Abstract
BackgroundTransgenic mice expressing disease-associated proteins have become standard tools for studying human neurological disorders. Transgenes are often expressed using promoters chosen to drive continuous high-level expression throughout life rather than temporal and spatial fidelity to the endogenous gene. This approach has allowed us to recapitulate diseases of aging within the two-year lifespan of the laboratory mouse, but has the potential for creating aberrant phenotypes by mechanisms unrelated to the human disorder.ResultsWe show that overexpression of the Alzheimer’s-related amyloid precursor protein (APP) during early postnatal development leads to severe locomotor hyperactivity that can be significantly attenuated by delaying transgene onset until adulthood. Our data suggest that exposure to transgenic APP during maturation influences the development of neuronal circuits controlling motor activity. Both when matched for total duration of APP overexpression and when matched for cortical amyloid burden, animals exposed to transgenic APP as juveniles are more active in locomotor assays than animals in which APP overexpression was delayed until adulthood. In contrast to motor activity, the age of APP onset had no effect on thigmotaxis in the open field as a rough measure of anxiety, suggesting that the interaction between APP overexpression and brain development is not unilateral.ConclusionsOur findings indicate that locomotor hyperactivity displayed by the tet-off APP transgenic mice and several other transgenic models of Alzheimer’s disease may result from overexpression of mutant APP during postnatal brain development. Our results serve as a reminder of the potential for unexpected interactions between foreign transgenes and brain development to cause long-lasting effects on neuronal function in the adult. The tet-off APP model provides an easy means of avoiding developmental confounds by allowing transgene expression to be delayed until the mice reach adulthood.
Highlights
Transgenic mice expressing disease-associated proteins have become standard tools for studying human neurological disorders
Delaying transgenic amyloid precursor protein (APP) overexpression until adulthood attenuates motor hyperactivity In our original characterization of the tet-off APP transgenic mice, we described severe hyperactivity due to APP overexpression that prevented us from assessing their performance on standard behavioral tasks [35]
Locomotor activity was normalized by lifelong suppression of the transgene, which demonstrated that the effect was not due to insertion site, and was replicated in multiple tetresponsive APP transgenic lines
Summary
Transgenic mice expressing disease-associated proteins have become standard tools for studying human neurological disorders. Transgenes are often expressed using promoters chosen to drive continuous highlevel expression throughout life rather than temporal and spatial fidelity to the endogenous gene This approach has allowed us to recapitulate diseases of aging within the two-year lifespan of the laboratory mouse, but has the potential for creating aberrant phenotypes by mechanisms unrelated to the human disorder. Recent transgenic models have incorporated promoters such as calcium-calmodulin kinase IIα (CaMKIIα) thought to be inactive before birth, thereby avoiding any prenatal effects of APP overexpression [33,34,35] Contrary to these assumptions, we discovered an unexpected interaction between postnatal brain development and transgenic overexpression of mutant APP that had behavioral consequences in the adult. Our findings indicate that even phenotypes with relevance to disease may not arise by the same mechanisms in transgenic models as in the human disorder
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