Sex-Specific Epigenetics: Implications for Environmental Studies of Brain and Behavior

Auditing the Editor: A Review of Key Translational Issues in Epigenetic Editing

Currently, most advances in site-specific epigenetic editing for human use are concentrated in basic research, yet, there is considerable interest to translate this technology beyond the bench. This review highlights recent developments with epigenetic editing technology in comparison with the canonical CRISPR-Cas genome editing, as well as the epistemic and ethical considerations with preemptive translation of epigenetic editing into clinical or commercial use in humans. Key considerations in safety, equity, and access to epigenetic editing are highlighted, with a spotlight on the ethical, legal, and social issues of this technology in the context of global health equity.

Unravelling the role of epigenetics in reproductive adaptations to early-life environment

Reproductive function adjusts in response to environmental conditions in order to optimize success. In humans, this plasticity includes age of pubertal onset, hormone levels and age at menopause. These reproductive characteristics vary across populations with distinct lifestyles and following specific childhood events, and point to a role for the early-life environment in shaping adult reproductive trajectories. Epigenetic mechanisms respond to external signals, exert long-term effects on gene expression and have been shown in animal and cellular studies to regulate normal reproductive function, strongly implicating their role in these adaptations. Moreover, human cohort data have revealed differential DNA methylation signatures in proxy tissues that are associated with reproductive phenotypic variation, although the cause-effect relationships are difficult to discern, calling for additional complementary approaches to establish functionality. In this Review, we summarize how adult reproductive function can be shaped by childhood events. We discuss why the influence of the childhood environment on adult reproductive function is an important consideration in understanding how reproduction is regulated and necessitates consideration by clinicians treating women with diverse life histories. The resolution of the molecular mechanisms responsible for human reproductive plasticity could also lead to new approaches for intervention by targeting these epigenetic modifications.

Sex-specific DNA methylation differences in people exposed to polybrominated biphenyl

Aim: Michigan residents were exposed to polybrominated biphenyls (PBBs) when it was accidentally added to the food supply. Highly exposed individuals report sex-specific health problems, but the underlying biological mechanism behind these different health risks is not known. Materials and methods: DNA methylation in blood from 381 women and 277 men with PBB exposure was analyzed with the MethylationEPIC BeadChip. Results: 675 CpGs were associated with PBBs levels in males, while only 17 CpGs were associated in females (false discovery rate <0.05). No CpGs were associated in both sexes. These CpGs were enriched in different functional regions and transcription factor binding sites in each sex. Conclusion: Exposure to PBBs may have sex-specific effects on the epigenome that may underlie sex-specific adverse health outcomes.

The role of environmental exposures and the epigenome in health and disease

The genetic material of every organism exists within the context of regulatory networks that govern gene expression, collectively called the epigenome. Epigenetics has taken center stage in the study of diseases such as cancer and diabetes, but its integration into the field of environmental health is still emerging. As the Environmental Mutagenesis and Genomics Society (EMGS) celebrates its 50th Anniversary this year, we have come together to review and summarize the seminal advances in the field of environmental epigenomics. Specifically, we focus on the role epigenetics may play in multigenerational and transgenerational transmission of environmentally induced health effects. We also summarize state of the art techniques for evaluating the epigenome, environmental epigenetic analysis, and the emerging field of epigenome editing. Finally, we evaluate transposon epigenetics as they relate to environmental exposures and explore the role of noncoding RNA as biomarkers of environmental exposures. Although the field has advanced over the past several decades, including being recognized by EMGS with its own Special Interest Group, recently renamed Epigenomics, we are excited about the opportunities for environmental epigenetic science in the next 50 years. Environ. Mol. Mutagen. 61:176-192, 2020. © 2019 Wiley Periodicals, Inc.

Hormone-Independent Sexual Dimorphism in the Regulation of Bone Resorption by Krox20

Krox20/EGR2 is a zinc finger transcription factor, implicated in the development of the hindbrain, nerve myelination, and tumor suppression. In skeletal biology, we have demonstrated that Krox20 also regulates adult bone metabolism. We and others have characterized several functions of Krox20 in the osteoclast lineage, namely, preosteoclast proliferation and differentiation, and mature osteoclast apoptosis. We have previously reported that systemically Krox20-haploinsufficient mice have a low bone mass with increased bone resorption. However, new data have now revealed that this phenotype is restricted to females. In addition, we discovered that conditional knockout of Krox20 (cKO) restricted to osteoclast progenitors is sufficient to induce the same female-specific bone loss observed in systemic mutants. To test whether this sexual dimorphism results from an interaction between Krox20 and sex hormones, we examined the sex- and hormone-dependent role of Krox20 deficiency on proliferation and apoptosis in osteoclastic cells. Our results indicate that male and female sex hormones (dihydrotestosterone [DHT] and estradiol [E2], respectively) as well as Krox20 inhibit preosteoclast proliferation and augment osteoclast apoptosis. The observation that Krox20 expression is inhibited by DHT and E2 negates the hypothesis that the effect of sex hormones is mediated by an increase in Krox20 expression. Interestingly, the effect of Krox20 deficiency was observed only with cells derived from female animals, regardless of any sex hormones added in vitro. In addition, we have identified sexual dimorphism in the expression of several Krox20-related genes, including NAB2. This sex-specific epigenetic profile was established at puberty, maintained in the absence of sex hormones, and explains the female-specific skeletal importance of Krox20. The findings described in this study emphasize the medical importance of sex differences, which may be determined at the epigenetic level. © 2019 American Society for Bone and Mineral Research.

A Life History Approach to the Female Sexual Orientation Spectrum: Evolution, Development, Causal Mechanisms, and Health

Women's capacity for sexual fluidity is at least as interesting a phenomenon from the point of view of evolutionary biology and behavioral endocrinology as exclusively homosexual orientation. Evolutionary hypotheses for female nonheterosexuality have failed to fully account for the existence of these different categories of nonheterosexual women, while also overlooking broader data on the causal mechanisms, physiology, ontogeny, and phylogeny of female nonheterosexuality. We review the evolutionary-developmental origins of various phenotypes in the female sexual orientation spectrum using the synergistic approach of Tinbergen's four questions. We also present femme-specific and butch-specific hypotheses at proximate and ultimate levels of analysis. This review article indicates that various nonheterosexual female phenotypes emerge from and contribute to hormonally mediated fast life history strategies. Life history theory provides a biobehavioral explanatory framework for nonheterosexual women's masculinized body morphology, psychological dispositions, and their elevated likelihood of experiencing violence, substance use, obesity, teenage pregnancy, and lower general health. This pattern of life outcomes can create a feedback loop of environmental unpredictability and harshness which destabilizes intrauterine hormonal conditions in mothers, leading to a greater likelihood of fast life history strategies, global health problems, and nonheterosexual preferences in female offspring. We further explore the potential of female nonheterosexuality to function as an alloparental buffer that enables masculinizing alleles to execute their characteristic fast life history strategies as they appear in the female and the male phenotype. Synthesizing life history theory with the female sexual orientation spectrum enriches existing scientific knowledge on the evolutionary-developmental mechanisms of human sex differences.

Decoding the Mechanism of Action of Rapid-Acting Antidepressant Treatment Strategies: Does Gender Matter?

Gender differences play a pivotal role in the pathophysiology and treatment of major depressive disorder. This is strongly supported by a mean 2:1 female-male ratio of depression consistently observed throughout studies in developed nations. Considering the urgent need to tailor individualized treatment strategies to fight depression more efficiently, a more precise understanding of gender-specific aspects in the pathophysiology and treatment of depressive disorders is fundamental. However, current treatment guidelines almost entirely neglect gender as a potentially relevant factor. Similarly, the vast majority of animal experiments analysing antidepressant treatment in rodent models exclusively uses male animals and does not consider gender-specific effects. Based on the growing interest in innovative and rapid-acting treatment approaches in depression, such as the administration of ketamine, its metabolites or electroconvulsive therapy, this review article summarizes the evidence supporting the importance of gender in modulating response to rapid acting antidepressant treatment. We provide an overview on the current state of knowledge and propose a framework for rodent experiments to ultimately decode gender-dependent differences in molecular and behavioural mechanisms involved in shaping treatment response.

Women who suffer from schizophrenia: Critical issues

Many brain diseases, including schizophrenia, affect men and women unequally - either more or less frequently, or at different times in the life cycle, or to varied degrees of severity. With updates from recent findings, this paper reviews the work of my research group over the last 40 years and underscores issues that remain critical to the optimal care of women with schizophrenia, issues that overlap with, but are not identical to, the cares and concerns of men with the same diagnosis. Clinicians need to be alert not only to the overarching needs of diagnostic groups, but also to the often unique needs of women and men.

Gender specificity improves the early-stage detection of clear cell renal cell carcinoma based on methylomic biomarkers

AIM

The two genders are different ranging from the molecular to the phenotypic levels. But most studies did not use this important information. We hypothesize that the integration of gender information may improve the overall prediction accuracy.

MATERIALS & METHODS

A comprehensive comparative study was carried out to test the hypothesis. The classification of the stages I + II versus III + IV of the clear cell renal cell carcinoma samples was formulated as an example.

RESULTS & CONCLUSION

In most cases, female-specific model significantly outperformed both-gender model, as similarly for the male-specific model. Our data suggested that gender information is essential for building biomedical classification models and even a simple strategy of building two gender-specific models may outperform the gender-mixed model.