Effect of melatonin from slow-release implants on aquaporins (AQP1 and AQP4) in the ovine choroid plexus

Aquaporins (AQPs) play important role in the cerebrospinal fluid (CSF) secretion and AQP1 and AQP4 are localized in the choroid plexus (CP), which is the main place of CSF production. In ewes, seasonally breeding animals, the turnover rate (TOR) of CSF is photoperiodically modulated and melatonin, a biochemical signal about changing photoperiod, is used to advance the onset of the breeding season by mimicking the stimulatory effect of short days (SD). This study evaluates the effect of melatonin implantation during long days (LD) on AQPs expression in the ovine CP. Studies were performed on ovariectomized, estradiol implanted ewes treated with placebo (n = 6) or with melatonin (n = 6) during LD. Ewes were sacrificed 40 days after melatonin/placebo implantation and CPs from the lateral/third brain ventricles were collected for Real-time and Western blot analyses. Additionally, for immunohistochemical analysis, CP samples were collected from ewes (n = 3) sacrificed during LD. We demonstrated an apical membrane localization of AQP1 and a diffused distribution of AQP4 in the epithelial cells of CP. The mRNA expression of AQP1 was 20 times higher than the expression of all AQP4 isoforms, and among them AQP4 isoforms containing exon 2 constituted approximately 38%. The melatonin implantation significantly (P < 0.05) increased the mRNA expression of AQP1 and AQP4 and the protein level of AQP4 isoforms (33 and 28 kDa). For AQP1 we observed a significant (P < 0.05) decrease of glycosylated (33 kDa) and a significant (P < 0.05) increase of unglycosylated (23 kDa) predominant protein form. Therefore it can be suggested that at least AQP1, which is involved in CSF production and has been demonstrated to be modulated by melatonin implantation, is linked with the photoperiodic modulation of the CSF production in ewes.