Inhibition of IL‐17 Alleviates Blood–Brain Barrier Disruption Following Diffuse Axonal Injury Accompanied by Hyperglycemia Through the NF‐κB Pathway

OBJECTIVE: To clarify the effects and mechanism of interleukin-17A (IL-17) in hyperglycemia (HG)-induced blood-brain barrier (BBB) breakdown following diffuse axonal injury (DAI). METHODS: Differentially expressed proteins (DEPs) were identified by proteomic analysis via 4D-SmartDIA between control and high-glucose groups of BBB model established by bEnd.3 cells in vitro. A rat model of DAI was built using an instantaneous rotational damage device, and HG was mimicked by intraperitoneal (i.p.) injection of 50% glucose. The localization and expression of the IL-17 receptor (IL-17R) were tested by double-label immunofluorescence and western blotting. IL-17 levels in brain tissue and serum, as well as the concentrations of inflammatory factors, were examined. Axonal injury morphology was evaluated via transmission electron microscopy (TEM) and immunohistochemical detection of β-amyloid precursor protein (β-APP) and neurofilament light chain and heavy chain (NF-L, NF-H). Glial response and apoptosis were also assessed. The detection of BBB permeability was via levels of Evans blue (EB) leakage and tight junction protein. The IL-17 pathway was inhibited using suberoylanilide hydroxamic acid (SAHA), and western blotting was used to detect the phosphorylation (p-p65/t-p65 ratio) of the nuclear factor-κB (NF-κB) pathway. Oxidative stress levels were assessed via colorimetric assays. RESULTS: Proteomic analysis revealed 444 upregulated and 159 downregulated proteins in high-glucose-stimulated bEnd.3 cells compared with those in normal cells, with the IL-17 signaling being one of the most significantly enriched pathways according to the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. IL-17 and IL-17R expression was elevated in brain tissue and serum following DAI, and HG further enhanced this upregulation; IL-17R was predominantly localized to vascular endothelial cells. HG aggravated axonal injury, increased cortical apoptosis and glial response, promoted BBB disruption, elevated proinflammatory factor levels, and increased oxidative stress after DAI. The inhibition of IL-17 reversed all the damage and protected BBB integrity by maintaining tight junctions and reducing the levels of proinflammatory factors and oxidative stress in vivo. Mechanistically, HG increased NF-κB p65 phosphorylation after DAI, whereas SAHA treatment significantly suppressed this phosphorylation. CONCLUSION: IL-17 mediates HG-induced axonal injury following DAI by destroying BBB integrity via NF-κB-dependent inflammation and oxidative stress, signifying IL-17 as a target for mitigating neurovascular damage in hyperglycemic DAI.