Expression of aquaporin 1 and aquaporin 4 water channels in rat choroid plexus

Abstract

The role of aquaporins in cerebrospinal fluid (CSF) secretion was investigated in this study. Western analysis and immunocytochemistry were used to examine the expression of aquaporin 1 (AQP1) and aquaporin 4 (AQP4) in the rat choroid plexus epithelium. Western analyses were performed on a membrane fraction that was enriched in Na(+)/K(+)-ATPase and AE2, marker proteins for the apical and basolateral membranes of the choroid plexus epithelium, respectively. The AQP1 antibody detected peptides with molecular masses of 27 and 32 kDa in fourth and lateral ventricle choroid plexus. A single peptide of 29 kDa was identified by the AQP4 antibody in fourth and lateral ventricle choroid plexus. Immunocytochemistry demonstrated that AQP1 is expressed in the apical membrane of both lateral and fourth ventricle choroid plexus epithelial cells. The immunofluorescence signal with the AQP4 antibody was diffusely distributed throughout the cytoplasm, and there was no evidence for AQP4 expression in either the apical or basolateral membrane of the epithelial cells. The data suggest that AQP1 contributes to water transport across the apical membrane of the choroid plexus epithelium during CSF secretion. The route by which water crosses the basolateral membrane, however, remains to be determined.

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

“…The mRNA expression profile of AQPs in the ovine CP showed 20 times higher expression of AQP1 compared to all isoforms of AQP4. AQP1 was found to be located almost exclusively in the apical membrane of the CP epithelium, which is in agreement with earlier studies that were conducted on rat CPs (Nielsen et al 1993;Speake et al 2003). This localization directly indicates the involvement of AQP1 in the transport of water through the apical membrane of the CP and, therefore, the involvement of AQP1 in CSF production (Owler et al 2010).…”

“…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).…”

The formation of cerebrospinal fluid: Nearly a hundred years of interpretations and misinterpretations

“…The third reason why the choroid plexuses are considered to the main site of formation should be the fact that the observations mentioned so far were accompanied by a significant number of concurrent studies that pointed to CSF formation by the choroid plexuses (Dandy, 1919;de Rougemont et al, 1960;Pollay et al, 1972;Weed, 1914;Welch, 1963) , and the secretory character of the choroid plexuses was confirmed by the application of the molecular biological methods during the past two decades (Brown et al, 2004;Johanson, 2008;Kanaka et al, 2001;Li et al, 2002;Oshio et al, 2005;Praetorius et al, 2004;Speake et al, 2003;Watts et al, 1991;Zlokovic et al, 1993).…”

“…The secretory character of choroid plexuses that involves pumps, cotransporters and antiporters, ion channels and aquaporins has been confirmed during the past 15 years by the application of molecular biological methods (Brown et al, 2004;Johanson, 2008;Kanaka et al, 2001;Li et al, 2002;Oshio et al, 2005;Praetorius et al, 2004;Speake et al, 2003;Watts et al, 1991;Zlokovic et al, 1993).…”