(A-23) Profiling the Neuroimmune Cascade in 3xTg Mice Exposed to Successive Mild Traumatic Brain Injuries

Introduction:: Repeated mild traumatic brain injuries (mTBIs) can lead to more severe outcomes than a single mTBI. We previously reported that acute increases in mitogen-activated protein kinase (MAPK) signaling and cytokine expression after multiple weight-drop injuries were associated with worse cognitive outcome in mice. Because cognitive and pathological outcome are closely associated, we hypothesized that repeated mTBI would also drive acute neuroimmune signaling in correlation with molecular markers of pathology.


Materials and Methods:: All animal protocols were approved by the Emory University Institutional Animal Care and Use Committee in accordance with National Institutes of Health guidelines. Female 3xTg mice at 2-4mo of age were subjected to 1, 3, or 5 once-daily weight-drop closed-head injuries (CHI). Animals were sacrificed and brains harvested immediately prior to or 30min, 4h, or 24h after the final CHI (n=8-10/time point/injury group) to quantify immune markers, pathological markers, and transcriptional profiles.


Results, Conclusions, and Discussions:: Results and Discussion: We found that a group of seven cytokines and two MAPK phospho-proteins show broad upregulation 24h after 1-4x CHI (Fig. 1) and 4h after 5xCHI. Eight were significantly correlated to phospho-tau T181 before and after injury, and six co-localized with neurons after injury. RNA sequencing together with weighted gene co-expression network analysis identified modules of genes associated with an early (24h) decrease of neuronal homeostatic genes and increase of pathology-related genes followed by gradual (72h+) elevation of immune- & stress-associated genes in astrocytes & microglia (Fig. 2).

Conclusions: Our data suggest that a concerted neuronal cytokine response occurs within 24h after single and repeated mTBI and may be involved in injury-induced pathogenesis. Transcriptional regulation of neuronal homeostatic processes and pathology-related processes may occur within 24h of a single mTBI, while changes in astrocytes and microglia appear to occur on a longer time scale (72h) or after multiple injuries (3xCHI).


Acknowledgements (Optional): : This project was supported by the National Institutes of Health R01 NS115994 (LBW/EMB). This work was also supported by the U.S. Department of Defense through the Congressionally Directed Medical Research Programs under Award No. W81XWH-18-1-0669 (LBW/EMB). Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the Department of Defense. AFP was supported in part by the National Institutes of Health Cell and Tissue Engineering Biotechnology Training Grant (T32-GM008433).

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