Yuan‑zhi‑san inhibits tau protein aggregation in an Aβ1‑40‑induced Alzheimer's disease rat model via the ubiquitin‑proteasome system

Abstract

Yuan‑zhi‑san (YZS) is a classic type of Traditional Chinese Medicine, which has been reported to aid in the treatment of Alzheimer's disease (AD). The present study aimed to investigate the effects of YZS on tau protein aggregation, a hallmark of AD pathology, and its possible mechanisms. The results demonstrated that YZS improved learning and memory abilities, and decreased the severity of AD pathology in β‑amyloid (Aβ_1‑40)‑induced AD rats. Moreover, YZS administration inhibited the hyperphosphorylation of tau protein at Ser199 and Thr231 sites. Several vital enzymes in the ubiquitin‑proteasome system (UPS), including ubiquitin‑activating enzyme E1a/b, ubiquitin‑conjugating enzyme E2a, carboxyl terminus of Hsc70‑interacting protein, ubiquitin C‑236 terminal hydrolase L1 and 26S proteasome, were all significantly downregulated in AD rats, which indicated an impaired enzymatic cascade in the UPS. In addition, it was identified that YZS treatment partly increased the expression levels of these enzymes in the brains of AD rats. In conclusion, the present results suggested that YZS could effectively suppress the hyperphosphorylation of tau proteins, which may be partially associated with its beneficial role in restoring functionality of the UPS.

Keywords: Alzheimer's disease; Yuan‑zhi‑san; tau protein; ubiquitin‑proteasome system.

Figure 1.

Effects of YZS on the spatial learning and memory abilities of Alzheimer's disease model rats in the Morris water maze test. (A) Representative tracks of the probe trials of rats in different groups. (B) Time of escape latency. (C) Times crossing the target platform. (D) Time in the target quadrant. (E) Exercise distance in the target quadrant. Data are presented as the mean ± SD (n=10). ^##P<0.01 vs. Sham group; *P<0.05, **P<0.01 vs. Model group. YZS, Yuan-zhi-san.

Figure 2.

Effects of YZS on the morphology and number of neurons in Alzheimer's disease model rats. (A) Representative images of hippocampal neurons from the CA1 region using hematoxylin and eosin (H&E) staining (magnification, ×400). (B) Representative images indicating the ultrastructure of nerve cells using transmission electron microscopy (magnification, ×2,500 and ×6,000). Orange arrows indicate nuclear membrane; blue arrows indicate endoplasmic reticulum; green arrows indicate mitochondrion. YZS, Yuan-zhi-san.

Figure 3.

Effects of YZS on the density of dendritic spines in Alzheimer's disease model rats. (A) Representative images of dendritic spines in the brain tissues using Golgi-Cox staining (magnification, ×600). (B) Analysis of density of dendritic spines in each group. Data are presented as the mean ± SD (rats n=6). ^##P<0.01 vs. Sham group; *P<0.05, **P<0.01 vs. Model group. YZS, Yuan-zhi-san.

Figure 4.

Effects of YZS on the expression levels of Tau5, p-S199, p-S396 and p-T231 in Alzheimer's disease model rats. (A) Representative immunohistochemistry images demonstrating the expression levels of Tau5, p-S199, p-S396 and p-T231 in the CA1 region from each group (magnification, ×400). Analysis of (B) Tau5, (C) p-S199, (D) p-S396 and (E) p-T231 protein expression levels in each group. Data are presented as the mean ± SD (n=10). ^##P<0.01 vs. Sham group; *P<0.05, **P<0.01 vs. Model group. p-S199, phosphorylated-Tau (Ser199); p-S396, phosphorylated-Tau (Ser396); p-T231, phosphorylated-Tau (Thr231); YZS, Yuan-zhi-san.

Figure 5.

Effects of YZS on the protein expression levels of UbE1a/b, UbE2a, CHIP, UCH-L1 and 26S proteasome in Alzheimer's disease model rats. (A) Representative western blotting images of UbE1a/b, UbE2a, CHIP, UCH-L1 and 26S proteasome in each group. Semi-quantification of (B) UbE1a/b, (C) UbE2a, (D) CHIP, (E) UCH-L1 and (F) 26S proteasome expression levels in each group. Data are presented as the mean ± SD (rats n=3). ^#P<0.05, ^##P<0.01 vs. Sham group; **P<0.01 vs. Model group. UbE1a/b, ubiquitin-activating enzyme E1a/b; UbE2a, ubiquitin-conjugating enzyme E2a; CHIP, carboxyl terminus of Hsc70-interacting protein; UCH-L1, ubiquitin C-236 terminal hydrolase L1; YZS, Yuan-zhi-san.