The Oxidative Stress-Induced Increase in the Membrane Expression of the Water-Permeable Channel Aquaporin-4 in Astrocytes Is Regulated by Caveolin-1 Phosphorylation

Abstract

The reperfusion of ischemic brain tissue following a cerebral stroke causes oxidative stress, and leads to the generation of reactive oxygen species (ROS). Apart from inflicting oxidative damage, the latter may also trigger the upregulation of aquaporin 4 (AQP4), a water-permeable channel expressed by astroglial cells of the blood-brain barrier (BBB), and contribute to edema formation, the severity of which is known to be the primary determinant of mortality and morbidity. The mechanism through which this occurs remains unknown. In the present study, we have attempted to address this question using primary astrocyte cultures treated with hydrogen peroxide (H2O2) as a model system. First, we showed that H2O2 induces a significant increase in AQP4 protein levels and that this is inhibited by the antioxidant N-acetylcysteine (NAC). Second, we demonstrated using cell surface biotinylation that H2O2 increases AQP4 cell-surface expression independently of it’s increased synthesis. In parallel, we found that caveolin-1 (Cav1) is phosphorylated in response to H2O2 and that this is reversed by the Src kinase inhibitor 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2). PP2 also abrogated the H2O2-induced increase in AQP4 surface levels, suggesting that the phosphorylation of tyrosine-14 of Cav1 regulates this process. We further showed that dominant-negative Y14F and phosphomimetic Y14D mutants caused a decrease and increase in AQP4 membrane expression respectively, and that the knockdown of Cav1 inhibits the increase in AQP4 cell-surface, expression following H2O2 treatment. Together, these findings suggest that oxidative stress-induced Cav1 phosphorylation modulates AQP4 subcellular distribution and therefore may indirectly regulate AQP4-mediated water transport.

Pharmacokinetics and pharmacodynamics of a single dose Nilotinib in individuals with Parkinson's disease

“…We previously showed that Nilotinib was detected in the human CSF 4 hours after administration but inhibition of CSF Abl extended up to 6 hours, 16 suggesting that free CSF Nilotinib may not be the final or total concentration of drug that enters the brain. Nilotinib exhibits strong and irreversible binding to its target and the level of CSF Nilotinib may reflect the dynamic pharmacological properties of tyrosine kinase inhibitors via interaction with the ATP-binding cassette efflux transporters, [34][35][36] According to the Novartis Investigator Brochure (IB), Nilotinib has a moderate passive permeability and is a PgP inhibitor with an IC50 of 1.7 μmol/L, and this is likely not relevant at the BBB given the low Cmax of 0.06 μmol/L. Furthermore, our mouse studies showed that Nilotinib concentration in the brain increased in an underproportional manner with dose.…”

Water transport proteins-aquaporins (AQPs) in cancer biology

“…H. pylori infection also stimulates the AQP3 level dependent production of proinflammatory cytokines IL-6, IL-8, and TNFα, which adds up to the progression of gastric carcinomas [ 101 ]. Oxidative stress induces an increase in the membrane expression of AQP4 in astrocytes and is regulated by caveolin-1 phosphorylation [ 102 ]. The oxidative stress induced increase in the membrane expression of AQP4 was inhibited by the antioxidant N-acetylcysteine (NAC) [ 102 ].…”

“…Oxidative stress induces an increase in the membrane expression of AQP4 in astrocytes and is regulated by caveolin-1 phosphorylation [ 102 ]. The oxidative stress induced increase in the membrane expression of AQP4 was inhibited by the antioxidant N-acetylcysteine (NAC) [ 102 ].…”

Effects of an Aquaporin 4 Inhibitor, TGN-020, on Murine Diabetic Retina

“…Moreover, NO also causes oxidative stress and death of neurons. Interestingly, another paper by Bi et al showed that hydrogen peroxide (H 2 O 2 ) induces a significant increase in the AQP4 levels in brain astrocytes, and elimination of the oxidative stress depresses the increase [19]. They also showed that H 2 O 2 increases AQP4 plasma membrane expression and that this change is independent of de novo AQP4 synthesis.…”