Impact of hyperoside on the blood-brain barrier in rats with bacterial meningitis through the microRNA-155/BDNF pathway

Objective: This study aims to elucidate the effect and mechanism of hyperoside on blood-brain barrier (BBB) damage in bacterial meningitis (BM) by regulating the microRNA-155 (miR-155)/brain-derived neurotrophic factor (BDNF) pathway. Methods: A rat model of meningitis was established via intracisternal injection of Streptococcus pneumoniae (SPN), while an in vitro BBB injury model was created by treating human cerebral microvascular endothelial cells (hCMEC/D3) with lipopolysaccharide (LPS). Hyperoside was administered in both models. Evans blue staining assessed BBB permeability in rats. Brain water content was determined using the wet-dry weight method. Transendothelial electrical resistance (TEER) was measured with an endothelial resistance meter. RT-qPCR, Western blot (WB), and ELISA assessed the expression of tight junction proteins in brain tissues and cell supernatants. ELISA was also used to measure inflammatory cytokine in cerebrospinal fluid and cell culture supernatants. Bioinformatics analysis and dual-luciferase reporter assays validated the regulatory relationship between miR-155 and BDNF. Results: Hyperoside treatment reduced BBB permeability, alleviated brain edema, and suppressed inflammatory cytokine expression in SPN-infected rats. In LPS-induced hCMEC/D3 cells, hyperoside significantly increased TEER values. Hyperoside markedly downregulated miR-155 and upregulated BDNF expression. miR-155 directly targeted BDNF and negatively regulated its expression in hCMEC/D3 cells. Importantly, the administration of a miR-155 mimic or BDNF knockdown (sh-BDNF) partially reversed the protective effects of hyperoside on TEER, tight junction protein expression (ZO-1, claudin-5, AQP4), and inflammatory cytokine levels (TNF-α, IL-1β, IL-6) in LPS-induced hCMEC/D3 cells. Conclusion: Hyperoside mitigates BBB damage in BM via reducing miR-155 expression and upregulating BDNF expression, leading to an increase in tight junction-related protein expression, a reduction in inflammatory factor secretion, and a decrease in BBB permeability.