Elsevier

Neurobiology of Aging

Volume 24, Issue 5, September 2003, Pages 645-653
Neurobiology of Aging

Alterations in β-amyloid production and deposition in brain regions of two transgenic models

https://doi.org/10.1016/S0197-4580(02)00153-7Get rights and content

Abstract

Mutations in the amyloid precursor protein (APP) gene are associated with altered production and deposition of amyloid beta (Aβ) peptide in the Alzheimer’s disease (AD) brain. The pathways that regulate APP processing, Aβ production and Aβ deposition in different tissues and brain regions remain unclear. To address this, we examined levels of various APP processing products as well as Aβ deposition in a genomic-based (R1.40) and a cDNA-based (Tg2576) transgenic mouse model of AD. In tissues, only brain generated detectable levels of the penultimate precursor to Aβ, APP C-terminal fragment-β. In brain regions, holoAPP levels remained constant, but ratios of APP C-terminal fragments and levels of Aβ differed significantly. Surprisingly, cortex had the lowest steady-state levels of Aβ compared to other brain regions. Comparison of Aβ deposition in Tg2576 and R1.40 animals revealed that R1.40 exhibited more abundant deposition in cortex while Tg2576 exhibited extensive deposition in the hippocampus. Our results suggest that AD transgenic models are not equal; their unique characteristics must be considered when studying AD pathogenesis and therapies.

Introduction

Alzheimer’s disease (AD) is defined by neuropathological hallmarks including intracellular accumulation of phosphorylated tau protein in neurofibrillary tangles and extracellular deposits of the amyloid beta (Aβ) peptide in senile plaques. AD neuropathology proceeds in a characteristic pattern with Aβ deposition first appearing in the basal neocortex, later in the hippocampus and eventually throughout the cortical layers [3], [4]. The biological pathways that regulate this regional pattern of Aβ deposition remain to be elucidated.

Aβ is derived from APP, a protein of unknown function with at least four tissue-specific protein isoforms of 695, 714, 751 and 770 amino acids [10], [18]. APP is proteolytically processed by α-secretase at Lys-16 of Aβ generating a C-terminal fragment (CTFα) which lacks the complete Aβ sequence. Alternatively, β-secretase cleavage at the N-terminus of Aβ generates a C-terminal fragment (CTFβ) that can be cleaved by γ-secretase to release full-length Aβ. APP and many of the secretases are expressed in a variety of tissues and throughout the brain, suggesting that unknown factors regulate the regional pattern of Aβ deposition in AD.

The most widely utilized transgenic mouse model of AD, Tg2576, expresses the 695 amino acid form of human APP containing the K670N/M671L mutation [23] found in a large Swedish familial AD pedigree, under the control of the hamster prion promoter. Tg2576 animals develop Aβ deposits in the brain at 9–11 months of age [13]. While Tg2576 and other cDNA-based transgenic models of AD have provided evidence that transgenic mice can develop Aβ deposits (reviewed by Hock and Lamb [12]), the different APP cDNAs in these models are not expressed in a temporal and spatial pattern that recapitulates the expression pattern of endogenous App.

In contrast to the cDNA-based models, we have focused on developing an accurate genomic-based model of AD that contains all the regulatory elements required for appropriate spatial and temporal expression of the transgene and for generation of alternatively-spliced transcripts and protein isoforms. Introduction of a genomic copy of APP with the Swedish mutation, yielded line R1.40 which develops Aβ deposits by 14 months of age in the homozygous state [19], [20], [21]. Importantly, the pattern of Aβ deposition and associated pathology in R1.40 mice closely resembles that observed in human AD.

The current manuscript characterizes tissue-specific and brain region-specific APP processing in the genomic-based R1.40 transgenic mice and compares these results to those obtained with the cDNA-based Tg2576 transgenic animals. In addition, we have examined the brains of aged R1.40 and Tg2576 animals for regional Aβ deposition. Our results demonstrate that the different APP transgenic models of AD have unique biochemical and pathological attributes that likely reflect their experimental design. These findings may have substantial implications for the testing of therapeutic approaches in transgenic models of AD.

Section snippets

Transgenic mice

R1.40 YAC transgenic mice were previously described [21]. For these studies the R1.40 line was maintained by crossing to the C57BL/6J inbred strain for two generations, and animals homozygous for the transgene were generated by intercrossing animals hemizygous for the transgene. Homozygotes were identified by Southern blotting and confirmed by progeny testing. All R1.40 animals used in these studies were homozygous for the transgene. The Tg2576 transgenics were kindly provided by Hsiao-Ashe

Tissue-specificity of APP processing in R1.40 transgenic mice

To further examine the tissue-specificity of APP processing, we analyzed the levels of APP processing products in tissues from R1.40 transgenic mice, where APP is expressed as specified by the endogenous human promoter. A number of tissues, including brain, heart, kidney, testes, lung, stomach, large intestine, small intestine, liver, uterus, ear, skeletal muscle, eye and pancreas were isolated from R1.40 homozygous transgenic mice, non-transgenic mice and App knockout mice. The App knockout

Discussion

Our results suggest that APP processing is a complex process regulated uniquely in various tissues of the body and in different regions within the brain. Furthermore, we demonstrate that the transgenic approach utilized to model AD impacts APP processing and AD-related neuropathological abnormalities including Aβ deposition.

Acknowledgements

We thank K. Hsiao-Ashe for the generous gift of Tg2576 animals and S. Gandy for the generous gift of 369 antibody. We also thank K. Herrup and P. Gambetti for their helpful discussions and critical reading of the manuscript. This work was supported by NIH Grant AG14451 and Alzheimer’s Association grant IIRG-99-1517 to B.T. Lamb as well as support from the University Alzheimer Center (AG08012) and the Ireland Cancer Center (CA43703). E.J.H. Lehman was supported in part by NIH training grant

References (34)

  • E.M. Sigurdsson et al.

    Immunization with a nontoxic/nonfibrillar amyloid-beta homologous peptide reduces Alzheimer’s disease-associated pathology in transgenic mice

    Am. J. Pathol.

    (2001)
  • S. Tanaka et al.

    Age-related changes in the proportion of amyloid precursor protein mRNAs in Alzheimer’s disease and other neurological disorders

    Brain Res. Mol. Brain Res.

    (1992)
  • S. Tanaka et al.

    Age-related change in the proportion of amyloid precursor protein mRNAs in the gray matter of cerebral cortex

    Neurosci. Lett.

    (1993)
  • G. Thinakaran et al.

    Metabolism of the “Swedish” amyloid precursor protein variant in Neuro2a (N2a) cells

    J. Biol. Chem.

    (1996)
  • H. Zheng et al.

    Beta-amyloid precursor protein-deficient mice show reactive gliosis and decreased locomotor activity

    Cell

    (1995)
  • H. Braak et al.

    Neuropathological staging of Alzheimer-related changes

    Acta Neuropathol.

    (1991)
  • H. Braak et al.

    Evolution of Alzheimer’s disease related cortical lesions

    J. Neural. Transm.

    (1998)
  • Cited by (50)

    • Oleocanthal-rich extra-virgin olive oil enhances donepezil effect by reducing amyloid-β load and related toxicity in a mouse model of Alzheimer's disease

      2018, Journal of Nutritional Biochemistry
      Citation Excerpt :

      Aβ is a product of amyloid precursor protein (APP), which is processed to produce Aβ40 and Aβ42. Prior to Aβ plaques formation, Aβ forms intermediate structures called Aβ oligomers (Aβo), which significantly contribute to the pathology of AD [3,4]. At present, only symptomatic treatments are available for AD composed mainly of acetylcholinesterase inhibitors (donepezil, rivastigmine and galantamine) and one glutamate receptor antagonist (memantine) [5].

    • Animal Models of Alzheimer's Disease

      2017, Animal Models for the Study of Human Disease: Second Edition
    • Tolfenamic acid downregulates BACE1 and protects against lead-induced upregulation of Alzheimer's disease related biomarkers

      2014, Neuropharmacology
      Citation Excerpt :

      Animals were bred in-house and the age of the mice used in this study was between 14 and 20 months. This AD animal model contains the entire human APP gene including the regulatory fragments and expresses elevated levels of Aβ especially the longer more aggregative forms Aβ42 and Aβ43 (Lamb et al., 1999, 1997; Lehman et al., 2003). Animals were housed in designated rooms within the animal facility at the University of Rhode Island under standard conditions with ad libitum food and water.

    View all citing articles on Scopus
    View full text