Essential Role of Smad3 in Angiotensin II–Induced Vascular Fibrosis

Abstract

Abstract-Angiotensin II (Ang II) plays a pivotal role in vascular fibrosis, which leads to serious complications in hypertension and diabetes. However, the underlying signaling mechanisms are largely unclear. In hypertensive patients, we found that arteriosclerosis was associated with the activation of Smad2/3. This observation was further investigated in vitro by stimulating mouse primary aorta vascular smooth muscle cells (VSMCs) with Ang II. There were several novel findings. First, Ang II was able to activate an early Smad signaling pathway directly at 15 to 30 minutes. This was extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) dependent but transforming growth factor-␤ (TGF-␤) independent because Ang II-induced Smad signaling was blocked by addition of ERK1/2 inhibitor and by dominant-negative (DN) ERK1/2 but not by DN-TGF-␤ receptor II (T␤RII) or conditional deletion of T␤RII. Second, Ang II was also able to activate the late Smad2/3 signaling pathway at 24 hours, which was TGF-␤ dependent because it was blocked by the anti-TGF-␤ antibody and DN-T␤RII. Finally, activation of Smad3 but not Smad2 was a key and necessary mechanism of Ang II-induced vascular fibrosis because Ang II induced Smad3/4 promoter activities and collagen matrix expression was abolished in VSMCs null for Smad3 but not Smad2. Thus, we concluded that Ang II induces vascular fibrosis via both TGF-␤-dependent and ERK1/2 MAPK-dependent Smad signaling pathways. Activation of Smad3 but not Smad2 is a key mechanism by which Ang II mediates arteriosclerosis.

Loss of angiotensin-converting enzyme 2 enhances TGF-β/Smad-mediated renal fibrosis and NF-κB-driven renal inflammation in a mouse model of obstructive nephropathy

“…We and other investigators have previously demonstrated that Ang II is able to activate the TGF-b/Smad signaling via both TGF-bdependent and -independent (through the ERK/p38 mitogen-activated protein kinase crosstalk pathway) mechanisms in vascular and renal cells. [15][16][17] In the present study, we also found that loss of Ace2 largely increased intrarenal Ang II signaling via the AT1-mediated activation of ERK1/2 mitogen-activated protein kinase pathway. This was associated with enhanced TGF-b/Smad signaling (Smad2/3 phosphorylation and nuclear translocation) and progressive tubulointerstitial fibrosis in Ace2 À/y mice when compared with Ace2 þ /y mice.…”

“…[15][16][17] We thus investigated whether enhanced renal fibrosis in the UUO kidney of Ace2 À/y mice is associated with an increase in Ang II-mediated TGF-b/Smad pathway. As shown in Figure 4a and b, significant higher levels of intrarenal Ang II and Ang 1-7 were detected in Ace2 þ /y mice after UUO.…”

TGF-β signaling in vascular biology and dysfunction

“…Angiotensin, a potent vasoconstrictor, stimulates TGF-β1 mRNA and protein expression and may through its induction of thrombospondin lead to TGF-β activation [109], indicating that TGF-β1 acts downstream of angiotensin signaling [107]. In addition, angiotensin has been shown to directly lead to Smad3 activation via a mechanism that is not well understood [110]. The renin-angiotensin system (RAS) plays an important role in cardiac remodeling and clinical trials have documented the beneficial effects of angiotensin II inhibition in patients with myocardial infarction and heart failure [111].…”

Angiotensin II as a Morphogenic Cytokine Stimulating Renal Fibrogenesis

“…62 In a more complex paradigm, Ang II within minutes can also rapidly stimulate the downstream mediators of the TGF␤ signaling pathway, Smad2/3, independently of the paracrine action of TGF␤. 63,64 The pathophysiological interposition of this pathway is unclear. Because renal fibrosis is a relatively slow and persistent process, progression likely depends primarily on persistent TGF␤-dependent Smad activation.…”