Salt diet induces neuroinflammatory response, microbiome dysregulation and is associated with longterm anxiety following repetitive closed head injury.

Concussions continue to be a prominent public health concern, with an estimated 1.6-3.8 million incidences annually in the United States. Younger populations are experiencing the highest rates of concussion and nearly all athletic endeavors have some risk of concussive injury. Concerns surrounding the potential risks of long-term cognitive and medical outcomes made adolescent traumatic brain injury (TBI) a central focus of public attention and started larger outcome discussions in the field. Coupled to these events, recent clinical studies have shown that lifestyle factors, including a diet high in salt, constitute additional risk affecting TBI consequences and neuropathophysiological outcomes. However, the impact of salt diet on the pathophysiology of TBI and whether it exacerbates post-injury outcomes still largely unknown. In this study we investigated if exposure to a high salt diet (HSD) would alter hemodynamics, behavior outcomes, microglial response post repetitive mild closed head injury in adolescent mice. Mice were injured with three hit daily (3HD) model of concussion and after 2 month of injury were put on either a HSD or kept on a standard diet (STD) for 12 weeks. We found that HSD didn’t alter the hemodynamics (systolic and diastolic blood pressure, and heart rate) compared with STD group. However, HSD associated with worsening anxiety-like behavior at 12 weeks post high salt diet in the injured group. HSD also induced microgliosis and pro-inflammatory microglial transcriptomic signature including up-regulation in interferon gamma, Interferon type beta, T cells proliferation pathways. Consistently, analysis of cortical tissue showed up-regulation of pro-inflammatory Tumor necrotic factor (TNF) compared to Sham HSD and TBI STD groups. We also evaluated the impact of salt on the diversity of microbiome and its association with outcomes. We found Lachnospiraceae and Rikenellaceae microbiota were associated with anxiety phenotype following injury and salt diet administration. Our findings suggest a diet rich in salt associated with increasing risk of worsening anxiety and exacerbating chronic neuroinflammation post repetitive head injury.