Monitoring Cell-to-cell Transmission of Prion-like Protein Aggregates in Drosophila Melanogaster

Summary

Accumulating evidence supports the idea that pathogenic protein aggregates associated with neurodegenerative diseases spread between cells with prion-like properties. Here, we describe a method that enables visualization of cell-to-cell spreading of prion-like aggregates in the model organism, Drosophila melanogaster.

Abstract

Protein aggregation is a central feature of most neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Protein aggregates are closely associated with neuropathology in these diseases, although the exact mechanism by which aberrant protein aggregation disrupts normal cellular homeostasis is not known. Emerging data provide strong support for the hypothesis that pathogenic aggregates in AD, PD, HD, and ALS have many similarities to prions, which are protein-only infectious agents responsible for the transmissible spongiform encephalopathies. Prions self-replicate by templating the conversion of natively-folded versions of the same protein, causing spread of the aggregation phenotype. How prions and prion-like proteins in AD, PD, HD, and ALS move from one cell to another is currently an area of intense investigation. Here, a Drosophila melanogaster model that permits monitoring of prion-like, cell-to-cell transmission of mutant huntingtin (Htt) aggregates associated with HD is described. This model takes advantage of powerful tools for manipulating transgene expression in many different Drosophila tissues and utilizes a fluorescently-tagged cytoplasmic protein to directly report prion-like transfer of mutant Htt aggregates. Importantly, the approach we describe here can be used to identify novel genes and pathways that mediate spreading of protein aggregates between diverse cell types in vivo. Information gained from these studies will expand the limited understanding of the pathogenic mechanisms that underlie neurodegenerative diseases and reveal new opportunities for therapeutic intervention.

Introduction

The prion hypothesis states that the infectious agent responsible for the transmissible spongiform encephalopathies (e.g., Creutzfeldt-Jakob disease in humans, scrapie in sheep, chronic wasting disease in deer and elk, and "mad cow disease" in cattle) is solely composed of protein and devoid of nucleic acids¹. In prion diseases, the cellular prion protein (PrP^C) assumes a non-native, stable fold (PrP^Sc) that is highly beta sheet-rich and can self-propagate by converting and recruiting monomeric PrP^C molecules into stable amyloid aggregates. PrP^Sc aggregates use this self-replicating m....

Protocol

1. Coupling Gal4- and QF-mediated Htt Transgene Expression in Drosophila

1. Collect and/or generate transgenic Drosophila melanogaster lines containing tissue-specific Gal4 or QF "drivers," as well as lines containing wild-type or mutant Htt transgenes downstream of the Gal4-UAS³⁸ or QF-QUAS³⁹. Ensure that the proteins that are expressed from these transgenes are fused to fluorescent proteins or epitope-tagged to allow for differentiation of mutant and wild-type Htt transgene products in the same fly. See Figure 1.
   ​NOTE: We typically use exon 1 fragments of t....

Results

The methods described here produce robust data demonstrating prion-like transfer of Htt protein aggregates from one cell population to another in the intact fly CNS. Conversion of wild-type Htt from diffuse to punctate is observed by direct fluorescence of this YFP fusion protein in recipient glia as a result of HttQ91-mCherry expression in donor ORNs (Figure 2A-C and Figure 4A, B). Accurate repo.......

Discussion

As the numbers of patients suffering from neurodegenerative diseases continues to increase, there is an urgent need to increase the understanding of the molecular pathogenesis of these diseases so that better therapies can be developed. Here, we describe methods that allow for monitoring prion-like transmission of pathogenic protein aggregates between different cell types in the model organism, Drosophila melanogaster. We have recently used this methodology to demonstrate prion-like transmission of mutant Htt ag.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Phosphate buffered saline (PBS), 10X, pH 7.4	ThermoFisher Scientific	AM9625	Dilute to 1X
Triton X-100	Sigma-Aldrich	T9284-1L
Kimwipes	Thomas Scientific	2904F24
20% paraformaldehyde (PFA)	Electron Microscopy Sciences	15713-S
Normal Goat Serum (NGS), filtered	Lampire Biological Laboratories	7332500	Aliquot and freeze upon receipt
Chicken anti-GFP	Aves Labs	GFP-1020	Use at 1:500 dilution
Rabbit anti-DsRed	Clontech	632496	Use at 1:2000 dilution; can recognize DsRed-based fluorescent proteins (e.g. mCherry, mStrawberry, tdTomato, etc.)
Mouse anti-Bruchpilot	Developmental Studies Hybridoma Bank	nc82	Use at 1:100 dilution; will label active pre-synaptic structures thoughout the fly brain
FITC anti-chicken	ThermoFisher Scientific	SA1-7200	Use at 1:250 dilution
Alexa Fluor 568 anti-rabbit	Life Technologies	A11011	Use at 1:250 dilution
Alexa Fluor 647 anti-mouse antibody	Life Technologies	A21235	Use at 1:250 dilution
Slowfade Gold Antifade Reagent	Life Technologies	S36936
Microscope Slides (25 x 75 x 1.0 mm)	Fisher Scientific	12-550-143
Cover Glass (22 x 22 mm)	Globe Scientific	1404-15
Dumont Biology Grade Forceps, Style 3	Ted Pella	503	use in non-dominant hand
Dumont Biology Grade Forceps, Style 5	Ted Pella	505	use in dominant hand
LAS X image analysis software	Leica
Imaris image analysis software	Bitplane