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Changes in rat sperm DNA methylation induced by age and by perinatal exposure to brominated flame retardant flame retardants 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47)

ABSTRACT: Advanced paternal age at fertilization has been suggested to be a risk factor for neurodevelopmental, psychiatric and other disorders in offspring. One emerging hypothesis suggests that altered offspring phenotype is linked with age-related accumulation of epigenetic changes in the sperm of fathers. Given that paternal age is increasing in the developed world, understanding aging-related epigenetic changes in sperm is needed as well as environmental factors that modify such changes. In this study, we characterize age-dependent changes in sperm DNA methylation profiles between young pubertal (postnatal day (PNDs) 65) and mature (PND120) Wistar rats. We also analyze these changes in rats exposed perinatally to 0.2 mg/kg of ubiquitous environmental xenobiotic 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47). Reduced representation bisulfite sequencing (RRBS) libraries were prepared from caudal epididymal sperm DNA and differentially methylated regions (DMRs; ≥ 10x coverage depth, ≥ 3 CpGs per cluster, ≥ 5% methylation change, q < 0.05) were identified via MethPipe package. We identified 21 and 9 exposure-related DMRs in sperm collected on PND65 and PND120, respectively. Two DMRs overlapped between the two time-points. This is the first study to demonstrate that environmentally-relevant perinatal exposure to PBDE results in long-lasting changes in sperm DNA methylation. In control animals, 5,319 age-dependent DMRs were identified, with 99.3% DMRs hypermethylated in mature animals compared to young pubertal rats. These age-related DMRs were enriched for functional categories essential for embryonic development, such as pattern specification, forebrain and sensory organ development, and the Wnt pathway. In BDE-47 exposed rats, sperm DNA methylation was higher in young pubertal and lower in mature animals when compared to controls, which resulted in a significant attenuation in the number of age-dependent DMRs (N = 189) identified in the exposed group. In conclusion, our results indicate that the natural aging process has profound effects on sperm methylation levels and this effect may be modified by environmental exposures. Moreover, our results further support the role of sperm DNA methylation as a likely mechanism by which advanced paternal age is associated with adverse offspring health and development.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE134362 | GEO | 2019/07/17

REPOSITORIES: GEO

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Project description:Purpose: Paternal life experiences impact offspring health via germline, and epigenetic inheritance provides a potential mechanism. However, global reprogramming during offspring embryogenesis and gametogenesis represents the largest hurdle to conceptualize it. Yet, detailed characterization of how sperm epigenetic alterations carrying “environmental memory” can evade offspring embryonic reprogramming remains elusive. Methods: we profiled the sperm DNA methylation patterns of three consecutive generations (F0, F1 and F2) in both control and stress groups by using whole-genome bisulfite sequencing (WGBS). A total of 18 sperm samples were analyzed, including three biological replicates for each generation under each treatment. In addition, small RNA sequencing was carried out on paternal sperm samples to investigate whether long-term psychological stress affected the enrichment of certain sncRNAs and to identify whether they participated in mediating the occurrence and paternal inheritance of the stress-induced DMRs Rsults: Using an optimized data analysis workflow, we obtained approximately 800 million clean reads per sample (build mm10) with strand-specific coverage ~21×, and the data covered ~96.00% of the total 21,867,837 reference CpG dinucleotides. A total of 24,427, 7,975, and 5,173 differentially methylated regions (DMRs) between control and stress groups were found in the F0, F1, and F2 generations, respectively. Inter- and transgenerational inheritance of paternal DMRs were at frequencies approximately 11.36% and 0.48%, respectively. These DMRs related to genes with functional implications for psychological stress response, and tissue inheritance of these DMRs passed paternal disorders epigenetically to offspring. More importantly, these DMRs evaded offspring embryonic reprogramming through erasure and subsequent reestablishment, but not via un-erasure way. Nonetheless, their reestablishment proportions in the primitive streak (E7.5) stage were altered. Furthermore, sncRNA-seq revealed that stress-induced tsRNA, miRNA and rsRNA dysregulation in paternal sperm might play important roles in DMRs occurrence and paternal inheritance.

Project description:The global prevalence of type 2 diabetes (T2D) is increasing, and it is contributing to the susceptibility to diabetes and its related epidemic in offspring. Although the impacts of paternal T2D on metabolism of offspring have been well established, the exact molecular and mechanistic basis that mediates these impacts remains largely unclear. Here we show that paternal T2D increases the susceptibility to diabetes in offspring through the gametic epigenetic alterations. Paternal T2D led to glucose intolerance and insulin resistance in offspring. Relative to controls, offspring of T2D fathers exhibited altered gene expression patterns in the pancreatic islets, with downregulation of several genes involved in glucose metabolism and insulin signaling pathway. Epigenomic profiling of offspring pancreatic islets revealed numerous changes in cytosine methylation depending on paternal T2D, including reproducible changes in methylation over several insulin signaling genes. Paternal T2D altered overall methylome patterns in sperm, with a large portion of differentially methylated genes overlapped with that of pancreatic islets in offspring. Our study revealed, for the first time, that T2D can be inherited transgenerationally through the mammalian germline by an epigenetic manner. For all comparisons shown, male F0 founders were weaned from mothers at 3 weeks of age, and sibling males were put into cages with high-fat diet (33% energy as fat) or control diet until 12 weeks of age, at which point mice fed with HFD were injected intraperitoneally with a low dose of STZ and kept on the same diet for 4 weeks. Fasting blood glucose was examined each week post-STZ for 4 weeks, and only glucose level at 7~11 mM was considered as type 2 diabetes. Females were always raised on standard diet. At 16 weeks, male F0 founders were mated with females. After 1 or 2 days, males were removed, and pregnant females were left alone until their litters were 3 weeks of age. Note that we always used virgin females to avoid confounding effects brought about by the females. At 3 weeks of age a portion of the offspring were sacrificed and islets were generated, each from an independent father.Samples from six control and six paternal type 2 diabetes offspring were chosen for microarray analysis.

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Changes in rat sperm DNA methylation induced by age and by perinatal exposure to brominated flame retardant flame retardants 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47)

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