Suppression of atrial natriuretic peptide/natriuretic peptide receptor-A-mediated signaling upregulates angiotensin-II-induced collagen synthesis in adult cardiac fibroblasts.

Cardiac hormone atrial natriuretic peptide (ANP) and its receptor natriuretic peptide receptor-A (NPR-A) system acts as an intrinsic negative regulator of abnormal extracellular matrix (ECM) remodeling in the heart. However, the underlying mechanism by which ANP/NPR-A system opposes the ECM remodeling in the diseased heart is not well understood. Here, we investigated the anti-fibrotic mechanism of ANP/NPR-A in fibrotic agonist Angiotensin- II (ANG II)-treated adult cardiac fibroblast (CF) cells. Normal and NPR-A-suppressed adult CF cells were treated with ANG II (10(-7) M) in the presence and absence of ANP (10(-8) M) for 24 h. Total collagen concentration, activity and expression of MMP-2 and MMP-9, and nuclear translocation of Nuclear factor-kappaB (NF-κB-p50) were studied. NPR-A-suppressed adult CF cells exhibited a more pronounced increase in collagen production, ROS generation, and NF-κB-p50 nuclear translocation as compared to adult CF cells treated with agonist alone. ANP co-treatment significantly reverses the agonist-induced above changes in normal adult CF cells, while it failed to reverse the agonist-induced collagen synthesis in the NPR-A-suppressed adult CF cells. The cGMP analog (8-bromo-cGMP) treatment significantly attenuated the agonist-induced collagen synthesis both in normal and NPR-A-suppressed adult cells. The results of this study suggest that ANP/NPR-A signaling system antagonizes the agonist-induced collagen synthesis via suppressing the activities of MMP-2, MMP-9, ROS generation, and NF-κB nuclear translocation mechanism.

Angiotensin-II down-regulates cardiac natriuretic peptide receptor-A mediated anti-hypertrophic signaling in experimental rat hearts.

Atrial natriuretic peptide (ANP) exerts anti-hypertrophic effects in the heart via natriuretic peptide receptor-A (NPR-A). However, ANP mediated anti-hypertrophic activity is decreased in the cardiomyopathic conditions. In the present investigation the in vivo effects of angiotensin II (Ang II), a hypertrophic agonist have been studied on the ventricular expression level of NPR-A in Wistar rat hearts. NPR-A expression at the protein and mRNA levels were found to be markedly reduced by 5-fold respectively in Ang II infused rats heart as compared with sham rat hearts. Moreover, cGMP production in response to ANP was reduced by 77% in the isolated cardiac membrane preparation from the Ang II infused rat hearts. Losartan treatment reversed NPR-A expression and responsiveness to ANP. This study suggests that Ang II down regulates cardiac NPR-A activity by suppressing Npr1 gene transcription.

Aminoguanidine inhibits ventricular fibrosis and remodeling process in isoproterenol-induced hypertrophied rat hearts by suppressing ROS and MMPs.

AIM: Aminoguanidine (AG), a well known inhibitor of advanced glycation end products, has been reported to attenuate cardiac hypertrophy and fibrosis. However, the underlying mechanism by which AG exerts its anti-fibrotic activity is not well understood. Reactive oxygen species (ROS) and matrix metalloproteinases (MMPs) are implicated as playing a major role in the development of cardiac fibrosis. Hence, the present study was designed to investigate the effect of AG on ROS generation and MMPs during the progress of hypertrophic growth. MAIN METHODS: Isoproterenol (ISO) (7 mg/kg/day, s.c., for 15 days) was used to induce cardiac hypertrophy in experimental adult Wistar rats. ISO-treated rats were co-treated with AG (50 mg/kg/day, i.p., for 15 days). Ventricular collagen deposition, gelatinase activity of MMP-2 and MMP-9, and the level of tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) were investigated. In addition, in silico docking of MMP-2 and MMP-9 proteins, ROS generation, and nuclear translocation of NF-κB-p65 were also studied. KEY FINDINGS: AG co-treatment markedly attenuated the ISO-induced hypertrophic growth and fibrosis. Heart-weight-to-body weight ratio and ventricular collagen levels were normalized upon AG co-treatment. A significantly decreased level of ventricular ROS generation (p < 0.001) and NF-κB-p65 nuclear translocation was observed in the rat hearts co-treated with AG. Furthermore, in silico docking analysis revealed that AG interacts at the active site of MMP-2 and MMP-9. SIGNIFICANCE: Anti-fibrotic and anti-hypertrophic activities of AG were mainly attributed to its ROS quenching efficacy and its direct interaction with MMP-2 and MMP-9.