PERSPECTIVE: Frozen and breathless: hypoxia’s role in sperm cryoresistance

Hypoxia is a critical factor influencing sperm viability by compromising their structural integrity, functional activity, and fertilizing capacity. In reproductive biology and cryobiology, both hypoxia and cryopreservation are known to independently induce cellular stress; however, their combined effects on sperm remain inadequately explored. Here we systematize current knowledge on the effects of hypoxia on sperm cryoresistance, elucidate the molecular mechanisms underlying these effects and evaluate modern strategies for mitigating the combined damage caused by hypoxia and cryopreservation on sperm structure and function. We conducted a comprehensive literature review by analyzing peer-reviewed studies focused on the molecular and cellular responses of mammalian spermatozoa to hypoxia and cryopreservation. Key mechanisms investigated included oxidative stress pathways, mitochondrial function, membrane homeostasis, ion transport and genetic and epigenetic changes. The review also considered current experimental approaches and therapeutic interventions targeting these mechanisms. The analysis revealed that hypoxia disrupts cellular energy metabolism and enhances oxidative stress, leading to reduced sperm survival following cryopreservation. Additionally, cryopreservation itself causes further damage through membrane destabilization, osmotic imbalance and impaired intracellular signaling. These cumulative effects intensify structural and functional deterioration in sperm cells. Emerging mitigation strategies, including antioxidant supplementation, ion regulation, alterations to cryopreservation protocols and the use of hypoxic adaptogens demonstrate potential for improving post-thaw sperm viability. The combined impact of hypoxia and cryopreservation significantly impairs sperm integrity and function, primarily through oxidative and metabolic stress mechanisms. Targeted interventions aimed at counteracting these effects hold promise for enhancing sperm cryoresistance. Finally, this work highlights important avenues for further research and practical applications in reproductive medicine, particularly in fertility preservation and assisted reproductive technologies.