Abstract
Hypobaric hypoxia encountered at high altitudes impairs reproductive health and fertility across species. Previous findings have demonstrated that maternal hypoxia exposure disrupts granulosa cell (GC) viability and oocyte maturation in female offspring; however, its transgenerational impact on male reproductive outcomes remains poorly elucidated. In this study, pregnant mice (F0) were subjected to hypoxic conditions, and male progeny across four generations (F1‒F4) were evaluated. Results revealed that maternal hypoxia induced mild alterations in sperm DNA methylation in F1 males but caused profound developmental defects in F2 embryos, predominantly affecting males. Following mating of F1 males with control females, a substantial proportion of male F2 fetuses were lost at embryonic day (E) 13.5, attributed to placental malformations. Integrated RNA sequencing and whole-genome bisulfite sequencing of placentas from male fetuses revealed aberrant expression of imprinted genes, including Gnas, Slc38a4, Jade1, and Kcnq1, which also exhibited differential methylation in F1 sperm. These findings demonstrate that maternal hypoxia disrupts epigenetic programming in F1 germ cells, impairing placental development and fetal viability in F2 males, thereby leading to an unbalanced sex ratio. Overall, this study elucidates the mechanisms by which environmental hypoxia influences sex ratios and offers critical insights into hypoxia-induced reproductive impairments in mammals.