Drosophila Exhibit Divergent Sex-Based Responses in Transcription and Motor Function After Traumatic Brain Injury

Abstract

Every year, millions of people in the US suffer brain damage from mild to severe traumatic brain injuries (TBI) that result from a sudden impact to the head. Despite TBI being a leading cause of death and disability worldwide, sex differences that contribute to varied outcomes post-injury are not extensively studied and therefore, poorly understood. In this study, we aimed to explore biological sex as a variable influencing response to TBI using Drosophila melanogaster as a model, since flies have been shown to exhibit symptoms commonly seen in other mammalian models of TBI. After inflicting TBI using the high-impact trauma device, we isolated w 1118 fly brains and assessed gene transcription changes in male and female flies at control and 1, 2, and 4 hr after TBI. Our results suggest that overall, Drosophila females show more gene transcript changes than males. Females also exhibit upregulated expression changes in immune response and mitochondrial genes across all time-points. In addition, we looked at the impact of injury on mitochondrial health and motor function in both sexes before and after injury. Although both sexes report similar changes in mitochondrial oxidation and negative geotaxis, locomotor activity appears to be more impaired in males than females. These data suggest that sex-differences not only influence the response to TBI but also contribute to varied outcomes post-injury.

Inhibiting Mitochondrial Cytochrome c Oxidase Downregulates Gene Transcription After Traumatic Brain Injury in Drosophila

“…Several studies in experimental models of brain injury have shown structural and functional damage to mitochondria being an early event in TBI which leads to activation of cell death pathways ( Fischer et al, 2016 ). In a previous study, we demonstrated an upregulation in gene transcription involved with immune response, cytoskeleton organization and apoptosis after injury in Drosophila ( Shah et al, 2020 ). Moreover, we have also shown sex-differences in mitochondrial stress and gene transcription in response to TBI ( Shah et al, 2020 ).…”

“…Expression analysis was conducted in collaboration with the Wayne State University Genome Sciences Core. Three biological replicates were used for each condition ( Shah et al, 2020 ).…”

“…Between 10–15 adult repo-GFP flies for each sex (control and every time point post-TBI) were inflicted with TBI using the HIT-device ( Katzenberger et al, 2013 ; Shah et al, 2020 ). Flies were anesthetized with CO 2 before brains were dissected in 1×PBS (phosphate-buffered saline) and fixed for 5 min with 4% PFA (paraformaldehyde).…”

Repetitive Mild Head Trauma Induces Activity-Mediated Lifelong Brain Deficits in a NovelDrosophilaModel

“…Taken together, this demonstrates sex differences following recovery from TBI and substantiates the importance of using both sexes in preclinical animal models. Interestingly, sex-dependent differences in function (climbing behavior) in fly head injury models has only been examined once prior, in which no differences between sex were revealed [43]. However, flies were only measured for 72 hours during the post-injury period, and the method for measuring behavior was done using the traditional approach to measure startle-induced climbing performance [53,54].…”

“…Fruit flies represent an excellent tractable model organism to dissect fundamental cellular and molecular disease mechanisms, including neurodegeneration [34][35][36], while taking advantage of their relatively short lifespan [37][38][39][40][41][42] that enables long-term outcome analyses related to head injury exposure. Several fly models have been developed to study traumatic brain injury in Drosophila, but the lack of controlled head-specific impacts may confound neuronalspecific responses [43][44][45]. Head-specific impact models have recently been developed in which physical head impacts were delivered to the heads of individually restrained flies [46][47][48], but no long-term study was carried out to examine the detrimental effects that might develop late in life.…”