Abstract-This study tested the hypothesis that atrial natriuretic peptide has direct antihypertrophic actions on the heart by modulating expression of genes involved in cardiac hypertrophy and extracellular matrix production. Hearts of male, atrial natriuretic peptide-null and control wild-type mice that had been subjected to pressure overload after transverse aortic constriction and control unoperated hearts were weighed and subjected to microarray, Northern blot, and immunohistochemical analyses. Microarray and Northern blot analyses were used to identify genes that are regulated differentially in response to stress in the presence and absence of atrial natriuretic peptide. Immunohistochemical analysis was used to identify and localize expression of the protein products of these genes. Atrial natriuretic peptide-null mice demonstrated cardiac hypertrophy at baseline and an exaggerated hypertrophic response to transverse aortic constriction associated with increased expression of the extracellular matrix molecules periostin, osteopontin, collagen I and III, and thrombospondin, as well as the extracellular matrix regulatory proteins, matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-3, and the novel growth factor pleiotrophin compared with wild-type controls. These results support the hypothesis that atrial natriuretic peptide protects against pressure overload-induced cardiac hypertrophy and remodeling by negative modulation of genes involved in extracellular matrix deposition. Key Words: atrial natriuretic factor Ⅲ constriction Ⅲ aorta Ⅲ pressure overload Ⅲ hypertrophy, cardiac Ⅲ extracellular matrix Ⅲ growth substances A trial natriuretic peptide (ANP) inhibits cell growth and proliferation and induces apoptosis in a variety of cell types, including vascular smooth muscle cells (VSMCs) and cardiomyocytes. 1-3 Intracardiac ANP might also play an important autocrine/paracrine role in modulating cardiac remodeling under stress conditions and might protect against the development of pathologic cardiac hypertrophy. 4 -7 Synthesis and release of ANP in the heart are increased under stressful conditions such as pressure and volume overloadinduced pathologic cardiac hypertrophy, exercise-induced physiologic cardiac hypertrophy, heart failure, and hypoxic pulmonary hypertension. 1,2 Expression of ANP is inversely related to cardiac growth/hypertrophy. 5,8 -11 Transgenic mice overexpressing ANP have smaller hearts than do wild-type mice, and ANP gene delivery attenuates cardiac hypertrophy in spontaneously hypertensive rats. 5,7 Conversely, transgenic mice with homozygous disruption of the pro-ANP gene (Nppa -/-mice) or the natriuretic peptide receptor-A (NPR-A) gene (Npr1 -/-mice) exhibit cardiac hypertrophy at baseline that is out of proportion to the modest elevations in blood pressure (BP) observed in these models. 8 -11 Furthermore, in Npr1 -/-mice, pressure overload induced by transverse aortic constriction (TAC) results in a greater (55%) increase in left ventricular (LV) weight than in Np...

Abstract-We hypothesized that a single copy of the proatrial natriuretic peptide gene (Nppa ϩ/Ϫ ) would not be adequate to protect heterozygous mice against exaggerated cardiac hypertrophy and remodeling after pressure-overload stress. Nppa ϩ/ϩ , Nppa ϩ/Ϫ , and Nppa Ϫ/Ϫ mice were subjected to sham surgery or transverse aortic constriction and fed a basal salt diet. Heart weight varied inversely with Nppa gene load by 1 week after either surgery. Fractional shortening did not differ among genotypes at baseline and fell in Nppa Ϫ/Ϫ mice only after transverse aortic constriction. There was a graded response in collagen deposition related to atrial natriuretic peptide (ANP) expression after either surgery. A robust interstitial and perivascular fibrosis was noted in Nppa Ϫ/Ϫ and Nppa ϩ/Ϫ but not in Nppa ϩ/ϩ mice after transverse aortic constriction. Our findings are consistent with a growing body of evidence that ANP is an important modulator of cardiac hypertrophy and remodeling in response to hemodynamic stress. The observation that partial ANP deficiency results in exaggerated hypertrophy and remodeling after pressure overload suggests that genetic or environmental variation in ANP levels may play a role in the development of cardiac hypertrophy, remodeling, and failure in humans. Key Words: atrial natriuretic factor Ⅲ natriuretic peptides Ⅲ receptors, atrial natriuretic factor Ⅲ hypertrophy, cardiac Ⅲ remodeling Ⅲ extracellular matrix Ⅲ collagen R ecent studies suggest that atrial natriuretic factor (ANP) is an autocrine/paracrine modulator of cardiac hypertrophy and remodeling in response to pathologic stimuli. [1][2][3][4][5][6][7][8][9][10] Mice with homozygous deletion of the pro-ANP gene (Nppa Ϫ/Ϫ ) or the natriuretic peptide receptor-A gene (Npr1 Ϫ/Ϫ ) exhibit cardiac hypertrophy under resting conditions 3,5,11-13 and develop exaggerated hypertrophy after volume or pressure overload. 6,12,13 Furthermore, these studies raise the question as to whether variation in ANP response to hemodynamic stress is an important mediator of cardiac hypertrophy and remodeling in human hypertension and heart failure. Although studies in Nppa Ϫ/Ϫ mice have clearly demonstrated the adverse effect of ANP deletion on cardiac hypertrophy and remodeling, the effect of a modest ANP deficiency on the development of cardiac hypertrophy, remodeling, and failure remains unknown.ANP-heterozygous mice (Nppa) have normal blood pressure on either a normal-(0.5% NaCl) or an intermediate-salt (2% NaCl) diet, 6,14 in contrast to the hypertension observed in Nppa Ϫ/Ϫ mice under these conditions. 11 On a very-high-salt (8% NaCl) diet, however, Nppa ϩ/Ϫ mice develop hypertension. 6 The cardiac phenotype of the heterozygous ANP-knockout has not been rigorously studied under either basal or stress conditions. However, in their original report of this model, John et al 6 did not find a significant difference in cardiac weight between Nppa ϩ/ϩ and Nppa ϩ/Ϫ mice. The relatively normal cardiac phenotype in the heterozygous ANP-knockout might indicate...