Adenosine kinase attenuates cardiomyocyte microtubule stabilization and protects against pressure overload-induced hypertrophy and LV dysfunction.

Adenosine exerts numerous protective actions in the heart, including attenuation of cardiac hypertrophy. Adenosine kinase (ADK) converts adenosine to adenosine monophosphate (AMP) and is the major route of myocardial adenosine metabolism, however, the impact of ADK activity on cardiac structure and function is unknown. To examine the role of ADK in cardiac homeostasis and adaptation to stress, conditional cardiomyocyte specific ADK knockout mice (cADK-/-) were produced using the MerCreMer-lox-P system. Within 4 weeks of ADK disruption, cADK-/- mice developed spontaneous hypertrophy and increased ß-Myosin Heavy Chain expression without observable LV dysfunction. In response to 6 weeks moderate left ventricular pressure overload (transverse aortic constriction;TAC), wild type mice (WT) exhibited ~60% increase in ventricular ADK expression and developed LV hypertrophy with preserved LV function. In contrast, cADK-/- mice exhibited significantly greater LV hypertrophy and cardiac stress marker expression (atrial natrurietic peptide and ß-Myosin Heavy Chain), LV dilation, reduced LV ejection fraction and increased pulmonary congestion. ADK disruption did not decrease protein methylation, inhibit AMPK, or worsen fibrosis, but was associated with persistently elevated mTORC1 and p44/42 ERK MAP kinase signaling and a striking increase in microtubule (MT) stabilization/detyrosination. In neonatal cardiomyocytes exposed to hypertrophic stress, 2-chloroadenosine (CADO) or adenosine treatment suppressed MT detyrosination, which was reversed by ADK inhibition with iodotubercidin or ABT-702. Conversely, adenoviral over-expression of ADK augmented CADO destabilization of MTs and potentiated CADO attenuation of cardiomyocyte hypertrophy. Together, these findings indicate a novel adenosine receptor-independent role for ADK-mediated adenosine metabolism in cardiomyocyte microtubule dynamics and protection against maladaptive hypertrophy.

An adenosinergic positive feedback loop extends pharmacological cardioprotection duration.

BACKGROUND AND PURPOSE: Adenosine receptor activation induces delayed, sustained cardioprotection against ischaemia-reperfusion (IR) injury (24-72 h), but the mechanisms underlying extended cardioprotection duration remain unresolved. We hypothesized that a positive feedback loop involving adenosine receptor-induced proteasomal degradation of adenosine kinase (ADK) and decreased myocardial adenosine metabolism extends the duration of cardioprotection. EXPERIMENTAL APPROACH: Mice were administered an ADK inhibitor, ABT-702, to induce endogenous adenosine signalling. Cardiac ADK protein and mRNA levels were analysed 24-120 h later. Theophylline or bortezomib was administered 24 h after ABT-702 to examine the late roles of adenosine receptors or proteasomal activity, respectively, in ADK expression and cardioprotection at 72 h. Coronary flow and IR tolerance were analysed by Langendorff technique. The potential for continuous adenosinergic cardioprotection was examined using heterozygous, cardiac-specific ADK KO (cADK+/-) mice. Cardiac ADK expression was also examined after A1 or A3 receptor agonist, phenylephrine, lipopolysaccharide or sildenafil administration. KEY RESULTS: ABT-702 treatment decreased ADK protein content and provided cardioprotection from 24 to 72 h. ADK mRNA upregulation restored ADK protein after 96-120 h. Adenosine receptor or proteasome inhibition at 24 h reversed ABT-702-induced ADK protein deficit and cardioprotection at 72 h. cADK+/- hearts exhibited continuous cardioprotection. Diverse preconditioning agents also diminished cardiac ADK protein expression. CONCLUSION AND IMPLICATIONS: A positive feedback loop driven by adenosine receptor-induced ADK degradation and renewed adenosine signalling extends the duration of cardioprotection by ABT-702 and possibly other preconditioning agents. The therapeutic potential of continuous adenosinergic cardioprotection is demonstrated in cADK+/- hearts.