Targeting mAKAPß expression as a therapeutic approach for ischemic cardiomyopathy.

Ischemic cardiomyopathy is a leading cause of death and an unmet clinical need. Adeno-associated virus (AAV) gene-based therapies hold great promise for treating and preventing heart failure. Previously we showed that muscle A-kinase Anchoring Protein ß (mAKAPß, AKAP6ß), a scaffold protein that organizes perinuclear signalosomes in the cardiomyocyte, is a critical regulator of pathological cardiac hypertrophy. Here, we show that inhibition of mAKAPß expression in stressed adult cardiomyocytes in vitro was cardioprotective, while conditional cardiomyocyte-specific mAKAP gene deletion in mice prevented pathological cardiac remodeling due to myocardial infarction. We developed a new self-complementary serotype 9 AAV gene therapy vector expressing a short hairpin RNA for mAKAPß under the control of a cardiomyocyte-specific promoter (AAV9sc.shmAKAP). This vector efficiently downregulated mAKAPß expression in the mouse heart in vivo. Expression of the shRNA also inhibited mAKAPß expression in human induced cardiomyocytes in vitro. Following myocardial infarction, systemic administration of AAV9sc.shmAKAP prevented the development of pathological cardiac remodeling and heart failure, providing long-term restoration of left ventricular ejection fraction. Our findings provide proof-of-concept for mAKAPß as a therapeutic target for ischemic cardiomyopathy and support the development of a translational pipeline for AAV9sc.shmAKAP for the treatment of heart failure.

Right ventricular mitochondrial respiratory function in a piglet model of chronic pulmonary hypertension.

OBJECTIVE: We aimed to assess the mitochondrial respiratory capacities in the right ventricle in the setting of ventricular remodeling induced by pressure overload. METHODS: Chronic thromboembolic pulmonary hypertension was induced in 8 piglets over a 12-week period (chronic thromboembolic pulmonary hypertension model). Right ventricular remodeling, right ventricular function, and mitochondrial respiratory function were assessed at 3, 6, and 12 weeks after induction of pulmonary hypertension and were compared with sham animals (n = 5). Right ventricular cardiomyocytes and mitochondrial structure were studied in transmission electronic microscopy after 12 weeks. RESULTS: As of 3 weeks, chronic pressure overload induced right ventricular dilatation, right ventricular hypertrophy, and right ventricular dysfunction. Maladaptive remodeling in the chronic thromboembolic pulmonary hypertension model was confirmed by the decrease of right ventricular pulmonary artery coupling and right fractional area change. Mitochondrial functional assays in permeabilized right ventricular myocardial fibers revealed that oxidative phosphorylation capacities (complex I, complex II, and IV of the mitochondrial respiratory chain) were degraded. Furthermore, no change in substrate preference of mitochondria was found in the overloaded right ventricle. There was a good correlation between maximal mitochondrial oxygen consumption rate and right ventricular pulmonary artery coupling (Pearson coefficient r = 0.83). Transmission electronic microscopy analysis showed that the composition of cardiomyocytes was no different between the chronic thromboembolic pulmonary hypertension group and the sham group. However, mitochondrial structure anomalies were significantly increased in the chronic thromboembolic pulmonary hypertension group. CONCLUSIONS: Mitochondrial respiratory function impairment is involved early in the development of right ventricular dysfunction in a piglet model of chronic thromboembolic pulmonary hypertension. Underlying mechanisms remain to be elucidated.