Effect of benzoapyrene exposure during pregnancy on learning and memory functions of rat offspring and expression levels of related genes

Background Polycyclic aromatic hydrocarbons represented by benzoapyrene are among the most significant occupational and environmental pollutants. Exposure to benzoapyrene during pregnancy can cause delayed intellectual development in offspring, and the mechanism may be related to the expression of protocadherin (Pcdh), a key molecule for learning and memory.

Objective To explore the possible role of Pcdh in impaired learning and memory function of pups caused by benzoapyrene exposure during pregnancy by establishing an animal model of cognitive impairment in pups caused by benzoapyrene exposure during pregnancy, and detecting the expression of Pcdh and its transcription-related factors in the hippocampal tissues of pups at different developmental stages.

Methods Sixty female and male SPF-grade rats were caged in a 1:1 ratio overnight, and the successfully mated female mice were randomly divided into blank control, 0 mg·kg⁻¹, 10 mg·kg⁻¹, 20 mg·kg⁻¹, and 40 mg·kg⁻¹ groups, with 6 mice in each group. They were intraperitoneally injected with benzoapyrene from the 17th to the 19th day of pregnancy to establish an exposure model. Learning and memory functions of the offspring were tested through Morris water maze on the 45th day after the birth (PND) of the pups. On the PND45 and PND75 of the pups, hippocampal tissues of 6 pups (per group) were collected respectively. The expression levels of PcdhαC1 and wings apart-like homolog (WAPL) genes and proteins were detected by fluorescence quantitative polymerase chain reaction (PCR) and Western blotting.

Results The results of Morris water maze showed that there was no interaction between the escape latency time of the pups and the dose groups of 0 mg·kg⁻¹, 10 mg·kg⁻¹, 20 mg·kg⁻¹, and 40 mg·kg⁻¹ (F _{time × group}=0.515, P>0.05). The escape latency of pups decreased with increase of training time (F _time=24.678, P<0.001, F _group=12.803, P<0.001). The PCR results showed that at PND45, compared with the blank group, the relative expression levels of PcdhαC1 mRNA in the 10 mg·kg⁻¹, 20 mg·kg⁻¹, and 40 mg·kg⁻¹ groups decreased (P<0.05), and the relative expression levels of WAPL mRNA increased (P<0.05). At PND75, compared with the blank group, the relative expression levels of PcdhαC1 mRNA in the 20 mg·kg⁻¹ and 40 mg·kg⁻¹ groups decreased (P<0.05), and the relative expression levels of WAPL mRNA increased (P<0.05). The Western blotting results showed that at PND45, compared with the blank group, the expression levels of PcdhαC1 protein in the 10 mg·kg⁻¹, 20 mg·kg⁻¹, and 40 mg·kg⁻¹ groups decreased (P<0.05), and the expression levels of WAPL protein increased (P<0.05). At PND75, compared with the blank group, the expression levels of PcdhαC1 protein in the 10 mg·kg⁻¹, 20 mg·kg⁻¹, and 40 mg·kg⁻¹ groups decreased (P<0.05), and the expression levels of WAPL protein increased (P<0.05).

Conclusion Exposure to benzoapyrene during pregnancy can cause impairment in the learning and memory abilities of PND45 offspring and may alter the expression of PcdhαC1 and WAPL genes and proteins.