Converging Effects of Three Different Endocrine Disrupters on Sox and Pou Gene Expression in Developing Rat Hippocampus: Possible Role of microRNA in Sex Differences

Abstract

Endocrine disrupting chemicals (EDCs) can impair hippocampus-dependent behaviors in rat offspring and in children. In search for key processes underlying this effect, we compared the transcriptomes of rat hippocampus on postnatal day 6 after gestational and lactational exposure to three different EDCs at doses known to impair development of learning and memory. Aroclor 1254, a commercial PCB mixture (5 mg/kg or 0.5 mg/kg), or bisphenol A (5 mg/kg or 0.5 mg/kg) were administered in chow, chlorpyrifos (3 mg/kg or 1 mg/kg) was injected subcutaneously. Male hippocampus exhibited a common effect of all three chemicals on genes involved in cell-autonomous processes, Sox6, Sox11, Pou2f2/Oct2, and Pou3f2/Brn2, all upregulated at the high dose. Additional genes of the Sox and Pou families were affected by only one or two of the chemicals. Real time RT PCR showed a comparable expression change for bisphenol A also at the lower dose. Female hippocampus exhibited much fewer genes with expression changes (almost none with false discovery rate <0.05), and none of the genes of the Sox and Pou families was affected. Since gene network analyses in male hippocampus suggested a link between Sox6 and miR-24, known to be repressed by activation of ER-alpha and to repress Sox6 in other tissues, this microRNA was measured. miR-24 was downregulated by all chemicals at the high dose in males. Values of Sox6 mRNA and miR-24 were inversely correlated in individual male hippocampus samples, supporting the hypothesis that the change in Sox6 expression resulted from an action of miR-24. In contrast, miR-24 levels remained unchanged in hippocampus of females. A sexually dimorphic response of miR-24 may thus be at the basis of the sex difference in Sox6 expression changes following exposure to the three chemicals. ER-alpha expression was also sex-dependent, but the expression changes did not parallel those of potential downstream genes such as Sox6. Sox6 is known to suppress differentiation of Parvalbumin (Pvalb)-expressing interneurons. Individual Sox6 levels (FPKM) were inversely correlated with levels of Pvalb, but not with markers of Sox6-independent interneuron subpopulations, Nos1 and 5HT3aR. Effects on interneuron development are further suggested, in males, by expression changes of Nrg1 and its receptor Erbb4, controlling interneuron migration. Our study disclosed new types of EDC-responsive morphogenetic genes, and illustrated the potential relevance of microRNAs in sexually dimorphic EDC actions.

microRNA-dependent regulation of gene expression in GABAergic interneurons

“…Data presented in this review indicate that the phenotypic and physiological features of IN subtypes depend not only on developmental spatiotemporal patterning of transcription factor activity and environmental cues, but also on miRNA expression and function (Strobl-Mazzulla et al, 2012;Tuncdemir et al, 2015;Dulcis et al, 2017). Furthermore, the interactions between gene expression, inductive events and miRNA activity not only determine IN developmental pathways but also impact mature network organization (Lichtensteiger et al, 2021;Taylor et al, 2022). In this manner, miRNAs are important elements of the gene regulatory network contributing to IN specification (Strobl-Mazzulla et al, 2012;Dulcis et al, 2017), as well as to the modification of network assemblies during critical developmental periods (Lichtensteiger et al, 2021;Taylor et al, 2022).…”

“…Furthermore, the interactions between gene expression, inductive events and miRNA activity not only determine IN developmental pathways but also impact mature network organization (Lichtensteiger et al, 2021;Taylor et al, 2022). In this manner, miRNAs are important elements of the gene regulatory network contributing to IN specification (Strobl-Mazzulla et al, 2012;Dulcis et al, 2017), as well as to the modification of network assemblies during critical developmental periods (Lichtensteiger et al, 2021;Taylor et al, 2022).…”

“…Gestational and lactational exposure to three endocrine disrupting chemicals (EDCs) in rats resulted in a sexspecific impairment of hippocampus-dependent behaviors and alternations in expression patterns of particular IN subtypes. Male, but not female offspring exposed to EDCs displayed learning and memory deficits accompanied by a decrease in miRNA-24 level, upregulation of mRNA for transcription factor Sox6, Sox11, Pou2f2/Oct2, Pou3f2/Brn2, and downregulation of mRNA for PV in the hippocampus (Lichtensteiger et al, 2021). Individual Sox6 mRNA levels correlated inversely with miRNA-24 and PV mRNA expression.…”

Activation of NLRP3 Inflammasome in Liver of Long Evans Lactating Rats and Its Perinatal Effects in the Offspring after Bisphenol F Exposure

“…Food and water were fed ad libitum. The doses of BPF used were chosen according to previous studies on BPA [ 26 , 33 ] and the large existing literature, where the dose range of BPA (2.5–50 mg/kg) induced impairment learning and memory loss in rodents when BPA was administered in the perinatal period. Thus, the high dose is 3.65 mg/kg higher than 2.5 mg/kg; while the low dose was 100 times lower, to investigate whether, even with such a small dose, any effects were observed.…”

Endocrine-Disrupting Chemicals and Hippocampal Development: The Role of Estrogen and Androgen Signaling

“…Since either mixed-sex pups or only male pups were used in these studies, we cannot conclude on whether the reported BPA effects on hippocampal synaptogenesis are sexually dimorphic. More recent studies show that developmental BPA induces sex-specific gene expression changes and epigenetic alterations in the rat hippocampus [126][127][128], although synaptogenic genes have not been examined.…”