Project Summary/Abstract Traumatic brain injury (TBI) afflicts about three million Americans every year. The highest incidence of TBI occurs in adults aged 75 and older who have higher mortality and worse long- term functional outcomes than younger adults. This age-associated outcome difference has also been reported in various animal studies. Yet, the molecular and cellular mechanisms have only been partially elucidated, and age specific TBI treatments are notably lacking. Our published microbiome analysis (16S RNA gene sequencing) data revealed that aged mice post-TBI demonstrate a greater loss of beneficial commensal gut bacteria and a higher rise in opportunistic deleterious species in the compared to young adult TBI mice. This increase in gut dysbiosis correlated with worse neurodegeneration and neurocognitive deficits in aged TBI mice. Of note preliminary data reveals a significant decrease in the size of the impact lesion and an attenuation of neurocognitive deficits with transfer of a healthy microbiome into young adult TBI mice via fecal microbiome transplantations (FMT) Hence, Dr. Davis hypothesizes that the post-TBI placement of a young microbiome into an aged mouse will attenuate neurodegeneration and neurocognitive deficits. For the K99 phase of the proposed research, Dr. Davis will validate the findings via single cell RNA sequencing (scRNA-seq) to interrogate the transcriptional profiles of microglia over the course of injury in aged mice FMT treated post-TBI. He will also compare microbiome scRNA-seq data to anatomic, neurocognitive, and pathologic outcome measures with quantitative MRI, behavioral phenotyping, and histopathology. For the R00 phase of the proposed research, Dr. Davis will utilize aged (80-weeks-old) germ-free (GF) C57BL/6 mice reconstituted with the SCFA- producing bacterium Butyrivibrio fibrosolvens (B. fib) before TBI or sham injury. Mutant B.fib that produces 10-fold less SCFA will be used as a control. A separate cohort of aged wild type C57BL/6 mice will receive water containing SCFAs (butyrate, acetate, and propionate) vs. vehicle after TBI. scRNAseq will be used to determine if targeted microbial replacement or SCFA dietary supplementation can attenuate microglia activation. Anatomic, neurocognitive, and pathologic outcome measures will be determined with MRI, behavioral phenotyping, and histopathology. Together, this proposal will fill current gaps in geriatric TBI research by providing new insights into the molecular and cellular mechanisms leading to aging-associated differential TBI outcomes, which can, in turn, pinpoint potential aging-specific TBI therapeutic targets, which are severely lacking.

Project Narrative Traumatic brain injury (TBI) afflicts about three million Americans every year. The highest incidence of TBI occurs in adults aged 75 and older who have higher mortality and worse long- term functional outcomes than younger adults. Schwulst lab at Northwestern University has established a well-reproducible and clinically applicable TBI murine model using controlled cortical impact (CCI). Preliminary data indicate that aged mice brains had significant gut dysbiosis correlating with worse outcomes post-TBI. This proposal will further investigate this observation using quantitative and multidimensional flow cytometry, microbiome modulation, short chain fatty acid supplementation and germ-free mice to study the mechanism for the gut dysbiosis and its functional role in the post-TBI aged brain.