Gut-brain axis at the intersection of aging and traumatic injury

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Project Summary The proposed studies will examine mechanisms by which advanced age increases intestinal permeability and neuroinflammation after burn injury using a clinically relevant mouse model. Regardless of age, most burn patients do not die from primary injuries, but rather from complications, such as sepsis. Further, aged burn patients often experience greater neurological impairments, which may stem from heightened neuroinflammation. Clinical and experimental evidence reveal that healthy aged subjects are in an elevated basal inflammatory state, referred to as “inflammaging,” which can contribute to deficits in tissue injury and repair. We and others believe that inflammaging is caused by translocation of bacterial products from the intestinal lumen and that exposure to these products triggers the production of pro-inflammatory cytokines and chemokines, including tumor necrosis factor alpha (TNF), interleukin (IL)-1β, IL-6, and C-C Motif Chemokine Ligand 2 (CCL2). Novel preliminary data in our clinically-relevant murine model of scald burn injury confirm that aged mice who sustain a burn injury have heightened circulating levels of danger-associated molecular patterns (DAMPs), and a greater breach in intestinal epithelial barrier integrity that coincides with an increase in markers of neuroinflammation. Both neuroinflammation and burn injury in the aged population have been correlated with breaches in the blood brain barrier, delirium, and other signs of cognitive decline. From these observations, we hypothesize that post-burn gut leakiness seen in aged mice is driven by excessive IEC death, ISC dysfunction, and reduced IEC proliferation. Additionally, these changes in the gut lead to leakiness of the blood brain barrier and neuroinflammation. To test this hypothesis, in Aim 1, we will investigate the mechanisms behind gut leakiness in young and aged sham and burn-injured mice by identifying intestinal epithelial cell apoptosis/necroptosis, epithelial cell proliferation, and intestinal stem cell markers in vivo and in vitro utilizing whole tissue, isolated epithelium, and intestinal organoids, along with measuring blood-borne gut-derived bacteria and bacterial cell wall components. In Aim 2, we will examine blood brain barrier integrity in young and aged sham and burn-injured mice using multiple measures of barrier permeability. Further, we will examine the levels of pro-inflammatory cytokines and chemokines, and microglial and astrocyte activation within brain regions. Finally, we will determine if limiting intestinal barrier damage after burn injury reduces neuroinflammatory markers in the brain. These studies will expand our understanding of how advanced age alters the gut in the context of burn injury and the impact of intestinal permeability on neuroinflammation. It is our hope that our work will lead to the development of novel therapies to treat the excessive inflammatory response and consequences of that inflammation in burn patients of all ages.