A Novel Method to Model Chronic Traumatic Encephalopathy in Drosophila

Summary

Here, we describe a new approach to inflict closed-head traumatic brain injury in Drosophila melanogaster. Our method has the advantage of directly delivering repetitive impacts with adjustable strength to the head alone. Further exploration of the invertebrate system will help to illuminate the pathogenesis of chronic traumatic encephalopathy.

Abstract

Chronic Traumatic Encephalopathy (CTE) is an established neurodegenerative disease that is closely associated with exposure to repetitive mild Traumatic Brain Injury (mTBI). The mechanisms responsible for its complex pathological changes remain largely elusive, despite a recent consensus to define the neuropathological criteria. Here, we describe a novel method to develop a model of CTE in Drosophila melanogaster (Drosophila ) in an attempt to identify the key genes and pathways that lead to the characteristic hyperphosphorylated tau accumulation and neuronal death in the brain. Adjustable-strength impacts to inflict mild closed injury are delivered directly to the fly head, subjecting the head to rapid acceleration and deceleration. Our method eliminates the potential problems inherent with other Drosophila mTBI models (e.g.,animal death might be induced by damage to other parts of the body or to internal organs). The less labor- and cost-intensive animal care, short life span, and extensive genetic tools make the fruit fly ideal to study CTE pathogenesis and make it possible to perform large-scale, genome-wide forward genetic and pharmacological screens. We anticipate that the ongoing characterization of the model will generate important mechanistic insights on disease prevention and therapeutic approaches.

Introduction

Chronic Traumatic Encephalopathy (CTE) has recently been recognized as a distinct neurodegenerative disorder, separate from other tauopathies such as Alzheimer's disease¹. Unlike Alzheimer's disease and other common tauopathies-whose most important risk factors are advancing age and a family history of dementia, CTE, as indicated by its name, implies a close association with a history of brain trauma, most likely seen in contact sports athletes, such as boxers and football players, as well as in military veterans^2,3,4,

Protocol

1. Assembly of the Strike Device (Figure 1)

1. Remove the plunger from a 1 mL tuberculin syringe. Cut the barrel at the 1 mL mark.
2. Remove an aerosol barrier (3 mm height x 4 mm diameter) from a 200 µL pipette tip and use it as an impactor. Place the impactor inside the syringe barrel. Gently tap the barrel to move the impactor to the tip end, with the flat side covering the nozzle opening.
3. Attach the barrel tip end to plastic tubing that is connected to the carbon dioxide (CO₂) flow regulator of a Drosophila anesthesia station.
4. Hold the barrel vertically and cl....

Results

To establish a CTE model using adult Drosophila, we determined the effectiveness of our device at inflicting a single closed-head injury. To eliminate the variations relating to genotype, sex, or age, we used 2-day-old Canton-S WT female flies in the experiment. We could easily control the strength of the impactor by regulating the flow rate of CO₂ at a constant gas pressure of 100 kPa. Flies exposed to a single strike at the highest flow rate (15 L/min) exhibited mini.......

Discussion

Animal models that faithfully model CTE features, including neurophysiological alterations, neuropathological hallmarks, and neurobehavioral deficits, are essential for uncovering disease mechanisms and for developing diagnostic and therapeutic targets. It is understandable that no animal model of a human disease is perfect at mimicking all clinically relevant endpoints. However, we believe that a robust CTE model should satisfy the following three requirements: (1) the impact must be directly applied to a head that has .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Aerosol Barrier	USA Scientific	1120-8810	Used as an impactor
200 μL Pipette Tip	USA Scientific	1111-0706	Used as a fly head holder
1000 μL Pipette Tip	USA Scientific	1122-1830	Used as a connector
1 mL Tuberculin Syringe	Becton Dickinson	309625
60 mm Petri Dishes	Fisher Scientific	FB0875713A	Used as a tracking arenas
Flow Regulator	Genesee Scientific	59-122WC
Standard Clamp Holder/stand	EISCO Scientific	CH0688
Fine Brush	Genesee Scientific	59-204
Flypad	Genesee Scientific	59-114
Sylgard Silicone Elastomer	Dow Corning	4019862
CCD Camera	Microsoft	HD-5000
Ctrax Walking Fly Tracker	Caltech	Ctrax 0.2.11
MATLAB Image Processing Toolbox	MATLAB	R2015b