Cardiac β-adrenergic receptors (β-AR) are key regulators of cardiac haemodynamics and size. The scaffolding protein A-kinase anchoring protein 79/150 (AKAP5) is a key regulator of myocardial signalling by β-ARs. We examined the function of AKAP5 in regulating cardiac haemodynamics and size, and the role of β-ARs and Ca²⁺-regulated intracellular signalling pathways in this phenomenon.

We used echocardiographic, histological, genetic, and biochemical methods to examine the effect of ablation of AKAP5 on cardiac haemodynamics, size, and signalling in mice. AKAP5^−/− mice exhibited enhanced signs of cardiac dilatation and dysfunction that progressed with age. Infusions of isoprenaline worsened cardiac haemodynamics in wild-type (WT) mice only, but increased the ratio of heart-to-body weight equally in WT and in AKAP5^−/− mice. Mechanistically, loss of AKAP5 was associated with enhanced activity of cardiac calmodulin kinase II (CaMKII) and calcineurin (CaN) as indexed by nuclear factor of activated T-cell-luciferase activity. Loss of AKAP5 interfered with the recycling of cardiac β₁-ARs, which was mediated in part by CaN binding to AKAP5. Carvedilol reversed cardiac hypertrophy and haemodynamic deficiencies in AKAP5^−/− mice by normalizing the activities of cardiac CaN and CaMKII.

These findings identify a novel cardioprotective role for AKAP5 that is mediated by regulating the activities of cardiac CaN and CaMKII and highlight a significant role for cardiac β-ARs in this phenomenon.