Laminar-specific and developmental expression of aquaporin-4 in the mouse hippocampus

• Published in: Neuroscience Vol. 178; pp. 21 - 32
• Main Authors: Hsu, M.S, Seldin, M, Lee, D.J, Seifert, G, Steinhäuser, C, Binder, D.K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 31-03-2011; Elsevier
• Subjects: Animals; aquaporin; Aquaporin 4 - biosynthesis; Aquaporin 4 - genetics; astrocyte; Astrocytes - metabolism; Astrocytes - physiology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Developmental - genetics; Gene Expression Regulation, Developmental - physiology; glial cell; Glial Fibrillary Acidic Protein - genetics; Glial Fibrillary Acidic Protein - metabolism; Hippocampus - growth & development; Hippocampus - metabolism; Hippocampus - physiology; Male; Membrane Potentials - physiology; Mice; Mice, Knockout; Mice, Transgenic; Nerve Growth Factors - metabolism; Neurology; Neurons - metabolism; Neurons - physiology; Patch-Clamp Techniques; potassium; Potassium Channels, Inwardly Rectifying - genetics; Reverse Transcriptase Polymerase Chain Reaction - methods; S100 Calcium Binding Protein beta Subunit; S100 Proteins - metabolism; Vertebrates: nervous system and sense organs; water; potassium; molecular layer; stratum lacunosum-moleculare; stratum pyramidale; AQP4; phosphate-buffered saline; aquaporin; EGFP; glial cell; SLM; SO; astrocyte; SP; WT; dentate granule cell layer; ML; SR; PBS; DGC; aquaporin-4; water; GFAP; stratum oriens; stratum radiatum; enhanced green fluorescent protein; wild-type; glial fibrillary acidic protein; Glial cell; Neuroglia; Rodentia; Central nervous system; Astrocyte; Encephalon; Vertebrata; Mammalia; Mouse; Animal; Development; Potassium; Aquaporin; Hippocampus
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2011.01.020

Abstract Mice deficient in the water channel aquaporin-4 (AQP4) demonstrate increased seizure duration in response to hippocampal stimulation as well as impaired extracellular K+ clearance. However, the expression of AQP4 in the hippocampus is not well described. In this study, we investigated (i) the developmental, laminar and cell-type specificity of AQP4 expression in the hippocampus; (ii) the effect of Kir4.1 deletion on AQP4 expression; and (iii) performed Western blot and RT-PCR analyses. AQP4 immunohistochemistry on coronal sections from wild-type (WT) or Kir4.1−/− mice revealed a developmentally-regulated and laminar-specific pattern, with highest expression in the CA1 stratum lacunosum-moleculare (SLM) and the molecular layer (ML) of the dentate gyrus (DG). AQP4 was colocalized with the glial markers glial fibrillary acidic protein (GFAP) and S100β in the hippocampus, and was also ubiquitously expressed on astrocytic endfeet around blood vessels. No difference in AQP4 immunoreactivity was observed in Kir4.1−/− mice. Electrophysiological and postrecording RT-PCR analyses of individual cells revealed that AQP4 and Kir4.1 were co-expressed in nearly all CA1 astrocytes. In NG2 cells, AQP4 was also expressed at the transcript level. This study is the first to examine subregional AQP4 expression during development of the hippocampus. The strikingly high expression of AQP4 in the CA1 SLM and DG ML identifies these regions as potential sites of astrocytic K+ and H2 O regulation. These results begin to delineate the functional capabilities of hippocampal subregions and cell types for K+ and H2 O homeostasis, which is critical to excitability and serves as a potential target for modulation in diverse diseases.