Transforming growth factor-β₁ elicits Nrf2-mediated antioxidant responses in aortic smooth muscle cells

摘要

The anti-inflammatory properties of transforming growth factor-β₁ (TGF-β₁) account for its protection against atherosclerotic plaque rupture. This study investigates whether activation of the Nrf2 (nuclear factor erythroid 2 [NF-E2]-related factor 2) transcription pathway is involved in TGF-β₁ mediated induction of the antioxidant enzyme heme oxygenase-1 (HO-1) in smooth muscle cells (SMC). Human aortic smooth muscle cells (HAoSMC) or wild-type and Nrf2-deficient mouse (MAoSMC) aortic SMC were treated with TGF-β₁ (2.5–10 ng/ml, 0–24 hrs). We report the first evidence that TGF-β₁ induces Nrf2 mediated HO-1 expression and antioxidant response element activity, which was paralleled by enhanced superoxide production and expression of the NAD(P)H oxidase subunit p22^phox. TGF-β₁ failed to induce HO-1 expression in MAoSMC derived from Nrf2-deficient mice, and HO-1 induction by TGF-β₁ in HAoSMC was attenuated by inhibition of extracellular signal regulated kinase or c-jun-N-terminal kinase but not p38 mitogen activated protein kinase. Inhibition of NAD(P)H oxidase or scavenging of superoxide diminished HO-1 induction in response to TGF-β₁. The oxidative stress agents glucose oxidase (GOx) and diethylmaleate enhanced TGF-β₁ generation and HO-1 expression in HAoSMC, while antagonism of TGF-β₁ signalling by adenoviral Smad7 overexpression attenuated their induction of HO-1. Pre-treatment of HAoSMC with TGF-β₁ reduced nuclear translocation of the pro-apoptotic mediator p53 elicited by GOx. Our findings demonstrate that Nrf2 is a new target of TGF-β₁ signalling in the vasculature which may contribute to the atheroprotective properties attributed to this growth factor.