Transient silencing of Npr3 gene expression improved the circulatory levels of atrial natriuretic peptides and attenuated β-adrenoceptor activation- induced cardiac hypertrophic growth in experimental rats.

Natriuretic peptide receptor-C (NPR-C) is considered as a clearance receptor that maintains the circulatory levels of natriuretic peptides. It has been suggested that augmented expression of NPR-C as a cause for the diminished anti-hypertrophic action of natriuretic peptides in the failing heart. Hence, we sought to determine the level of Npr3 gene (coding for NPR-C) expression in the Isoproterenol (ISO) treated Wistar rats. In addition, we studied the effect of Npr3 gene silencing on the hypertrophic growth. A significant increase in heart weight-to-body weight ratio (HW/BW-24%,P<0.01), an indicator of cardiac hypertrophic growth was observed in the ISO (10mg/kg BW/day,i.p for 7 days) treated rats. As expected, the cardiac NPR-C protein expression was significantly increased by 4 fold as compared to control rats. In parallel, the circulatory atrial natriuretic peptide (ANP) level was significantly decreased (2 fold) in ISO treated rats. Upon treatment with siRNA-Npr3, a significant decrease in the cardiac NPR-C protein expression (70%,P<0.01), HW/BW ratio (70%,P<0.01) and hypertrophic marker genes (α-Sk, β-MHC, c-fos, P<0.01, respectively) mRNA expression were observed. Interestingly, the circulatory ANP level was increased by 1.5 fold in the siRNA-Npr3 treated rats as compared to ISO treated rats. Moreover, the cardiac collagen content, matrixmetalloprotinases-2 (MMP-2) and enzymatic antioxidant status (P<0.01, respectively) were found to be restored back to near normal upon siRNA-Npr3 treatment. Taken together, the results of this study indicates that specific down-regulation of Npr3 gene improves the circulatory levels of ANP and antioxidant system and there by attenuates the β-adrenoceptor over-activation mediated cardiac hypertrophic growth in experimental rats.

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