The Systemic Nature of Severe Traumatic Brain Injury

Severe traumatic brain injury (sTBI) is a devastating condition with no targeted therapies. Our pilot data in adolescents demonstrate that brain injury initiates an acute, strong immune response, marked by blood-brain barrier disruption and autoantibody formation, suggesting a novel avenue for therapeutic direction. Alterations in the gut-brain axis serve as a potential nidus of increasing immunogenicity and thus antibody formation. The major goal of this project is to define the immune mechanisms responsible for the interaction between brain injury and alterations in gut permeability via the gut-brain axis. Specifically, we will apply a novel multi-platform metabolomics approach, coupled with RNA sequencing, enabling identification of the mechanism responsible for early immune activation, secondary and tertiary brain injury, and neurodegeneration in adults with sTBI.

Current acute-management strategies remain largely focused on stabilizing cerebral physiology rather than addressing the molecular drivers of injury progression. The initial kinetic impact and subsequent secondary injury, such as neuroinflammation, neurotoxicity, and compromise of the blood brain barrier (BBB), potentiate a vigorous autoimmune response. Our pilot studies in adolescents demonstrated the activation of this strong immune response, marked by BBB disruption and autoantibody formation. This results in short and long-term inflammatory sequalae, including exacerbation of the initial injury, progression to chronic neurodegenerative diseases, and heightened disability and death.

Metabolomics comprehensively profiles (identifies and quantify) the small-molecule metabolites produced by cells, tissues, and microorganisms enabling the elucidation of metabolic pathways and their roles in addressing specific biological question. Although several omics studies have profiled time-resolved changes in adult and experimental models, no comparable work has been performed using multi-omics strategies in sTBI which remains essential. This represents a critical gap in our understanding of the developmental context of injury evolution. Lipids are essential for cellular functioning due to their pivotal roles in membrane composition, signaling, and energy metabolism, especially in the brain. Lipidomics, a subfamily of metabolomics, identifies and quantifies lips across cell types, organs, or full organisms. The investigation of cellular lipid pathways and networks provides critical insight into the molecular mechanisms underlying TBI. Emerging lipidomic studies show that circulating and CNS-derived lipid signatures correlate with injury severity, BBB breakdown, and long-term neurodegenerative risk thus making lipidomics essential in the comprehensive evaluation of sTBI pathogenesis.

The gut-brain axis, a bidirectional communication network between the gastrointestinal tract and central nervous system, has been identified in the pathophysiology of various forms of neurodegenerative disorders and recently implicated with TBI. Following sTBI, rapid alterations occur in gut motility, epithelial barrier integrity, immune signaling, and microbial community structure, collectively leading to gut dysbiosis and increased intestinal permeability. This is likely due to diffuse mucosal barrier dysfunction. In the gut, maintenance of mucosal integrity requires careful coordination between the epithelial lining and associated junctions, with immunologic contribution in regulating these relationships to alter permeability and absorption. The BBB, in contrast, carries a much greater degree of regulation and is relatively impermeable under normal physiological conditions, however, it is increased with brain injury thus permitting the influx of molecules that would not be present under normal conditions. These peripheral disturbances exacerbate neuroinflammation, oxidative stress, and neurodegeneration via the altered BBB. However, the precise mechanism by which this occurs has yet to be determined and remains a main objective of this study.

To discern the cells responsible for these alterations, scRNA-seq will be paired with global metabolomics, with an emphasis on detecting unique gut metabolites such as bacterial products and food antigens, not typically found in serum. scRNA will be used to identify circulatory cell type and clonal activation, integrated with metabolomics to specifically define the mechanism underlying the cytotoxicity of the gut permeability to the brain. This will be the first study to fully build a model examining the precise mechanism down to the cellular and molecular level with far-reaching impact. Ultimately, this may potentially identify targets for monoclonal deactivation and attenuation of secondary and tertiary brain injury.