Human APP Gene Expression Alters Active Zone Distribution and Spontaneous Neurotransmitter Release at the Drosophila Larval Neuromuscular Junction.

Ekaterina A Saburova,Svetlana V Sarantseva,Elena V Ryabova,Violetta V Kravtsova,Igor I Krivoi,Alexander N Vasiliev,Olga I Bolshakova,Andrey L Zefirov

doi:10.1155/2017/9202584

Abstract

This study provides further insight into the molecular mechanisms that control neurotransmitter release. Experiments were performed on larval neuromuscular junctions of transgenic Drosophila melanogaster lines with different levels of human amyloid precursor protein (APP) production. To express human genes in motor neurons of Drosophila, the UAS-GAL4 system was used. Human APP gene expression increased the number of synaptic boutons per neuromuscular junction. The total number of active zones, detected by Bruchpilot protein puncta distribution, remained unchanged; however, the average number of active zones per bouton decreased. These disturbances were accompanied by a decrease in frequency of miniature excitatory junction potentials without alteration in random nature of spontaneous quantal release. Similar structural and functional changes were observed with co-overexpression of human APP and β-secretase genes. In Drosophila line with expression of human amyloid-β42 peptide itself, parameters analyzed did not differ from controls, suggesting the specificity of APP effects. These results confirm the involvement of APP in synaptogenesis and provide evidence to suggest that human APP overexpression specifically disturbs the structural and functional organization of active zone and results in altered Bruchpilot distribution and lowered probability of spontaneous neurotransmitter release.

Highlights

Increased synthesis and accumulation of amyloid-β-protein (Aβ) that is produced through proteolytic processing of amyloid precursor protein (APP) by β- and γ-secretases is considered to be a major cause of Alzheimer’s disease [1,2,3]
It has been demonstrated that APPL regulates synaptic structure and promotes synapse differentiation at the neuromuscular junction (NMJ) [9]
Muscle 4 NMJs in APP and APP+BACE lines demonstrated a significant (P < 0 01) increase in the number of both 1b and satellite boutons per NMJ compared to the control; total bouton number per NMJ increased (Table 1)

Summary

Introduction

Increased synthesis and accumulation of amyloid-β-protein (Aβ) that is produced through proteolytic processing of amyloid precursor protein (APP) by β- and γ-secretases is considered to be a major cause of Alzheimer’s disease [1,2,3]. Data obtained on mammals indicate that APP takes part in synapse formation and in the regulation of synaptic and neuronal function, and alteration of APP expression affects cognitive and memory processes [4,5,6]. Present mammalian experimental models do not allow the effects of APP and Aβ to be studied separately. It has been demonstrated that APPL regulates synaptic structure and promotes synapse differentiation at the neuromuscular junction (NMJ) [9]. Experiments with expression of the human APP gene in Drosophila melanogaster demonstrated neurodegenerative changes, altered cognition and memory processes, changes in locomotion behavior, and multiple morphofunctional changes in the NMJ [10,11,12,13,14]. Altered presynaptic function and Neural Plasticity decreased levels of the synaptic vesicle exocytosis proteins synaptotagmin and synaptobrevin were observed [12, 15]

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Discussion

Conclusion