Altered Gut DNA virome diversity associated HMGB1 release regulates reactive Astrocytes-induced IL6 release preferably via TLR4-NFkB pathway in experimental Gulf War Illness

Abstract

Abstract In a recent study, we showed that the gut DNA bacteriophage dysbiosis in Gulf War Illness (GWI) was strongly associated with compromised intestinal epithelial cell integrity, increased circulatory IL6 and neuroinflammation. The current study further investigates the mechanism of DNA bacteriophage-IL6 axis in neuroinflammation. Advancing the previous findings, we show that viral dysbiosis positively correlated with high mobility group box protein 1 (HMGB1; a damage-associated molecular pattern) expression and release in circulation following GWI induction in mice. The circulatory HMGB1 activated brain Astrocytes via altering brain endothelial tight junction proteins and crossing the blood-brain barrier. Interestingly, both in GWI mice and mouse primary Astrocytes cell culture showed an increased brain IL6 mRNA and subsequent protein expression. However, GWI mice treated with Ribavirin (used for partial gut viral sterility) showed decreased intestinal HMGB1 and brain IL6 expression. Mechanistically, HMGB1 activated innate immune response via IRAKs-IKKα-NFkB instead of either RAGE-MAPK or PI3K-mTOR pathway. Surprisingly, inhibition of RAGE or PI3K pathway in HMGB1 primed mouse Astrocyte cells showed a significant increase in IL6 expression and release suggesting NFkB activation as a preferential pathway in GWI-Astrocyte-induced IL6 release. In summary, GWI-associated gut viral dysbiosis associated intestinal HMGB1 release activates brain Astrocytes and IL6 release via toll-like receptor 4-NFkB dependent pathway, thus causing neuroinflammation in GWI. The above mechanism can form a basis for studying inflammation-associated neurocognitive abnormalities in GWI.