Geniposidic acid ameliorates spatial learning and memory deficits and alleviates neuroinflammation via inhibiting HMGB-1 and downregulating TLR4/2 signaling pathway in APP/PS1 mice

Geniposidic acid (GPA) is an extract from Eucommia ulmoides Oliv. Bark (Eucommiaceae). Accumulating evidences have reported GPA has anti-aging, anti-oxidative stress, anti-inflammatory and neurotrophic effects on neurons. However, whether GPA could alleviate memory deficits in Alzheimer's disease animal models is not clear. We aimed to investigate the effect of GPA treatment on cognitive performance, Aβ deposition and glial cells activation in the transgenic mouse model of AD. 6-7 months APP/PS1 mice were given GPA for 90 days; behavioral experiments were executed to estimate the memory and spatial learning abilities of mice, and the mechanism of neuroprotective effect of GPA was investigated with a focus on amyloid-β deposition, astrocytes and microglia activation and neuroinflammation. GPA treatment significantly improved the spatial learning and memory abilities and also decreased cerebral amyloid-β deposition in APP/PS1 mice. Via HE staining, we found that GPA could ameliorate histopathological changes in cerebrum. We also found that GPA treatment inhibited the activation of astrocytes and microglia, down-regulated the expression of pro-inflammatory cytokines and iNOS, and up-regulated the expression of anti-inflammatory cytokines and Arg-1. In addition, GPA down-regulated the gene expression of HMGB-1 receptors (TLR2, TLR4 and RAGE) then mediated MyD88, TRAF6 and phospho-ERK1/2, subsequently modulated the expression of key AP-1 and NF-κB family members (c-Fos, c-Jun and p65). The reversal of the pro-inflammatory state suggested GPA can serves as a multi-target candidate by alleviating Aβ deposition and neuroinflammation for the auxiliary therapy of Alzheimer's disease.