Glial immune-related pathways mediate effects of closed head traumatic brain injury on behavior and lethality in Drosophila

Abstract

In traumatic brain injury (TBI), the initial injury phase is followed by a secondary phase that contributes to neurodegeneration, yet the mechanisms leading to neuropathology in vivo remain to be elucidated. To address this question, we developed a Drosophila head-specific model for TBI termed Drosophila Closed Head Injury (dCHI), where well-controlled, nonpenetrating strikes are delivered to the head of unanesthetized flies. This assay recapitulates many TBI phenotypes, including increased mortality, impaired motor control, fragmented sleep, and increased neuronal cell death. TBI results in significant changes in the transcriptome, including up-regulation of genes encoding antimicrobial peptides (AMPs). To test the in vivo functional role of these changes, we examined TBI-dependent behavior and lethality in mutants of the master immune regulator NF-κB, important for AMP induction, and found that while sleep and motor function effects were reduced, lethality effects were enhanced. Similarly, loss of most AMP classes also renders flies susceptible to lethal TBI effects. These studies validate a new Drosophila TBI model and identify immune pathways as in vivo mediators of TBI effects.

Unraveling the Role of Antimicrobial Peptides in Insects

“…AMPs are important for regulation of normal functions of the insect brain, e.g., sleep and non-associative learning in Drosophila [ 25 , 26 ]. Results reported by Dissel et al showed that the transcript levels of metchnikowin ( Mtk ), drosocin ( Dro ), and attacin ( Att ) were differentially increased in glia, neurons, and the head fat body, respectively, in sleep-deprived flies.…”

“…In contrast, loss of Def extended survival, indicating that the Drosophila immune response to TBI, including the induction of AMP expression, may result in different effects. Moreover, in this research, a link between the immune response and sleep in flies was demonstrated, as loss of Relish protected against impaired control of sleep and movement after TBI [ 26 ].…”

Antimicrobial peptides do not directly contribute to aging inDrosophila, but improve lifespan by preventing dysbiosis

“…While Drosophila AMPs were initially investigated for their contribution to host defence, AMP upregulation is also observed in non-immune contexts, including anti-tumor defence [26][27][28], neurodegeneration [29][30][31][32][33], and aging [34,35]. This suggests that AMPs could have roles beyond their traditional function as microbicidal agents.…”

“…The copyright holder for this preprint this version posted August 25, 2022. ; https://doi.org/10.1101/2022.08. 24.504952 doi: bioRxiv preprint tumor defence [26][27][28], neurodegeneration [29][30][31][32][33], and aging [34,35]. This suggests that AMPs could have roles beyond their traditional function as microbicidal agents.…”

“…temperature, sex, mating status, nutrition) (Camus et al, 2019;Dobson et al, 2018;Landis et al, 2015;Miquel et al, 1976), microbiome differences, which could help explain contradictory findings on the impact of germ-free conditions on lifespan (Brummel et al, 2004;Ren et al, 2007), or lack of control over genetic background, including transgene insertions (Ferreiro et al, 2017;Sasaki et al, 2021), all of which can influence longevity. In the absence of mutants, these studies have relied on the use of over-expression or RNAi to modulate AMPs, methodologies with certain limitations (Tower et al, 2017;van der Graaf et al, 2022). As a result, exactly how AMPs contribute to aging remains unclear.…”