Drosophila melanogaster as a model to study age and sex differences in brain injury and neurodegeneration after mild head trauma

Abstract

Repetitive physical insults to the head, including those that elicit mild traumatic brain injury (mTBI), are a known risk factor for a variety of neurodegenerative conditions including Alzheimer's disease (AD), Parkinson's disease (PD), and chronic traumatic encephalopathy (CTE). Although most individuals who sustain mTBI typically achieve a seemingly full recovery within a few weeks, a subset experience delayed-onset symptoms later in life. As most mTBI research has focused on the acute phase of injury, there is an incomplete understanding of mechanisms related to the late-life emergence of neurodegeneration after early exposure to mild head trauma. The recent adoption of Drosophila-based brain injury models provides several unique advantages over existing preclinical animal models, including a tractable framework amenable to high-throughput assays and short relative lifespan conducive to lifelong mechanistic investigation. The use of flies also provides an opportunity to investigate important risk factors associated with neurodegenerative conditions, specifically age and sex. In this review, we survey current literature that examines age and sex as contributing factors to head trauma-mediated neurodegeneration in humans and preclinical models, including mammalian and Drosophila models. We discuss similarities and disparities between human and fly in aging, sex differences, and pathophysiology. Finally, we highlight Drosophila as an effective tool for investigating mechanisms underlying head trauma-induced neurodegeneration and for identifying therapeutic targets for treatment and recovery.

Keywords: aging; neurodegeneration; risk factors; sex difference; traumatic brain injury.

Figure 1

Drosophila melanogaster as a model to study neurodegenerative diseases and TBI. (A) Representative neurodegenerative diseases modeled in Drosophila. (B) Schematics showing four Drosophila models for TBI-related research. HIT: high impact trauma model by Katzenberger et al. (2013). dCHI: Drosophila controlled head-impact model by van Alphen et al. (2022). dTBI: Drosophila TBI model using a Piezoelectric actuator by Saikumar et al. (2020). HIFLI: Headfirst Impact FLy Injury model by Behnke et al. (2021).

Figure 2

Aging and sex differences in human and fly. (A) A simplified summary of sex maturation, reproduction, and aging in human. Key events leading to physical, physiological, and hormonal changes in male and female are indicated arrows. (B) The schematic summary of the short lifespan of Drosophila flies, in which mating is known to trigger extensive changes in females. (C) A schematic plot highlighting the aging-associated functional declines that are common for human and fly, sexually dimorphic, and influenced by sex hormones and/or reproductive status.