title: Aquaporin-4 expression in cultured astrocytes after fluid percussion injury.
abstract: The development of cytotoxic brain edema resulting in increased intracranial pressure is a major cause of death occurring in the early phase of traumatic brain injury (TBI). Such edema predominantly develops as a consequence of astrocyte swelling. We recently documented that fluid percussion injury (FPI) to cultured astrocytes causes cell swelling. Since aquaporin-4 (AQP4) has been strongly implicated in the development of brain edema/astrocyte swelling in various neurological conditions, this study examined the effect of in vitro trauma on AQP4 protein expression in cultured astrocytes. Exposure of astrocytes to FPI resulted in a significant upregulation of AQP4 protein in the plasma membrane due to neosynthesis, as cycloheximide blocked the trauma-induced AQP4 upregulation. Silencing the aqp4 gene by siRNA resulted in a significant reduction in trauma-induced astrocyte swelling, indicating a critical role of AQP4 in this process. We recently documented that oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), and activation of mitogen-activated protein kinases (MAPKs), contribute to trauma-induced astrocyte swelling in culture. We now show that inhibition of these factors reduces the upregulation of AQP4 following trauma. Since TBI has been shown to activate nuclear factor-kappa B (NF-κB), as well as the Na(+),K(+),Cl(-) co-transporter (NKCC), both of which are implicated in brain edema/astrocyte swelling in other conditions, we also examined the effect of BAY 11-7082 and bumetanide, inhibitors of NF-κB and NKCC, respectively, and found that these agents also significantly inhibited the trauma-induced AQP4 upregulation. Our findings show that in vitro trauma upregulates AQP4, and that ONS, MAPKs, mPT, NF-κB, and NKCC are involved in its upregulation.
authors.affiliation: Department of Pathology, University of Miami Miller School of Medicine, Miami, Florida 33101, USA.
authors.forename: Kakulavarapu V Rama
authors.initials: KV
authors.lastname: Rao
authors.forename: Pichili V B
authors.initials: PV
authors.lastname: Reddy
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Curtis
authors.forename: Michael D
authors.initials: MD
authors.lastname: Norenberg
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D051401:Aquaporin 4 / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D015153:Blotting, Western; D001929:Brain Edema / Q000235:genetics / Q000378:metabolism*; D001930:Brain Injuries / Q000235:genetics / Q000378:metabolism*; D002034:Bumetanide / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D048429:Cell Size; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D009570:Nitriles / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects / Q000235:genetics; D034741:RNA, Small Interfering; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D049994:Sodium Potassium Chloride Symporter Inhibitors / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: C434003:3-(4-methylphenylsulfonyl)-2-propenenitrile; D051401:Aquaporin 4; D016328:NF-kappa B; D009570:Nitriles; D034741:RNA, Small Interfering; D049994:Sodium Potassium Chloride Symporter Inhibitors; D013450:Sulfones; D002034:Bumetanide; D020928:Mitogen-Activated Protein Kinases