Activation of Nrf2 contributes to the protective effect of Exendin-4 against angiotensin II-induced vascular smooth muscle cell senescence
Published online on August 03, 2016
Abstract
Oxidative stress and impaired antioxidant defense are believed to be contributors to the cardiovascular aging process. The transcription factor NF-E2 related factor 2 (Nrf2) plays a key role in orchestrating cellular antioxidant defenses and maintaining redox homeostasis. Our previous study showed that Exendin-4, a GLP-1 analogue, alleviates angiotensin II (Ang II)-induced VSMC senescence by inhibiting Rac1 activation via cAMP/PKA. The objective of this study is to investigate if Nrf2 mediates the anti-senescent effect of Exendin-4 in Ang II-induced VSMCs. Here we report that Exendin-4 triggered Nrf2 nuclear translocation, a downstream target of cAMP responsive element-binding protein (CREB) and expressions of antioxidant genes heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase-1 (NQO-1) in a dose- and time-dependent manner. In addition, knock-down of Nrf2 attenuated the inhibitory effects of Exendin-4 on Ang II-induced superoxidant generation and VSMC senescence. PKA/CREB pathway participated in the upregulations of HO-1 and NQO-1 induced by Exendin-4. Notably, our study revealed that Exendin-4 dose-dependently increased the acetylation of Nrf2 and the the recruitment of transcriptional coactivator CREB binding protein (CBP) to Nrf2. The Exendin-4-induced Nrf2 transactivation was diminished in the presence of CBP siRNA. Microscope imaging of Nrf2 as well as immunoblotting for Nrf2 showed that the Exendin-4-evoked Nrf2 acetylation favored its nuclear retention. Importantly, CBP silencing attenuated the suppressing effects of Exendin-4 on Ang II-induced VSMC senescence and superoxidant production. In conclusion, these results provide a mechanistic insight into how Nrf2 signaling mediates the anti-senescent and anti-oxidative effects induced by Exendin-4 in VSMCs.