Elsevier

Neuroscience

Volume 275, 5 September 2014, Pages 322-339
Neuroscience

Neuronal degeneration, synaptic defects, and behavioral abnormalities in tau45-230 transgenic mice

https://doi.org/10.1016/j.neuroscience.2014.06.017Get rights and content

Highlights

  • Tau45-230 induces cell death and synaptic loss in hippocampal neurons.

  • Changes in NMDA receptors are present in tau45-230-expressing neurons.

  • The expression of tau45-230 associates with mild memory loss.

  • Tau45-230 induces anxiety-like behavior.

Abstract

The complement of mechanisms underlying tau pathology in neurodegenerative disorders has yet to be elucidated. Among these mechanisms, abnormal tau phosphorylation has received the most attention because neurofibrillary tangles present in Alzheimer’s disease (AD) and related disorders known as tauopathies are composed of hyperphosphorylated forms of this microtubule-associated protein. More recently, we showed that calpain-mediated cleavage leading to the generation of the 17 kDa tau45-230 fragment is a conserved mechanism in these diseases. To obtain insights into the role of this fragment in neurodegeneration, we generated transgenic mice that express tau45-230 and characterized their phenotype. Our results showed a significant increase in cell death in the hippocampal pyramidal cell layer of transgenic tau45-230 mice when compared to wild-type controls. In addition, significant synapse loss was detected as early as six months after birth in transgenic hippocampal neurons. These synaptic changes were accompanied by alterations in the expression of the N-methyl-d-aspartate glutamate (NMDA) receptor subunits. Furthermore, functional abnormalities were detected in the transgenic mice using Morris Water Maze and fear conditioning tests. These results suggest that the accumulation of tau45-230 is responsible, at least in part, for neuronal degeneration and some behavioral changes in AD and other tauopathies. Collectively, these data provide the first direct evidence of the toxic effects of a tau fragment biologically produced in the context of these diseases in vertebrate neurons that develop in situ.

Introduction

The microtubule-associated protein (MAP) tau plays an important role during neuronal development by stabilizing the microtubule network in growing axons (Drubin and Kirschner, 1986, Ferreira et al., 1989, Dreschel et al., 1992, Bramblett et al., 1993). Therefore, conditions that altered the levels of expression of this MAP during development led to abnormal axonal elongation (Caceres and Kosik, 1990, Knops et al., 1991, Dawson et al., 2001). Tau has also been implicated in axonal degeneration and cell death in the context of Alzheimer’s disease (AD) and related disorders known as tauopathies (Kosik et al., 1986, Wood et al., 1986, Kondo et al., 1988, Rapoport et al., 2002, Yancopoulou and Spillantini, 2003, Parihar and Hemnani, 2004, Roberson et al., 2007). The mechanisms by which tau mediates neuronal degeneration are not completely understood; however, a growing body of evidence indicates that abnormal posttranslational modifications of this MAP underlie tau pathology. Numerous studies have focused on the role of tau phosphorylation in AD because neurofibrillary tangles, pathological hallmarks of this disease, are formed mainly by hyperphosphorylated tau isoforms (Kosik et al., 1986, Wood et al., 1986, Kondo et al., 1988, Takashima et al., 1993, Ferreira et al., 1997, Alvarez et al., 1999, Ekinci et al., 1999, Parihar and Hemnani, 2004). More recently, it has been suggested that cleavage could also underlie tau toxicity. Thus, we have shown that calpain-mediated tau cleavage is a conserved mechanism in multiple tauopathies (Ferreira and Bigio, 2011). This cleavage induces the generation of the 17 kDa tau45-230 fragment (Park and Ferreira, 2005; Park et al., 2007, Reinecke et al., 2011). The toxic effects of this tau fragment were first detected in hippocampal neurons transfected with a tau45-230-green fluorescent protein (GFP) construct (Park and Ferreira, 2005). Similar effects were demonstrated in a Drosophila model of tauopathy (Reinecke et al., 2011).

Conflicting results regarding the identity and toxicity of this tau fragment have been recently published (Garg et al., 2011). Although these authors described the formation of a tau fragment of similar apparent molecular weight, it contained a different N-terminus as a result of the cleavage by a different calpain isoform. This fragment failed to induce neurodegeneration in cultured neurons (Garg et al., 2011).

To address this discrepancy and obtain insights into the toxic effects of the 17-kDa tau45-230 fragment in mammalian central neurons that develop in situ, we generated and characterized transgenic mice that express this fragment in hippocampal neurons. Our results showed enhanced cell death of pyramidal neurons and synaptic loss in the hippocampus of transgenic tau45-230 mice. In addition, these changes were accompanied by behavioral abnormalities. Collectively, these data indicate that indeed tau45-230 has toxic effects that could contribute to the progressive degeneration of central neurons in AD and related disorders.

Section snippets

Generation of tau45-230-GFP transgenic mice

Transgenic mice were generated by injecting the pronucleus of a single-cell fertilized C57BL/6J mouse embryo with the tau45-230-GFP transgene under the control of the Thy 1.2 promoter. This transgene was derived from a peGFP-N1 plasmid (Invitrogen, Grand Island, NY, USA) containing the human cDNA coding sequence for the tau45-230 fragment cloned into the multiple cloning site as previously described (Park and Ferreira, 2005). The 7.8-kb transgene containing all regulatory elements and the

Generation of transgenic tau45-230 mice

We have previously shown that the expression of the 17-kDa tau45-230 fragment in otherwise healthy cultured hippocampal neurons led to degeneration and cell death (Park and Ferreira, 2005). Similar results were obtained in a tauopathy model system in Drosophila (Reinecke et al., 2011). To test whether the expression of this fragment could also induce neurodegeneration in vertebrate hippocampal neurons that develop in situ, we generated strains of transgenic mice carrying tau45-230-GFP cDNA

Discussion

This report provides the first direct evidence of a tau fragment (tau45-230) generated in the context of AD and related disorders capable of inducing neuronal death and synaptic loss when expressed in mouse hippocampal neurons that develop in situ. In addition, the data presented herein indicate that these hippocampal changes are accompanied by functional abnormalities that could have some bearings on the cognitive and/or behavioral deficits associated with these diseases.

Previous studies have

Acknowledgments

This work was supported by NIH grant NS39080 and Northwestern University start-up funds to AF. The genetically engineered mice were generated with the assistance of Northwestern University Transgenic and Targeted Mutagenesis Laboratory. The Northwestern University Behavioral Phenotyping Core conducted the behavioral tests included in this study. The authors are grateful to Lindsey Wold for her participation in the initial stages of the establishment of the mouse colonies. The authors declare no

References (77)

  • S. Garg et al.

    Cleavage of tau by calpain in Alzheimer’s disease: the quest for the toxic 17 kDa fragment

    Neurobiol Aging

    (2011)
  • J.W. Geddes et al.

    Density and distribution of NMDA receptors in the human hippocampus in Alzheimer’s disease

    Brain Res

    (1986)
  • C.X. Gong et al.

    Phosphorylation of microtubule-associated protein tau is regulated by protein phosphatase 2A in mammalian brain. Implications for neurofibrillary degeneration in Alzheimer’s disease

    J Biol Chem

    (2000)
  • F. Grynspan et al.

    Active site-directed antibodies identify calpain II as an early-appearing and pervasive component of neurofibrillary pathology in Alzheimer’s disease

    Brain Res

    (1997)
  • J. Harada et al.

    Activation of caspase-3 in beta-amyloid-induced apoptosis of cultured rat cortical neurons

    Brain Res

    (1999)
  • B. Kelly et al.

    Beta-amyloid-induced dynamin I depletion in hippocampal neurons: a potential mechanisms for early cognitive decline in Alzheimer’s disease

    J Biol Chem

    (2005)
  • D.L. King et al.

    Maintained synaptophysin immunoreactivity in Tg2576 transgenic mice during aging: correlations with cognitive impairment

    Brain Res

    (2002)
  • J. Kondo et al.

    The carboxyl third of tau is tightly bound to paired helical filaments

    Neuron

    (1988)
  • O.H. Lowry et al.

    Protein measurement with the Folin phenol reagent

    J Biol Chem

    (1951)
  • N. Marin et al.

    Beta-amyloid-induced activation of caspase-3 in primary cultures of rat neurons

    Mech Ageing Dev

    (2000)
  • L. Martin et al.

    Post-translational modifications of tau protein: Implications for Alzheimer’s disease

    Neurochem Intl

    (2011)
  • E. Masliah et al.

    The synaptic organization of the neocortex in Alzheimer’s disease

    Med Hypothesis

    (1993)
  • A.J. Mishizen-Eberz et al.

    Biochemical and molecular studies of NMDA receptor subunits NR1/2A/2B in hippocampal subregions throughout progression of Alzheimer’s disease pathology

    Neurobiol Dis

    (2004)
  • E.B. Mukaetova-Ladinska et al.

    Staging of cytoskeletal and β-amyloid changes in human isocortex reveals biphasic synaptic protein response during progression of Alzheimer’s disease

    Am J Pathol

    (2000)
  • M.S. Parihar et al.

    Alzheimer’s disease pathogenesis and therapeutic interventions

    J Clin Neurosci

    (2004)
  • S.Y. Park et al.

    Caspase-3- and calpain-mediated tau cleavage are differentially prevented by estrogen and testosterone in beta-amyloid-treated hippocampal neurons

    Neuroscience

    (2007)
  • T. Peri et al.

    Psychophysiologic assessment of adversive conditioning in posttraumatic stress disorder

    Biol Psychiatry

    (2000)
  • T.T. Rohn et al.

    Correlation between caspase activation and neurofibrillary tangle formation in Alzheimer’s disease

    Am J Pathol

    (2001)
  • A. Simón et al.

    Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Aβ levels

    Neurobiol Dis

    (2009)
  • R.C. Sinjoanu et al.

    The novel calpain inhibitor A-705253 potently inhibits oligomeric beta-amyloid-induced dynamin 1 and tau cleavage in hippocampal neurons

    Neurochem Intl

    (2008)
  • T.L. Spires et al.

    Transgenic models of Alzheimer’s disease: learning from animals

    J Am Soc Exp Neurother

    (2005)
  • J.H. Su et al.

    Activated caspase-3 expression in Alzheimer’s and aged control brain: correlation with Alzheimer pathology

    Brain Res

    (2001)
  • K. Watase et al.

    A Long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility in selective neurodegeneration

    Neuron

    (2002)
  • A.F. Yakunin et al.

    A luminol/iodophenol chemiluminescent detection system for western immunoblots

    Anal Biochem

    (1998)
  • K.L. Anderson et al.

    α1 integrin activation: a link between β-amyloid deposition and neuronal death in aging hippocampal neurons

    J Neurosci Res

    (2004)
  • C. Andorfer et al.

    Cell-cycle reentry and cell death in transgenic mice expressing nonmutant human tau isoforms

    J Neurosci

    (2005)
  • J.E. Bottenstein et al.

    Growth of a rat neuroblastoma cell line in serum-free supplemented medium

    Proc Natl Acad Sci USA

    (1979)
  • A. Caceres et al.

    Inhibition of neurite polarity by tau antisense oligonucleotides in primary cerebellar neurons

    Nature

    (1990)
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