Aging-induced Changes in Sperm DNA Methylation are Modified by Low Dose of Perinatal Flame retardants

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. 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, Hippo and Wnt pathways. Age-related changes in sncRNA, reported in different study, target similar list of genes and biological categories.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 epigenetic mechanisms as a likely link betwen paternal age and offspring health and development.

Aging Induces Profound Changes in sncRNA in Rat Sperm and These Changes Are Modified by Perinatal Exposure to Environmental Flame Retardant

“…Interestingly, another study from our group, using the same rat model, reported similar effects of BDE-47 exposure on age-dependent changes in sperm DNA methylation [ 35 ]. In this study, exposure had minor effects on DNA methylation when exposed and control animals of the same age were compared.…”

“…Protein-coding genes—targets of piRNA and miRNA (11)—were enriched with categories related to embryonic development (12). Numbers shown in red stars indicate findings concordant with the analysis of DNA methylation in the same rat model [ 35 ]: 3—exposure to BDE-47 had a minor effect on DNA methylation if exposed and control animals of the same age were compared; 4—age-dependent differences in DNA methylation were significant in control animals; 5—these differences were attenuated by BDE-47 exposure due to the “convergence” effect, 11—gene targets of age-dependent sncRNA and genes associate with age-dependent differentially methylated regions of DNA overlapped significantly; 12—these genes were highly enriched for embryonic development.…”

“…Interestingly, other studies from our group, using the same rat model to analyze age- and exposure-associated changes in sperm DNA methylation, reported that, in control animals, genes associated with differentially methylated regions (DMRs) were significantly enriched with gene targets of age-dependent miRNA ( p < 0.00001) and piRNA ( p = 0.035) [ 35 ]. Additionally, genes ( n = 1052) overlapping as miRNA targets and as DMR-associated genes were highly enriched (−log 10(P) ranged 14–22) for categories related to embryonic development.…”

Potential implications of sperm DNA methylation functional properties in aquaculture management

“…Epigenetic programming is essential for post-fertilization success and offspring healthy development in the mammal's gametes. 105,106 Abnormal spermatozoa quality is associated with alternative DNA methylation in imprinted regions of the genes that play a vital role in reproduction. In mammals, it has been shown that spermatozoa concentration, motility and morphology are associated with DNA methylation levels.…”

“…168 The age-related differentially methylated regions (DMRs) in rat spermatozoa were shown to be enriched for embryonic development. 106 The multiple age-associated DMRs in human spermatozoa were used to speculate chronological age with high accuracy. 169 Recently, spermatozoa ageing has been an important topic in aquaculture management, particularly as short-term storage sperm are used for artificial reproduction.…”