Prenatal diesel exhaust exposure alters hippocampal synaptic plasticity in offspring

Abstract

Diesel exhaust particles (DEPs) are major air pollutants emitted from automobile engines. Prenatal exposure to DEPs has been linked to neurodevelopmental and neurodegenerative diseases associated with aging. However, the specific mechanism by DEPs impair the hippocampal synaptic plasticity in the offspring remains unclear. Pregnant C57BL/6 mice were administered DEPs solution via the tail vein every other day for a total of 10 injections, then the male offsprings were studied to assess learning and memory by the Morris water maze. Additionally, protein expression in the hippocampus, including CPEB3, NMDAR (NR1, NR2A, NR2B), PKA, SYP, PSD95, and p-CREB was analyzed using Western blotting and immunohistochemistry. The alterations in the histomorphology of the hippocampus were observed in male offspring on postnatal day 7 following prenatal exposure to DEPs. Furthermore, 8-week-old male offspring exposed to DEPs during prenatal development exhibited impairments in the Morris water maze test, indicating deficits in learning and memory. Mechanistically, the findings from our study indicate that exposure to DEPs during pregnancy may alter the expression of CPEB3, SYP, PSD95, NMDAR (NR1, NR2A, and NR2B), PKA, and p-CREB in the hippocampus of both immature and mature male offspring. The results offer evidence for the role of the NMDAR/PKA/CREB and CPEB3 signaling pathway in mediating the learning and memory toxicity of DEPs in male offspring mice. The alterations in signaling pathways may contribute to the observed damage to synaptic structure and transmission function plasticity caused by DEPs. The findings hold potential for informing future safety assessments of DEPs.

Keywords: CPEB3; NMDA receptor; diesel exhaust particles; hippocampus; neurotoxicity.

Figure 1

Body weight and organ weight of male offspring after prenatal DEPs exposure. (A) The body weight of male offspring. (B) The body weight, brain weight and relative brain of 7 days male offspring. (C) The body weight, brain weight, relative brain, hippocampal weight and relative hippocampal of 56 days male offspring. The values shown are the mean ± SD. Compared to control; * p < 0.05, ** p < 0.01. N0,7day (Con: Control group; LD: low dose group; MD: medium dose group) =22, N0, 7 day (HD:High dose group)=12, N14-56day (each group)=12.

Figure 2

Histopathological changes in the hippocampus tissues of male offspring mice following pregnancy exposure to DEPs through hematoxylin and eosin (H&E) staining. 100 or 200 × magnification. (A) Control group. The morphology of hippocampus tissues was normal. (B–D) DEPs (0.235, 0.47 and 0.94 μg/mouse) treatment groups. Scale bar: 100 μm. N=4.

Figure 3

Performance of the different groups of mice in the Morris water maze test. (A) The time required to locate the hidden platform in the water maze during the learning stage. (B) The time elapsed in the correct quarter of the water maze during the probe trial. (C) Number of platform crossings in the four quadrants of the Morris maze during the probe trial. (D) Representative spatial and nonspatial probe trial tracings of four subjects. In the spatial version, the placement of the quadrant remained constant over trials. Con: Control group; LD: low dose group; MD: medium dose group; HD: high dose group. The values shown are the mean ± SD (n_{each group}=12), Compared to control; ** p < 0.01.

Figure 4

Protein expression of NMDA/PKA/CREB and CPEB3 signaling pathway-associated genes in hippocampus samples of 7 days male offspring mice. (A) Western blot analysis of p-CREB, CREB, PKA, N2A, N2B and NR1 protein in hippocampus. (B) Western blot analysis of CPEB3, NEUN, PSD-95 and SYN protein in hippocampus. (C) Immunohistochemical analysis of NR1, N2B and N2A protein in hippocampus. (a–c) Control group (CON). (d–f) DEPs treatment groups (DEPs, the MD group). (D) Immunohistochemical analysis of SYN, PSD-95 and NEUN protein in hippocampus. (a–c) Control group (CON). (d–f) DEPs treatment groups (DEPs, the MD group). The values shown are the mean ± SD (NAB=6, NCD=4), Compared to control; ** p < 0.01.

Figure 5

Protein expression of NMDA/PKA/CREB and CPEB3 signaling pathway-associated genes in hippocampus samples of 56 days male offspring mice. (A) Western blot analysis of p-CREB, CREB, PKA, N2A, N2B and NR1 protein in hippocampus. (B) Western blot analysis of CPEB3, NEUN, PSD-95 and SYN protein in hippocampus. (C) Immunohistochemical analysis of NR1, N2B and N2A protein in hippocampus. (a–c) Control group (CON). (d–f) DEPs treatment groups (DEPs, the MD group). (D) Immunohistochemical analysis of SYN, PSD-95 and NEUN protein in hippocampus. (a–c) Control group (CON). (d–f) DEPs treatment groups (DEPs, the MD group). The values shown are the mean ± SD of (N_AB=9, N_CD=3). Compared to control; * p < 0.05, ** p < 0.01.