Aims: 

The anti-inflammatory properties of transforming growth factorb-1 (TGFb-1) account for its protection against atherosclerotic plaque rupture. This study investigates whether activation of the Nrf2 transcription pathway is involved in TGFb-1 mediated induction of the antioxidant enzyme heme oxygenase-1 (HO-1) in smooth muscle cells (SMC).

Methods: 

Human (HAoSMC) or wild-type and Nrf2 deficient mouse (MAoSMC) aortic SMC were treated (0-24 h) with TGFb-1 or the oxidative stress agents glucose oxidase (GO) or diethylmaleate (DEM). Nrf2, HO-1, p53 and p22^phox expression and kinase activation were determined by western blot analyses. Superoxide generation was measured using lucigenin or L-012 enhanced chemiluminescence.

Results: 

TGFb-1 induced Nrf2 mediated HO-1 induction, paralleled by enhanced superoxide production and expression of the NADPH oxidase subunit p22^phox. TGFb-1 failed to induce HO-1 expression in MAoSMC derived from Nrf2 deficient mice. HO-1 induction by TGFb-1 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 NADPH oxidase or scavenging of superoxide diminished HO-1 induction in response to TGFb-1. GO and DEM enhanced TGFb-1 generation and HO-1 expression in HAoSMC, while antagonism of TGFb-1 signaling by adenoviral Smad7 overexpression attenuated their induction of HO-1. Pretreatment of HAoSMC with TGFb-1 reduced nuclear translocation of the pro-apoptotic mediator p53 elicited by GO.

Conclusions: 

Our findings demonstrate that Nrf2 is a new target of TGFb-1 signaling in the vasculature which may contribute to the atheroprotective properties attributed to this growth factor.

Support: 

British Heart Foundation, EU COST Action B35, Great Britain Sasakawa Foundation.