Abstract-Angiotensin II (Ang II) may cause cardiac hypertrophy via type 1 Ang II receptors (AT 1 ) on cardiomyocytes and through growth factors released from cardiac fibroblasts. Whereas cardiomyocyte-specific AT 1 receptor expression produces cardiac hypertrophy and remodeling in vivo, delineation of the signals that mediate growth to Ang II is challenging because the prevailing in vitro model (cultured neonatal cardiomyocytes) expresses low levels of AT 1 receptor and responds inconsistently to Ang II. In this study, when AT 1A receptors were expressed using adenovirus in cultured neonatal cardiomyocytes, Ang II stimulated a robust hypertrophy that was not secondary to the release of cardiac fibroblast-derived factors, specifically endothelin-1. Hypertrophy was accompanied by the induction of the immediate-early response genes, c-fos and c-jun, and reexpression of atrial natriuretic peptide (ANP). Ang II-induced activation of an ANP promoter-reporter was inhibited by the dominant/negative mutants, G␣qI and N17Ras, indicating that hypertrophic signaling by the AT 1A receptor is via heterotrimeric G protein coupling and downstream Ras pathways. AT 1A -mediated cardiomyocyte hypertrophy and mitogen-activated protein kinase (MAPK) activation were inhibited by the MAPK kinase inhibitor, PD98059, and the epidermal growth factor (EGF) receptor kinase antagonist, AG1478, but not by PKC inhibitor, bisindolylmaleimide-1. Moreover, Ang II-induced MAPK activation was prevented by treatment with a matrix metalloproteinase inhibitor, consistent with the tyrosine phosphorylation of the EGF receptor in response to AT 1A receptor activation. These data unequivocally demonstrate that Ang II can directly promote cardiac myocyte growth via AT 1A receptors expressed on these cells and reveal for the first time the important contribution of EGF receptor-transactivated MAPK signaling to this process. Key Words: AT 1A receptor Ⅲ angiotensin Ⅲ cardiomyocyte hypertrophy Ⅲ adenovirus Ⅲ EGF receptor transactivation A ngiotensin II (Ang II) regulates blood pressure, cardiovascular homeostasis, and cellular growth via type 1 (AT 1 ) angiotensin receptors, which activate G␣ q/11 -phospholipase C-␤1 to generate inositol trisphosphate and diacylglycerol, and thereby increase intracellular calcium and activate protein kinase C (PKC). 1 Activation of PKC and the calcium-dependent phosphatase, calcineurin, has been linked to Ang II-mediated growth. 2,3 Activation of AT 1 receptors also promotes tyrosine phosphorylation, stimulation of mitogen-activated protein kinases, and growth, particularly in vascular and cardiac cells. 1 How AT 1 receptors, which lack intrinsic tyrosine kinase activity, induce tyrosine phosphorylation, MAP kinase, and growth factor signaling pathways is not clear, but recent evidence from vascular smooth muscle cells, 4 liver epithelial cells, 5 and cardiac fibroblasts 6 suggest that a major mechanism is the "transactivation" 7 of the EGF receptor (EGFR).Cardiac hypertrophy involves cardiomyocyte growth as well as extracell...

Background-␤-Adrenergic signaling is downregulated in the failing heart, and the significance of such change remains unclear. Methods and Results-To address the role of ␤-adrenergic dysfunction in heart failure (HF), aortic stenosis (AS) was induced in wild-type (WT) and transgenic (TG) mice with cardiac targeted overexpression of ␤ 2 -adrenergic receptors (ARs), and animals were studied 9 weeks later. The extents of increase in systolic arterial pressure (PϽ0.01 versus controls), left ventricular (LV) hypertrophy (TG, 94Ϯ6 to 175Ϯ7 mg; WT, 110Ϯ6 to 168Ϯ10 mg; both PϽ0.01), and expression of ANP mRNA were similar between TG and WT mice with AS. TG mice had higher incidences of premature death and critical illness due to heart failure (75% versus 23%), pleural effusion (81% versus 45%), and left atrial thrombosis (81% versus 36%, all PϽ0.05). A more extensive focal fibrosis was found in the hypertrophied LV of TG mice (PϽ0.05). These findings indicate a more severe LV dysfunction in TG mice. In sham-operated mice, LV dP/dt max and heart rate were markedly higher in TG than WT mice (both PϽ0.01). dP/dt max was lower in both AS groups than in sham-operated controls, and this tended to be more pronounced in TG than WT mice (Ϫ32Ϯ5% versus Ϫ16Ϯ6%, Pϭ0.059), although dP/dt max remained higher in TG than WT groups (PϽ0.05). Conclusions-Elevated

Abstract-Urotensin II (UII) is a somatostatin-like peptide recently identified as a potent vasoconstrictor. In this study, we examined whether UII promotes cardiac remodeling through nonhemodynamic effects on the myocardium. In a rat model of heart failure after myocardial infarction (MI), increased UII peptide and UII receptor protein expression was observed in both infarct and noninfarct regions of the left ventricle compared with sham. Moreover, post-MI remodeling was associated with a significant 75% increase in UII receptor gene expression in the heart (PϽ0.05 versus sham controls), with this increase noted in both regions of the left ventricle. In vitro, UII (10 Ϫ7 mol/L) stimulation of neonatal cardiac fibroblasts increased the level of mRNA transcripts for procollagens ␣ 1 (I), ␣ 1 (III), and fibronectin by 139Ϯ15% (PϽ0.01), 59Ϯ5% (PϽ0.05), and 141Ϯ14% (PϽ0.01), respectively, with a concomitant 23Ϯ2% increase in collagen peptide synthesis as determined by 3 H-proline incorporation (PϽ0.01). UII had no effect on cellular hypertrophy, as determined by changes in total protein content in isolated neonatal cardiomyocytes. However, expression of recombinant rat UII receptor in neonatal cardiomyocytes resulted in significant UII-dependent activation of hypertrophic signaling as demonstrated by increased total protein content (unstimulated, 122.4Ϯ4.0 g/well; rat UII, 147.6Ϯ7.0 g/well; PϽ0.01) and activation of the hypertrophic phenotype through G␣q-and Ras-dependent pathways. These results indicate that, in addition to potent hemodynamic effects, UII may be implicated in myocardial fibrogenesis through increased collagen synthesis by cardiac fibroblasts and may also be an important determinant of pathological cardiac hypertrophy in conditions characterized by UII receptor upregulation. Key Words: urotensin Ⅲ myocardial infarction Ⅲ remodeling Ⅲ collagen Ⅲ hypertrophy L eft ventricular dysfunction, regardless of the underlying etiology, is associated with activation of various neurohormonal systems that compensate for the consequent loss of ventricular function and peripheral homeostasis. These include the renin-angiotensin and endothelin systems, which act to restore the early decline in cardiac output through positive inotropic effects and peripheral vasoconstriction. Although these effects may be beneficial in the short term, prolonged activation, both local and systemic, may additionally contribute to worsening of contractile function through adverse cardiac remodeling, a process characterized by necrosis, 1 myocyte hypertrophy, 2 inflammation, 3 and the pathological accumulation of extracellular matrix material within the interstitium (fibrosis). 4 More recently, the vasoconstrictor peptide urotensin II (UII) has emerged as a likely contributor to cardiovascular physiology and pathology. UII is a somatostatin-like cyclic peptide synthesized by proteolytic cleavage from a precursor molecule, prepro-UII, and has recently been identified as a potent vasoconstrictor. 5 UII has been identified within the heart, ...