addition, a significantly slowed worsening from day 0 to day 14 was found in AMPK-S491A-AAV9 infected mice for internal diameter in systole and diastole as well as posterior wall. However, the changes from day 0 to day 21 were similar for these parameters in both groups. Furthermore, a tendency to prolonged survival was observed in AMPK-S491A-AAV9 infected mice.

In summary, cardiac expression of a non-inactivatable AMPK-α2 mutant has a cardioprotective effect and partially blunts iCMAKT1/2KO-mediated heart failure. Therefore, inhibitory serine 485/491 phosphorylation of AMPK promotes the observed cardiac phenotype of iCMAKT1/2KO.