Uncoupling neuronal death and dysfunction in Drosophila models of neurodegenerative disease

Abstract

Common neurodegenerative proteinopathies, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD), are characterized by the misfolding and aggregation of toxic protein species, including the amyloid beta (Aß) peptide, microtubule-associated protein Tau (Tau), and alpha-synuclein (αSyn) protein. These factors also show toxicity in Drosophila; however, potential limitations of prior studies include poor discrimination between effects on the adult versus developing nervous system and neuronal versus glial cell types. In addition, variable expression paradigms and outcomes hinder systematic comparison of toxicity profiles. Using standardized conditions and medium-throughput assays, we express human Tau, Aß or αSyn selectively in neurons of the adult Drosophila retina and monitor age-dependent changes in both structure and function, based on tissue histology and recordings of the electroretinogram (ERG), respectively. We find that each protein causes a unique profile of neurodegenerative pathology, demonstrating distinct and separable impacts on neuronal death and dysfunction. Strikingly, expression of Tau leads to progressive loss of ERG responses whereas retinal architecture and neuronal numbers are largely preserved. By contrast, Aß induces modest, age-dependent neuronal loss without degrading the retinal ERG. αSyn expression, using a codon-optimized transgene, is characterized by marked retinal vacuolar change, progressive photoreceptor cell death, and delayed-onset but modest ERG changes. Lastly, to address potential mechanisms, we perform transmission electron microscopy (TEM) to reveal potential degenerative changes at the ultrastructural level. Surprisingly, Tau and αSyn each cause prominent but distinct synaptotoxic profiles, including disorganization or enlargement of photoreceptor terminals, respectively. Our findings highlight variable and dynamic properties of neurodegeneration triggered by these disease-relevant proteins in vivo, and suggest that Drosophila may be useful for revealing determinants of neuronal dysfunction that precede cell loss, including synaptic changes, in the adult nervous system.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0333-4) contains supplementary material, which is available to authorized users.

Label‐free distribution of anti‐amyloid D‐AIP in Drosophila melanogaster: prevention of Aβ42‐induced toxicity without side effects in transgenic flies

“…; Chouhan et al . ). Alternatively, our current study utilized live confocal microscopy to image the flies longitudinally (i.e.…”

Retromer subunit, VPS29, regulates synaptic transmission and is required for endolysosomal function in the aging brain

“…During aging, the positions of light-exposed vials were randomly shuffled within racks. ERG recordings were performed as previously described (Chouhan et al, 2016). In brief, adult flies were anesthetized and glued to a glass slide, with electrodes placed on the corneal surface and the thorax.…”

“…For analysis of central brain ultrastructure, fly heads were dissected by removing cuticles and eyes to ensure complete penetration of fixative, leaving each head affixed to the thorax. All samples were processed for TEM as previously described (Chouhan et al, 2016) using a Ted Pella Bio Wave processing microwave with vacuum attachment. Briefly, dissected samples were fixed (4% paraformaldehyde, 2% glutaraldehyde, and 0.1 M sodium cacodylate, pH 7.2) at 4°C for 48 hours, and then submerged in 1% osmium tetroxide for 45 minutes.…”

Genetic strategies to tackle neurological diseases in fruit flies

“…However, in the area of neurobiology there has been a strong bias towards screens that affect neuronal development in flies, and very few high-throughput screens have attempted to isolate mutants that affect neuronal function [27–29] and/or cause the demise of neurons [30,31]. Indeed, most efforts to study genes associated with neurodegeneration have been based on reverse genetic strategies [32,33]. …”