Background-Adenylyl cyclases (ACs) are a family of effector molecules for G-protein-coupled receptors. The 2 ACs most abundantly expressed in cardiac myocytes are types 5 (AC5) and 6 (AC6), which have 65% amino acid homology. It has been speculated that coexpression of 2 AC types in cardiac myocytes represents redundancy, but the specific role of AC6 in cardiac physiology and its differences from AC5 remain to be defined. Methods and Results-We generated transgenic mice with targeted deletion of AC6. Deletion of AC6 was associated with reduced left ventricular contractile function (Pϭ0.026) and relaxation (Pϭ0.041). The absence of AC6 was associated with a 48% decay in ␤-adrenergic receptor-stimulated cAMP production in cardiac myocytes (Pϭ0.003) and reduced protein kinase A activity (Pϭ0.015). In addition, phospholamban phosphorylation was reduced (Pϭ0.015), sarcoplasmic reticulum Ca 2ϩ -ATPase activity was impaired (PϽ0.0001), and cardiac myocytes showed marked abnormalities in calcium transient formation (Pϭ0.001). Conclusions-The

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Urocortin-2 (UCn2) peptide infusion increases cardiac function in patients with heart failure, but chronic peptide infusion is cumbersome, costly, and provides only short-term benefits. Gene transfer would circumvent these shortcomings. Here we ask whether a single intravenous injection of adeno-associated virus type 8 encoding murine urocortin-2 (AAV8.UCn2) could provide long-term elevation in plasma UCn2 levels and increased left ventricular (LV) function. Normal mice received AAV8.UCn2 (5 · 10 11 genome copies, intravenous). Plasma UCn2 increased 15-fold 6 weeks and > 11-fold 7 months after delivery. AAV8 DNA and UCn2 mRNA expression was persistent in LV and liver up to 7 months after a single intravenous injection of AAV8.UCn2. Physiological studies conducted both in situ and ex vivo showed increases in LV + dP/dt and in LV -dP/dt, findings that endured unchanged for 7 months. SERCA2a mRNA and protein expression was increased in LV samples and Ca 2 + transient studies showed an increased rate of Ca 2 + decline in cardiac myocytes from mice that had received UCn2 gene transfer. We conclude that a single intravenous injection of AAV8.UCn2 increases plasma UCn2 and increases LV systolic and diastolic function for at least 7 months. The simplicity of intravenous injection of a long-term expression vector encoding a gene with paracrine activity to increase cardiac function is a potentially attractive strategy in clinical settings. Future studies will determine the usefulness of this approach in the treatment of heart failure.

Congestive heart failure is associated with increased expression of pro-inflammatory cytokines, and the levels of these cytokines correlate with heart failure severity and prognosis. Chronic interleukin 6 (IL-6) stimulation leads to LV hypertrophy and dysfunction, and deletion of IL-6 reduces LV hypertrophy after angiotensin II infusion. In this study, we tested the hypothesis that IL-6 deletion has favorable effects on pressure-overloaded hearts. We performed transverse aortic constriction on IL-6-deleted (IL6KO) mice and C57BL/6J mice (CON) to induce pressure overload. Pressure overload was associated with similar LV hypertrophy, dilation, and dysfunction in CON and IL6KO mice. Re-activation of the fetal gene program was also similar in pressure-overloaded CON and IL6KO mice. There were no differences between CON and IL6KO mice in LV fibrosis or expression of extracellular matrix proteins after pressure overload. In addition, no group differences in apoptosis or autophagy were seen. These data indicate that IL-6 deletion does not block LV remodeling and dysfunction induced by pressure overload. Attenuated content of interleukin 11 appears to be a compensatory mechanism for IL-6 deletion in pressure-overloaded hearts. We infer from these data that limiting availability of IL-6 alone is not sufficient to attenuate LV remodeling and dysfunction in failing hearts.

Increased expression of adenylyl cyclase VI has beneficial effects on the heart, but strategies that increase cAMP production in cardiac myocytes usually are harmful. Might adenylyl cyclase VI have beneficial effects unrelated to increased ␤-adrenergic receptor-mediated signaling? We previously reported that adenylyl cyclase VI reduces cardiac phospholamban expression. Our focus in the current studies is how adenylyl cyclase VI influences phospholamban phosphorylation. In cultured cardiac myocytes, increased expression of adenylyl cyclase VI activates Akt by phosphorylation at serine 473 and threonine 308 and is associated with increased nuclear phospho-Akt. Activated Akt phosphorylates phospholamban, a process that does not require ␤-adrenergic receptor stimulation or protein kinase A activation. These previously unrecognized signaling events would be predicted to promote calcium handling and increase contractile function of the intact heart independently of ␤-adrenergic receptor activation. We speculate that phospholamban phosphorylation, through activation of Akt, may be an important mechanism by which adenylyl cyclase VI increases the function of the failing heart. Adenylyl cyclase (AC) 4 catalyzes ATP to generate cAMP, a second messenger that is required for many intracellular events. AC is the effector molecule in the ␤-adrenergic receptor (␤AR)-Gs-AC signaling pathway and for many other G-protein-coupled receptors in cardiac myocytes and other cells (1-2). Cardiac myocytes express predominantly AC type V and AC type VI (AC VI ) (3). Cardiac-directed expression of AC VI in murine cardiomyopathy increases cardiac function, attenuates myocardial hypertrophy, and increases survival (4, 5). However, when cardiac-directed ␤AR expression is used in this same model, life is shortened (6, 7). Clearly there are marked differences in effects that are evoked by these two elements in the ␤AR-Gs-AC signaling pathway, even though both strategies increase cAMP.The objective of the current study was to determine whether increased AC VI expression has effects not directly linked with ␤AR stimulation and protein kinase A (PKA) activation, thereby providing a mechanistic explanation for the unanticipated favorable effects of increased cardiac AC VI expression in heart failure. We previously reported that AC VI reduces cardiac phospholamban (PLB) expression through increased expression of activating transcription factor-3, which suppresses PLB promoter activity (8). We now focus on how AC VI influences PLB phosphorylation. We test the hypothesis that AC VI increases PLB phosphorylation independently of ␤AR stimulation and PKA activation. This would result in increased cardiac function but would circumvent deleterious effects of sustained PKA activation (9).

Cardiac-directed expression of adenylyl cyclase type VI (AC VI ) increases stimulated cAMP production, improves heart function, and increases survival in cardiomyopathy. In contrast, pharmacological agents that increase intracellular levels of cAMP have detrimental effects on cardiac function and survival. We wondered whether effects that are independent of cAMP might be responsible for these salutary outcomes associated with AC VI expression. We therefore conducted a series of experiments focused on how gene transcription is influenced by AC VI in cultured neonatal rat cardiac myocytes, with a particular focus on genes that might influence cardiac function. We found that overexpression of AC VI down-regulated mRNA and protein expression of phospholamban, an inhibitor of the sarcoplasmic reticulum Ca 2؉ -ATPase. We determined that the cAMPresponsive-like element in the phospholamban (PLB) promoter was critical for down-regulation by AC VI . Overexpression of AC VI did not alter the expression of CREB, CREM, ATF1, ATF2, or ATF4 proteins. In contrast, overexpression of AC VI increased expression of ATF3 protein, a suppressor of transcription. Following AC VI gene transfer, when cardiac myocytes were stimulated with isoproterenol or NKH477, a water-soluble forskolin analog that directly stimulates AC, expression of ATF3 protein was increased even more, which correlated with reduced expression of PLB. We then showed that AC VI -induced ATF3 protein binds to the cAMP-responsive-like element on the PLB promoter and that overexpression of ATF3 in cardiac myocytes inhibits PLB promoter activity. These findings indicate that AC VI has effects on gene transcription that are not directly dependent on cAMP generation. Adenylyl cyclase (AC)1 is the effector molecule in the ␤-adrenergic receptor-G-protein-AC signaling pathway in cardiac myocytes and other cells. Previous studies showed that the amount of AC sets a limit on the ability of cardiac myocytes to generate cAMP (1), and cardiac-directed expression of AC type VI (AC VI ) has pronounced favorable effects on cardiovascular function in normal and failing hearts (2-6).The mechanisms explaining these favorable effects of AC VI are not precisely known. The most direct explanation is that the benefits stem from increased intracellular levels of cAMP; this explanation is contrary to current dogma in heart failure which asserts that inotropic agents that increase cAMP are bad for the heart. Indeed, pharmacological agents that stimulate the ␤-adrenergic receptor or decrease the breakdown of cAMP increase cardiac function but do not appear to prolong life (7-9). In contrast, AC VI , a dominant AC isoform in mammalian cardiac myocytes, improves global cardiac function, attenuates myocardial hypertrophy, and increases survival in murine cardiomyopathy (3, 4). However, when cardiac-directed ␤-adrenergic receptor expression is used to treat this same model, life is shortened (10), underscoring the marked differences evoked by these signaling elements, both of which are associated w...

We tested the hypothesis that deletion of adenylyl cyclase type V (AC(V)) would be associated with decreased left ventricular (LV) contractile function and responsiveness to beta-adrenergic receptor (betaAR) stimulation. Absence of cardiac AC(V) expression was confirmed by RT-PCR and immunoblotting in AC(V)-deleted mice (AC(V) (-/-)). Compared to sibling mice with normal amounts of AC(V) (CON), basal and water-soluble forskolin derivative NKH477-stimulated cAMP production was reduced in both LV homogenates and in isolated cardiac myocytes. Basal LV +dP/dt (isolated perfused hearts) was increased (CON: 3,649 +/- 247 mmHg/s; AC(V) (-/-): 4,625 +/- 350 mmHg/s; p = 0.035, n = 10), but the potency of dobutamine on LV +dP/dt was decreased by AC(V) deletion (log EC(50): CON: -6.83 +/- 0.14 M; AC(V) (-/-): -5.99 +/- 0.15 M; p = 0.0007, n = 10). The initial rates of ATP-dependent sarcoplasmic reticulum calcium uptake, assessed in LV homogenates, showed that AC(V) deletion increased SERCA2a affinity for Ca(2+) (log EC(50): CON: -5.94 +/- 0.03 M; AC(V) (-/-): -6.09 +/- 0.02 M; p = 0.001, n = 8). AC(V) deletion is also associated with increased phospholamban phosphorylation, decreased type 1 protein phosphatase catalytic subunit content and activity, and reduced cardiac Galphas protein content. In conclusion, AC(V) deletion has a favorable effect on basal LV function despite reduced cAMP levels. Increased SERCA2a affinity for Ca(2+) and increased phospholamban phosphorylation are contributing factors. However, AC(V) deletion is associated with reduced LV contractile responsiveness to betaAR stimulation, an effect that is associated with reduced Galphas protein content and reduced cAMP generating capacity in cardiac myocytes.

Calcium malfunction plays a central role in heart failure. Here, we provide evidence that adenylyl cyclase type VI restores sarco(endo)plasmic reticulum 2a (SERCA2a) affinity for calcium and maximum velocity of cardiac calcium uptake by sarcoplasmic reticulum in murine dilated cardiomyopathy. Restoration of normal SERCA2a affinity for calcium is associated not only with decreased phospholamban protein expression but also with increased phospholamban phosphorylation by PKA activation. The ratio of phosphorylated ryanodine receptor 2 (RyR2) to RyR2 protein was increased, but the amount of phosphorylated RyR2 was unaffected. These data provide a possible mechanism by which adenylyl cyclase type VI (in contrast to other signaling elements associated with increased cAMP generation) has a salutary effect in the failing heart.