Previous studies showed that
angiotensin-(1-7) [Ang-(1-7)] attenuates cardiac remodeling by reducing both interstitial and perivascular
fibrosis. Although a high affinity binding site for Ang-(1-7) was identified on cardiac fibroblasts, the molecular mechanisms activated by the heptapeptide
hormone were not identified. We isolated cardiac fibroblasts from neonatal rat hearts to investigate signaling pathways activated by Ang-(1-7) that participate in fibroblast proliferation. Ang-(1-7) reduced (3)H-thymidine, -
leucine and -
proline incorporation into cardiac fibroblasts stimulated with serum or the
mitogen endothelin-1 (ET-1), demonstrating that the heptapeptide
hormone decreases
DNA,
protein and
collagen synthesis. The reduction in
DNA synthesis by Ang-(1-7) was blocked by the AT((1-7)) receptor antagonist [d-Ala(7)]-Ang-(1-7), showing specificity of the response. Treatment of cardiac fibroblasts with Ang-(1-7) reduced the Ang II- or ET-1-stimulated increase in phospho-ERK1 and -ERK2. In contrast, Ang-(1-7) increased
dual-specificity phosphatase DUSP1 immunoreactivity and
mRNA, suggesting that the heptapeptide
hormone increases DUSP1 to reduce MAP
kinase phosphorylation and activity. Incubation of cardiac fibroblasts with ET-1 increased
cyclooxygenase 2 (COX-2) and
prostaglandin synthase (PGES) mRNAs, while Ang-(1-7) blocked the increase in both
enzymes, suggesting that the heptapeptide
hormone alters the concentration and the balance between the proliferative and anti-proliferative
prostaglandins. Collectively, these results indicate that Ang-(1-7) participates in maintaining cardiac homeostasis by reducing proliferation and
collagen production by cardiac fibroblasts in association with up-regulation of DUSP1 to reduce MAP
kinase activities and attenuation of the synthesis of mitogenic
prostaglandins. Increased Ang-(1-7) or agents that enhance production of the heptapeptide
hormone may prevent abnormal
fibrosis that occurs during cardiac pathologies.