BACE1 gene deletion prevents neuron loss and memory deficits in 5XFAD APP/PS1 transgenic mice

https://doi.org/10.1016/j.nbd.2006.12.008Get rights and content

Abstract

Evidence suggests that β-amyloid (Aβ) peptide triggers a pathogenic cascade leading to neuronal loss in Alzheimer’s disease (AD). However, the causal link between Aβ and neuron death in vivo remains unclear since most animal models fail to recapitulate the dramatic cell loss observed in AD. We have recently developed transgenic mice that overexpress human APP and PS1 with five familial AD mutations (5XFAD mice) and exhibit robust neuron death. Here, we demonstrate that genetic deletion of the β-secretase (BACE1) not only abrogates Aβ generation and blocks amyloid deposition but also prevents neuron loss found in the cerebral cortex and subiculum, brain regions manifesting the most severe amyloidosis in 5XFAD mice. Importantly, BACE1 gene deletion also rescues memory deficits in 5XFAD mice. Our findings provide strong evidence that Aβ ultimately is responsible for neuron death in AD and validate the therapeutic potential of BACE1-inhibiting approaches for the treatment of AD.

Introduction

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia among the elderly population, but no treatments addressing the underlying cause of disease have been developed. One of the hallmarks of AD is extensive neuronal death in the brain, approaching 90% loss in certain regions such as entorhinal cortex and nucleus basalis (for review, see Morrison and Hof, 1997). Although the precise mechanisms of AD and related cell loss and memory deficits are not fully determined, data support the hypothesis that amyloid-β (Aβ) peptides trigger a pathologic cascade ultimately leading to neuron death and cognitive impairment in AD (Hardy and Selkoe, 2002, LaFerla and Oddo, 2005, Selkoe and Schenk, 2003, Sisodia and St George-Hyslop, 2002, Turner et al., 2003). Mutations in the genes for amyloid precursor protein (APP) and presenilins 1/2 (PS1/2) cause familial AD (FAD) and increase production of the 42-amino acid form of Aβ (Aβ42). Furthermore, Aβ kills neurons in culture (for review, see Yankner, 1996), and Aβ also appears neurotoxic in vivo. For example, when directly injected into the brains of aged primates, fibrillar Aβ causes neuron death around the injection site (Geula et al., 1998). However, the case for the role of Aβ in neuron death has been challenged because many APP transgenic mice that overproduce Aβ form amyloid plaques and develop memory deficits but do not lose significant numbers of neurons (Irizarry et al., 1997a, Irizarry et al., 1997b; for review, see McGowan et al., 2006). Recently, new APP/PS1 transgenic mouse lines developed by our group and others show considerable neuron loss in the hippocampus (Casas et al., 2004, Schmitz et al., 2004) or the cortex and subiculum (Oakley et al., 2006). These studies suggest that Aβ does kill neurons in vivo, although they cannot formally exclude the possibility that overexpression of APP and PS1 with multiple FAD mutations is the cause of neuron death in these mouse models.

β-Site APP-cleaving enzyme 1 (BACE1) has been identified as the β-secretase, the protease that initiates cleavage of APP to generate pathogenic Aβ peptides (Haniu et al., 2000, Hussain et al., 1999, Sinha et al., 1999, Vassar et al., 1999, Yan et al., 1999). As the rate-limiting enzyme for Aβ production, BACE1 is a prime therapeutic target for lowering cerebral Aβ levels in AD. Targeted deletion of the BACE1 gene (BACE1−/) in mice abrogates the production of Aβ (Cai et al., 2001, Luo et al., 2001, Roberds et al., 2001). Moreover, APP transgenic mice with the BACE1 null genotype do not form amyloid plaques (Laird et al., 2005, Luo et al., 2003) and are prevented from developing Aβ-dependent memory deficits (Laird et al., 2005, Ohno et al., 2006, Ohno et al., 2004; for review, see Ohno, 2006). In the present study, we have used BACE1−/− mice to demonstrate that Aβ, rather than mutant APP or PS1 overexpression, is the cause of neuron loss in our APP/PS1 transgenic mouse line, 5XFAD (Oakley et al., 2006, Ohno et al., 2006). We determined that BACE1-deficient 5XFAD (BACE1−/−·5XFAD) mice do not have the amyloid plaques, astogliosis or memory deficits found in age-matched 5XFAD mice with wild-type BACE1 genes. Most importantly, neuron death in the cerebral cortex and subiculum was prevented in the BACE1−/−·5XFAD mice. To our knowledge, this is the first demonstration of genetic rescue of neuronal loss via ablation of BACE1, and consequently of Aβ, in an Alzheimer’s transgenic mouse model and provides strong evidence that Aβ ultimately kills neurons in vivo.

Section snippets

Animals

We used APP/PS1 doubly transgenic mice that co-express and co-inherit both human APP and PS1 transgenes with a total of five FAD mutations under transcriptional control of the neuron-specific mouse Thy-1 promoter [5XFAD mice, Tg6799 line (Oakley et al., 2006, Ohno et al., 2006)]. In 5XFAD mice, an APP transgene carrying triple FAD mutations [the Swedish mutation: K670N, M671L (Mullan et al., 1992); the Florida mutation: I716V (Eckman et al., 1997); the London mutation: V717I (Goate et al., 1991

Results

APP transgenic mouse models recapitulate several features of AD, such as amyloid pathology, synaptic dysfunction, and behavioral deficits, but there has been little demonstration of extensive neuronal loss in these models (Ashe, 2001, Dodart et al., 2002, German and Eisch, 2004, Irizarry et al., 1997a, Irizarry et al., 1997b, Janus and Westaway, 2001, Kobayashi and Chen, 2005, McGowan et al., 2006). We recently developed a novel APP/PS1 doubly transgenic mouse line [5XFAD mice, Tg6799 line (

Discussion

It is well established that Aβ kills neurons in culture (Pike et al., 1991, Roher et al., 1991, Yankner et al., 1990a, Yankner et al., 1989, Yankner et al., 1990b), but the link between Aβ and neuron loss in vivo has been equivocal. Cerebral injection of Aβ preparations into primates and rodents has produced variable effects, with some experiments demonstrating neurodegenerative changes (Frautschy et al., 1991, Geula et al., 1998, Kowall et al., 1991), while others yielding negative results (

Acknowledgments

This work was supported by National Institutes of Health grants R01 MH067251 (M.O.), R01 AG022560 (R.V.), P01 AG021184 (R.V. and R.B.) and R37 AG08796 (J.F.D).

References (75)

  • I. Hussain et al.

    Identification of a novel aspartic protease (Asp 2) as β-secretase

    Mol. Cell. Neurosci.

    (1999)
  • C. Janus et al.

    Transgenic mouse models of Alzheimer’s disease

    Physiol. Behav.

    (2001)
  • F. Kamenetz et al.

    APP processing and synaptic function

    Neuron

    (2003)
  • F.M. LaFerla et al.

    Alzheimer’s disease: Aβ, tau and synaptic dysfunction

    Trends Mol. Med.

    (2005)
  • K.W. Lee et al.

    Progressive neuronal loss and behavioral impairments of transgenic C57BL/6 inbred mice expressing the carboxy terminus of amyloid precursor protein

    Neurobiol. Dis.

    (2006)
  • S.F. Lichtenthaler et al.

    The cell adhesion protein P-selectin glycoprotein ligand-1 is a substrate for the aspartyl protease BACE1

    J. Biol. Chem.

    (2003)
  • Y. Luo et al.

    BACE1 (β-secretase) knockout mice do not acquire compensatory gene expression changes or develop neural lesions over time

    Neurobiol. Dis.

    (2003)
  • E. McGowan et al.

    A decade of modeling Alzheimer’s disease in transgenic mice

    Trends Genet.

    (2006)
  • M. Ohno et al.

    BACE1 deficiency rescues memory deficits and cholinergic dysfunction in a mouse model of Alzheimer’s disease

    Neuron

    (2004)
  • C.J. Pike et al.

    In vitro aging of β-amyloid protein causes peptide aggregation and neurotoxicity

    Brain Res.

    (1991)
  • L.D. Plant et al.

    Amyloid β peptide as a physiological modulator of neuronal ‘A’-type K+ current

    Neurobiol. Aging

    (2006)
  • A.E. Roher et al.

    β-Amyloid from Alzheimer disease brains inhibits sprouting and survival of sympathetic neurons

    Biochem. Biophys. Res. Commun.

    (1991)
  • C. Schmitz et al.

    Hippocampal neuron loss exceeds amyloid plaque load in a transgenic mouse model of Alzheimer’s disease

    Am. J. Pathol.

    (2004)
  • P.R. Turner et al.

    Roles of amyloid precursor protein and its fragments in regulating neural activity, plasticity and memory

    Prog. Neurobiol.

    (2003)
  • C.A. vonArnim et al.

    The low density lipoprotein receptor-related protein (LRP) is a novel β-secretase (BACE1) substrate

    J. Biol. Chem.

    (2005)
  • H.K. Wong et al.

    β Subunits of voltage-gated sodium channels are novel substrates of β-site amyloid precursor protein-cleaving enzyme (BACE1) and γ-secretase

    J. Biol. Chem.

    (2005)
  • B.A. Yankner

    Mechanisms of neuronal degeneration in Alzheimer’s disease

    Neuron

    (1996)
  • H. Yu et al.

    APP processing and synaptic plasticity in presenilin-1 conditional knockout mice

    Neuron

    (2001)
  • L.G. Apostolova et al.

    Conversion of mild cognitive impairment to Alzheimer disease predicted by hippocampal atrophy maps

    Arch. Neurol.

    (2006)
  • K.H. Ashe

    Learning and memory in transgenic mice modeling Alzheimer’s disease

    Learn. Mem.

    (2001)
  • M. Bobinski et al.

    Relationships between regional neuronal loss and neurofibrillary changes in the hippocampal formation and duration and severity of Alzheimer disease

    J. Neuropathol. Exp. Neurol.

    (1997)
  • M. Buttini et al.

    β-Amyloid immunotherapy prevents synaptic degeneration in a mouse model of Alzheimer’s disease

    J. Neurosci.

    (2005)
  • H. Cai et al.

    BACE1 is the major β-secretase for generation of Aβ peptides by neurons

    Nat. Neurosci.

    (2001)
  • M.E. Calhoun et al.

    Neuron loss in APP transgenic mice

    Nature

    (1998)
  • S.H. Choi et al.

    Memory impairment and cholinergic dysfunction by centrally administered Aβ and carboxyl-terminal fragment of Alzheimer’s APP in mice

    FASEB J.

    (2001)
  • J.C. Dodart et al.

    Does my mouse have Alzheimer’s disease?

    Genes Brain Behav.

    (2002)
  • C.B. Eckman et al.

    A new pathogenic mutation in the APP gene (I716V) increases the relative proportion of Aβ42(43)

    Hum. Mol. Genet.

    (1997)
  • Cited by (0)

    View full text