Dependence of TBI Outcomes on Mitochondrial Genes - PROJECT SUMMARY Traumatic brain injury (TBI) is a leading cause of disability and death, with patient outcomes varying significantly, even among individuals with similar injuries. This variation suggests the presence of intrinsic recovery mechanisms that, if identified, could be targeted to improve outcomes for poorly recovering patients. Outcome variation arises from modifiers of pathways that prevent, promote, or repair secondary injuries. However, known modifiers such as age, diet, or even nuclear genetic background do not fully account for differences in TBI outcomes. Although mitochondrial DNA (mtDNA) variation is strongly linked to neurodegenerative diseases, its role in TBI has been largely overlooked. Human studies suggest that mtDNA variation influences TBI outcomes, linking mitochondrial haplogroups to age-dependent effects and identifying a mtDNA polymorphism associated with prognosis, but direct experimental evidence for causality remains absent. To address this critical gap, we developed a novel experimental system that pairs a Drosophila TBI model with the Drosophila Genetic Reference Panel (DGRP), a powerful resource of sequenced lines with diverse mitochondrial and nuclear genomes. Because flies share the same 37 mtDNA-encoded genes as humans and offer unmatched genetic tractability, this system, relative to mammalian models, provides an unparalleled opportunity to dissect how mtDNA variation influences TBI outcomes. Our preliminary data provide the first definitive evidence in any system that mtDNA variation contributes to differences in TBI outcomes. To isolate effects of mtDNA from nuclear DNA, we performed reciprocal female-male crosses between two inbred Drosophila lines, generating offspring with identical nuclear genomes but differing mitochondrial genomes. These genetically-matched progeny showed a significant difference in early mortality (within 24 hours post-injury), demonstrating that mtDNA haplotype influences the acute response to TBI. Furthermore, among DGRP lines, those with the largest age- dependent difference in early mortality had polymorphisms in two mtDNA genes, COX3 and CYTB, reinforcing the conclusion from human studies that effects of age on TBI outcome are dependent on mtDNA haplotype. These findings challenge the long-standing view that TBI outcomes are modified solely by nuclear genetic background and biological and environmental factors, highlighting instead a key role for mtDNA genes. By uncovering a direct role for mtDNA, and its interaction with aging, in shaping TBI responses, this work opens new avenues for mechanistic insight and therapeutic development in neurotrauma research. Our specific aims are to (1) Identify mtDNA polymorphisms that modulate early mortality following TBI and (2) Define the impact of mtDNA haplotype on short- and long-term outcomes following TBI.
