AQP4 expression in striatal primary cultures is regulated by dopamine – implications for proliferation of astrocytes

Abstract

Proliferation of astrocytes plays an essential role during ontogeny and in the adult brain, where it occurs following trauma and in inflammation and neurodegenerative diseases as well as in normal, healthy mammals. The cellular mechanisms underlying glial proliferation remain poorly understood. As dopamine is known to modulate proliferation in different cell populations, we investigated the effects of dopamine on the proliferation of striatal astrocytes in vitro. We found that dopamine reduced proliferation. As proliferation involves, among other things, a change in cell volume, which normally comes with water movement across the membrane, water channels might represent a molecular target of the dopamine effect. Therefore we studied the effect of dopamine on aquaporin 4 (AQP4) expression, the main aquaporin subtype expressed in glial cells, and observed a down-regulation of the AQP4-M23 isoform. This down-regulation was the cause of the dopamine-induced decrease in proliferation as knockdown of AQP4 using siRNA techniques mimicked the effects of dopamine on proliferation. Furthermore, stimulation of glial proliferation by basic fibroblast growth factor was also abolished by knocking down AQP4. In addition, blocking of AQP4 with 10 mum tetraethylammonium inhibited osmotically induced cell swelling and stimulation of glial cell proliferation by basic fibroblast growth factor. These results demonstrate a clear-cut involvement of AQP4 in the regulation of proliferation and implicate that modulation of AQP4 could be used therapeutically in the treatment of neurodegenerative diseases as well as in the regulation of reactive astrogliosis by preventing or reducing the glia scar formation, thus improving regeneration following ischemia or other trauma.

Aggravated inflammation and increased expression of cysteinyl leukotriene receptors in the brain after focal cerebral ischemia in AQP4-deficient mice

“…such an inhibition could also be induced by knockdown of AQP4 using siRNA in vitro [19] . The attenuated astrocyte responses might be related to aggravated cellular inflammation in AQP4-KO mice.…”

“…In these changes, NMOIgG-induced dysfunction of astrocytes is the determining event because activated astrocytes limit the development of inflammation [12,18] . AQP4 is also important in astrocyte proliferation, one of the responses to inflammation, because AQP4 knockdown using siRNA inhibits astrocyte proliferation [19] .…”

Dopamine Regulates the Expression of the Glutamate Transporter GLT1 but Not GLAST in Developing Striatal Astrocytes

“…Visualization of the primary antibody was performed by incubating membranes with the corresponding secondary antisera for 1 h at RT followed by enzyme-linked chemoluminescence reaction (Amersham). Quantitative analysis of western blots was accomplished densitometrically with a fluorescent scanner (ImageMaster, Pharmacia, Germany) as described (Küppers et al 2008a, b).…”

Astrocyte Function in Alcohol Reward and Addiction

“…Rapid swelling and regulatory volume decrease is facilitated by astrocytic water channels built up by the protein aquaporin-4 [81,82], and reduced aquaporin-4 expression has in fact also been linked to excessive alcohol consumption [83]. Interestingly, aquaporin-4 expression is depressed by dopamine, while genetic deletion of aquaporin-4 reduces accumbal dopamine [81]. Antagonists targeting dopamine D1 and D2 receptors has also been shown to increase astrocyte calcium excitability, synchrony and gap junction coupling [84], indicating that astrocytes may monitor extra synaptic dopamine levels.…”

“…Considering the role of dopamine in mediating the rewarding sensation of drugs of abuse, it is thus possible that astrocytes are indirectly involved in ethanol-induced reinforcement [65, 79,80]. Rapid swelling and regulatory volume decrease is facilitated by astrocytic water channels built up by the protein aquaporin-4 [81,82], and reduced aquaporin-4 expression has in fact also been linked to excessive alcohol consumption [83]. Interestingly, aquaporin-4 expression is depressed by dopamine, while genetic deletion of aquaporin-4 reduces accumbal dopamine [81].…”