Effects of CREB and miR-132-3p on aluminum-induced abnormal phosphorylation of tau protein in rat hippocampus

Background Cyclic AMP response element binding protein (CREB) and miR-132-3p have been proved to be related to many neurodegenerative diseases. Our research group previously has demostrated that the neurotoxicity of aluminum is relevant to abnormal phosphorylation of tau protein, but whether aluminum affects the abnormal phosphorylation of tau protein through GREB and miR-132-3p has not been reported yet .

Objective To investigate the effect of aluminum on CREB and miR-132-3p during abnormal phosphorylation of tau protein in rat hippocampus.

Methods Twenty-eight two-month-old SD rats with comparable weigh, were randomly assigned to four groups: control group (saline) and low, middle, and high dose exposure groups 10, 20, and 40 μmol·kg⁻¹ Al(mal)₃ with each group containing 7 rats, and the exposure period was 3 months by intraperitoneal injection every other day. After rats’ exposure to aluminum, Morris water maze was employed to assess their capabilities of learning and memory. The miR-132-3p gene expression level was detected by quantitative real-time PCR (qRT-PCR). The levels of CREB, phosphorylated CREB (p-CREB) (Ser133), RAS p21 protein activator 1 (RASA1) tau, and p-tau (Ser396) proteins were determined by Western blot.

Results The results of Morris water maze showed that in the navigation experiment (from first day to the fifth day), the average escape latency of the rats exposed to three doses of aluminum was longer than that of the control rats (P<0.05). The middle dose group and the high dose group demonstrated shorter duration and lower frequency of platform traversal in the designated quadrant when compared to the control group and the low dose group (P<0.05). Moreover, the duration in the target quadrant of the rats exposed to high dose aluminum was shorter than that of the rats exposed to medium dose aluminum (P<0.05). The results of Morris water maze suggested that aluminum could damage the learning and memory ability of rats. The qRT-PCR findings indicated a decline in miR-132-3p gene expression in rat hippocampus correlating with higher Al(mal)₃ dose (P<0.05). The Western blot test showed that the protein expressions of CREB and p-CREB (Ser133) were reduced in both the middle dose group and the high dose group (P<0.05) when compared to the control group and the low dose group, and likewise, compared to the control group, the group receiving low dose exhibited lower level of p-CREB (Ser133) protein expression (P<0.05). It was found that the further increase of aluminum exposure dose would lead to the further decrease of CREB and p-CREB (Ser133) protein expression levels (F=36.429, P<0.001; F=78.672, P<0.001), aluminum exposure dose was negatively correlated with the expression levels of the two proteins (r=−0.848, P<0.001; r=−0.928, P<0.001). The expression levels of RASA1 protein and tau protein in the aluminum exposure groups surpassed those in the control group (P<0.05). The tau protein phosphorylation level was higher in the middle dose group than in the control group (P<0.05), while the high dose group showed elevated phosphorylation level relative to the control group, the low dose group, and the middle dose group (P<0.05).

Conclusion Aluminum may promote abnormal phosphorylation of tau protein by affecting CREB and miR-132-3p, which eventually leads to the impairment of learning and memory ability.