Background
The births of more than 8 million infants have been enabled globally through assisted reproductive technologies (ARTs), including conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) with either fresh embryo transfer (ET) or frozen embryo transfer (FET). However, the safety issue regarding ARTs has drawn growing attention with accumulating observations of rising health risks, and underlying epigenetic mechanisms are largely uncharacterized.
Methods
In order to clarify epigenetic risks attributable to ARTs, we profiled DNA methylome on 137 umbilical cord blood (UCB) and 158 parental peripheral blood (PPB) samples, histone modifications (H3K4me3, H3K4me1, H3K27me3 and H3K27ac) on 33 UCB samples and transcriptome on 32 UCB samples by reduced representation bisulfite sequencing (RRBS), chromatin immunoprecipitation sequencing (ChIP-seq), and RNA sequencing (RNA-seq), respectively. Findings: We revealed that H3K4me3 was the most profoundly impacted by ICSI and freeze-thawing operation compared with the other three types of histone modifications. IVF-ET seemed to introduce less disturbance into infant epigenomes than IVF-FET or ICSI-ET did. ARTs also decreased the similarity of DNA methylome within twin pairs, and we confirmed that ART per se would introduce conservative changes locally through removal of parental effect. Importantly, those unique and common alterations induced by different ART procedures were highly enriched in the processes related to nervous system, cardiovascular system and glycolipid metabolism etc., which was in accordance with those findings in previous epidemiology studies and suggested some unexplored health issues, including in the immune system and skeletal system. Interpretation: Different ART procedures can induce local and functional epigenetic abnormalities, especially for DNA methylation and H3K4me3, providing an epigenetic basis for the potential long-term health risks in ART-conceived offspring. Funding sources: This study was funded by National Natural Science Foundation of China (81730038; 81521002), National Key Research and Development Program (2018YFC1004000; 2017YFA0103801; 2017YFA0105001) and Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16020703). Yang Wang was supported by Postdoctoral Fellowship of Peking-Tsinghua Center for Life Science.