Genetic differences in hippocampus of mice susceptible to sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis, which can lead to long-term cognitive impairment and anxiety in patients, and may even contribute to mortality in septic individuals. There is substantial individual variability in the incidence and severity and susceptibility of SAE, but the mechanisms regulating susceptibility remain unclear. Previous studies have shown that hippocampal damage is directly associated with cognitive and emotional disturbances in SAE. This study aims to explore the impact of hippocampal differentially expressed genes on SAE susceptibility in a mouse model.

Male specific pathogen-free (SPF)-grade C57BL/6 mice (6-8 weeks old) were randomly divided into a saline control group (Con group) and an SAE model group. SAE was induced by intraperitoneal injection of 10 mg/kg lipopolysaccharide (LPS), while control mice received an equivalent volume of saline. Cognitive and anxiety-like behaviors were assessed using the open field test (OFT), novel object recognition (NOR), and Y-maze test. Based on mean±standard deviation of behavioral results from the Con group, SAE mice were further classified into high-sensitivity (HS) and low-sensitivity (LS) subgroups. Immunohistochemistry was performed to detect the expression of immediate early gene c-Fos and neuronal marker neuronal nuclei (NeuN). Nissl staining was used to assess neuronal injury in the dentate gyrus (DG), cornu ammonis 1 (CA1), and cornu ammonis 3 (CA3) regions of the hippocampus. RNA sequencing (RNA-seq) was conducted on hippocampal tissues from HS and LS mice to identify differentially expressed genes, followed by pathway enrichment analysis.

No significant behavioral susceptibility differences were observed between the overall SAE group and controls. However, HS mice showed severer cognitive deficits and anxiety-like behavior compared to LS mice. Immunohistochemistry revealed significantly higher expression of c-Fos in the hippocampus of LS mice (P<0.05), while Nissl and NeuN staining revealed milder neuronal damage in the hippocampus of LS mice than that of HS mice (both P<0.05). RNA-seq analysis identified 130 upregulated and 142 downregulated DEGs in LS and HS mice, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that upregulated genes in LS mice were primarily involved in pluripotency regulation, cyclic adenosine monophosphate (cAMP) signaling, and Wnt signaling pathways, in contrast, the downregulated genes were mainly related to cell adhesion, neuroactive ligand-receptor interaction, and calcium signaling pathways.

Differential gene expression in the hippocampus may contribute to individual susceptibility to cognitive and emotional dysfunction in SAE, suggesting potential genetic targets for individualized intervention.