Angiotensin-(1-7) Activates A Tyrosine Phosphatase And Inhibits Angiotensin Ⅱ-Induced Signaling In Cardiac Fibroblasts

Objective: Angiotensin-(1-7)[Ang-(1-7)], acting through the Masreceptor, opposes the actions of angiotensin II (Ang II). Molecularmechanisms for this are unclear. Here we sought to determine themechanism of Ang-(1-7) antagonizing Ang II-induced signaling responsesin rat cardiac fibroblasts.Methods: Primary culture and identification of cardiacfibroblasts of neonatal Sprague-Dawley rats was performed. The expressionlevels of extracellular signal-related kinase1/2(ERK1/2) and thephospho-ERK1/2was assayed by immunoblot, SHP-1activity wasmeasured by immunoprecipitation capture assays, and gene expression oftransforming growth factor-beta1(TGF-β1), collagen I and collagen III wereassayed by realtime PCR.Results: Ang II increased phosphorylation of extracellularsignal-related kinase (p-ERK1/2) and the ratio of (p-ERK1/2)/(ERK1/2),while Ang-(1-7) induced opposite effects; furthermore, Ang-(1-7) couldantagonize Ang II induced changes via the Mas receptor. Ang-(1-7) increased SHP-1activity via the receptor Mas, and antagonized Ang IIinduced decrease of SHP-1activity. Inhibiting the activity of SHP-1, theeffects of Ang-(1-7) antagonizing AngII-induced increase of p-ERK1/2and ratio of p-ERK/ERK were inhibited. An inhibitor of tyrosinephosphatase, phenylarsine oxide (PAO), reversed the inhibitory effect ofAng-(1-7) on Ang Ⅱ-stimulated p-ERK1/2. Ang-(1-7) had not significanteffects on the gene expression of TGF-β1, collagen I and collagen III, butcould antagonize the stimulatory effect of Ang II on TGF-β1, collagen I andcollagen III.Conclusions: These data indicate that in neonatal rats cardiacfibroblasts, binding of Ang-(1-7) to the receptor Mas stimulates SHP-1,associated with the inhibition of angiotensin II-induced increase ofp-ERK1/2and the ratio of p-ERK/ERK. Ang-(1-7) also could antagonize thestimulatory effect of Ang II on the gene expression of TGF-β1, collagen Iand collagen III. These phenomena may represent a protective mechanism incardiac fibroblasts whereby potentially deleterious effects of Ang II arecounterregulated by Ang-(1-7).