Accelerated Deficits of Spatial Learning and Memory Resulting From Prenatal Inflammatory Insult Are Correlated With Abnormal Phosphorylation and Methylation of Histone 3 in CD-1 Mice

Abstract

Gestational infection causes various neurological deficits in offspring, such as age-related spatial learning and memory (SLM) decline. How inflammation causes age-related SLM dysfunction remains unknown. Previous research has indicated that histone modifications, such as phosphorylation of H3S10 (H3S10p) and trimethylation of H3K9 (H3K9me3) may be involved. In our study, pregnant mice received an intraperitoneal injection of lipopolysaccharide (LPS, 50 or 25 μg/kg) or normal saline during gestational days 15-17. After normal parturition, the offspring were randomly separated into 1-, 6-, 12-, 18-, and 22-month-old groups. SLM performance was assessed using a radial six-arm water maze (RAWM). The hippocampal levels of H3S10p and H3K9me3 were detected using an immunohistochemical method. The results indicated that the offspring had significantly impaired SLM, with decreased H3S10p and increased H3K9me3 levels from 12 months onward. Maternal LPS exposure during late gestation significantly and dose-dependently exacerbated the age-related impairment of SLM, with the decrease in H3S10p and increase in H3K9me3 beginning at 12 months in the offspring. The histone modifications (H3S10p and H3K9me3) were significantly correlated with impairment of SLM. Our findings suggest that prenatal exposure to inflammation could exacerbate age-related impairments of SLM and changes in histone modifications in CD-1 mice from 12 months onward, and SLM impairment might be linked to decreased H3S10p and increased H3K9me3.

Keywords: aging; histone; lipopolysaccharide; memory; methylation; phosphorylation.

Figure 1

Radial six-arm water maze (RAWM) performances of control mice in different age groups. Latency (A) and number of errors (B) during the learning phase; and latency (C) and number of errors (D) during the memory phase. All values are means ± SD. *P < 0.05 and **P < 0.01 indicate significant differences compared to the 1-month-old mice; ^#P < 0.05 and ^##P < 0.01 indicate significant differences compared to the 6-month-old mice; ^&P < 0.05 and ^&&P < 0.01 indicate significant differences compared to the 12-month-old mice.

Figure 2

RAWM performances of L-lipopolysaccharide (LPS) mice in different age groups. Latency (A) and number of errors (B) during the learning phase; and latency (C) and number of errors (D) during the memory phase. All values are means ± SD. *P < 0.05 and **P < 0.01 indicate significant differences compared to the 1-month-old mice; ^#P < 0.05 and ^##P < 0.01 indicate significant differences compared to the 6-month-old mice; ^&P < 0.05 and ^&&P < 0.01 indicate significant differences compared to the 12-month-old mice.

Figure 3

RAWM performances of H-LPS mice in different age groups. Latency (A) and number of errors (B) during the learning phase; and latency (C) and number of errors (D) during the memory phase. All values are means ± SD. *P < 0.05 and **P < 0.01 indicate significant differences compared to the 1-month-old mice; ^#P < 0.05 and ^##P < 0.01 indicate significant differences compared to the 6-month-old mice; ^&P < 0.05 and ^&&P < 0.01 indicate significant differences compared to the 12-month-old mice.

Figure 4

Effects of LPS treatment on the performances of 1-month-old mice. Latency (A) and number of errors (B) during the learning phase; and latency (C) and number of errors (D) during the memory phase. There were no significant treatment effects in either phase. All values are means ± SD.

Figure 5

Effects of LPS treatment on the performances of 6-month-old mice. Latency (A) and number of errors (B) during the learning phase; and latency (C) and number of errors (D) during the memory phase. There were no significant treatment effects in either phase. All values are means ± SD.

Figure 6

Effects of LPS treatment on the performances of 12-month-old mice. Learning latency (A) and number of errors (B), and memory latency (C) and number of errors (D). All values are means ± SD. There were significant treatment effects regarding the two memory phase parameters. *P < 0.05 indicates significant treatment effects compared to the same-age controls.

Figure 7

Effects of LPS treatment on the performances of 18-month-old mice. Learning latency (A) and number of errors (B), and memory latency (C) and number of errors (D). All values are means ± SD. There were significant treatment effects on the two learning phase parameters and two memory phase parameters. *P < 0.05 and **P < 0.01 indicate significant treatment effects compared to the same-age controls.

Figure 8

Effects of LPS treatment on the performances of 22-month-old mice. Learning latency (A) and number of errors (B), and memory latency (C) and number of errors (D). All values are means ± SD. There were significant treatment effects on the two learning phase parameters and two memory phase parameters. *P < 0.05 and **P < 0.01 indicate significant treatment effects compared to the same-age controls.

Figure 9

The H3S10p (A–C), H3K9me3 (D–F), and total H3 (G–I) levels in the dorsal hippocampus of 12-month-old CD-1 mice. Low-magnification images of the whole dorsal hippocampus are shown. Scale bar = 400 μm.

Figure 10

Immunoreactivities of H3S10p (A–C), H3K9me3 (D–F), and total H3 (G–I) in the dorsal hippocampus of 18-month-old mice. Low-magnification images of the whole dorsal hippocampus are shown. Scale bar = 400 μm.

Figure 11

Immunoreactivities of H3S10p (A–C), H3K9me3 (D–F), and total H3 (G–I) in the dorsal hippocampus of 22-month-old mice. Low-magnification images of the whole dorsal hippocampus are shown. Scale bar = 400 μm.

Figure 12

Relative levels of H3S10p (A–C), H3K9me3 (D–F), and total H3 (G–I) represented by the average optical density (AOD) of immunoreactivity in the hippocampal dentate gyrus (DG), CA1, and CA3 in different treatment groups. Panels (A,D,G) represent the H-LPS group; (B,E,H) represent the L-LPS group; and (C,F,I) represent the control group. All values are means ± SD. *P < 0.05 and **P < 0.01 indicate significant differences compared to the 1-month-old mice; ^#P < 0.05 and ^##P < 0.01 indicate significant differences compared to the 6-month-old mice; ^&P < 0.05 and ^&&P < 0.01 indicate significant differences compared to the 12-month-old mice.

Figure 13

Relative levels of H3S10p (A–C), H3K9me3 (D–F), and total H3 (G–I) represented by AOD of immunoreactivity in the hippocampal DG, CA1, and CA3 in different age groups. Panels (A,D,G) represent 12-month-old mice; (B,E,H) represent 18-month-old mice; and (C,F,I) represent 22-month-old mice. All values are means ± SD. *P < 0.05 and **P < 0.01 indicate significant treatment effects compared to the same-age controls.