Modulation of synaptic damage by Bushen Tiansui Decoction via the PI3K signaling pathway in an Alzheimer’s disease model

Abstract

Objective

To explore the therapeutic effect and mechanism of Bushen Tiansui Decoction (补肾填髓方, BSTSD) and its active component icariin on Alzheimer’s disease (AD).

Methods

(i) Animal experiments. This study conducted experiments using specific pathogen-free (SPF) grade male C57BL/6J wild-type (WT) mice and APP/PS1 double transgenic mice. The animals were divided into three groups: WT group (WT mice, n = 5, receiving distilled water daily), APP/PS1 group (APP/PS1 double transgenic mice, n = 5, receiving distilled water daily), and BSTSD group [APP/PS1 double transgenic mice, n = 5, treated with BSTSD suspension at a dosage of 27 g/(kg·d) for 90 d]. Cognitive function was assessed using the Morris water maze (MWM). Post-experiment, hippocampal tissues were collected for analysis of pyramidal cell and synaptic morphology through hematoxylin-eosin (HE) staining and transmission electron microscopy (TEM). (ii) Cell experiments. The HT-22 cells were divided into control group (untreated), Aβ_25-35 group (treated with 20 μmol/L Aβ_25-35 for 24 h), icariin group (pre-treated with 20 μmol/L icariin for 60 min, followed by 20 μmol/L Aβ_25-35 for an additional 24 h), and icariin + LY294002 group [treated with 20 μmol/L icariin and 20 μmol/L LY294002 (an inhibitor of the phosphoinostitide 3-kinases (PI3K) signaling pathway) for 60 min, then exposed to 20 μmol/L Aβ_25-35 for 24 h], and cell viability was measured. Western blot was used to detect the expression levels of synapse-associated proteins [synaptophysin (SYP) and postsynaptic density-95 (PSD-95)] and PI3K signaling pathway associated proteins [phosphorylated (p)-PI3K/PI3K, p-protein kinase B (Akt)/Akt, and p-mechanistic target of rapamycin (mTOR)/mTOR].

Results

(i) Animal experiments. Compared with APP/PS1 group, BSTSD group showed that escape latency was significantly shortened (P < 0.01) and the frequency of crossing the original platform was significantly increased (P < 0.01). Morphological observation showed that pyramidal cells in the hippocampal CA1 region were arranged more regularly, nuclear staining was uniform, and vacuole-like changes were reduced after BSTSD treatment. TEM showed that the length of synaptic active zone in BSTSD treatment group was increased compared with APP/PS1 group (P < 0.01), and the width of synaptic gap was decreased (P < 0.01). (ii) Cell experiments. Icariin had no obvious toxicity to HT-22 cells when the concentration was not more than 20 μmol/L (P > 0.05), and alleviated the cell viability decline induced by Aβ_25-35 (P < 0.01). Western blot results showed that compared with Aβ_25-35 group, the ratios of p-PI3K/PI3K, p-Akt/Akt and p-mTOR/mTOR in icariin group were significantly increased (P < 0.01), while the protein expression levels of SYP and PSD-95 were increased (P < 0.01). These effects were blocked by LY294002 (P < 0.01).

Conclusion

BSTSD and icariin enhance cognitive function and synaptic integrity in AD models and provide potential therapeutic strategies through activation of the PI3K/Akt/mTOR pathway.