Maternal hypoxia exposure perturbs the methylation of imprinted genes in adult sperm and causes intergenerational placental impairments in male offspring

Hypobaric hypoxia at high altitudes adversely affects the health and fertility of humans and animals globally. Previously, we showed that maternal hypoxia exposure led to granulosa cell (GC) autophagic cell death and oocyte maturation defects in female offspring. However, the impact of maternal hypoxia exposure on the reproduction and development of offspring in successive generations in mammals has yet to be fully elucidated. In this study, we exposed pregnant mice to hypoxia (F0) and examined the impact of maternal hypoxia exposure on male offspring in four generations (F1‒F4). The results revealed that maternal hypoxia mildly affected sperm DNA methylation in F1 males and caused severe developmental defects in F2 offspring in a male-biased manner. Notably, after mating F1 males with control females, a significant number of the male F2 fetuses were lost at embryonic day (E) 13.5 because of placental defects. Integrated analyses of RNA-seq and genome-wide DNA methylation (WGBS) data revealed that placentae from these male fetuses aberrantly expressed a list of imprinted genes, including Slc38a4, Jade1, Kcnq1 and Gnas, which are also differentially methylated in F1 sperm. These results indicated that maternal hypoxia altered the DNA methylation of imprinted genes in F1 sperm and affected the placental function and development of F2 males, leading to an unbalanced sex ratio. The findings of this study provide insight into the hypoxia environmental influences of the sex ratio and have important implications for deciphering hypoxia-induced reproductive impairments in mammals.