Abstract
Simple SummaryCryopreservation is the method for the long-term preservation of gametes and embryos. In recent years, intensive research has focused on improving cryopreservation protocols for the determination of optimal freezing conditions and cryoprotective agents’ concentration for each cell type. The optimal cryopreservation protocol comprises the adequate balance between the freezing rate and the correct concentration of cryoprotective agents to achieve controlled cellular dehydration and minimal intracellular ice formation. Osmoregulation is, therefore, central in cryobiology. Water and some solutes can cross the plasma membrane, whereas facilitating transport takes a great part in intracellular/extracellular fluid homeostasis. Cells express water channels known as aquaporins that facilitate the transport of water and small uncharged solutes on their plasma membrane, including some cryoprotective agents. This review explores the expression and the function of aquaporins in gametes and embryos. In addition, the putative role of aquaporins for cryopreservation procedures is discussed.Cryopreservation is globally used as a method for long-term preservation, although freeze-thawing procedures may strongly impair the gamete function. The correct cryopreservation procedure is characterized by the balance between freezing rate and cryoprotective agents (CPAs), which minimizes cellular dehydration and intracellular ice formation. For this purpose, osmoregulation is a central process in cryopreservation. During cryopreservation, water and small solutes, including penetrating cryoprotective agents, cross the plasma membrane. Aquaporins (AQPs) constitute a family of channel proteins responsible for the transport of water, small solutes, and certain gases across biological membranes. Thirteen homologs of AQPs (AQP0-12) have been described. AQPs are widely distributed throughout the male and female reproductive systems, including the sperm and oocyte membrane. The composition of the male and female gamete membrane is of special interest for assisted reproductive techniques (ART), including cryopreservation. In this review, we detail the mechanisms involved in gamete cryopreservation, including the most used techniques and CPAs. In addition, the expression and function of AQPs in the male and female gametes are explored, highlighting the potential protective role of AQPs against damage induced during cryopreservation.
Highlights
Cryopreservation is used as an efficient method for the long-term storage of reproductive cells and embryos to use in human and animal-assisted reproduction [1,2]
Based on the current literature, we review the mechanisms involved in gamete cryopreservation of animals, detailing the most used techniques and cryoprotective agents (CPAs)
The complex interaction between high CPA concentration, freezing rate, and time of exposure makes the optimization of cryopreservation protocols very challenging
Summary
Cryopreservation is used as an efficient method for the long-term storage of reproductive cells and embryos to use in human and animal-assisted reproduction [1,2]. Christopher Polge et al were successful in cryopreserving sperm and accidentally discovered the beneficial properties of glycerol as a cryoprotective agent (CPA) in 1949 [5]. Bunge and Sherman achieved successful pregnancies and live births with cryopreserved human sperm [7]. Sherman reported that cryopreserved human sperm had no loss of motility after one year of storage [8]. Notwithstanding all the improvements in the gamete cryopreservation technique over the years, this process causes damage to the cell and compromises cellular functions and the ability for fertilization. The expression and function of AQPs in the male and female gametes are explored, highlighting the potential protective role of AQPs against damage induced during cryopreservation
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