Adenosine triggers early astrocyte reactivity that provokes microglial reaction and drives the pathogenesis of sepsis-associated encephalopathy

Molecular pathways mediating systemic inflammation entering the brain parenchyma to induce sepsis-associated encephalopathy (SAE) remain elusive. Here, we report that in mice during the first 6 hours of peripheral lipopolysaccharide (LPS)-evoked systemic inflammation (6 hpi), the plasma level of adenosine quickly increased and enhanced the tone of central extracellular adenosine which then provoked neuroinflammation by triggering early astrocyte reactivity. Specific ablation of astrocytic A1 adenosine receptors (A1ARs) prevented this early reactivity and reduced the levels of inflammatory factors (e.g., CCL2, CCL5, and CXCL1) in astrocytes, thereby alleviating microglial reaction, ameliorating blood-brain barrier disruption, peripheral immune cell infiltration, neuronal dysfunction, and depression-like behaviour in the mice. Chemogenetic stimulation of Gi signaling in A1AR-deficent astrocytes at 2 and 4 hpi of LPS injection could restore neuroinflammation and depression-like behaviour, highlighting astrocytes rather than microglia as early drivers of neuroinflammation. Our results identify early astrocyte reactivity towards peripheral and central levels of adenosine as a novel pathway driving SAE and highlight the potential of targeting A1ARs for therapeutic intervention. To determine the contribution of astrocyte-specific A1ARs to LPS-induced neuroinflammation, we cross-bred GLAST-CreERT2 mice with temporal control of astrocyte-specific gene recombination to floxed A1AR mice, thereby generating inducible astrocytic A1AR cKO mice. In addition, we crossbred RiboTag mice enabling specific and direct purification of mRNAs from Cre-expressing cells in cerebral cortices to avoid pitfalls inherent to cell-sorting procedures. mRNA from astrocyte was purified at 0, 6, 24 hpi by Ribotag strategy and sent to sequencing.