Endocrine disruption of gene expression and microRNA profiles in hippocampus and hypothalamus of California mice: Association of gene expression changes with behavioural outcomes

Abstract

The hypothalamus and hippocampus are sensitive to early exposure to endocrine disrupting chemicals (EDCs). Two EDCs that have raised particular concerns are bisphenol A (BPA), a widely prevalent chemical in many common household items, and genistein (GEN), a phyto-oestrogen present in soy and other plants. We hypothesised that early exposure to BPA or GEN may lead to permanent effects on gene expression profiles for both coding RNAs (mRNAs) and microRNAs (miRs), which can affect the translation of mRNAs. Such EDC-induced biomolecular changes may affect behavioural and metabolic patterns. California mice (Peromyscus californicus) male and female offspring were developmentally exposed via the maternal diet to BPA (5 mg kg^-1 feed weight low dose [LD] and 50 mg kg^-1 feed weight upper dose [UD]), GEN (250 mg kg^-1 feed weight) or a phyto-oestrogen-free diet (AIN) control. Behavioural and metabolic tests were performed at 180 days of age. A quantitative polymerase chain reacttion analysis was performed for candidate mRNAs and miRs in the hypothalamus and hippocampus. LD BPA and GEN exposed California mice offspring showed socio-communication impairments. Hypothalamic Avp, Esr1, Kiss1 and Lepr were increased in LD BPA offspring. miR-153 was elevated but miR-181a was reduced in LD BPA offspring. miR-9 and miR-153 were increased in the hippocampi of LD BPA offspring, whereas GEN decreased hippocampal miR-7a and miR-153 expression. Correlation analyses revealed neural expression of miR-153 and miR-181a was associated with socio-communication deficits in LD BPA individuals. The findings reveal a cause for concern such that developmental exposure of BPA or GEN in California mice (and potentially by translation in humans) can lead to long standing neurobehavioural consequences.

Keywords: bisphenol A; brain; cognition; communication; epigenetics; genistein; miRNA; non-coding RNA.

Figure 1.

Effects of BPA and GEN exposure on social behaviors. A) Number of times spent investigating Stranger 1 in Trial 3 of social testing. GEN exposed individuals showed reduced incidences of investigating Stranger 1 in this trial. B) Number of times spent investigating Stranger 2 in Trial 3 of social testing. Both LD BPA and GEN exposed individuals had reduced number of incidences investigating Stranger 2 in this trial. C) Duration of time spent investigating Stranger 1 in Trial 3 of social testing. GEN exposed individuals showed reduced duration of investigating Stranger 1 in this trial. D) Duration of time spent investigating Stranger 2 in Trial 3 of social testing. GEN exposed individuals showed reduced duration of investigating Stranger 2 in Trial 3 of social testing. N = 12 individuals (males and females combined)/treatment group.

Figure 2.

Effects of BPA and GEN on vocalization behaviors. A) Average number of calls. Individuals exposed to UD BPA exhibited greater number of calls when placed in isolation. B) Average duration of calls. LD BPA and GEN exposed individuals showed reduced duration of calls. C) Average number of calls in a burst. UD BPA individuals showed greater number of calls in each burst. D) Average duration of bursts. LD BPA and GEN exposed individuals showed reduced duration of bursts. N = 12 individuals (males and females combined)/treatment group.

Figure 3.

RQ value and walking speed during the light cycle. A) Average RQ value for females during the light cycle. LD BPA and UD BPA female showed increased RQ value during the light cycle. B) Average RQ value for males during the light cycle. UD BPA males showed increased RQ value during the light cycle. C) Average walking speed for females during the light cycle. No differences were detected between female groups. D) Average walking speed for males during the light cycle. UD BPA male showed reduced walking speed during the light cycle. N = 6 individuals/treatment group and sex.

Figure 4.

RQ value during the dark cycle. A) Average RQ value for females during the light cycle. LD BPA and UD BPA female showed increased RQ value during the dark cycle. B) Average RQ value for males during the light cycle. UD BPA males showed increased RQ value during the dark cycle. N = 6 individuals/treatment group and sex.

Figure 5.

Hypothalamic gene expression as determined by qPCR analysis for Avp, Esr1, Kiss1, Lepr, and Oxtr. Significant differences relative to AIN controls are depicted with an asterisk and associated p value. N = 12 individuals (males and females combined)/treatment group.

Figure 6.

Hippocampal gene expression as determined by qPCR analysis for Avp, Esr1, Kiss1, Lepr, and Oxtr. Significant differences relative to AIN controls are depicted with an asterisk and associated p value. N = 12 individuals (males and females combined)/treatment group.

Figure 7.

Hypothalamic and hippocampal miR expression as determined by qPCR. Significant differences relative to AIN controls are depicted with an asterisk and associated p value. N = 12 individuals (males and females combined)/treatment group.

Figure 8.

Circos plot correlations for LD BPA exposed females vs. AIN control females. Correlation value was set to 0.85. Red lines in the center indicate a positive correlation (Panel A); whereas blue lines (Panel B) indicate a negative correlation. Lines on the outside of the circle indicate whether the value was greater in controls (blue) or LD BPA (orange).

Figure 9.

Circos plot correlations for GEN exposed females vs. AIN control females. Correlation value was set to 0.85. Red lines in the center indicate a positive correlation (Panel A); whereas blue lines (Panel B) indicate a negative correlation. Lines on the outside of the circle indicate whether the value was greater in controls (blue) or GEN (orange).

Figure 10.

Circos plot correlations for LD BPA exposed males vs. AIN control males. Correlation value was set to 0.85. Red lines in the center indicate a positive correlation (Panel A); whereas blue lines (Panel B) indicate a negative correlation. Lines on the outside of the circle indicate whether the value was greater in controls (blue) or LD BPA (orange).

Figure 11.

Circos plot correlations for GEN exposed males vs. AIN control males. Correlation value was set to 0.85. Red lines in the center indicate a positive correlation (Panel A); whereas blue lines (Panel B) indicate a negative correlation. Lines on the outside of the circle indicate whether the value was greater in controls (blue) or GEN (orange).