Abstract
Background: Traumatic brain injury (TBI) is an underrecognized public health threat. The constitutive activation of microglia after TBI has been linked to long-term neurocognitive deficits and the progression of neurodegenerative disease. Evolving evidence indicates a critical role for the gut-brain axis in this process. Specifically, TBI has been shown to induce the depletion of commensal gut bacteria. The resulting gut dysbiosis is associated with neuroinflammation and disease. Hypothesis: We hypothesized that fecal microbiota transplantation would attenuate microglial activation and improve neuropathology after TBI. Methods: C57Bl/6 mice were subjected to severe TBI (n = 10) or sham injury (n = 10) via an open-head controlled cortical impact. The mice underwent fecal microbiota transplantation (FMT) or vehicle alone via oral gavage once weekly for 4 weeks after injury. At 59 days after TBI, mice underwent three-dimensional, contrast-enhanced magnetic resonance imaging. Following imaging, mice were killed, brains harvested at 60 DPI, and CD45+ cells isolated via florescence-activated cell sorting. cDNA libraries were prepared using the 10x Genomics Chromium Single Cell 3' Reagent kit followed by sequencing on a HiSeq4000 instrument, and computational analysis was performed. Results: Fecal microbiota transplantation resulted in a >marked reduction of ventriculomegaly (P < 0.002) and preservation of white matter connectivity at 59 days after TBI (P < 0.0001). In addition, microglia from FMT-treated mice significantly reduced inflammatory gene expression and enriched pathways involving the heat-shock response compared with mice treated with vehicle alone. Conclusions: We hypothesized that restoring gut microbial community structure via FMT would attenuate microglial activation and reduce neuropathology after TBI. Our data demonstrated significant preservation of cortical volume and white matter connectivity after an injury compared with mice treated with vehicle alone. This preservation of neuroanatomy after TBI was associated with a marked reduction in inflammatory gene expression within the microglia of FMT-treated mice. Microglia from FMT-treated mice enriched pathways in the heat-shock response, which is known to play a neuroprotective role in TBI and other neurodegenerative disease processes.