Expression of Aquaglyceroporins in Spermatozoa from Wild Ruminants Is Influenced by Photoperiod and Thyroxine Concentrations

Abstract

This work identified the presence of AQPs in frozen-thawed sperm of wild ruminants and assessed the influence of the interaction between photoperiod and thyroxine on AQP expression, and on testosterone secretion. Thyroxine and melatonin were administered to ibexes. In a second experiment, performed in mouflons, circulating thyroxine was reduced via treatment with propylthiouracil (PTU), and an artificial long day (LD) photoperiod established. In the ibexes, the melatonin treatment increased the blood plasma testosterone concentration, reduced the cryoresistance ratio (CR) for sperm viability and the presence of an intact acrosome, and increased the percentage of sperm with AQP7 in the acrosome and of AQP3 and AQP10 in the midpiece. In the mouflons, neither the PTU treatment, the LD, nor the combination of both affected the CR of any sperm variable. The percentage of sperm with AQP3 increased in the post-acrosome region but decreased in the tail in the LD+PTU group. The percentage of sperm with AQP10 in the principal piece and endpiece was lower in the PTU+LD group than in the control and LD groups. The influence of photoperiod/melatonin on AQP expression might be indirectly exerted through changes in the testosterone concentration, and thus ultimately affect sperm cryoresistance.

Variation of existence and location of aquaporin 3 in relation to cryoresistance of ram spermatozoa

“…This is the first study identifying AQP3 in ram sperm. The location of AQP3 in ram spermatozoa was similar to that seen in their wild ancestor, the mouflon ( Ovis musimon ): the acrosome, midpiece, principal piece, and end piece ( 15 ). This location has also been found in dromedary ( 16 ), and boar sperm ( 13 ).…”

“…WB assay showed a band of 32–33 kDa, similar than in wild small ruminants (i.e., mouflon and ibex) ( 15 ), and human, in which a dimer of 62 kDa dimer is also found ( 29 ). Similarly, in stallion sperm, two bands of 30 kDa and 60 kDa (dimer) were observed ( 14 ).…”

“…However, many factors might affect these results; indeed, in other boar sperm study by the same research group, no differences were observed in terms of AQP3 content between GFE and PFE ( 13 ). Among the plausible factors of variation, along with differences in WB procedures (e.g., types and dilution of primary antibodies), we should consider factors that could temporarily affect AQPs location, such as fluctuations of certain hormones: thyroxine, testosterone and melatonin ( 15 ). In addition, some individuals always produce ejaculates with good or bad resistance to cryopreservation processes, but sometimes the same individual may provide ejaculates with a variable cryoresistance, according to their endocrine status, the season ( 7 ), or to unidentified factors.…”

“…In wild ruminant species (ibex, mouflon), with a strong reproductive seasonality, the rutting season is accompanied by the rise of testosterone secretion which, in turn, appears to be linked with the decrease of sperm freezability and the increase of the proportion of spermatozoa with AQP3 in the midpiece ( 27 ). A greater expression of AQP3 in the midpiece of ibex and mouflon frozen-thawed spermatozoa might result in a rapid water and glycerol flux and thus major osmotic stress ( 15 ); however, this study was made exclusively with frozen-thawed samples, so it is unknown if occurred a possible relocation of AQP3. In our study, the increase of AQP3 in both midpiece and principal piece after thawing compared to fresh samples, in GFE ejaculates, might suggest a greater capacity of AQP relocation in ejaculates with better cryoresistance.…”

“…The presence and localization of AQPs in spermatozoa vary between species and cell domains. AQP3 has been identified in bull ( 12 ), boar ( 13 ), stallion ( 14 ), mouflon and ibex ( 15 ), dromedary camel ( 16 ), mouse and human ( 17 ) sperm. Prior to cryopreservation, relative amounts of AQP3 have been found to be higher in ejaculates from boar sperm with good freezability than in ejaculates with poor freezability ( 18 ).…”