Age-dependent alterations in the presynaptic active zone in a Drosophila model of Alzheimer's disease.

The accumulation of beta amyloid (Aß) can cause synaptic impairments, but the characteristics and mechanisms of the synaptic impairment induced by the accumulation of Aß in Alzheimer's disease (AD) remain unclear. In identified single neurons in a newly developed Drosophila AD model, in which Aß accumulates intraneuronally, we found an age-dependent reduction in the synaptic vesicle release probability that was associated with a decrease in the density of presynaptic calcium channel clusters and an increase in the presynaptic and postsynaptic contact length. Moreover, these alterations occurred in the absence of presynaptic bouton loss. In addition, we found that Aß expression also produced an age-dependent decrease in the amount of Bruchpilot (Brp), which plays an important role in controlling Ca(2+) channel clustering and synaptic vesicle release in the presynaptic active zone. Our study indicates that the chronic accumulation of intraneuronal Aß can induce functional and structural changes in the presynaptic active zone prior to a loss of presynaptic buttons in the same neuron.

Expression of beta-amyloid induced age-dependent presynaptic and axonal changes in Drosophila.

Alzheimer's disease (AD) is attributable to synapse dysfunction and loss, but the nature and progression of the presynaptic structural and functional changes in AD are essentially unknown. We expressed wild-type or arctic form of beta amyloid(1-42) (Abeta) in a small group of neurons in the adult fly and performed extensive time course analysis of the function and structure of both axon and presynaptic terminals at the identified single-neuron level. Abeta accumulated intracellularly and induced a range of age-dependent changes, including depletion of presynaptic mitochondria, slowdown of bi-directional transports of axonal mitochondria, decreased synaptic vesicles, increased large vacuoles, and elevated synaptic fatigue. These structural and functional synaptic changes correlated with age-dependent deficit in motor behavior. All these alterations were accelerated in flies expressing the arctic form of Abeta. The depletion of presynaptic mitochondria was the earliest detected phenotype and was not caused by the change in axonal transport of mitochondria. Moreover, axonal mitochondria exhibited a dramatic reduction in number but a significant increase in size in aged Abeta-expressing flies, indicating a global depletion of mitochondria in the neuron and an impairment of mitochondria fission. These results suggest that Abeta accumulation depletes presynaptic and axonal mitochondria, leading to other presynaptic deficits.