The effect of Scutellaria baicalensis stem-leaf flavonoids on spatial learning and memory in chronic cerebral ischemia-induced vascular dementia of rats

Abstract

Flavonoids have been shown to improve cognitive function and delay the dementia progression. However, the underlying mechanisms remain elusive. In the present study, we examined the effect of Scutellaria baicalensis stem-leaf total flavonoids (SSTFs) extracted from S. baicalensis Georgi on spatial learning and memory in a vascular dementia (VaD) rat model and explored its molecular mechanisms. The VaD rats were developed by permanent bilateral occlusion of the common carotid artery. Seven days after recovery, the VaD rats were treated with either 50 or 100 mg/kg of SSTF for 60 days. The spatial learning and memory was evaluated in the Morris water maze (MWM) test. The tau hyperphosphorylation and the levels of the related protein kinases or phosphatases were examined by western blot analysis. In VaD rats, SSTF treatment at 100 mg/kg significantly reduced the escape latency in training trial in MWM test. In the probe trial, SSTF treatment increased the searching time and travel distance in the target quadrant. SSTF treatment inhibited the tau phosphorylation in both cortex and hippocampus in VaD rats. Meanwhile, SSTF reduced the activity of glycogen synthase kinase 3β and cyclin-dependent kinase 5 in VaD rats. In contrast, SSTF treatment increased the level of the protein phosphatase 2A subunit B in VaD rats. SSTF treatment significantly improved the spatial cognition in VaD rats. Our results suggest that SSTF may alleviate tau-hyperphosphorylation-induced neurotoxicity through coordinating the activity of kinases and phosphatase after a stroke. SSTF may be developed into promising novel therapeutics for VaD.

Keywords: deficits of spatial learning and memory; flavonoid; hyperphosphorylated tau; vascular dementia.

Figure 1.

SSTF did not decrease infarct area in the CCI rats Graph shows the quantification of infarct volume after 60 days of SSTF treatment. Data are shown as the mean ± SEM (n = 5). *P < 0.05, **P < 0.01, ***P < 0.001, and ns: not significant. Sham, the sham group; Control, the CCI control group; SSTF-50, the group treated with 50 mg/kg of SSTF; and SSTF-100, the group treated with 100 mg/kg of SSTF.

Figure 2.

SSTF treatment improved spatial learning and memory in VaD rats in MWM test Sixty days of SSTF (100 mg/kg) treatment reduced daily escape latency (A) in training trials from Day 3 (P < 0.05, performance of the sham group on Day 2 in comparison with that on Day 1; ^#P < 0.05, differences to the performance on Day 1 of the training trails within the same group; *P < 0.01, performance differences among the groups in each day). In probe trail, SSTF (100 mg/kg) treatment significantly increased the searching time (B) and travel distance (C) in the target quadrant. Data are shown as the mean ± SEM (n = 9). *P < 0.05 and **P < 0.01.

Figure 3.

SSTF treatment reduced tau phosphorylation in the VaD rat brain Representative immunoblots for the expression of tau and phosphorylated tau in the cortex (A) and hippocampus (B). Sixty days of SSTF (100 mg/kg) treatment did not alter the total tau (C), but significantly reduced levels of phosphorylated tau at sites Ser199 (D), Ser202 (E), Thr205 (F), Ser396 (G), and Ser404 (H) in the cortex and hippocampus. The total tau or phosphorylated tau was normalized to either GAPDH or total tau, respectively. The relative levels of total tau or phosphorylated tau of sham group were set at 100%. Data are shown as the mean ± SEM (n = 9). *P < 0.05 and **P < 0.01.

Figure 4.

SSTF increased GSK3β phosphorylation at Serine 9 Representative immunoblots of GSK3β and p-GSK3β in the rat cortex (A) and hippocampus (B). SSTF treatment (100 mg/kg) did not alter the GSK3β expression in the cortex (C) and the hippocampus (D), but significantly altered the GSK3β phosphorylation at Serine 9 in the cortex (E) and hippocampus (F). The expression of the total GSK3β or p-GSK3β was normalized to GAPDH or total GSK3β, respectively. The relative amount of GSK3β of the sham group was set as 100%. Data are shown as the mean ± SEM (n = 9). **P < 0.01.

Figure 5.

SSTF reduced the expression levels of p35 and p25 Representative immunoblots showing the expression of Cdk5, p35 (Cdk5 activator), and p25 (p35 cleavage product) in the cortex (A) and the hippocampus (B). SSTF treatment (100 mg/kg) did not alter the expression of Cdk5 (C and D), but significantly reduced p35 and p25 in the VaD rat cortex (E and G) and hippocampus (F and H). The expression levels of Cdk5, p35, and p25 were normalized to GAPDH. The relative value of sham group was set as 100%. Data are shown as the mean ± SEM (n = 9). *P < 0.05 and **P < 0.01.

Figure 6.

SSTF increased PP2A expression Representative immunoblots for the expression of PP2A subunit B (sub B) in the rat cortex (A) and hippocampus (B). Treatment with 100 mg/kg SSTF significantly increased PP2A-sub B expression in the VaD rat cortex (C) and hippocampus (D). The expression of PP2A-sub B was normalized to GAPDH. The relative levels of sham group were set as 100%. Data are shown as the mean ± SEM (n = 9). **P < 0.01.