Aquaporin 4 correlates with apparent diffusion coefficient and hydrocephalus severity in the rat brain: A combined MRI–histological study

Hydrocephalus features include ventricular dilatation and periventricular edema due to transependymal resorption of cerebrospinal fluid (CSF). Aquaporin 4 (AQP4), a water channel protein located at the blood-brain barrier, might facilitate the removal of this excess of water from the parenchyma into the blood. First, we hypothesized a link between AQP4 expression and the severity of hydrocephalus. We further hypothesized that movements of water through AQP4 could affect apparent diffusion coefficient (ADC) measurements. Communicating inflammatory hydrocephalus was induced in 45 rats, and at various stages, magnetic resonance imaging (MRI) was used to measure CSF volume and periventricular ADC, with immunostaining being used to determine periventricular AQP4. We found an up-regulation of periventricular AQP4 in hydrocephalic rats that was strongly correlated with both CSF volume (Pearson=0.87, p<0.00001) and periventricular ADC (Pearson=0.85, p<0.00001). AQP4 were first located on astrocyte endfeet, but later on the whole membrane of astrocytes that became hypertrophic in the most severe and chronic hydrocephalic rats. These results show that AQP4 expression follows an adaptative profile to the severity of hydrocephalus, which is probably a protective response mechanism. They also suggest that ADC, on top of informing about cell sizes and interstitial bulk water, might also indirectly reflect quantitative water channel expression.

[1]  Hajime Arima,et al.  Interleukin-1beta induces the expression of aquaporin-4 through a nuclear factor-kappaB pathway in rat astrocytes. , 2006, Journal of neurochemistry.

[2]  M. Papadopoulos,et al.  Aquaporin-4 expression is increased in oedematous human brain tumours , 2002, Journal of neurology, neurosurgery, and psychiatry.

[3]  Tony Wyss-Coray,et al.  Insights into the Pathogenesis of Hydrocephalus from Transgenic and Experimental Animal Models , 2004, Brain pathology.

[4]  D. Le Bihan The ‘wet mind’: water and functional neuroimaging , 2007, Physics in medicine and biology.

[5]  Ole Petter Ottersen,et al.  An α-syntrophin-dependent pool of AQP4 in astroglial end-feet confers bidirectional water flow between blood and brain , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[6]  Pierre J Magistretti,et al.  Aquaporins in Brain: Distribution, Physiology, and Pathophysiology , 2002, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[7]  O. P. Ottersen,et al.  Towards a molecular understanding of water homeostasis in the brain , 2004, Neuroscience.

[8]  W. Bradley,et al.  Flowing cerebrospinal fluid in normal and hydrocephalic states: appearance on MR images. , 1986, Radiology.

[9]  Williams Ma,et al.  Cerebrospinal fluid circulation, cerebral edema, and intracranial pressure. , 1993 .

[10]  G. Manley,et al.  Aquaporin‐4 facilitates reabsorption of excess fluid in vasogenic brain edema , 2004, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[11]  M. D. Bigio,et al.  Neuropathological changes caused by hydrocephalus , 2004, Acta Neuropathologica.

[12]  S. Browd,et al.  Failure of cerebrospinal fluid shunts: part I: Obstruction and mechanical failure. , 2006, Pediatric neurology.

[13]  B Quesson,et al.  In vivo evaluation of remyelination in rat brain by magnetization transfer imaging , 2000, Journal of the Neurological Sciences.

[14]  Jonathan Nissanov,et al.  Assessment of axonal fiber tract architecture in excised rat spinal cord by localized NMR q‐space imaging: Simulations and experimental studies , 2004, Magnetic resonance in medicine.

[15]  Ayako Nakamura,et al.  Enhanced expression of aquaporin 4 in human brain with inflammatory diseases , 2005, Acta Neuropathologica.

[16]  A Benazzouz,et al.  Lysolecithin-induced demyelination in primates: preliminary in vivo study with MR and magnetization transfer. , 1995, AJNR. American journal of neuroradiology.

[17]  J. Baraban,et al.  Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance. , 1994, Proceedings of the National Academy of Sciences of the United States of America.

[18]  Geoffrey T Manley,et al.  Accelerated Progression of Kaolin-Induced Hydrocephalus in Aquaporin-4-Deficient Mice , 2006, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[19]  Hajime Arai,et al.  Expression of the water-channel protein aquaporin 4 in the H-Tx rat: possible compensatory role in spontaneously arrested hydrocephalus. , 2006, Journal of neurosurgery.

[20]  Denis Le Bihan,et al.  Looking into the functional architecture of the brain with diffusion MRI , 2003, Nature Reviews Neuroscience.

[21]  P. Agre,et al.  Specialized Membrane Domains for Water Transport in Glial Cells: High-Resolution Immunogold Cytochemistry of Aquaporin-4 in Rat Brain , 1997, The Journal of Neuroscience.

[22]  Geoffrey T. Manley,et al.  Involvement of aquaporin-4 in astroglial cell migration and glial scar formation , 2005, Journal of Cell Science.

[23]  Petter Laake,et al.  Temporary loss of perivascular aquaporin-4 in neocortex after transient middle cerebral artery occlusion in mice , 2006, Proceedings of the National Academy of Sciences.

[24]  A S Verkman,et al.  Three distinct roles of aquaporin-4 in brain function revealed by knockout mice. , 2006, Biochimica et biophysica acta.

[25]  M. D. Del Bigio,et al.  Aquaporin 4 changes in rat brain with severe hydrocephalus , 2006, The European journal of neuroscience.

[26]  Hajime Arima,et al.  Interleukin‐1β induces the expression of aquaporin‐4 through a nuclear factor‐κB pathway in rat astrocytes , 2006 .

[27]  Geoffrey T Manley,et al.  Aquaporin‐4 gene deletion in mice increases focal edema associated with staphylococcal brain abscess , 2005, Journal of neurochemistry.

[28]  Kenji Ikeda,et al.  Enhanced expression of aquaporin 4 in human brain with infarction , 2003, Acta Neuropathologica.

[29]  M. C. Papadopoulos,et al.  Molecular mechanisms of brain tumor edema , 2004, Neuroscience.