Elsevier

Neurobiology of Disease

Volume 51, March 2013, Pages 161-167
Neurobiology of Disease

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

https://doi.org/10.1016/j.nbd.2012.11.006Get rights and content

Abstract

The accumulation of beta amyloid (Aβ) can cause synaptic impairments, but the characteristics and mechanisms of the synaptic impairment induced by the accumulation of Aβ in Alzheimer's disease (AD) remain unclear. In identified single neurons in a newly developed Drosophila AD model, in which Aβ 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 Aβ expression also produced an age-dependent decrease in the amount of Bruchpilot (Brp), which plays an important role in controlling Ca2 + channel clustering and synaptic vesicle release in the presynaptic active zone. Our study indicates that the chronic accumulation of intraneuronal Aβ can induce functional and structural changes in the presynaptic active zone prior to a loss of presynaptic buttons in the same neuron.

Highlights

► Expression of beta amyloid induced the following age-dependent changes ► Reduction in the synaptic vesicle release probability ► Decrease in the density of presynaptic calcium channel clusters ► Increase in the presynaptic and postsynaptic contact length ► Decrease in the expression of Bruchpilot

Introduction

Alzheimer's disease (AD) is the most common neurodegenerative disease in elderly people. The most prominent pathological changes in the brains of AD patients are senile plaques, neurofibrillary tangles, and the loss of synapses and neurons. Synapse loss occurs early (Scheff et al., 2006) and is the best correlate of cognitive deficits in AD patients (DeKosky and Scheff, 1990, Terry et al., 1991). Synaptic impairment and loss were also found to occur early and to correlate with cognitive deficits in rodent models of AD (Jacobsen et al., 2006, Mucke et al., 2000). Thus, synaptic abnormality was believed to be a major cause of cognitive deficits in AD patients and animal models. Long-term potentiation (LTP) of synaptic strength is thought to be the cellular basis of learning and memory, in which the hippocampus plays a critical role. Thus, LTP in glutamatergic synapses has been extensively examined in hippocampal slices from mouse AD models and from wild type mice treated with Aβ. Impairments in LTP have been repetitively observed (Palop and Mucke, 2010). In addition, the enhancement of long-term depression (LTD) of synaptic strength by Aβ application in vivo and in vitro has also been reported (Hsieh et al., 2006, Kim et al., 2001, Shankar et al., 2008). The impairment of both LTP and LTD by Aβ was mainly ascribed to changes in the postsynaptic glutamate receptors and their downstream signaling cascades (Knobloch and Mansuy, 2008, Palop and Mucke, 2010).

In addition to postsynaptic effects, the disruption or regulation of presynaptic structure and function by Aβ has also been reported. In cultured hippocampal neurons, the extracellular application of Aβ rapidly reduced the size and number of synaptic vesicle markers (Calabrese et al., 2007). An acute elevation in extracellular Aβ by inhibition of its degradation enhanced the probability of release of synaptic vesicles (Abramov et al., 2009). In the squid giant axon, a presynaptic injection of Aβ acutely diminished the pool of docked synaptic vesicles (Moreno et al., 2009). In transgenic Aβ flies, Aβ accumulated intraneuronally and produced an age-dependent depletion of presynaptic mitochondria and synaptic vesicles and an acceleration of synaptic fatigue (Zhao et al., 2010).

The presynaptic active zone (AZ) is a specialized area of presynaptic plasma membrane where synaptic vesicles cluster, dock and fuse and where neurotransmitter is released. A variety of proteins have been found to be associated with the AZ, including Elks/CAST, acting as structural and functional determinants of the AZ (Schoch and Gundelfinger, 2006, Sigrist and Schmitz, 2011). Bruchpilot (Brp), the only Drosophila homolog of Elks/CAST, promotes active zone assembly, Ca2 + channel clustering, and vesicle release at the presynaptic zone (Kittel et al., 2006, Wagh et al., 2006).

As a follow-up to a previous study of presynaptic changes induced by Aβ expression in fruit flies (Zhao et al., 2010), here, we report that Aβ expression also produced an age-dependent reduction in synaptic release probability that was associated with a decrease in the density of presynaptic Ca2 + channel clusters, an increase in pre- and post-synaptic contact length and a decrease in the amount of Brp protein.

Section snippets

Genetics and stocks

Drosophila stocks were cultured on standard medium at 23–25 °C. After pupation, the adult flies were cultured on standard medium and entrained into a 12 h light/dark cycle at 28.5 °C. The upstream activating sequence (UAS) transgenic line (UAS-Aβarc) used to express the arctic mutant Aβ42 was a generous gift from Dr. Crowther (Cambridge University, Cambridge, UK) (Crowther et al., 2005). The UAS-cac1-egfp, and P[Gal4–elav.L]3 lines were purchased from the Bloomington Drosophila Stock Center. The

Aβ expression induces an age-dependent decline in synaptic vesicle release probability

In our previous study, we expressed an arctic mutant form of Aβ42 (E22G, Aβarc) in neurons of the Giant Fiber system (Fig. 1) and a subgroup of neurons elsewhere in the adult Drosophila brain using the Gal4-UAS method. Aβarc was found to accumulate intraneuronally (Zhao et al., 2010). We investigated the effects of Aβ expression on the synaptic function of DLM neuromuscular synapses by performing two-electrode voltage-clamp (TEVC) recordings of excitatory junction currents (EJCs) in the DLM

Discussion

In a previous study of the Drosophila AD model, Aβ was found to accumulate intraneuronally and produce an age-dependent depletion of presynaptic mitochondria and synaptic vesicles and an acceleration of synaptic fatigue (Zhao et al., 2010). In this study, we found that Aβ expression induced an age-dependent reduction in synaptic vesicle release probability, reflected by the reduced decline rate in the peak amplitudes of the 2nd and 3rd excitatory postsynaptic currents evoked by repetitive

Conclusion

Chronic accumulation of intraneuronal Aβ can induce functional and structural changes in the presynaptic active zone prior to a loss of presynaptic buttons in the same neuron.

The following are the supplementary data related to this article.

Supplementary Fig. 1.

Acknowledgments

We thank Dr. D Crowther for the UAS-Aβarc transgenic line, Dr. C O'Kane for the [Gal4]A307 line, and the Drosophila Bloomington stock for providing fly stocks. This work was supported by the 973 program 2013CB530900 and 2011CBA00408 by the National Natural Science Foundation of China (grant no. 31171014).

References (29)

  • S.T. DeKosky et al.

    Synapse loss in frontal cortex biopsies in Alzheimer's disease: correlation with cognitive severity

    Ann. Neurol.

    (1990)
  • B. Dellinger

    Genetic modifiers of the Drosophila NSF mutant, comatose, include a temperature-sensitive paralytic allele of the calcium channel alpha1-subunit gene, cacophony

    Genetics

    (2000)
  • J.S. Jacobsen

    Early-onset behavioral and synaptic deficits in a mouse model of Alzheimer's disease

    Proc. Natl. Acad. Sci. U. S. A.

    (2006)
  • F. Kawasaki

    A temperature-sensitive paralytic mutant defines a primary synaptic calcium channel in Drosophila

    J. Neurosci.

    (2000)
  • Cited by (36)

    • Amyloid-β42 clearance and neuroprotection mediated by X-box binding protein 1 signaling decline with aging in the Drosophila brain

      2017, Neurobiology of Aging
      Citation Excerpt :

      These results indicate that in our model, the CNS toxicity elicited by Aβ42 is associated with the accumulation of nonfibrillar Aβ species and requires neuronal expression of the peptide. Consistent with several reports using conditional Aβ expression, aging seems to be an important variable influencing peptide accumulation and neurotoxicity (Huang et al., 2013; Ling and Salvaterra, 2011; Rogers et al., 2012; Sofola et al., 2010). Aβ42 is capable of triggering the activation of the UPR in Drosophila eye and in specific neuronal groups in the CNS (Casas-Tinto et al., 2011).

    • Neural changes in Alzheimer's disease from circuit to molecule: Perspective of optogenetics

      2017, Neuroscience and Biobehavioral Reviews
      Citation Excerpt :

      Synaptic plasticity was also disrupted by reducing postsynaptic Kidney/Brain expression (KIBRA) protein in hippocampus, SNP clarified KIBRA was an important factor of AD (Kawai et al., 2015; Pantzar et al., 2014; Tracy et al., 2016). It was also reported that presynaptic Ca2+channel clustering and transmitter release (also named boutons) were disrupted in AD (Chakroborty et al., 2012; Huang et al., 2013; Mitew et al., 2013; Waites and Garner, 2011). APP cleavage also occurs within synaptic vesicles, and that synaptic vesicles typically recycle from Rab5-positive endosomes within boutons [reviewed in (Mitew et al., 2013)].

    • Animal Models of Alzheimer's Disease

      2017, Animal Models for the Study of Human Disease: Second Edition
    • Modeling the complex pathology of Alzheimer's disease in Drosophila

      2015, Experimental Neurology
      Citation Excerpt :

      In adult flies, expression of Aβ42 induced progressive failure of transmission in the giant fiber system together with depletion of mitochondria in presynaptic terminals due to slow axonal transport (Fig. 3) (Lin et al., 2014; Zhao et al., 2010). Further studies found reduced number of presynaptic vesicles, probability of vesicle release, calcium channels, and active zones (Huang et al., 2013). These critical changes in the presynaptic terminal preceded and might be responsible for the loss of presynaptic boutons.

    View all citing articles on Scopus
    1

    Division of Life Science and Technology Research, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201203, China.

    View full text