Ferroptotic vulnerability of post-meiotic germ cells skews sex chromosome ratios in aged testis

Age-related testicular germ cell depletion has been predominantly attributed to apoptosis; however, the contribution of alternative cell death modalities remains unclear. Using young and aged mice, we demonstrate compartment-specific cell-death signatures in the testis. Apoptotic cell increased in peripheral germ layers, whereas the luminal round spermatid (RS) layer mainly accumulated non-apoptotic events sharing features with ferroptosis, a lipid-peroxidation dependent cell death. Lipidomic analysis revealed age-related phospholipid remodelling in whole testis, while RS-enriched fractions showed increased lipid peroxidation. Interestingly, aging shifted the balance of sex-chromosome-bearing RS toward Y-bearing cells, and this bias persisted in mature sperm. Dietary vitamin E modulated these phenotypes bidirectionally: vitamin E deficiency in young mice increased RS lipid peroxidation and reproduced the Y-skew, whereas supplementation in aged mice lowered RS lipid peroxidation, decreased non-apoptotic events, and restored the skewed RS sex-chromosome ratio. These findings define an age-related RS vulnerability linking redox stress to haploid spermatogenic output.