Acute vascular disruption and aquaporin 4 loss after stroke.
OBJECTIVE
Ischemic protection has been demonstrated by a decrease in stroke-infarct size in transgenic mice with deficient Aquaporin 4 (AQP4) expression. However, it is not known whether AQP4 is rapidly reduced during acute stroke in animals with normal AQP4 phenotype, which may provide a potential self-protective mechanism.


METHODS
Adult male rats underwent transient occlusion of the middle cerebral artery (tMCAo) for 1 to 8 hours followed by reperfusion for 30 minutes. Protein and mRNA expression of AQP4 and glial fibrillary acidic protein (GFAP) were determined by Western blot and rtPCR. Fluorescence quantitation was obtained with laser scanning cytometry (LSC) for Cy5-tagged immunoreactivity along with fluorescein signals from pathological uptake of plasma-borne high-molecular-weight fluorescein-dextran. Cell death was assessed with in vivo Propidium Iodide (PI) nucleus labeling.


RESULTS
In the ischemic hemisphere in tissue sections, patches of fluorescein-dextran uptake were overlapped with sites of focal loss of AQP4 immunoreactivity after tMCAo of 1 to 8 hours duration. However, the average levels of AQP4 protein and mRNA, determined in homogenates of whole striatum, were not significantly reduced after 8 hours of tMCAo. Tissue section cytometry (LSC) of immunoreactivity in scan areas with high densities of fluorescein-dextran uptake demonstrated reductions in AQP4, but not in IgG or GFAP, after tMCAo of 2 hours or longer. Scan areas with low densities of fluorescein-dextran did not lose AQP4. There was sparse astrocyte cell death as only 1.7+/-0.85% (mean, SD) of DAPI labeled cells were PI- and GFAP-labeled after 8 hours of tMCAo.


CONCLUSIONS
During acute tMCAo, a rapid loss of AQP4 immunoreactivity from viable astrocytes can occur. However, AQP4 loss is spatially selective and occurs primarily in regions of vascular damage.
Friedman
Beth
B
Department of Neurosciences, UCSD School of Medicine, San Diego, CA, USA.
Schachtrup
Christian
C
Tsai
Philbert S
PS
Shih
Andy Y
AY
Akassoglou
Katerina
K
Kleinfeld
David
D
Lyden
Patrick D
PD
D000208:Acute Disease; D000818:Animals; D051401:Aquaporin 4 / Q000378:metabolism*; D001253:Astrocytes / Q000473:pathology; D001808:Blood Vessels / Q000378:metabolism* / Q000473:pathology*; D015153:Blotting, Western; D001929:Brain Edema / Q000473:pathology; D002196:Capillaries / Q000473:pathology; D004396:Coloring Agents; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D008297:Male; D036641:Microscopy, Fluorescence, Multiphoton; D020768:Middle Cerebral Artery / Q000473:pathology; D011419:Propidium; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley; D015424:Reperfusion; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020521:Stroke / Q000473:pathology*
D051401:Aquaporin 4; D004396:Coloring Agents; D005904:Glial Fibrillary Acidic Protein; D011419:Propidium; D012313:RNA