The Journal of Neuroscience, December 31, 2008, 28(53):14511-14521; doi:10.1523/JNEUROSCI.3417-08.2008
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Neurobiology of Disease
Spatial Learning Impairment, Enhanced CDK5/p35 Activity, and Downregulation of NMDA Receptor Expression in Transgenic Mice Expressing Tau-Tubulin Kinase 1
Shinji Sato, *
Jiqing Xu, *
Satoshi Okuyama, *
Lindsey B. Martinez,
Shannon M. Walsh,
Michael T. Jacobsen,
Russell J. Swan,
Joshua D. Schlautman,
Pawel Ciborowski, and
Tsuneya Ikezu
Department of Pharmacology and Experimental Neuroscience and Center for Neurovirology and Neurodegenerative Disorders, University of Nebraska Medical Center, Omaha, Nebraska 68198-5880
Correspondence should be addressed to Tsuneya Ikezu, 985880 Nebraska Medical Center, Omaha, NE 68198-5880. Email: tikezu{at}unmc.edu
Tau-tubulin kinase-1 (TTBK1) is involved in phosphorylation of tau protein at specific Serine/Threonine residues found in paired helical filaments, suggesting its role in tauopathy pathogenesis. We found that TTBK1 levels were upregulated in brains of human Alzheimer' disease (AD) patients compared with age-matched non-AD controls. To understand the effects of TTBK1 activation in vivo, we developed transgenic mice harboring human full-length TTBK1 genomic DNA (TTBK1-Tg). Transgenic TTBK1 is highly expressed in subiculum and cortical pyramidal layers, and induces phosphorylated neurofilament aggregation. TTBK1-Tg mice show significant age-dependent memory impairment as determined by radial arm water maze test, which is associated with enhancement of tau and neurofilament phosphorylation, increased levels of p25 and p35, both activators of cyclin-dependent protein kinase 5 (CDK5), enhanced calpain I activity, and reduced levels of hippocampal NMDA receptor types 2B (NR2B) and D. Enhanced CDK5/p35 complex formation is strongly correlated with dissociation of F-actin from p35, suggesting the inhibitory mechanism of CDK5/p35 complex formation by F-actin. Expression of recombinant TTBK1 in primary mouse cortical neurons significantly downregulated NR2B in a CDK5- and calpain-dependent manner. These data suggest that TTBK1 in AD brain may be one of the underlying mechanisms inducing CDK5 and calpain activation, NR2B downregulation, and subsequent memory dysfunction.
Key words: transgenic; protein kinase; Alzheimer's disease; NMDA receptor; memory; neuropathology; phosphorylation
Received July 21, 2008;
revised Nov. 5, 2008;
accepted Nov. 10, 2008.
Correspondence should be addressed to Tsuneya Ikezu, 985880 Nebraska Medical Center, Omaha, NE 68198-5880. Email: tikezu{at}unmc.edu