Abstract
Sperm cryopreservation represents a powerful tool for livestock breeding. Several efforts have been made to improve the efficiency of sperm cryopreservation in different ruminant species. However, a significant amount of sperm still suffers considerable cryodamage, which may affect sperm quality and fertility. Recently, the use of different “omics” technologies in sperm cryobiology, especially proteomics studies, has led to a better understanding of the molecular modifications induced by sperm cryopreservation, facilitating the identification of different freezability biomarkers and certain proteins that can be added before cryopreservation to enhance sperm cryosurvival. This review provides an updated overview of the molecular mechanisms involved in sperm cryodamage, which are in part responsible for the structural, functional and fertility changes observed in frozen–thawed ruminant sperm. Moreover, the molecular basis of those factors that can affect the sperm freezing resilience of different ruminant species is also discussed as well as the molecular aspects of those novel strategies that have been developed to reduce sperm cryodamage, including new cryoprotectants, antioxidants, proteins, nanoparticles and vitrification.
Highlights
Sperm cryopreservation has become an essential tool for the long-term preservation of genetically superior males, relevant transgenic lines and endangered species [1,2]
Peris-Frau et al [71] compared the ability of Structure Assay (SCSA) and a variant of the Sperm Chromatin Dispersion test (SCD) to evaluate sperm DNA damage, but only the latter method detected a higher proportion of cryopreserved ram sperm showing DNA damage after 180 min of incubation
There is a wide variety of extenders that can be used during sperm cryopreservation in different ruminant species; not all of them offer the same protection against sperm cryodamage
Summary
Sperm cryopreservation has become an essential tool for the long-term preservation of genetically superior males, relevant transgenic lines and endangered species [1,2]. Molecular studies during sperm cryopreservation offer the possibility of recognizing those specific elements (proteins, lipids, ions, carbohydrates, etc.) altered by the freezing–thawing process that are in part responsible for the structural and functional changes observed in cryopreserved sperm (Figure 1). Besides the negative effect of sperm cryopreservation on metabolic enzymes, cytoskeletal proteins are temperature-sensitive This fact explains why some cytoskeletal proteins decrease in abundance (TEKT4, ODF2, ROPN1, ACTRT2, ACTL7B and actin) or change their distribution (F-actin, actin and β-dystrobrevin) during freezing–thawing in bull, ram, gazelle and buffalo sperm [38,43,47,48,56,57]. The reduced motility of cryopreserved sperm is probably the result of both axonemal protein damage and alterations in energy availability due to enzyme modifications
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