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The Journal of Neuroscience, August 20, 2008, 28(34):8430-8441; doi:10.1523/JNEUROSCI.2752-08.2008

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Neurobiology of Disease
Role of Dickkopf-1, an Antagonist of the Wnt/β-Catenin Signaling Pathway, in Estrogen-Induced Neuroprotection and Attenuation of Tau Phosphorylation

Quan-Guang Zhang,^1,2 Ruimin Wang,³ Mohammad Khan,^1,2 Virendra Mahesh,^1,2 and Darrell W. Brann^1,2

¹Developmental Neurobiology Program, Institute of Molecular Medicine and Genetics, and ²Department of Neurology, Medical College of Georgia, Augusta, Georgia 30912, and ³Research Center for Molecular Biology, North China Coal Medical University, Tangshan 063000, China

Correspondence should be addressed to Dr. Darrell W. Brann, Regents' Professor, Director, Graduate Program in Neuroscience, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912. Email: dbrann{at}mcg.edu

17β-Estradiol (E2) has been implicated to be neuroprotective in a variety of neurodegenerative disorders, although the mechanism remains poorly understood. The current study sheds light on this issue by demonstrating that low physiological levels of E2 protects the hippocampus CA1 against global cerebral ischemia by preventing elevation of dickkopf-1 (Dkk1), an antagonist of the Wnt/β-catenin signaling pathway, which is a principal mediator of neurodegeneration in cerebral ischemia and Alzheimer's disease. E2 inhibition of Dkk1 elevation correlated with a reduction of phospho-β-catenin and elevation of nuclear β-catenin levels, as well as enhancement of Wnt-3, suggesting E2 activation of the Wnt/β-catenin signaling pathway. In agreement, the β-catenin downstream prosurvival factor, survivin, was induced by E2 at 24 and 48 h after cerebral ischemia, an effect observed only in surviving neurons because degenerating neurons lacked survivin expression. E2 suppression of Dkk1 elevation was found to be caused by attenuation of upstream c-Jun N-terminal protein kinase (JNK)/c-Jun signaling, as E2 attenuation of JNK/c-Jun activation and a JNK inhibitor significantly blocked Dkk1 induction. Tau hyperphosphorylation has been implicated to have a prodeath role in Alzheimer's disease and cerebral ischemia, and E2 attenuates tau hyperphosphorylation. Our study demonstrates that tau hyperphosphorylation is strongly induced after global cerebral ischemia, and that E2 inhibits tau hyperphosphorylation by suppressing activation of the JNK/c-Jun/Dkk1 signaling pathway. Finally, exogenous Dkk1 replacement via intracerebroventricular administration completely reversed E2-induced neuroprotection, nuclear β-catenin induction, and phospho-tau attenuation, further suggesting that E2 inhibition of Dkk1 is a critical mechanism underlying its neuroprotective and phospho-tau regulatory effects after cerebral ischemia.

Key words: 17β-estradiol; cerebral ischemia; hippocampus; survivin; Alzheimer's disease; neuronal cell death

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Received July 10, 2008; accepted July 10, 2008.

Correspondence should be addressed to Dr. Darrell W. Brann, Regents' Professor, Director, Graduate Program in Neuroscience, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912. Email: dbrann{at}mcg.edu

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				Q.-G. Zhang, L. Raz, R. Wang, D. Han, L. De Sevilla, F. Yang, R. K. Vadlamudi, and D. W. Brann Estrogen Attenuates Ischemic Oxidative Damage via an Estrogen Receptor {alpha}-Mediated Inhibition of NADPH Oxidase Activation J. Neurosci., November 4, 2009; 29(44): 13823 - 13836. [Abstract] [Full Text] [PDF]

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