Aquaporins in the male reproductive tract and sperm: Functional implications and cryobiology

Abstract

Contents Aquaporins (AQPs) play a vital role for the transport of water and solutes across cell membranes. Classification of these ubiquitous proteins into three categories (orthodox AQPs, aquaglyceroporins and superaquaporins) is based on their sequence similarity and substrate selectivity. In the male reproductive tract of mammals, most AQPs (except AQP6 and AQP12) are found in different organs (including testis, efferent ducts and epididymis). AQP1 and AQP9 are the most abundant AQPs in the efferent ducts and epididymis and play a crucial role for the secretion/reabsorption dynamics of luminal fluid during sperm transport and maturation. AQP3, AQP7, AQP8 and AQP11 are the most abundant AQPs in sperm and are involved in the regulation of their volume, which is required for the differentiation of spermatids into spermatozoa during spermatogenesis, as well as in sperm transit along environments of different osmolality (male and female reproductive tracts). While different studies conducted in oocytes and embryos have demonstrated that AQPs are important for cryotolerance, data in sperm are scarce. At present, mounting evidence indicates that AQP3, AQP7 and AQP11 are involved in the sperm response to variations of osmolality and to freeze‐thawing procedures. All these studies contribute to understand the physiology of both male reproductive tract and sperm, and open up new research ventures on the improvement of sperm cryopreservation protocols.

Cryotolerance of Stallion Spermatozoa Relies on Aquaglyceroporins rather than Orthodox Aquaporins

“…While AQPs have been identified in sperm cells from different mammalian species in the last decade (reviewed in [2]), their precise function and mechanism of action are yet to be fully addressed. In the case of horses, AQP3, AQP7 and AQP11 have been identified in stallion spermatozoa [4].…”

“…Aquaporins (AQPs) are a family of ubiquitous transmembrane proteins that allow for the facilitated diffusion of water. Some AQPs are also permeable to small solutes [2]. To date, 13 AQPs (AQP0-AQP12) have been identified in mammalian cells and have been classified into three different groups (orthodox AQPs, aquaglyceroporins (GLPs), and superAQPs), which differ in their sequence and solute permeability.…”

“…In mammalian spermatozoa, AQP1 has been identified in porcine [3]; AQP3, AQP7 and AQP11 in equine [4], porcine [5,6], murine [7][8][9], human [10,11] and bovine species [12,13]; AQP8 has been found in mouse [8] and human spermatozoa [10,11]; and AQP9 is present in boar spermatozoa [14]. In the male gamete, AQPs are involved in the regulation of cell volume and osmotic balance, which are crucial for spermatogenesis [15] and post-ejaculation events, including the activation of sperm motility upon ejaculation and sperm adaptation to the female environment (reviewed in [2]).…”

High‐resolution imaging of the actin cytoskeleton and epithelial sodium channel, CFTR, and aquaporin‐9 localization in the vas deferens

“…Of these, the family of aquaporin (AQP) water channels that includes 13 isoforms has been most extensively studied as these channels are involved in water absorption that leads to the concentration of the luminal fluid. Twelve of the AQP isoforms are expressed in the male and female reproductive systems (Yeste, Morató, Rodríguez‐Gil, Bonet, & Prieto‐Martínez, 2017; Zhang, Tan, Qu, Sheng, & Huang, 2012). Specifically, the expressions of AQP1, AQP2, AQP7, and AQP9 have been documented in the vas deferens of several species (Andonian & Hermo, 1999; Khadijah Ramli, Giribabu, Karim, & Salleh, 2019; Pastor‐Soler et al, 2001; Rojek et al, 2007; Schimming, Pinheiro, de Matteis, Machado, & Domeniconi, 2015; Yeste et al, 2017).…”

Tyrosine phosphorylation is not a relevant mechanism to modulate aquaporin 2 activity in gestational queen endometrium and placenta

“…One of the most important mechanisms involved in the modulation of intracellular water fluxes is aquaporins (AQPs). These proteins regulate water intake in eukaryotic cells (Gomes et al, ), including uterus and placenta (Agre & Kozono, ; Richard, Gao, Brown, & Reese, ; Yeste, Morató, Rodríguez‐Gil, Bonet, & Prieto‐Martínez, ).…”