Human umbilical cord mesenchymal stem cell transplantation protects against reproductive damage induced by high-altitude hypoxia exposure in male mice

• Human umbilical cord mesenchymal stem cell transplantation alleviates hypoxia-induced testicular and epididymal edema and structural damage. • Stem cell transplantation restores mitochondrial membrane potential and reduces reactive oxygen species levels in hypoxic mouse testes. • Stem cell transplantation improves sperm motility in hypoxic mice, indicating functional recovery of spermatogenesis. • Transplanted stem cells primarily home to lung tissue, with limited homing to the testis, suggesting a paracrine or systemic mechanism.