Hypoxic postconditioning activates the Wnt/β-catenin pathway and protects against transient global cerebral ischemia through Dkk1 Inhibition and GSK-3β inactivation

The Wingless/Int (Wnt)/beta-catenin pathway plays an essential role in cell survival. Although postconditioning with 8% oxygen can alleviate transient global cerebral ischemia (tGCI)-induced neuronal damage in hippocampal CA1 subregion in adult rats as demonstrated by our previous studies, little is understood about the role of Wnt/beta-catenin pathway in hypoxic postconditioning (HPC)-induced neuroprotection. This study tried to investigate the involvement of Wnt/beta-catenin pathway in HPC-induced neuroprotection against tGCI and explore the underlying molecular mechanism thereof. We observed that HPC elevated nuclear beta-catenin level as well as increased Wnt3a and decreased Dickkopf-1 (Dkk1) expression in CA1 after tGCI. Accordingly, HPC enhanced the expression of survivin and reduced the ratio of B-cell lymphoma/lewkmia-2 (Bcl-2)-associated X protein (Bax) to Bcl-2 following reperfusion. Moreover, our study has shown that these effects of HPC were abolished by lentivirus-mediated overexpression of Dkk1, and that the overexpression of Dkk1 completely reversed HPC-induced neuroprotection. Furthermore, HPC suppressed the activity of glycogen synthase kinase-3 beta (GSK-3 beta) in CA1 after tGCI, and the inhibition of GSK-3 beta activity with SB216763 increased the nuclear accumulation of beta-catenin, up-regulated the expression of survivin, and reduced the ratio of Bax to Bcl-2, thus preventing the delayed neuronal death after tGCI. Finally, the administration of LY294002, an inhibitor of PI3K, increased GSK-3 beta activity and blocked nuclear beta-catenin accumulation, thereby decreasing survivin expression and elevating the Bax-to-Bcl-2 ratio after HPC. These results suggest that activation of the Wnt/beta-catenin pathway through Dkk1 inhibition and PI3K/protein kinase B pathway-mediated GSK-3 beta inactivation contributes to the neuroprotection of HPC against tGCI.-Zhan, L., Liu, D., Wen, H., Hu, J., Pang, T., Sun, W., Xu, E. Hypoxic postconditioning activates the Wnt/beta-catenin pathway and protects against transient global cerebral ischemia through Dkk1 inhibition and GSK-3 beta inactivation.