Biochemical Sequelae of Repetitive Mild Traumatic Brain Injury in a Murine Model Treated with Young Blood Plasma

Erin Doherty

Advisor: Jane M Flinn, PhD, Department of Psychology

Committee Members: Geraldine Grant, Craig McDonald

David J. King Hall, #2027
August 13, 2024, 01:00 PM to 03:00 PM

Abstract:

Mild traumatic brain injuries (mTBI)—i.e., “concussions”—are experienced widely by athletes in contact sports and in military personnel. There is growing evidence to suggest that these populations are at increased risk to sustain repetitive mTBI (rmTBI) and that damage is cumulative with each subsequent injury. The pathology that succeeds rmTBI is linked to the development of other neurodegenerative disorders, such as Alzheimer’s disease (AD) and chronic traumatic encephalopathy (CTE). Within the last decade, researchers have discovered the promising effects of transfusing healthy young blood plasma for the reduction of neurological decline. Young blood plasma treatment has been shown to significantly ameliorate the neuronal damage, synaptic loss, and cognitive deficits associated with aging and AD. This study performed biochemical assays to investigate whether young blood plasma may also be an effective treatment for the neurodegenerative sequelae of rmTBI and CTE-type pathology in young mice. Brain and blood plasma samples were sourced from a previous doctoral dissertation that employed a controlled cortical impact model of rmTBI in C57Bl/6J mice starting at 8 weeks of age (Barkey, 2022). Half of the mice received one mTBI every 48 hours (5 mTBI total) while the other half received “sham” injuries as a healthy control. Following the rmTBI protocol, injury and sham mice received 150 µL healthy young blood plasma (donated from 8–10-week-old non-injury mice) or 150 µL saline every 48 hours for 16 total tail-vein injections. Plasma and saline injections were delivered in the form of either immediate treatment (24 hours after the last TBI) or delayed treatment (1 month after TBI). To examine the effects of immediate and delayed treatment following rmTBI, western blots measured brain lysate proteins related to memory function and synaptic plasticity—cAMP-response element binding (CREB) protein, phosphorylated CREB (pCREB), synaptophysin—and a biomarker with high specificity for post-TBI damage, ubiquitin C-terminal hydrolase-L1 (UCH-L1). Mice given immediate saline treatment exhibited higher densities of pCREB in the brain than those given plasma (p = .044); pCREB also trended higher in sham mice than those withrmTBI (p = .084). No significant differences were found when probing for total CREB, synaptophysin, or UCH-L1. An enzyme-linked immunosorbent assay (ELISA) was also conducted to quantify peripheral changes in the circulating blood plasma of rmTBI and sham mice that were administered the delayed plasma or saline treatment. Although growth differentiation factor 11 (GDF11) has been previously recognized as a prime circulatory factor in delivering the benefits of plasma treatment, the results demonstrated no differences in the GDF11 concentration between plasma-treated and saline-treated mice, nor between rmTBI and sham mice. A second ELISA assessed the plasma concentration of C-C Motif Chemokine Ligand 11 (CCL11), a potential biomarker for CTE-type pathology. However, there were no observed differences in CCL11 levels between rmTBI and sham mice, nor between mice given delayed plasma and saline treatment at 1 month post-TBI. Further plasma analyses for immediate treatment effects will be explored in follow-up studies. The results of this study suggest that rmTBI incurred at a young age may not produce damaging effects to the brain’s plasticity-related proteins (e.g., CREB, synaptophysin), and the affected mice may have been too young to present lasting inflammatory changes (e.g., UCH-L1, CCL11). Future research should continue to probe for diagnostic/prognostic rmTBI biomarkers that can be observed even at a young age, as brain injuries still produce long-term consequences in young athletes.