Abstract
Amyloid precursor protein (APP), a type I transmembrane protein, has different aspects, namely, performs essential physiological functions and produces β-amyloid peptide (Aβ). Overexpression of neuronal APP is responsible for synaptic dysfunction. In the central nervous system, astrocytes - a major glial cell type - have an important role in the regulation of synaptic transmission. Although APP is expressed in astrocytes, it remains unclear whether astrocytic overexpression of mutant APP affects synaptic transmission. In this study, the effect of astrocytic overexpression of a mutant APP on the excitatory synaptic transmission was investigated using coculture system of the transgenic (Tg) cortical astrocytes that express the human APP695 polypeptide with the double mutation K670N+M671L found in a large Swedish family with early onset Alzheimer's disease, and wild-type hippocampal neuron. Significant secretion of Aβ 1-40 and 1-42 was observed in cultured cortical astrocytes from the Tg2576 transgenic mouse that genetically overexpresses Swedish mutant APP. Under the condition, Tg astrocytes did not affect excitatory synaptic transmission of cocultured wild-type neurons. However, aged Tg astrocytes cultured for 9weeks elicited a significant decrease in excitatory synaptic transmission in cocultured neurons. Moreover, a reduction in the number of readily releasable synaptic vesicles accompanied a decrease in the number of excitatory synapses in neurons cocultured with aged Tg astrocytes. These observations indicate that astrocytic expression of the mutant APP is involved in the downregulation of synaptic transmission with age.
Highlights
Alzheimer’s disease (AD) is a neurodegenerative disorder accompanied by progressive memory deterioration
Because astrocytes have an important role in the information processing by synapses of the central nervous system (Allen and Barres 2009; Eroglu and Barres 2010), we speculated that the synaptic transmission may be attenuated by chronic exposure to amyloid b (Ab) 1–40 and 1–42 released from the Tg astrocytes
To assess the synaptic transmission, hippocampal neurons obtained from newborn ICR mice were plated on microislands of cultured astrocytes that had been isolated from Tg2576 mice
Summary
Alzheimer’s disease (AD) is a neurodegenerative disorder accompanied by progressive memory deterioration. Progressive loss of synapses aggravates memory impairment before the formation of senile plaques. Morphological abnormalities such as the loss of synapses, deposition of senile plaques, and changes in fibrillogenesis are major characteristics of the AD brain. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
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