Aquaporin 1 and aquaporin 4 expression in human brain after subarachnoid hemorrhage and in peritumoral tissue.

Aquaporins (AQPs) are a protein family of water channels which facilitate the water flux through the plasmatic membranes. The expression of AQPs has been described in rat brain by several studies. Despite recent reports that have shown an over-expression of AQP1 and 4 in human tumoral cells, little is known about AQP expression in human brain. The purpose of this study was to investigate the expression of AQP1 and AQP4 in human brain after subarachnoid hemorrhage (SAH) and in peritumoral tissue by western blot and immunohistochemistry. The results showed a marked increase of the expression of AQP1 and AQP4. This over-expression occurred on the astrocytic processes and polarization on astrocytic end-feet was lost. No expression was observed on neuronal cells. This study is the first demonstration of the induction of AQP1 and AQP4 on reactive astrocytes in an acute brain injury, such as SAH. These results reinforce the hypothesis that AQPs may be involved in the dynamics of brain edema formation or resolution. Further studies are needed to understand their functional role.

Early acquisition of typical metabolic features upon differentiation of mouse neural stem cells into astrocytes.

Specific metabolic features, such as glutamate reuptake, have been associated with normal functions of mature astrocytes. In this study, we examined whether these characteristics are acquired together with classical phenotypic markers of differentiated astrocytes. Differentiation of E14 mouse neurospheres into astrocytes was induced by the addition of fetal bovine serum (FBS). Degree of differentiation was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence for both GFAP and nestin. Neural stem cells expressed nestin but not GFAP, while differentiated astrocytes were immunopositive for GFAP but displayed low levels of nestin expression. A strong increase in the expression of the glutamate transporter GLAST and the monocarboxylate transporter MCT1 accompanied phenotypic changes. In addition, active glutamate transport appeared in differentiated astrocytes, as well as their capacity to increase aerobic glycolysis in response to glutamate. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor, but not interleukin-6, triggered the expression of phenotypic and morphological characteristics of astrocytes. In addition, exposure to LIF led to the appearance of metabolic features typically associated with astrocytes. Altogether, our results show that acquisition of some specific metabolic features by astrocytes occurs early in their differentiation process and that LIF represents a candidate signal to induce their expression.