Tau hyperphosphorylation is associated with spatial learning and memory after exposure to benzo[a]pyrene in SD rats

As a representative substance of the polycyclic aromatic hydrocarbons, benzo[a]pyrene (B[a]P) is a widely distributed environmental contaminant. Several studies have indicated that B[a]P exposure could impair learning and memory function in human population and animal models. Abnormal hyperphosphorylation and aggregation of microtubule-associated protein tau play a crucial role in neurodegenerative diseases manifesting deficits of learning and memory. In the present study, we investigated the involvement of tau hyperphosphorylation in memory impairment after espousing to B[a]P in SD rats. Male SD rats were randomly divided into five groups: the blank control group received no treatment and the others received intraperitoneal injection of B[a]P (0, 1.0, 2.5, 6.25 mg/kg bw) for 1, 2, and 3 months, respectively. Morris water maze was employed to observe the learning and memory impairment. To find the relationship between cognitive functions and tau protein, we measured the site-specific phosphorylation of tau at Ser199, Ser396, Thr181, and Thr231, which are related with spatial and memory deficits in the brain of rats. The spatial and learning of rats were impaired after exposing to B[a]P for 1 month, so as 2 and 3 months compared to blank control groups, respectively. Rats exposed to 2.5 and 6.25 mg/kg bw B[a]P for either 2 or 3 months had modified behavior compared to control as indicated by the increased latencies, increased the first time arriving at the target space and decreased number crossing the platform and time in target quadrant. B[a]P led to tau hyperphosphorylation at Ser199, Thr181, and Thr231 epitopes. And with time and dose expanded, tau protein, Ser199, Thr181, and Thr231 expression increased. However, the differences in expression of Ser396 at different doses or points were not statistically significant. Moreover, we observed a correlation between memory impairments and tau phosphorylation levels. The present results indicate that Tau hyperphosphorylation is associated with the observed deficits in spatial learning and memory following exposure to B[a]P in SD rats.