Prenatal Iron Deficiency and Choline Supplementation Interact to Epigenetically Regulate Jarid1b and Bdnf in the Rat Hippocampus into Adulthood

Abstract

Early-life iron deficiency (ID) causes long-term neurocognitive impairments and gene dysregulation that can be partially mitigated by prenatal choline supplementation. The long-term gene dysregulation is hypothesized to underlie cognitive dysfunction. However, mechanisms by which iron and choline mediate long-term gene dysregulation remain unknown. In the present study, using a well-established rat model of fetal-neonatal ID, we demonstrated that ID downregulated hippocampal expression of the gene encoding JmjC-ARID domain-containing protein 1B (JARID1B), an iron-dependent histone H3K4 demethylase, associated with a higher histone deacetylase 1 (HDAC1) enrichment and a lower enrichment of acetylated histone H3K9 (H3K9ac) and phosphorylated cAMP response element-binding protein (pCREB). Likewise, ID reduced transcriptional capacity of the gene encoding brain-derived neurotrophic factor (BDNF), a target of JARID1B, associated with repressive histone modifications such as lower H3K9ac and pCREB enrichments at the Bdnf promoters in the adult rat hippocampus. Prenatal choline supplementation did not prevent the ID-induced chromatin modifications at these loci but induced long-lasting repressive chromatin modifications in the iron-sufficient adult rats. Collectively, these findings demonstrated that the iron-dependent epigenetic mechanism mediated by JARID1B accounted for long-term Bdnf dysregulation by early-life ID. Choline supplementation utilized a separate mechanism to rescue the effect of ID on neural gene regulation. The negative epigenetic effects of choline supplementation in the iron-sufficient rat hippocampus necessitate additional investigations prior to its use as an adjunctive therapeutic agent.

Sex-Specific Effects of Early-Life Iron Deficiency and Prenatal Choline Treatment on Adult Rat Hippocampal Transcriptome

“…Particularly in females, genes that were activated included ones negatively associated with cognition, emotion, and anxiety. The findings further confirm our previous speculation that choline and iron interact to regulate hippocampal gene expression (25, 28) and highlight differential effects of such an interaction between sexes. For instance, BDNF and APP gene networks showed opposite effects in male and female ISch rats, respectively (Figure 5B), illustrating the sex-specific effects of prenatal choline supplement in the iron-sufficient rats.…”

“…Consistent with our previous findings in a neonatal model of PIA (8), substantially more gene expression changes in the hippocampal transcriptome were found in female than male rodents, indicating a more robust gene regulatory response to early-life ID in female rats. Prenatal choline supplementation, a promising adjunct therapy that prevents some long-term behavioral abnormalities following early-life ID, led to even more DEGs in both sexes of iron-sufficient compared to iron-deficient groups, further supporting previous observations of the interaction between choline and iron status in regulating hippocampal gene expression (25, 28). Collectively, both ID and choline supplementation caused sex-specific changes in hippocampal gene regulation, affecting distinct gene networks and biological processes.…”

“…Rats were maintained in a 12-hr:12-hr light/dark cycle with ad lib food and water. ID was induced by dietary manipulation as described previously (25). In brief, to generate iron-deficient pups, pregnant dams were given a purified iron-deficient diet (4 mg Fe/kg, TD.80396; Harlan Teklad) from G2 to postnatal day (P) 7 when lactating dams were switched to a purified iron-sufficient diet (200 mg Fe/kg, TD.09256; Harlan Teklad).…”

“…Both diets were similar in all respects except for the iron (ferric citrate) content. Half of the dams on the iron-sufficient or iron-deficient diet received dietary choline supplementation (5.0 g/kg choline chloride supplemented; iron-sufficient with choline: TD.1448261, iron-deficient with choline: TD.110139; Harlan Teklad) from G11-G18, while the other half of the dams received their iron-sufficient or iron-deficient diet with standard choline content (1.1 g/kg) as previously described (25). Thus, dams and their litters were randomly assigned to one of four groups based on maternal diet: iron-deficient with choline supplementation (IDch), iron-deficient without supplemental choline (ID), always iron-sufficient with choline supplementation (ISch), always iron-sufficient without supplemental choline (IS, control group).…”

ATAC and histone H3K9me3 landscapes revealed the altered epigenome by fetal-neonatal iron deficiency in the adult male rat hippocampus

“…Choline supplementation can be beneficial in mitigating the deleterious developmental effects of early life adverse exposure and aberrant genetic factors on brain development (Wozniak et al, 2013; Mellott et al, 2017; Chin et al, 2019; Agam et al, 2020). In the context of fetal-neonatal iron deficiency, choline supplementation can influence hippocampal gene expression and epigenomic changes in an iron status-dependent manner (Kennedy et al, 2014, 2018; Tran et al, 2016; Liu et al, 2021). These findings suggest an interaction between these two essential nutrients in influencing the brain’s epigenetic landscape.…”