Abstract of online articleMotor deficits, neuron loss, and reduced anxiety coinciding with axonal degeneration and intraneuronal Aβ aggregation in the 5XFAD mouse model of Alzheimer's disease
Introduction
Alzheimer's disease (AD) is a severe neurodegenerative disorder representing the most frequent form of dementia. It is characterized by the deposition of extracellular plaques composed of the mainly 40–42 amino acid Aβ peptide, as well as intracellular neurofibrillary tangles consisting of hyperphosphorylated Tau protein. Over the past years numerous transgenic mouse models of AD have been generated, reflecting underlying pathological alterations (Duyckaerts et al., 2008). Extracellular Aβ deposition, as well as therapeutic strategies for plaque removal, have dominated research efforts in AD during the last years, however, the presence of intraneuronal Aβ accumulations has recently gained in importance. It has been shown that Aβ42 accumulates within neurons in AD-vulnerable brain regions in AD (Gouras et al., 2000) and Down syndrome patients (Gyure et al., 2001) and that neurons from sporadic and familial AD cases contain increased Aβ42 levels and an increased Aβ42/Aβ40 ratio (Aoki et al., 2008).
The data in AD mouse models regarding intraneuronal Aβ are much more consistent and an increasing consensus can be observed during the past years. Early intraneuronal accumulation has been reported in several mouse models, including APPSDLPS1M146L (Wirths et al., 2001), APPSLPS1M146L (Wirths et al., 2002), Tg2576 (Takahashi et al., 2002), 3xTg-AD (Oddo et al., 2003), 5XFAD (Oakley et al., 2006), APPArc (Knobloch et al., 2007, Lord et al., 2006), APPT714I mice (Van Broeck et al., 2008), in APPSLPS1KIM233T, L235P mice (Casas et al., 2004) in which it was recently shown to correlate with neuron loss (Breyhan et al., 2009; Christensen et al., 2008; Christensen et al., 2010), as well as in TBA2 mice expressing pyroglutamate modified Aβ3-42 (Wirths et al., 2009).
5XFAD mice expressing human APP with the Swedish, Florida (I716V) and London mutations, together with mutant PS1 (M14 6L, L28 6V) under the control of the murine Thy-1 promoter (Oakley et al., 2006) are particularly interesting due to cointegration of the transgenes, enabling easy generation of multitransgenic AD mouse models. These mice were generated on a B6/SJL-hybrid background and have been backcrossed with C57Bl6/J mice for five generations to facilitate comparison with other models which are mostly kept on the C57Bl6 genetic background.
In the present report, we extent previous findings in the 5XFAD mouse model and demonstrate that they develop an age-dependent motor phenotype in addition to working memory deficits in an alternation task and reduced anxiety levels as shown in the elevated plus maze task. Quantification of cortical layer 5 neurons in 12 month old 5XFAD mice by means of design-based stereology confirmed the previously assumed loss of neurons in this brain regions (Oakley et al., 2006, Ohno et al., 2007), however, the overall neuron number in frontal cortex and hippocampal CA1 layer was unchanged compared with age-matched wild-type littermates. This observation coincides with the accumulation of intraneuronal Aβ peptides only in cortical Layer 5, but not in CA1. The motor phenotype correlates well with abundant spinal cord pathology, including intraneuronal Aβ accumulation and development of an age-dependent axonal degeneration.
Section snippets
Transgenic mice
The generation of 5XFAD mice (Tg6799) has been described previously (Oakley et al., 2006). In brief, 5XFAD overexpress the 695 amino acids isoform of the human amyloid precursor protein (APP695) carrying the Swedish, Florida, and London mutations under the control of the murine Thy-1-promoter. In addition, human presenilin-1 (PS1) carrying the M14 6L and L28 6V mutations mice is expressed also under the control of the murine Thy-1-promoter. Five male mice on a C57Bl/6 x SJL genetic background
Phenotypical characterization
5XFAD mice showed a reduced body weight in comparison with their WT littermates. Analysis by Two-way ANOVA revealed a significant genotype effect starting at 9 months of age (p < 0.05, Fig. 1A). In addition, 5XFAD mice showed a characteristic clasping phenotype presented by an unusual simultaneous retraction of both fore- and hind paws. Quantitative measurement of this behavior at 12 mo of age, by suspending the animals by their tail and evaluating the clasping score, revealed a significant
Discussion
The 5XFAD mouse model represents a double transgenic APP/PS1 mouse line coexpressing five familial Alzheimer disease (5XFAD) mutations that are inherited together and lead to accelerated plaque formation and increased Aβ42 levels. It was previously described as one of the few AD models showing several AD hallmarks, including neuron loss (Oakley et al., 2006). The aim of the present work was to perform a detailed characterization of the 5XFAD mouse model on a C57/BLJ genetic background,
Disclosure statement
Animal studies were performed with the approval of the Local Research Ethics Committee in accordance with national and international guidelines. All efforts were made to minimize animal suffering and the number of animals used. The authors have no financial, personal, or other conflicts of interest to disclose.
Acknowledgements
The expert technical assistance of Petra Tucholla is gratefully acknowledged. We thank Gerd Multhaup for the generous gift of 23850 and 692 antibodies. This work was supported by The European Commission, Marie Curie Early Stage Training, MEST-CT-2005-020013 (NEURAD), Alzheimer Ph.D. Graduate School, Alzheimer Forschung Initiative e.V. (to O.W.), and the Competence Network Degenerative Dementias of the German Federal Ministry of Education (grant no. 01 GI 0718, to T.A.B.).
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