Histone Modifications: Epigenetic Mediators of Environmental Exposure Memory

Lactating exposure to microplastics at the dose of infants ingested during artificial feeding induced reproductive toxicity in female mice and their offspring

Microplastics (MPs) pollution poses a global environmental challenge with significant concerns regarding its potential impact on human health. Toxicological investigations have revealed multi-system impairments caused by MPs in various organisms. However, the specific reproductive hazards in human contexts remain elusive, and understanding the transgenerational reproductive toxicity of MPs remains limited. This study delves into the reproductive toxicity resulting from lactational exposure to polystyrene MPs (PS-MPs) in female mice, extending the inquiry to assess the reproductive effects on their offspring bred by rigorous natural mating. The MPs dosage corresponds to the detected concentration in infant formula prepared using plastic bottles. By systematically evaluating the reproductive phenotypes of F0 female mice from birth to adulthood, we found that female mice exposed to PS-MPs exhibited delayed puberty, disturbed estrous cyclicity, diminished fertility, elevated testosterone, abnormal follicle development, disrupted ovarian steroidogenesis, and ovarian inflammation. Importantly, the observed inheritable reproductive toxicity manifested with gender specificity, showcasing more pronounced abnormalities in male offspring. Specifically, reproductive disorders did not manifest in female offspring; however, a significant decrease in sperm count and viability was observed in PS-MPs-exposed F1 males. Testicular transcriptomics analysis of F1 males significantly enriched pathways associated with reproductive system development and epigenetic modification, such as male germ cell proliferation, DNA methylation, and histone modification. In summary, real-life exposure to PS-MPs impaired the reproductive function of female mice and threateningly disrupted the spermatogenesis of their F1 male offspring, which raises serious concerns about inter- and trans-generational reproductive toxicities of MPs in mammals. These findings underscore the potential threats of MPs to human reproductive health, emphasizing the need for continued vigilance and research in this critical area.

Inter- and Transgenerational Effects of Paternal Exposure to Inorganic Arsenic

The rise of metabolic disorders in modern times is mainly attributed to the environment. However, heritable effects of environmental chemicals on mammalian offsprings' metabolic health are unclear. Inorganic arsenic (iAs) is the top chemical on the Agency for Toxic Substances and Disease Registry priority list of hazardous substances. Here, we assess cross-generational effects of iAs in an exclusive male-lineage transmission paradigm. The exposure of male mice to 250 ppb iAs causes glucose intolerance and hepatic insulin resistance in F1 females, but not males, without affecting body weight. Hepatic expression of glucose metabolic genes, glucose output, and insulin signaling are disrupted in F1 females. Inhibition of the glucose 6-phosphatase complex masks the intergenerational effect of iAs, demonstrating a causative role of hepatic glucose production. F2 offspring from grandpaternal iAs exposure show temporary growth retardation at an early age, which diminishes in adults. However, reduced adiposity persists into middle age and is associated with altered gut microbiome and increased brown adipose thermogenesis. In contrast, F3 offspring of the male-lineage iAs exposure show increased adiposity, especially on a high-calorie diet. These findings have unveiled sex- and generation-specific heritable effects of iAs on metabolic physiology, which has broad implications in understanding gene-environment interactions.

Maternal exposure to environmental bisphenol A impairs the neurons in hippocampus across generations

Humans from fetal to adult stages are chronically and passively exposed to bisphenol A (BPA, an endocrine disruptor) due to its ubiquitous existence in daily life. To investigate the long-term neurotoxicity of maternal exposure to BPA for offspring, mice were used as the animal model. In this study, pregnant mice (F0) were orally dosed with BPA (i.e. mice from low-, medium- and high-exposed groups were treated with 0.5, 50, 5000 μg/kg·bw of BPA per day) until weaning. Then, the first generation (F1) mice were used to generate the F2 ones. The offspring of mice not exposed to BPA served as the control groups. The Y-maze test, comet assay, hematoxylin-eosin (HE) staining method, Golgi-Cox assay and liquid chromatography-tandem mass spectrometry (LC/MS/MS) were conducted to study any alterations to learning and memory abilities, the morphological variations in hippocampal neurons and transmitter levels of F1 and F2 mice induced by BPA exposure. Results showed that even a low-dose of maternal BPA exposure could sex-dependently and significantly impair the learning and memory ability of F1 male mice, but not of generation F2. Furthermore, decreased neuron quantities and spine densities in hippocampi were observed in both F1 and F2 generations after maternal BPA exposure. However, DNA damage of brain cells were only limited to F1 offspring, in which DNA damage was only observed in the low-exposed male mice and medium-exposed female mice. Additionally, maternal BPA exposure leads to variations in hippocampal neurotransmitter levels, indicated by the decreased ratio of Glu/GABA in F1 offspring. In conclusion, maternal exposure to an environmental dose of BPA resulted in lasting adverse effects on neurological development for offspring mice.

Transgenerational Bisphenol A Causes Deficits in Social Recognition and Alters Postsynaptic Density Genes in Mice

Bisphenol A (BPA) is a ubiquitous endocrine-disrupting chemical. Developmental exposure produces changes in behavior and gene expression in the brain. Here, we examined social recognition behaviors in mice from the third familial generation (F3) after exposure to gestational BPA. Second-generation mice were bred in one of four mating combinations to reveal whether characteristics in F3 were acquired via maternal or paternal exposures. After repeated habituation to the same mouse, offspring of dams from the BPA lineage failed to display increased investigation of a novel mouse. Genes involved in excitatory postsynaptic densities (PSDs) were examined in F3 brains using quantitative PCR. Differential expression of genes important for function and stability of PSDs were assessed at three developmental ages. Several related PSD genes-SH3 and multiple ankyrin repeat domains 1 (Shank1), Homer scaffolding protein 1c (Homer1c), DLG associated protein 1 (Gkap), and discs large MAGUK scaffold protein 4 (PSD95)-were differentially expressed in control- vs BPA-lineage brains. Using a second strain of F3 inbred mice exposed to BPA, we noted the same differences in Shank1 and PSD95 expression in C57BL/6J mice. In sum, transgenerational BPA exposure disrupted social interactions in mice and dysregulated normal expression of PSD genes during neural development. The fact that the same genetic effects were found in two different mouse strains and in several brain regions increased potential for translation. The genetic and functional relationship between PSD and abnormal neurobehavioral disorders is well established, and our data suggest that BPA may contribute in a transgenerational manner to neurodevelopmental diseases.