Abstract Text: The incidence of traumatic brain injury (TBI) has been a persistent risk in the military population and involves neuropathological mechanisms that may include reactive astrogliosis and fluid dysregulation. Aquaporin 4 (AQP4), a predominant astrocyte water channel, has been identified to play an important role in glymphatic fluid regulation as well as both cytotoxic and vasogenic edema after TBI. In this study we used immunohistochemistry combined with western blotting to investigate the time course changes of AQP4 expression and its distribution within perivascular astrocytes in a blast-induced TBI model. Rats under isoflurane anesthesia received a single blast overpressure (BOP) exposure of ~130 kPa (18.85 PSI) in frontal orientation to the blast wave and were euthanized 2-3 hours (h), 24 h, 3, 14, and 28 days post-blast (n=5/group). Sham animals were exposed to all procedures except for BOP exposure and were euthanized 2-3 h after exposure to sham procedures (n=5). The localization of AQP4 in perivascular astrocytic endfeet was visualized by double labeling with the astrocyte marker, glial fibrillary acidic protein (GFAP). Compared with sham group, the overall fluorescence intensity of AQP4 in cortex was significantly increased 2-3 h post-BOP and remained ~20% higher than sham at 24 h. No significant elevations were observed after 24 h. The fluorescence intensity of GFAP in cortex did not change with BOP exposure, which was confirmed by western blotting performed on tissue from a separate cohort of animals exposed to the same blast and time conditions. When fluorescence intensity analyses were performed in perivascular regions only in the cortex, the data show significant increases in AQP4 and GFAP immunofluorescence in the early phase, 24 h post-BOP, compared to sham. In addition, AQP4 was more likely to co-localize with GFAP in the perivascular regions (Pearson’s r=0.67 in BOP vs.0.56 in sham; p< 0.05). Although the fluorescence intensity of AQP4 in perivascular area was similar to sham levels 28 days post-BOP, GFAP was significantly lower at that time point. The data show that BOP exposure may result in acute dysregulation of AQP4 and reactive astrogliosis in the perivascular space and may induce a chronic perivascular astrocytic degeneration. Our data suggests that expressions of perivascular AQP4 and GFAP were significantly altered over time after blast exposure, with redistribution of AQP4 to astrocytic endfeet 24h after BOP exposure. These changes may play a significant part in the formation of neurophysiological deficits observed in military personnel exposed to blast.
DISCLAIMER: The views expressed in this abstract reflect the results of research conducted by the author and do not necessarily reflect the official policy or position of the of The Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., Parsons Corporation, the Department of the Navy, or the Department of Defense (DoD). Mention of trade names, commercial products, or organizations does not imply endorsement by the U.S. Government. This work was supported/funded by work unit number 603115HP.3520.001.A1411. The study protocol was reviewed and approved by the Walter Reed Army Institute of Research/Naval Medical Research Center Institutional Animal Care and Use Committee in compliance with all applicable Federal regulations governing the protection of animals in research. The experiments reported herein were conducted in compliance with the Animal Welfare Act and per the principles set forth in the "Guide for Care and Use of Laboratory Animals," Institute of Laboratory Animals Resources, National Research Council, National Academy Press, 2011 Some of the authors are military service members or federal/contracted employees of the United States Government This work was prepared as part of their official duties. Title 17 U.S.C. § 105 provides that 'Copyright protection under this title is not available for any work of the United States Government.' Title 17 U.S.C. § 101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person's official duties.
