Abstract-Connective tissue growth factor (CTGF) plays a critical role in angiotensin II (Ang II)-mediated hypertensive nephropathy. The present study investigated the mechanisms and specific roles of individual Smads in Ang II-induced CTGF and collagen I expression in tubular epithelial cells with deletion of transforming growth factor (TGF)-

Abstract-Although Smad3 is a key mediator of fibrosis, the functional role of Smad3 in hypertensive cardiovascular disease remains unclear. The present study tested the hypothesis that angiotensin II may activate the transforming growth factor-␤/Smad3 pathway to mediate hypertensive cardiac remodeling in Smad3 knockout (KO) and wild-type mice by subcutaneous angiotensin II infusion and in the primary culture of Smad3 KO cardiac fibroblasts. Fourteen days after angiotensin II infusion, both Smad3 KO and wild-type mice developed equal levels of high blood pressure. However, hypertensive cardiac fibrosis and inflammation were developed in Smad3 wild-type but not in Smad3 KO mice. This was demonstrated by the findings that mice lacking Smad3 were protected against a fall in left ventricular ejection fraction (PϽ0.05), an increase in left ventricular mass (PϽ0.05), and the development of cardiac fibrosis and inflammation, including upregulation of transforming growth factor-␤1, connective tissue growth factor, collagen I/III, ␣-smooth muscle actin, interleukin 1␤, tumor necrosis factor-␣, monocyte chemoattractant protein 1, intercellular adhesion molecule 1, and an increase in macrophage and T-cell infiltration in left ventricular tissues (all PϽ0.01, respectively). Additional studies in vitro also revealed that angiotensin II-induced cardiac fibrosis and inflammation were prevented in Smad3 KO cardiac fibroblasts. Inactivation of both Smad3 and nuclear factor B/p65 signaling pathways was a key mechanism by which Smad3 KO mice were protected from angiotensin II-mediated hypertensive cardiac remodeling. In conclusion, Smad3 plays an essential role in hypertensive cardiac remodeling. Results from this study suggest that targeting Smad3 may be a novel therapeutic strategy for hypertensive cardiovascular disease. (Hypertension. 2010;55:1165-1171.)

Angiotensin II (Ang II) is a key mediator of chronic kidney disease, in which epithelial-mesenchymal transition (EMT) is a critical process mediated by the TGFbeta/Smad signalling pathway. The present study examined the specific role of Smads in Ang II-induced EMT in vitro and in vivo. We found that Ang II signalled through the receptor of AT1, not AT2, to activate Smad2/3 and induce EMT in a normal rat tubular epithelial cell line (NRK52E). Activation of Smads by Ang II was attributed to degradation of an inhibitory Smad7, which was mediated by the AT1-Smurf2-dependent ubiquitin degradation mechanism because blockade of AT1 receptor or knockdown of Smurf2 inhibited Smad7 loss, thereby reducing Smad2/3 activation and EMT in response to Ang II. In contrast, over-expression of Smad7 inhibited Ang II-induced Smad2/3 activation and EMT in NRK52E cells and in a rat model of remnant kidney disease. Moreover, knockdown of Smad3, not Smad2, attenuated Ang II-induced EMT. In conclusion, Ang II activates Smad signalling to induce EMT, which is mediated by a loss of Smad7 through the AT1-Smurf2-dependent ubiquitin degradation pathway. Smad3, but not Smad2, may be a mediator of EMT, while Smad7 may play a protective role in EMT in response to Ang II.

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