β-amyloid-induced dynamin 1 degradation is mediated by N-methyl-D-aspartate receptors in hippocampal neurons

Alzheimer disease (AD) is a progressive, neurodegenerative disorder that leads to debilitating cognitive deficits. Although little is known about the early functional or ultrastructural changes associated with AD, it has been proposed that a stage of synaptic dysfunction might precede neurodegeneration in the development of this disease. Unfortunately, the molecular mechanisms that underlie such synaptic dysfunction remain largely unknown. Recently we have shown that beta-amyloid (A beta), the main component of senile plaques, induced a significant decrease in dynamin 1, a protein that plays a critical role in synaptic vesicle recycling, and hence, in the signaling properties of the synapse. We report here that this dynamin 1 degradation was the result of calpain activation induced by the sustained calcium influx mediated by N-methyl-D-aspartate receptors in hippocampal neurons. In addition, our results showed that soluble oligomericA beta, and not fibrillar A beta, was responsible for this sustained calcium influx, calpain activation, and dynamin 1 degradation. Considering the importance of dynamin 1 to synaptic function, these data suggest that A beta soluble oligomers might catalyze a stage of synaptic dysfunction that precedes synapse loss and neurodegeneration. These data also highlight the calpain system as a novel therapeutic target for early stage AD intervention.