Loss of type 9 adenylyl cyclase triggers reduced phosphorylation of Hsp20 and diastolic dysfunction

Abstract

Adenylyl cyclase type 9 (AC9) is found tightly associated with the scaffolding protein Yotiao and the IKs ion channel in heart. But apart from potential IKs regulation, physiological roles for AC9 are unknown. We show that loss of AC9 in mice reduces less than 3% of total AC activity in heart but eliminates Yotiao-associated AC activity. AC9−/− mice exhibit no structural abnormalities but show a significant bradycardia, consistent with AC9 expression in sinoatrial node. Global changes in PKA phosphorylation patterns are not altered in AC9−/− heart, however, basal phosphorylation of heat shock protein 20 (Hsp20) is significantly decreased. Hsp20 binds AC9 in a Yotiao-independent manner and deletion of AC9 decreases Hsp20-associated AC activity in heart. In addition, expression of catalytically inactive AC9 in neonatal cardiomyocytes decreases isoproterenol-stimulated Hsp20 phosphorylation, consistent with an AC9-Hsp20 complex. Phosphorylation of Hsp20 occurs largely in ventricles and is vital for the cardioprotective effects of Hsp20. Decreased Hsp20 phosphorylation suggests a potential baseline ventricular defect for AC9−/−. Doppler echocardiography of AC9−/− displays a decrease in the early ventricular filling velocity and ventricular filling ratio (E/A), indicative of grade 1 diastolic dysfunction and emphasizing the importance of local cAMP production in the context of macromolecular complexes.

Auto-inhibition of adenylyl cyclase 9 (AC9) by an isoform-specific motif in the carboxyl-terminal region

“…Genetic deletion of AC9 is mostly embryonic lethal [6,41,42], but a small fraction of AC9 null homozygotes survive [42,43]. Examination of the cardiac function of these animals [43] showed that the cAMP-dependent phosphorylation of the heat-shock protein Hsp20 is compromised, raising the possibility that AC9 in the heart may have a cardioprotective role [44]. Taken together, switching of the responsiveness of AC9 via proteolysis in the C2b domain may determine the spectrum of intracellular cAMP effectors activated in a complex extracellular stimulus environment such as that seen in neuronal development or myocardial hypertrophy.…”

Insights into the Regulatory Properties of Human Adenylyl Cyclase Type 9

“…Of the AC isoforms, AC9 is the most divergent in sequence and the most understudied. Expression analysis shows that AC9 is widely expressed in the central nervous system, heart, and other tissues (Premont et al, 1996;Paterson et al, 2000;Sosunov et al, 2001;Berndt et al, 2013;Li et al, 2017). Although AC9 knockout mice were initially reported to be embryonically lethal (Antoni, 2006), mice lacking AC9 protein expression are viable despite a preweaning subviable homozygous phenotype with incomplete penetrance (Li et al, 2017).…”

“…Expression analysis shows that AC9 is widely expressed in the central nervous system, heart, and other tissues (Premont et al, 1996;Paterson et al, 2000;Sosunov et al, 2001;Berndt et al, 2013;Li et al, 2017). Although AC9 knockout mice were initially reported to be embryonically lethal (Antoni, 2006), mice lacking AC9 protein expression are viable despite a preweaning subviable homozygous phenotype with incomplete penetrance (Li et al, 2017). Knockdown and gene-trapping studies provide clear in vivo roles for AC9 in neutrophil chemotaxis (Liu et al, 2010(Liu et al, , 2014 and cardiac function (Li et al, 2017).…”

“…Although AC9 knockout mice were initially reported to be embryonically lethal (Antoni, 2006), mice lacking AC9 protein expression are viable despite a preweaning subviable homozygous phenotype with incomplete penetrance (Li et al, 2017). Knockdown and gene-trapping studies provide clear in vivo roles for AC9 in neutrophil chemotaxis (Liu et al, 2010(Liu et al, , 2014 and cardiac function (Li et al, 2017). In addition, polymorphism of the ADCY9 gene is associated with risk for asthma and mood and body weight disorders (Small et al, 2003;Berndt et al, 2013).…”

“…In addition, polymorphism of the ADCY9 gene is associated with risk for asthma and mood and body weight disorders (Small et al, 2003;Berndt et al, 2013). The association of AC9 with the A-kinase anchoring protein Yotiao facilitates protein kinase A (PKA) phosphorylation of potassium voltage-gated channel subfamily Q member 1 (KCNQ1) and likely serves to regulate I Ks channel activity and cardiac repolarization (Piggott et al, 2008;Li et al, 2012Li et al, , 2017.…”