Expression of Keap1–Nrf2 system and antioxidative proteins in mouse brain after transient middle cerebral artery occlusion

Reactive oxygen species and their detrimental effects on the brain after transient ischemia have been implicated in the pathogenesis of the ischemic injury. The Kelch-like ECH-associated protein 1 (Keap1)–nuclear factor erythroid 2-related factor 2 (Nrf2) system is currently recognized as the major cellular defense mechanism under oxidative stress, but the involvement of the Keap1–Nrf2 system in the ischemic brain injuries has not been fully investigated to date. In the present study, we investigated temporal changes of Keap1, Nrf2, and their downstream antioxidative proteins in post-ischemic mice brains with respect to spacial differences between the peri-infarct regions and the regions destined to infarct. In the peri-infarct regions, a steady level of Keap1 showed a decremental expression started at 2 h of reperfusion after 60 min of transient middle cerebral artery occlusion (tMCAO). In contrast, Nrf2 began to show a significant increase at 2 h with a peak at 8 h of reperfusion after tMCAO. Both Keap1 and Nrf2 are mainly expressed in neuronal cells but not in glial cells. In the same peri-infarct region, downstream antioxidative proteins such as thioredoxin, glutathione, and heme oxygenase-1 showed significant increases at later time-points of 24–72 h of reperfusion after tMCAO. In the regions destined to infarct, a similar trend of expression changes to those in the peri-infarct regions was observed in Keap1, Nrf2, and 3 downstream antioxidative proteins with much less reactions. The changes found in this study suggest that the induced antioxidative stress proteins after cerebral ischemia may play an important endogenous neuroprotective response under oxidative stress after ischemic stroke.

Research Highlights
► Oxidative stress promotes decreased Keap1 and increased Nrf2 in the ischemic brain.
► Nrf2-inducible antioxidative proteins preferentially increased in the ischemic penumbra.
► Keap1–Nrf2 system may play an important endogenous neuroprotective response after stroke.