Involvement of PI3K/Akt pathway in the neuroprotective effect of sonic hedgehog on cortical neurons under oxidative stress

Abstract

The Sonic hedgehog (SHH) signaling pathway plays a pivotal role in neurogenesis and brain damage repair. Our previous work demonstrated that the SHH signaling pathway was involved in the neuroprotection of cortical neurons against oxidative stress. The present study was aimed to further examine the underlying mechanism. The cortical neurons were obtained from one-day old Sprague-Dawley neonate rats. Hydrogen peroxide (H₂O₂, 100 μmol/L) was used to treat neurons for 24 h to induce oxidative stress. Exogenous SHH (3 μg/mL) was employed to activate the SHH pathway, and cyclopamine (20 μmol/L), a specific SHH signal inhibitor, to block SHH pathway. LY294002 (20 μmol/L) were used to pre-treat the neurons 30 min before H₂O₂ treatment and selectively inhibit the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. The cell viability was measured by MTT and apoptosis rate by flow cytometry analysis. The expression of p38, p-p38, ERK, p-ERK, Akt, p-Akt, Bcl-2, and Bax in neurons was detected by immunoblotting. The results showed that as compared with H₂O₂ treatment, exogenous SHH could increase the expression of p-Akt by 20% and decrease the expression of p-ERK by 33%. SHH exerted no significant effect on p38 mitogen-activated protein kinase (p38 MAPK) pathway. Blockade of PI3K/Akt pathway by LY294002 decreased the cell viability by 17% and increased the cell apoptosis rate by 2-fold. LY294002 treatment could up-regulate the expression of the pro-apoptotic gene Bax by 12% and down-regulate the expression of the anti-apoptotic gene Bcl-2 by 54%. In conclusion, SHH pathway may activate PI3K/Akt pathway and inhibit the activation of the ERK pathway in neurons under oxidative stress. The PI3K/Akt pathway plays a key role in the neuroprotection of SHH. SHH/PI3K/Bcl-2 pathway may be implicated in the protection of neurons against H₂O₂-induced apoptosis.

Keywords

Sonic hedgehog / PI3K/Akt / apoptosis / oxidative stress / cortical neuron

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