High salt diet induces microbiome dysregulation, neuroinflammation, and anxiety in the chronic period after mild repetitive closed head injury in adolescent mice

Abstract

Abstract The associations between human concussions and subsequent sequelae of chronic neuropsychiatric and cardiovascular such as hypertension have been reported; however, little is known about the underlying biological processes. We hypothesized that dietary changes, including a high salt diet, disrupt the bidirectional gut-brain axis, resulting in worsening neuroinflammation and emergence of cardiovascular and behavioral phenotypes in the chronic period after repetitive closed head injury in adolescent mice. Adolescent mice were subjected to three daily closed head injuries, recovered for 12 weeks, and then maintained on a high salt diet or a normal diet for an additional 12 weeks. Experimental endpoints were hemodynamics, behavior, microglial gene expression (bulk RNA sequencing), brain inflammation (brain tissue quantitative PCR), and microbiome diversity (16S RNA sequencing). High salt diet did not affect systemic blood pressure or heart rate in Sham or injured mice. High salt diet increased anxiety-like behavior in injured mice compared to Sham mice fed with high salt diet and injured mice fed with normal diet. Increased anxiety in injured mice that received a high salt diet was associated with microgliosis and a proinflammatory microglial transcriptomic signature, including upregulation in interferon-gamma (IFN-γ), interferon beta (IFN- β), and oxidative stress related pathways. Accordingly, we found upregulation of tumor necrosis factor-alpha (TNF-α) and IFN-γ mRNA in the brain tissue of high salt diet-fed injured mice. High salt diet had a larger effect on the gut microbiome composition than repetitive close head injury. Increases in gut microbes in the families Lachnospiraceae, Erysipelotrichaceae, and Clostridiaceae were positively correlated with anxiety-like behaviors. In contrast, Muribaculaceae, Acholeplasmataceae, and Lactobacillaceae were negatively correlated with anxiety in injured mice that received a high salt diet, a time-dependent effect. The findings suggest that high salt diet, administered after a recovery period, may affect neurologic outcomes following mild repetitive head injury, including the development of anxiety. This effect was linked to microbiome dysregulation and an exacerbation of microglial inflammation, which may be physiological targets to prevent behavioral sequelae in the chronic period after mild repetitive head injury. The data suggest an important contribution of diet in determining long-term outcomes after mild repetitive head injury.