Abstract 1767: Mice Lacking Smad3 are Protected against Angiotensin II-Induced Cardiac Inflammation and Fibrosis
Angiotensin II (Ang II) is a key mediator of cardiac inflammation and fibrosis in chronic heart diseases. It is known that Ang II mediates vascular fibrosis by activating TGF-β/Smad signaling in vitro. We thus hypothesized that Ang II may activate Smad3 to mediate cardiac inflammation and fibrosis. The critical role for Smad3 in Ang II-mediated cardiac inflammation and fibrosis was examined in groups of 8 Smad3 knockout (KO) and wild-type (WT) mice by subcutaneous infusion of Ang II (or saline control) at a dose of 1000ng/kg/min via osmotic minipumps for 14 days. After Ang II infusion, both Smad3 KO and WT mice developed equal levels of high blood pressure (158–161 ± 5.4 mmHg vs saline control 100 –112 ± 2.6 mmHg, p < 0.001). However, cardiac inflammation and fibrosis were developed in Smad3 WT, but not in Smad3 KO mice. Real-time PCR and immunohistochemistry demonstrated that there was a 10 –20 fold increase in cardiac inflammation (including IL-1β, TNFα, MCP-1, ICAM-1, macrophage and T cell infiltration) and fibrosis (collagen I, III, α-SMA) in Smad3 WT mice (all p < 0.01), which was abrogated in Smad3 KO mice (all p < 0.01). Further studies revealed that prevention of Ang II-induced cardiac inflammation and fibrosis in Smad3 KO mice was associated with inhibition of cardiac TGF-β 1 and CTGF, a loss of Smad3 signaling, and inactivation of the NF.β B/p65 pathway (all p < 0.01). These findings were further confirmed in Smad3 WT and KO cardiac fibroblasts in vitro. Western blot and real-time PCR demonstrated that loss of Smad3 prevented Ang II-induced inflammation and fibrosis in primary culture of cardiac fibroblasts. Smad3 plays an essential role in cardiac inflammation and fibrosis in response to Ang II, which suggests that targeting Smad3 signaling may represent a novel therapeutic strategy for chronic cardiovascular diseases.