Angiotensin-(1–7) inhibits angiotensin II-stimulated phosphorylation of

JF GIANI, MM GIRONACCI, MC MUÑOZ, D TURYN, FP DOMINICI

Buenos Aires

Congreso; World Congress of Cardiology; 2008

Angiotensin (ANG) II contributes to cardiac remodelling after myocardial infarction by stimulating myocyte hypertrophy and myofibroblast proliferation. In contrast, ANG-(1–7)infusion after myocardial infarction reduces myocyte size and attenuates ventricular dysfunctionand remodelling. The effects of ANG II are mediated by the G protein-coupled receptor AT1(AT1R). Downstream signaling effectors of the AT1R that participate in the growth-promotingand proliferative effects of ANG II include the signal transducers and activators of transcriptionSTAT 3 and 5 and mitogen-activated protein (MAP) extracellular signal-regulated kinases (ERK1/2). ANG-(1–7) is produced in the heart, although its effects on the ANG II stimulation of theSTAT and MAP kinase (MAPK) signaling pathways are unknown. Accordingly, in the currentstudy, we examined whether ANG-(1–7) affects ANG II-mediated STAT and MAPK signalingpathways in rat heart. Our hypothesis was that ANG-(1–7) might exert its anti-proliferativeeffects by inhibiting these pathways, suggesting that it acts as a counterregulatory factor toANG II in the heart. Male Sprague-Dawley rats at 2 months of age were used. In vivo stimulation of the heart was obtained by the injection of solutions of normal saline (0.9% NaCl) into the vena cava containing ANG II (8 pmol/Kg) plus ANG-(1–7) at increasing doses (0.08–800 pmol/Kg). The effects of ANG-(1–7) on ERK 1/2 and STAT 3 and 5 phosphorylation were determined by immunoprecipitation followed by immunoblotting with phospho-specific antibodies. Results were compared with those obtained by stimulation with either ANG II or ANG-(1–7) in an 8 pmol/Kg dose. ANG II and ANG-(1–7) stimulated the phosphorylation of STAT3 and 5 to a similar extent (2.1  0.2 fold increase over saline for STAT3; 2.2  0.2 fold increase over saline for STAT5; p
0.05, n  5 for both proteins). However, only ANG II stimulated the phosphorylation of ERK 1/2 (2.0  0.1 fold increase over saline, p
0.05, n  5). ANG-(1–7) prevented the ANG II-mediated phosphorylation of ERK 1/2 in a dose dependent manner. In summary, we have shown that similarly to ANG II, ANG-(1–7) induces the activation of STAT3 and 5 in the heart. On the other hand ANG-(1–7) failed to stimulate ERK 1/2 phosphorylation and inhibited the ANG II-stimulated phosphorylation of ERK 1/2. This result could represent a mechanism for the anti-proliferative effects of ANG-(1–7) in the heart,reinforcing the notion that production of this hormone in this organ may have a protective roleby counteracting the proliferative effects of locally generated ANG II.