Aquaporin 9 is expressed in the epididymis of immature and mature pigs

Abstract

Aquaporins (AQPs) are channel proteins that facilitate the transepithelial and bidirectional movement of water. AQP9 is an aquaporin that is expressed in the mammalian epididymis. This water transport contributes to epididymal sperm concentration. This study aimed to examine the morphology of epididymal epithelium in piglets and boars, as well as the expression and immunolocalization of AQP9. The piglets presented an epididymal epithelium in differentiation with principal, basal and apical cells. The cellular population of the epididymal epithelium in boars consisted of principal, basal, apical, clear and narrow cells. The migratory cells known as halo cells were observed in the epididymis of both piglets and boars. AQP9 expression presented differences between piglets and boars. Moderate intensity of AQP9 immunoreaction was observed in the apical border of the epididymal epithelium of the caput and cauda regions in the piglet epididymis. A moderate-to-intense reaction for AQP9 was observed in the nuclei of epithelial cells of the three epididymal regions in the boar epididymis. The region of the cauda epididymis showed reactivity for AQP9 also in the apical border of the epithelium. It is believed that the AQP9 is already functional in piglets at only 1 week of age and is more active, playing a pivotal role in the caput and cauda regions of the epididymis. Moreover, the intense AQP9 expression in the apical border of epithelial cells in the cauda region of the boar epididymis suggests a higher performance of AQP9 in this region, where sperm complete their maturation process, stored and concentrated.

The expression and localization of V-ATPase and cytokeratin 5 during postnatal development of the pig epididymis

“…In this study, we initially examined the early development and differentiation of CCs and BCs in pig epididymis using antibodies directed against B1-VATPase and KRT5, Consistent with the findings of previous studies using rodents, we observed that both of these cell types initially appear in the vas deferens, then in the cauda, and subsequently in more proximal segments of the pig epididymis. Contrastingly, previous studies have indicated that CCs do not appear in the epididymis until PND7 and are present in the caput and cauda of adult epididymides, whereas BCs are detected in all regions of the pig epididymis from PND7 [23]. We suspect that these disparities between observations made in the present and previous studies can be attributed to differences in the techniques used to detect epididymal epithelial cells.…”

“…It has been suggested that species-specific mechanisms are required for the maintenance of luminal acidification. Recently, it has been demonstrated that AQP9 is expressed in the nuclei of epithelial cells in the caput and cauda regions of the pig epididymis, whereas in the distal region of the duct, the cauda epididymis, this protein is expressed at the apical surface of the epithelium [23]. These observations suggest the possibility that PCs in the cauda and thus interact to a greater extent with the BCs to regulate luminal acidification [16].…”

“…Accordingly, it is necessary to employ cell-specific markers to identify each type of epithelial cell during early postnatal development. Recently, Schimming et al [23] reported that BCs can be detected in all regions of the pig epididymis at PND7. However, in the present study, we were unable to detect the ubiquitous distribution of these cells in the epididymis until PND60.…”

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

“…In several species, such as rats, sheep, pigs, cats, dogs and horses, AQP9 is present in the plasma membrane of the Leydig cells, microvilli of non‐ciliated cells of the efferent ducts, microvilli of principal cells in all epididymal regions and in the epithelial cells of the prostate and coagulating gland (Arrighi & Aralla, ; Badran & Hermo, ; Domeniconi, Orsi, Justulin, Beu, & Felisbino, ; Ford et al., ; Hermo & Smith, ; Klein et al., ; Pastor‐Soler et al., ; Schimming et al., ; Schimming, Baumam, Pinheiro, de Matteis, & Domeniconi, ; Table ). Nevertheless, there are some variations between species.…”

“…() observed that AQP9 staining was stronger in corpus and cauda than in caput epididymis and also found AQP9 in the initial segment of the vas deferens. In the pig, localization of AQP9 has been found to vary along the age (Schimming et al., ). In effect, whereas AQP9 is restricted to the apical region of epithelial cells in caput and corpus of pre‐pubertal animals, post‐pubertal animals show AQP9 staining in the nuclei of epithelial cells of all the epididymal regions (Schimming et al., ).…”