GJ-4 alleviates Aβ_25-35-induced memory dysfunction in mice through protecting the neurovascular unit

Alzheimer's disease (AD) is the most common neurodegenerative disease. AD has become an important social health problem but there are few therapeutic drugs. Many researchers devote to the development of drugs for the treatment of AD. GJ-4 is crocin enrichments from Gardenia jasminoides J. Ellis, and our previous studies have shown GJ-4 had potent neuroprotective effects on several AD animal models. However, the underlying mechanisms have not been fully elucidated. The aim of the present study was to explore the mechanism of GJ-4 on a Aβ_25-35-intoxicated mouse model. The results demonstrated that GJ-4 treatment significantly improved spatial learning and memory abilities of the AD mice challenged by Aβ_25-35. Mechanistic study indicated that GJ-4 could alleviate endothelial dysfunction, as GJ-4 markedly reduced endothelial cell edema, as well as improved tight junction structures by up-regulating Zonula occludens-1 (ZO-1), Claudin-5 and Occludin expressions. Moreover, GJ-4 markedly reduced receptor for advanced glycation end products (RAGE) expression and increased low-density lipoprotein receptor-related protein-1 (LRP-1) expression, suggesting endothelial transduction and clearance of toxic species capabilities improved by GJ-4 treatment. The results also indicated that GJ-4 significantly decreased IL-6 and IL-1β mRNA expressions, as well as intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) expressions, implying the inhibition of glial activation and vascular inflammation by GJ-4 treatment. Furthermore, GJ-4 treatment inhibited glial activation mediated neuroinflammation through inhibiting high-mobility group box protein 1(HMGB-1)/RAGE/NF-κB signaling pathway, which might confer to the neuroprotection. In conclusion, our present study proved GJ-4 could protect the neurovascular unit (NVU), through attenuating endothelial cell damage, enhancing tight junction function, inhibiting of glial activation and protecting of neurons. This study provided evidence that the beneficial effects of GJ-4 on AD might be owing to its protection on NVU.