BackgroundThis proof-of-principle study examines whether postnatal, low-dose exposure to environmental chemicals modifies the composition of gut microbiome. Three chemicals that are widely used in personal care products—diethyl phthalate (DEP), methylparaben (MPB), triclosan (TCS)—and their mixture (MIX) were administered at doses comparable to human exposure to Sprague-Dawley rats from birth through adulthood. Fecal samples were collected at two time points: postnatal day (PND) 62 (adolescence) and PND 181 (adulthood). The gut microbiome was profiled by 16S ribosomal RNA gene sequencing, taxonomically assigned and assessed for diversity.ResultsMetagenomic profiling revealed that the low-dose chemical exposure resulted in significant changes in the overall bacterial composition, but in adolescent rats only. Specifically, the individual taxon relative abundance for Bacteroidetes (Prevotella) was increased while the relative abundance of Firmicutes (Bacilli) was reduced in all treated rats compared to controls. Increased abundance was observed for Elusimicrobia in DEP and MPB groups, Betaproteobacteria in MPB and MIX groups, and Deltaproteobacteria in TCS group. Surprisingly, these differences diminished by adulthood (PND 181) despite continuous exposure, suggesting that exposure to the environmental chemicals produced a more profound effect on the gut microbiome in adolescents. We also observed a small but consistent reduction in the bodyweight of exposed rats in adolescence, especially with DEP and MPB treatment (p < 0.05), which is consistent with our findings of a reduced Firmicutes/Bacteroidetes ratio at PND 62 in exposed rats.ConclusionsThis study provides initial evidence that postnatal exposure to commonly used environmental chemicals at doses comparable to human exposure is capable of modifying the gut microbiota in adolescent rats; whether these changes lead to downstream health effects requires further investigation.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-016-0173-2) contains supplementary material, which is available to authorized users.

BackgroundDNA double-strand breaks (DSBs) caused by ionizing radiation or by the stalling of DNA replication forks are among the most deleterious forms of DNA damage. The ability of cells to recognize and repair DSBs requires post-translational modifications to histones and other proteins that facilitate access to lesions in compacted chromatin, however our understanding of these processes remains incomplete. UHRF1 is an E3 ubiquitin ligase that has previously been linked to events that regulate chromatin remodeling and epigenetic maintenance. Previous studies have demonstrated that loss of UHRF1 increases the sensitivity of cells to DNA damage however the role of UHRF1 in this response is unclear.ResultsWe demonstrate that UHRF1 plays a critical role for facilitating the response to DSB damage caused by γ-irradiation. UHRF1-depleted cells exhibit increased sensitivity to γ-irradiation, suggesting a compromised cellular response to DSBs. UHRF1-depleted cells show impaired cell cycle arrest and an impaired accumulation of histone H2AX phosphorylation (γH2AX) in response to γ-irradiation compared to control cells. We also demonstrate that UHRF1 is required for genome integrity, in that UHRF1-depleted cells displayed an increased frequency of chromosomal aberrations compared to control cells.ConclusionsOur findings indicate a critical role for UHRF1 in maintenance of chromosome integrity and an optimal response to DSB damage.

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Exposure to environmental chemicals has been linked to altered mammary development and cancer risk at high doses using animal models. Effects at low doses comparable to human exposure remain poorly understood, especially during critical developmental windows. We investigated the effects of two environmental phenols commonly used in personal care products – methyl paraben (MPB) and triclosan (TCS) – on the histology and transcriptome of normal mammary glands at low doses mimicking human exposure during critical windows of development. Sprague-Dawley rats were exposed during perinatal, prepubertal and pubertal windows, as well as from birth to lactation. Low-dose exposure to MPB and TCS induced measurable changes in both mammary histology (by Masson’s Trichrome Stain) and transcriptome (by microarrays) in a window-specific fashion. Puberty represented a window of heightened sensitivity to MPB, with increased glandular tissue and changes of expression in 295 genes with significant enrichment in functions such as DNA replication and cell cycle regulation. Long-term exposure to TCS from birth to lactation was associated with increased adipose and reduced glandular and secretory tissue, with expression alterations in 993 genes enriched in pathways such as cholesterol synthesis and adipogenesis. Finally, enrichment analyses revealed that genes modified by MPB and TCS were over-represented in human breast cancer gene signatures, suggesting possible links with breast carcinogenesis. These findings highlight the issues of critical windows of susceptibility that may confer heightened sensitivity to environmental insults and implicate the potential health effects of these ubiquitous environmental chemicals in breast cancer.

Xeroderma pigmentosum B (XPB/ERCC3/p89) is an ATP-dependent 3′→5′ directed DNA helicase involved in basal RNA transcription and the nucleotide excision repair (NER) pathway. While the role of NER in alleviating oxidative DNA damage has been acknowledged it remains poorly understood. To study the involvement of XPB in repair of oxidative DNA damage, we utilized primary fibroblasts from a patient suffering from XP with Cockayne syndrome and hydrogen peroxide (H2O2) to induce oxidative stress. Mutant cells retained higher viability and cell cycle dysfunction after H2O2 exposure. Cytokinesis blocked micronucleus assay revealed increased genome instability induced by H2O2. Single cell gel electrophoresis (comet) assay showed that the missense mutation caused a reduced repair capacity for oxidative DNA damage. Mutant fibroblasts also displayed decreased population doubling rate, increased telomere attrition rate and early emergence of senescent characteristics under chronic low dose exposure to H2O2. Fibroblasts from a heterozygous individual displayed intermediate traits in some assays and normal traits in others, indicating possible copy number dependence. The results show that a deficiency in functional XPB paradoxically renders cells more sensitive to the genotoxic effects of oxidative stress while reducing the cytotoxic effects. These findings have implications in the mechanisms of DNA repair, mutagenesis and carcinogenesis and ageing in normal physiological systems.