engleski

Gender differences exist in the expression of AQP1 along the rat nephron

Objective. Aquaporin 1 (AQP1) is a constitutive water channel in the mammalian proximal tubules and descending thin limbs, where it exists in both nonglycosylated (NG) and glycosylated (G) forms. (Patho)physiological conditions that may influence AQP1 expression along the nephron have been poorly investigated. Material and methods. To study possible gender differences and effects of sex hormones on renal AQP1 expression, we used a polyclonal, C-terminal peptide-specific antibody, and performed immunocytochemistry (IC) on cryostat tissue sections and Western blotting (WB) of cell membranes isolated from various kidney zones of the adult, pre-pubertal and gonadectomized male (M) and female rats (F), and of F in various stages of the estrus cycle. Results. Quantitative IC revealed that the AQP1-related immunostaining (average pixel intensity) in the cortex (C), outer stripe (OS), inner stripe (IS), and inner medulla (IM) was by 23%, 37%, 48%, and 33%, respectively, stronger in adult M than in F (P<0.05). These findings were confirmed by densitometric evaluation of the WB data in total cell membranes (TCM) from various tissue zones, and in brush-border and basolateral membranes isolated from the kidney C and OS. However, the observed gender differences were clearly confined only to the G form of the protein, and were always stronger in membranes from the OS. In TCM from various renal zones in prepubertal (3-week-old) rats, gender differences in the expression of AQP1 could not be demonstrated. Following castration in adult M, the expression of AQP1 both forms in TCM from various kidney zones remained unchanged, but following ovariectomy in F, the expression of G form in TCM from the OS significantly increased. Searching for possible effects of the estrus cycle upon renal AQP1, we correlated the expression of this water channel in various kidney zones with the serum levels of sex hormones in 4 stages of the cycle. Limited effects were found in the C, where expression of the protein was low in the stage D1 (high progesterone/low estrogen), high in the stage D2 (low progesterone/low estrogen), and intermediate in the stages P (low progesterone/high estrogen) and E (low progesterone/low estrogen), whereas in the OS, no clear effects were observed. Conclusions. The data indicate that: a) gender differences exist in the expression of AQP1 along the adult rat nephron (M>F), which are largely confined to the G form of the protein, b) the observed gender differences are caused by the inhibitory effects of female sex hormones, and c) the expression of AQP1 along the rat nephron may be to some extent modulated by ovarian hormones in the estrus cycle.

estrus cycle; kidney; membrane transporters; sex differences; sex hormones; water channels

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