Scar formation occurs during the late stages of the inflammatory response but, when excessive, produces fibrosis that can lead to functional and structural damage of tissues. Here, we show that the profibrogenic agonist, transforming growth factor β1, transcriptionally decreases expression of Exchange protein activated by cAMP 1 (Epac1) in fibroblasts/fibroblast-like cells from multiple tissues (i.e., cardiac, lung, and skin fibroblasts and hepatic stellate cells). Overexpression of Epac1 inhibits transforming growth factor β1-induced collagen synthesis, indicating that a decrease of Epac1 expression appears to be necessary for the fibrogenic phenotype, an idea supported by evidence that Epac1 expression in cardiac fibroblasts is inhibited after myocardial infarction. Epac and protein kinase A, a second mediator of cAMP action, have opposite effects on migration but both inhibit synthesis of collagen and DNA by fibroblasts. Epac is preferentially activated by low concentrations of cAMP and stimulates migration via the small G protein Rap1 but inhibits collagen synthesis in a Rap1-independent manner. The regulation of Epac expression and activation thus appear to be critical for the integration of pro- and anti-fibrotic signals and for the regulation of fibroblast function.

The amount of AC sets a limit on cardiac beta-adrenergic signaling in vivo, and increased AC, independent of betaAR number and G-protein content, provides a means to regulate cardiac responsiveness to betaAR stimulation. Overexpressing an effector (AC) does not alter transmembrane signaling except when receptors are activated, in contrast to receptor/G-protein overexpression, which yields continuous activation and has detrimental consequences. Our findings establish the importance of AC content in modulating beta-adrenergic signaling in the heart, suggesting a new target for safely increasing cardiac responsiveness to betaAR stimulation.

Background-We tested the hypothesis that increased cardiac myocyte adenylyl cyclase (AC) content increases cardiac function and response to catecholamines in cardiomyopathy. Methods and Results-Transgenic mice with cardiac-directed expression of AC type VI (AC VI ) were crossbred with mice with cardiomyopathy induced by cardiac-directed G q expression. G q mice had dilated left ventricles, reduced heart function, decreased cardiac responsiveness to catecholamine stimulation, and impaired ␤-adrenergic receptor (␤AR)-dependent and AC-dependent cAMP production. G q /AC mice showed improved basal cardiac function in vivo (Pϭ0.01) and ex vivo (PϽ0.0005). When stimulated through the ␤AR, cardiac responsiveness was increased (Pϭ0.02), and cardiac myocytes showed increased cAMP production in response to isoproterenol (Pϭ0.03) and forskolin (PϽ0.0001). Key Words: receptors, adrenergic, beta Ⅲ gene therapy A hallmark of dilated cardiomyopathy is decreased generation of cAMP by cardiac myocytes in response to ␤-adrenergic receptor (␤AR) stimulation. However, treatments for clinical heart failure that increase myocardial cAMP content with pharmacological agents that stimulate the ␤AR or decrease the breakdown of cAMP generally have failed, perhaps because of deleterious consequences of unrelenting stimulation of the ␤AR. Indeed, overexpression of cardiac ␤ARs in transgenic mice caused increased basal heart rate, function, and cAMP generation, 1 and mice overexpressing cardiac G s␣ developed cardiomyopathy due to sustained ␤AR stimulation. 2 Cardiac-directed overexpression of ␤ARs failed to improve heart function and increased mortality in murine dilated cardiomyopathy. 3 We recently showed that cardiac myocytes with increased expression of adenylyl cyclase (AC) produce more cAMP when stimulated through the ␤AR or AC. 4 Cardiac-directed expression of AC type VI (AC VI ) results in a phenotypically normal heart with normal basal function and cAMP levels but supranormal responses to catecholamine stimulation. 5 Thus, receptor/G-protein overexpression and standard inotropic therapy yield continuous ␤AR activation and detrimental consequences, whereas overexpression of cardiac AC VI alters transmembrane signaling only when receptors are activated. Conclusions-IncreasingThis could provide increased cAMP generation in heart failure in a manner that circumvents the deleterious consequences of sustained activation.Cardiac-directed expression of G q results in reduced left ventricular (LV) function, decreased cardiac responsiveness to catecholamines, and impaired ␤AR-dependent and ACdependent cAMP production. 6 The exact mechanism for dilation is unknown, but G q is coupled to endothelin, angiotensin II, and ␣ 1 -adrenergic receptors, pathways that influence cardiac myocyte growth and remodeling. This model provides an opportunity to test the hypothesis that cardiacdirected AC expression can increase cAMP generation and restore heart function and response to catecholamines in dilated cardiomyopathy. Methods AnimalsAnimal use followed...

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