Immunolocalization of AQP9 in Liver, Epididymis, Testis, Spleen, and Brain

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“…In the brain, Aqp9 mRNA was first found in rat astrocytes (11) and confirmed by immunohistochemical studies in the rodent brain (17,264,269,270). In these initial studies, Elkjaer and colleagues (264) reported expression of AQP9 in certain glial cells, including ependymal cells lining the ventricles and tanycytes of the mediobasal hypothalamus, but not in astrocytes or neurons, which was reproduced by others (270).…”

“…Subsequent protein studies confirmed abundant expression in liver, where it was shown to be localized in hepatocytic plasma membranes facing the sinusoids (264,(269)(270)(271). AQP9 protein and mRNA has also been demonstrated in several other organs and cells, including testis (264,271) spleen (264), leukocytes (12,272), lung (12), bone marrow (12), retina (273), adipose tissue (274,275), small intestine and brain (17,264,269).…”

“…To date, eight aquaporins have been described in rodent brain cells, AQP1, AQP2, AQP3, AQP4, AQP5, AQP8, AQP9 and AQP11 (18,(259)(260)(261)(262)(263)(264)(265). Most of them are studied in cell cultures and only three of them are demonstrated in brain at both protein and mRNA level, namely AQP1, AQP4 and AQP9 (15,163).…”

“…In these initial studies, Elkjaer and colleagues (264) reported expression of AQP9 in certain glial cells, including ependymal cells lining the ventricles and tanycytes of the mediobasal hypothalamus, but not in astrocytes or neurons, which was reproduced by others (270). Using PCR, immunocytochemistry and Western blotting, Badaut and colleagues (269) reported the presence of AQP9 in endothelial cells of pial vessels and in astrocyte cell bodies and processes in mice, with high intensity in glia limitans and white matter, as well as in the subfornical organ and cerebellar Bergmann glia (17).…”

“…The presence of AQP9 in astrocytes of glia limitans bordering the subarachnoid space and in tanycytes in the ependymal lining of the cerebral ventricles points to a possible role in water regulation between cerebrospinal fluid and brain parenchyma (264,269), while its location in white matter and hypothalamic nuclei suggests that it may be involved in extracellular water homeostasis. This putative role has been demonstrated in a mouse model of transient focal cerebral ischemia, showing an increase in AQP9 expression in the infarct border zone (269), similarly to AQP4 (291,292), possibly contributing to edema formation.…”