Epigenetic regulation of 5α reductase-1 underlies adaptive plasticity of reproductive function and pubertal timing

Association of childhood dehydroepiandrosterone sulfate concentration, pubertal development, and DNA methylation at puberty-related genes

OBJECTIVE

High concentrations of dehydroepiandrosterone sulfate (DHEAS) often precede premature puberty and sometimes polycystic ovary syndrome (PCOS). We hypothesized that the underlying mechanisms might involve DNA methylation. As an indicator of the downstream effects of DHEAS, we looked for associations between prepubertal DHEAS concentration, pubertal progression, and DNA methylation at puberty-related genes in blood cells.

DESIGN

Blood methylome and DHEAS concentration at 7.5 and 8.5 years, respectively, were analyzed in 91 boys and 82 girls. Pubertal development data were collected between 8.1 and 17 years (all from UK birth cohort, Avon Longitudinal Study of Parents and Children [ALSPAC]).

METHODS

Correlation between DHEAS and pubertal measurements was assessed by Spearman's correlation. DHEAS association with methylation at individual CpGs or regions was evaluated by linear regression, and nearby genes examined by enrichment analysis and intersection with known puberty-related genes.

RESULTS

Boys and girls with higher childhood DHEAS concentrations had more advanced pubic hair growth throughout puberty; girls also had advanced breast development, earlier menarche, and longer menstrual cycles. DHEAS concentration was associated with methylation at individual CpGs near several puberty-related genes. In boys, 14 genes near CpG islands with DHEAS-associated methylation were detected, and in girls, there were 9 which included LHCGR and SRD5A2; FGFR1 and FTO were detected in both sexes.

CONCLUSIONS

The association between DHEAS and pubertal development, as reported previously, suggests a physiological connection. Our novel findings showing that DHEAS concentration correlates negatively and linearly with DNA methylation levels at regulatory regions of key puberty-related genes, provide a mechanism for such a functional relationship.

Srd5a1 is Differentially Regulated and Methylated During Prepubertal Development in the Ovary and Hypothalamus

5α-reductase-1 catalyzes production of various steroids, including neurosteroids. We reported previously that expression of its encoding gene, Srd5a1, drops in murine ovaries and hypothalamic preoptic area (POA) after early-life immune stress, seemingly contributing to delayed puberty and ovarian follicle depletion, and in the ovaries the first intron was more methylated at two CpGs. Here, we hypothesized that this CpG-containing locus comprises a methylation-sensitive transcriptional enhancer for Srd5a1. We found that ovarian Srd5a1 mRNA increased 8-fold and methylation of the same two CpGs decreased up to 75% between postnatal days 10 and 30. Estradiol (E2) levels rise during this prepubertal stage, and exposure of ovarian cells to E2 increased Srd5a1 expression. Chromatin immunoprecipitation in an ovarian cell line confirmed ESR1 binding to this differentially methylated genomic region and enrichment of the enhancer modification, H3K4me1. Targeting dCas9-DNMT3 to this locus increased CpG2 methylation 2.5-fold and abolished the Srd5a1 response to E2. In the POA, Srd5a1 mRNA levels decreased 70% between postnatal days 7 and 10 and then remained constant without correlation to CpG methylation levels. Srd5a1 mRNA levels did not respond to E2 in hypothalamic GT1-7 cells, even after dCas9-TET1 reduced CpG1 methylation by 50%. The neonatal drop in POA Srd5a1 expression occurs at a time of increasing glucocorticoids, and treatment of GT1-7 cells with dexamethasone reduced Srd5a1 mRNA levels; chromatin immunoprecipitation confirmed glucocorticoid receptor binding at the enhancer. Our findings on the tissue-specific regulation of Srd5a1 and its methylation-sensitive control by E2 in the ovaries illuminate epigenetic mechanisms underlying reproductive phenotypic variation that impact life-long health.

Chemical Effects on Breast Development, Function, and Cancer Risk: Existing Knowledge and New Opportunities

Population studies show worrisome trends towards earlier breast development, difficulty in breastfeeding, and increasing rates of breast cancer in young women. Multiple epidemiological studies have linked these outcomes with chemical exposures, and experimental studies have shown that many of these chemicals generate similar effects in rodents, often by disrupting hormonal regulation. These endocrine-disrupting chemicals (EDCs) can alter the progression of mammary gland (MG) development, impair the ability to nourish offspring via lactation, increase mammary tissue density, and increase the propensity to develop cancer. However, current toxicological approaches to measuring the effects of chemical exposures on the MG are often inadequate to detect these effects, impairing our ability to identify exposures harmful to the breast and limiting opportunities for prevention. This paper describes key adverse outcomes for the MG, including impaired lactation, altered pubertal development, altered morphology (such as increased mammographic density), and cancer. It also summarizes evidence from humans and rodent models for exposures associated with these effects. We also review current toxicological practices for evaluating MG effects, highlight limitations of current methods, summarize debates related to how effects are interpreted in risk assessment, and make recommendations to strengthen assessment approaches. Increasing the rigor of MG assessment would improve our ability to identify chemicals of concern, regulate those chemicals based on their effects, and prevent exposures and associated adverse health effects.