Immunolocalization of aquaporin 7 in human sperm and its relationship with semen parameters

Abstract

Aquaporins (AQPs) are a family of 13 small hydrophobic transmembrane proteins expressed in numerous tissues and cells. Some AQPs work as strict water channels, others are permeable to a range of substances, including glycerol. In the male reproductive system their localization in testis, efferent ducts, epididymis, and spermatozoa has been described. We studied the distribution of AQP7 in ejaculated human sperm and the relationship between AQP7 labeling and sperm characteristics. Semen samples from 33 men were examined by light and transmission electron microscopy (TEM). TEM data were quantified using a mathematical formula that calculates a fertility index (FI) and the percentages of sperm apoptosis, immaturity, and necrosis. Immunocytochemistry with a polyclonal antibody anti-AQP7 was performed on the sperm samples. Normal sperm were labeled in the pericentriolar area, midpiece, equatorial segment, and weakly in the tail (grade 1). Abnormal sperm showed a diffuse low intensity of fluorescence evident in the cytoplasmic residues, coiled tails, in the entire head, and acrosome (grade 2). A high number of motile sperm obtained by swim up were labeled in a dotted manner in the mitochondria. A significant positive correlation was found between the spermatozoa with AQP7 grade 1 labeling and the percentage of normal form (P < 0.008), progressive motility and FI (P < 0.005); a negative correlation was noted with the percentages of cytoplasmic residues (P < 0.010) and immaturity (P < 0.006) and coiled tails (P < 0.012). The link between AQP7 distribution and sperm morphology and the particular dotted labeling in swim up selected motile sperm are novel and deserve additional studies.

Subcellular Localization of Selectively Permeable Aquaporins in the Male Germ Line of a Marine Teleost Reveals Spatial Redistribution in Activated Spermatozoa1

“…Nevertheless, in this study we found that during seawater activation, seabream Aqp8b is relocated from the plasma membrane of the anterior flagellum into the mitochondrion of spermatozoa, which did not occur for the other aquaporins. Although such a mechanism for AQP8 has not been previously observed in mammalian sperm, the accumulation of AQP7 in the mitochondria of human activated spermatozoa [26], as well as the presence of AQP8 in the inner membrane of the mitochondria of several tissues [84][85][86][87], has been reported. Since AQP7 and -8 are permeable to ammonia in addition to water and solutes [48,88], and AQP8 does not appear to contribute greatly to the facilitated transport of water across the mitochondrial membrane [82,89,90], it is plausible that the major function of mitochondrial AQP8 is ammonia diffusional transport [90].…”

“…In addition, the Western blot analyses indicated that in nonactivated spermatozoa the amount of Aqp1ab and -10b in the plasma membrane seems to be lower than that of Aqp1aa, -7, or -8b. The spermatozoa of mammals also express the AQP7 and -8 orthologs, but their localization differs from that in the seabream, since AQP7 is localized in the cytoplasmic droplet and/or the middle piece of the tail and AQP8 is present as a punctuated pattern in the cytoplasmic droplet and along the tail [21,24,26,77]. The expression of Aqp10b in the head and flagella of seabream spermatozoa agrees with our previous report [7], but this is not the case for Aqp1aa, which was previously detected in the head and tail.…”

“…Although the function of AQP11 in the testis is not yet known, because knockout mice die of renal failure before puberty [25], it has been suggested that this channel could be involved in the release of the residual body during spermiogenesis [22]. AQP7, -8, and -11, together with AQP3, are also present in spermatozoa [26][27][28], but they are spatially separated in the head and along the sperm flagellum. In spermatozoa, AQP3 has been suggested to play a role in osmoadaptation and migration [28], AQP7 in sperm energy metabolism and motility [21,26], and AQP8 in spermatozoan volume regulation in response to osmotic challenge [27].…”

Membrane Stress During Thawing Elicits Redistribution of Aquaporin 7 But Not of Aquaporin 9 in Boar Spermatozoa

“…Aquaglyceroporins have been described in fat tissue, suggesting involvement in glycerol export during lipolysis, an important and novel function for these polypeptides . As well, AQP-7 has been found in human spermatozoa (Moretti et al 2011) and in the seminiferous epithelium, suggested as associated with volume regulation in germ cells ). AQP-7 has been immunocytochemically (ICC) detected in boar spermatozoa using different commercial antibodies (Prieto-Mart ınez et al 2014;Vicente-Carrillo 2015) and its role related to sperm quality (Prieto-Mart ınez et al 2014) and/or capacity to react under different osmotic pressures (Vicente-Carrillo 2015).…”

“…Aquaglyceroporins have been described in fat tissue, suggesting involvement in glycerol export during lipolysis, an important and novel function for these polypeptides 14 . As well, AQP-7 has been found in human spermatozoa 15 and in the seminiferous epithelium, being suggested as associated with volume regulation in germ cells 16 . Presumably, this AQP-7 would also provide a port for glycerol as a carbon source for mature sperm metabolism.…”