Nrf2-mediated neuroprotection against oxygen-glucose deprivation/reperfusion injury by emodin via AMPK-dependent inhibition of GSK-3β.

OBJECTIVES: Our study verified the neuroprotective properties of emodin against oxygen-glucose deprivation/reoxygenation (OGD/R) and demonstrated its mechanism.

METHODS: Human neuronal SH-SY5Y cells were investigated by analysing cell viability, lactate dehydrogenase levels, expression of molecules related to apoptotic cell death, and using biochemical techniques, flow cytometry and Western blot assays.

KEY FINDINGS: Emodin reduced OGD/R-lead to neurotoxicity in SH-SY5Y cells. OGD/R significantly increased levels of cleaved poly ADP ribose polymerase, cleaved caspase-3, cleaved caspase-9, p53, p21 and Bax protein. However, emodin treatment effectively inhibited these OGD/R-induced changes. Emodin treatment also increased HO-1 and NQO1 expression in a concentration- and time-dependent manner and caused antioxidant response element (ARE) transcription activity and nuclear Nrf2 accumulation. Emodin phosphorylated AMPK and GSK3β, and pretreatment of cells with an AMPK inhibitor suppressed emodin-induced nuclear Nrf2 accumulation and HO-1 and NQO1 expression. AMPK inhibitor treatment decreased GSK3β phosphorylation, suggesting that AMPK is upstream of GSK3β, Nrf2, HO-1 and NQO1. Emodin's neuroprotective effect was completely blocked by HO-1, NQO1 and Nrf2 knock-down and an AMPK inhibitor, indicating the action of AMPK/GSK3β/Nrf2/ARE in the neuroprotective effect of emodin subjected to OGD/R.

CONCLUSIONS: Emodin treatment protected against OGD/R-lead to neurotoxicity by potentiating Nrf2/ARE-regulated neuroprotection through the AMPK/GSK3β pathway, indicating that emodin may be useful for treating neurodegenerative disorders.