Stichoposide C and Rhizochalin as Potential Aquaglyceroporin Modulators.

Aquaporins (AQPs) are a family of integral membrane proteins that selectively transport water and glycerol across the cell membrane. Because AQPs are involved in a wide range of physiological functions and pathophysiological conditions, AQP-based therapeutics may have the broad potential for clinical utility, including for disorders of water and energy balance. However, AQP modulators have not yet been developed as suitable candidates for clinical applications. In this study, to identify potential modulators of AQPs, we screened 31 natural products by measuring the water and glycerol permeability of mouse erythrocyte membranes using a stopped-flow light scattering method. None of the tested natural compounds substantially affected the osmotic water permeability. However, several compounds considerably affected the glycerol permeability. Stichoposide C increased the glycerol permeability of mouse erythrocyte membranes, whereas rhizochalin decreased it at nanomolar concentrations. Immunohistochemistry revealed that AQP7 was the main aquaglyceroporin in mouse erythrocyte membranes. We further verified the effects of stichoposide C and rhizochalin on aquaglyceroporins using human AQP3-expressing keratinocyte cells. Stichoposide C, but not stichoposide D, increased AQP3-mediated transepithelial glycerol transport, whereas the peracetyl aglycon of rhizochalin was the most potent inhibitor of glycerol transport among the tested rhizochalin derivatives. Collectively, stichoposide C and the peracetyl aglycon of rhizochalin might function as modulators of AQP3 and AQP7, and suggests the possibility of these natural products as potential drug candidates for aquaglyceroporin modulators.

Differential Expressions of Aquaporin Subtypes in the Adult Mouse Testis.

Many efforts have been made to study the expression of aquaporins (AQP) in the mammalian reproductive system, but there are not enough data available regarding their localized expression to fully understand their specific roles in male reproduction. The present study investigated the expression and localization patterns of different AQP subtypes in the adult mouse testes and testicular spermatozoa using an immunofluorescence assay. All the studied AQPs were expressed in the testes and revealed subtype-specific patterns in the intensity and localization depending on the cell types of the testes. AQP7 was the most abundant and intensive AQP subtype in the seminiferous tubules, expressing in Leydig cells and Sertoli cells as well as all stages of germ cells, especially the spermatids and testicular spermatozoa. The expression pattern of AQP3 was similar to that of AQP7, but with higher expression in the basal and lower adluminal compartments rather than the upper adluminalcompartment. AQP8 expression was limited to the spermatogonia and Leydig cells whereas AQP9 expression was exclusive to tails of the testicular spermatozoa and elongated spermatids. Taken together, the abundance and distribution of the AQPs across the different cell types in the testes indicating to their relavance in spermatogenesis, as well as in sperm maturation, transition, and function.

Differential Expressions of Aquaporin Subtypes in Female Reproductive Tract of Mice.

Although many aquaporin (AQP) transcripts have been demonstrated to express in the female reproductive tract, the defined localizations and functions of AQP subtype proteins remain unclear. In this study, we investigated the expression of AQP1, AQP3, AQP5, AQP6, and AQP9 proteins in female reproductive tract of mouse and characterized their precise localizations at the cellular and subcellular levels. Immunofluorescence analyses for AQP1, AQP3, AQP6, and AQP9 showed that these proteins were abundantly expressed in female reproductive tract and that intense immunoreactivities were observed in mucosa epithelial cells with a subtype-specific pattern. The most abundant aquaporin in both vagina and uterine cervix was AQP3. Each of AQP1, AQP3, AQP6, and AQP9 exhibited its distinct distribution in stratified squamous or columnar epithelial cells. AQP9 expression was predominant in oviduct and ovary. AQP1, AQP3, AQP6, and AQP9 proteins were mostly seen in apical membrane of ciliated epithelial cells of the oviduct as well as in both granulosa and theca cells of ovarian follicles. Most of AQP subtypes were also expressed in surface epithelial cells and glandular cells of endometrium in the uterus, but their expression levels were relatively lower than those observed in the vagina, uterine cervix, oviduct and ovary. This is the first study to investigate the expression and localization of 5 AQP subtype proteins simultaneously in female reproductive tract of mouse. Our results suggest that AQP subtypes work together to transport water and glycerol efficiently across the mucosa epithelia for lubrication, proliferation, energy metabolism and pH regulation in female reproductive tract.