Angiotensin II down-regulates natriuretic peptide receptor-A expression and guanylyl cyclase activity in H9c2 (2-1) cardiac myoblast cells: Role of ROS and NF-κB.

Atrial natriuretic peptide (ANP)/natriuretic peptide receptor-A (NPR-A) system is suggested as an endogenous anti-hypertrophic protective mechanism of the heart. We have shown previously that Angiotensin II (ANG II), an effector molecule of renin-angiotensin-aldosterone system, down-regulates NPR-A expression and its activity in vivo rat heart. However, the underlying mechanism by which ANG II down-regulates NPR-A expression in the heart is not well understood. Hence, the present investigation was aimed to determine whether ANG II-stimulated reactive oxygen species (ROS) and NF-κB are involved in the down-regulation of NPR-A activity in H9c2 (2-1) cardiac myoblast cells. The H9c2 (2-1) cardiac myoblast cells were exposed to ANG II (10(-7) M for 20 h) with/or without blocker treatment (losartan-10 µM, N-acetyl cysteine (NAC)-10 mM and pyrrolidine dithiocarbamate (PDTC)-100 µM). On exposure, ANG II induced a significant decrease (P < 0.001) in the expression of Npr1 (coding for NPR-A) gene and NPR-A receptor-dependent guanylyl cyclase (GC) activity. The level of expression of proto-oncogenes (c-fos, c-myc, and c-jun) and natriuretic peptides (ANP and BNP) was increased in ANG II-treated cells when compared with control cells. Interestingly, ANG II-dependent repression of Npr1 gene expression and guanylyl cyclase (GC) activity was completely restored on treatment with losartan, while only a partial reversal was observed in NAC- and PDTC-co-treated cells. In conclusion, the results of this study suggest that ROS-mediated NF-κB activation mechanism is critically involved in the ANG II-mediated down-regulation of NPR-A expression and its GC activity.