Beta-amyloid disrupted synaptic vesicle endocytosis in cultured hippocampal neurons

Abstract

Neuronal death leading to gross brain atrophy is commonly seen in Alzheimer's disease (AD) patients. Yet, it is becoming increasingly apparent that the pathogenesis of AD involves early and more discrete synaptic changes in affected brain areas. However, the molecular mechanisms that underlie such synaptic dysfunction remain largely unknown. Recently, we have identified dynamin 1, a protein that plays a critical role in synaptic vesicle endocytosis, and hence, in the signaling properties of the synapse, as a potential molecular determinant of such dysfunction in AD. In the present study, we analyzed beta-amyloid (Aβ)-induced changes in synaptic vesicle recycling in cultured hippocampal neurons. Our results showed that Aβ, the main component of senile plaques, caused ultrastructural changes indicative of impaired synaptic vesicle endocytosis in cultured hippocampal neurons that have been stimulated by depolarization with high potassium. In addition, Aβ led to the accumulation of amphiphysin in membrane fractions from stimulated hippocampal neurons. Moreover, experiments using FM1-43 showed reduced dye uptake in stimulated hippocampal neurons treated with Aβ when compared to untreated stimulated controls. Similar results were obtained using a dynamin 1 inhibitory peptide suggesting that dynamin 1 depletion caused deficiency in synaptic vesicle recycling not only in Drosophila but also in mammalian neurons. Collectively, these results showed that Aβ caused a disruption of synaptic vesicle endocytosis in cultured hippocampal neurons. Furthermore, we provided evidence suggesting that Aβ-induced dynamin 1 depletion might play an important role in this process. Keywords synaptic dysfunction; amphiphysin; beta-amyloid; endocytosis; FM1-43 Alzheimer disease (AD) is a debilitating disorder that leads to significant cognitive deficits. Pathologically, AD is characterized by the presence of extracellular senile plaques, composed of the amyloid-beta protein (Aβ), and intraneuronal neurofibrillary tangles, composed of the tau protein (Glenner and Wong 1984;Grundke-Iqbal et al. 1986). In addition, significant atrophy due to the loss of neurons in the cholinergic and glutamatergic areas of the brain have been detected in this disease (Teipel et al. 2005;van de Pol et al. 2006). While neuronal death is important and could contribute to the decline in cognition, synapse loss is the best correlate with the severity of dementia in AD (Davies et al. 1987;Terry et al. 1991). However, this loss Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (Koenig and Ikeda 1989). Collectively, these...

The Neurotoxic Tau45-230 Fragment Accumulates in Upper and Lower Motor Neurons in Amyotrophic Lateral Sclerosis Subjects

“…The accumulation of tau in ALS motor neurons provided evidence of an alternative molecular mechanism by which excitotoxicity could lead to neurodegeneration of motor neurons. In contrast to what has been described in AD and other tauopathies, calpain dysregulation in the context of ALS does not lead to aberrant cleavage of dynamin 1 ( Vintilescu and Ferreira, unpublished observations, see also 61,62). This protein is involved in the recycling of synaptic vesicles and could be responsible for synaptic dysfunction underlying the cognitive deficits characteristic of these diseases.…”

“…The calpain dysregulation observed in AD culture and animal models was induced by enhanced extracellular calcium influx mediated by glutamate N-methyl-D-aspartate (NMDA) receptors (61,62). Glutamate excitotoxicity has also been of endogenously generated tau in the context of neurons that develop in situ versus those detected when the recombinant tau fragment is incubated in the presence of an inducer of aggregation.…”

β-Amyloid Carrying the Dutch Mutation Has Diverse Effects on Calpain-Mediated Toxicity in Hippocampal Neurons

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“…The synaptic dysfunction observed in the presence of WT Aβ was mediated, at least in part, by a decrease in dynamin 1 levels due to calpain-mediated cleavage both in cultured hippocampal neurons and in an AD animal model system (4,5,9). To test whether E22Q Aβ has similar synaptic effects, we analyzed dynamin 1 levels in cultured hippocampal neurons incubated in the presence of increasing concentrations of this mutant Aβ form.…”

“…Dynamin 1 is a neuronspecific mechanochemical GTPase responsible for vesicle scission from the synaptic terminal membrane (7,8). Aβ-induced calpain activation resulted in dynamin 1 cleavage altering synaptic vesicle recycling and, hence, synaptic transmission in hippocampal neurons (4,5,9). In addition, abnormally activated calpain cleaved the microtubuleassociated protein tau leading to the generation of a 17-kDa neurotoxic fragment in hippocampal neurons (10)(11)(12).…”