Novel insights on cryostress, cryoinjury and cryotolerance in sperm - a review

Sperm cryopreservation is a critical component of assisted reproductive technologies employed for both livestock breeding and human fertility management. Sperm are the highly specialized motile cells prone to cryodamage during freezing. Moreover, buffalo, pig and sheep sperm are more susceptible to cryoinjury leading to increased semen rejection rates and substantial economic losses due to reduced fertility. Advances in freezing protocols and modulation in composition of semen diluents protect sperm from cryodamage; however, inconsistency and inter-individual variability in semen freezability exist due to multifactorial etiology. The use of molecular technologies, particularly genomics, transcriptomics, proteomics, and metabolomics led to identification of potential biomarkers associated with cryotolerance. These omics-driven insights have not only enlightened our understanding of the molecular basis of cryoinjury but also has the potential in selecting bulls with good semen freezability. A multidisciplinary approach toward the development of targeted strategies such as supplementing extenders with novel cryotolerant biomolecules to mitigate the sperm damage. This review consolidates current knowledge on the molecular and physiological underpinnings of sperm cryodamage offering a holistic perspective that may guide refinement of existing cryopreservation protocols and extenders for improving sperm cryo-survivability in breeding males.