Expression of Aquaporins in the Rat Choroid Plexus

Abstract

Background: Aquaporins (AQPs) are water channels that play a key role in water transport in many epithelia. Recent studies have shown that AQP1, located in the apical membrane of choroid plexus cells, has an important role in cerebrospinal fluid (CSF) production. However, the mechanism of water transport through the basolateral membrane of choroid plexus (CP) cells is yet to be determined. Objectives: In this study, the expression and localization of AQP1, AQP4 and AQP5 in the rat lateral ventricle CP were investigated by immunocytochemistry, western analysis and flowcytometry. Materials and Methods: Choroidal epithelial cells of the lateral ventricle in Wistar rats were isolated and grown in Dulbecco's Modified Eagle's medium (DMEM) supplement, which was refreshed every two days. After five days, the expression patterns of AQP1, AQP4 and AQP5 were determined by immunoblotting, immuncytochemistry and flowcytometry. Results: The immunocytochemistry data revealed the expression of AQP1 and AQP4 in the membrane and the cytoplasmof AP cells, respectively. Through western analysis, the AQP1 antibody detected two bands of approximately 27 and 32 kDa. A single peptide of 29 kDa was recognized by the AQP4 antibody. Quantitative flowcytometry revealed CP cells exhibiting a high level of AQP1 and AQP4 proteins (95.39% and 92.21%, respectively). According to immunocytochemistry, AQP5 is weakly expressed in the cytoplasm of CP cells. Anti-AQP5 antibody recognized a pale band of approximately28 kDa by western analysis. Conclusions: These observations suggested that AQP4 may have an important role in CSF secretion; however, expression of AQP4 or AQP5 was not detected in the cell membrane. Thus, how water crosses the basolateral membrane of CP cells remains to be determined.

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

“…Using Western blot we showed the presence of 33 and 23 kDa bands, which seems to be immunoreactive AQP1 protein, since their signals were completely or mostly blocked through using pre-adsorbed antibodies. Our results are similar to that obtained by Nesic et al (2008) demonstrating the presence of fuzzy band of 37 kDa in cytosolic fraction and 24 kDa band in the membrane fraction of rat spi- Nazari et al (2015) observed 32 and 27 kDa immunoreactive bands in the rat CP. According to Nielsen et al (1993) these bands may correspond with glycosylated and unglycosylated forms of AQP1, respectively.…”

“…According to Nielsen et al (1993) these bands may correspond with glycosylated and unglycosylated forms of AQP1, respectively. The localization of AQP4 in the ovine CP, which can be characterized as diffuse in the cytoplasm of epithelial cells, is in line with the findings of Speake et al (2003) and Nazari et al (2015). It has been demonstrated that rat AQP4 has six cDNA isoforms which are differentially expressed in the kidney and brain (Moe et al 2008).…”

“…AQP1 is abundant on the apical (CSF-facing) surface of rat CPs from the fourth and lateral ventricles (Nielsen et al 1993;Speake et al 2003), therefore during the CSF secretion it plays a major role in mediating water transport across the apical membrane (Oshio et al 2005). The mRNA for AQP4 was initially detected in rat CPs from lateral ventricles, using the hybridization in situ method (Venero et al 1999), thereafter also AQP4 protein was detected as diffusely distributed throughout the epithelial cells of rat CPs from the fourth and lateral ventricles (Speake et al 2003;Nazari et al 2015). It has been demonstrated that in rats the expression of AQP4 protein in astrocytes and AQP1 protein in spinal cord may be modulated by melatonin (Kaur et al 2006;Nesic et al 2008).…”

“…AQPs, small integral membrane proteins (molecular weight (MW) ~30 kDa) constitute a ten-member family of water channels which play a major role during water transport in the kidney, brain secretory epithelia, and other organs (Agre et al 2002). From this family, AQP1, AQP4, AQP5, AQP9, and AQP11 have been identified in the central nervous system (King and Agre 1996;Nazari et al 2015). AQP4 and AQP1 play vital roles in the dynamic regulation of brain water homeostasis and the regulation of CSF production (Venero et al 2001).…”

“…The CSF secretion involves regulated transport of Na + , Cl -, and HCO 3 -from the blood to the ventricles, creating an osmotic gradient driving the transcellular secretion of water through water channels -aquaporins (AQPs) (Nazari et al 2015). AQPs, small integral membrane proteins (molecular weight (MW) ~30 kDa) constitute a ten-member family of water channels which play a major role during water transport in the kidney, brain secretory epithelia, and other organs (Agre et al 2002).…”