Increased expression of aquaporin-4 in human traumatic brain injury and brain tumors

Increased expression of aquaporin-4 in human traumatic brain injury and brain tumors 1 2 first-author 3 1 1 3 1 1 1 †E-mail:weieq2001@yahoo.com †E-mail:weieq2001@yahoo.com weieq2001@yahoo.com Department of Neurosurgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310009, China Department of Neurosurgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310009, China Department of Pharmacology, School of Medicine, Zhejiang University, Hangzhou 310031, China Department of Pharmacology, School of Medicine, Zhejiang University, Hangzhou 310031, China Department of Pathology, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310003, China Department of Pathology, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou 310003, China Objective: 2 To characterize the expression of aquaporin-4 (AQP4), one of the aquaporins (AQPs), in human brain specimens from patients with traumatic brain injury or brain tumors. Methods: 2 Nineteen human brain specimens were obtained from the patients with traumatic brain injury, brain tumors, benign meningioma or early stage hemorrhagic stroke. MRI or CT imaging was used to assess brain edema. Hematoxylin and eosin staining were used to evaluate cell damage. Immunohistochemistry was used to detect the AQP4 expression. Results: 2 AQP4 expression was increased from 15 h to at least 8 d after injury. AQP4 immunoreactivity was strong around astrocytomas, ganglioglioma and metastatic adenocarcinoma. However, AQP4 immunoreactivity was only found in the centers of astrocytomas and ganglioglioma, but not in metastatic adenocarcinoma derived from lung. Conclusion: 2 AQP4 expression increases in human brains after traumatic brain injury, within brain-derived tumors, and around brain tumors. Aquaporin-4 (AQP4) Traumatic brain injury Astrocytoma Ganglioglioma Metastatic adenocarcinoma Brain edema INTRODUCTION 1 Brain edema is associated with common brain injuries such as head trauma, brain tumor, stroke, brain abscess and circulation failure. Water transport across microvasculature is a main cause of brain edema, a phenomenon that was once believed to be the result of simple diffusion. A recently described family of water channel proteins (aquaporins, AQPs) facilitates the passage of water and other small solutes across membranes and through cells, including the vascular endothelium, so study of aquaporins may shed light on the treatment of brain edema (Denker et al., 1988 1988 ). AQP4 belongs to the aquaporin family, which includes 11 subtypes (AQP0 to AQP10). Among these, AQP4 is unique because of its exceptionally high intrinsic water permeability and predominant location in brain (Yang and Verkman, 1997 1997 ). AQP4 is expressed in astrocyte foot processes adjacent to vascular endothelial cells, and in the basolateral membrane of the ependymal cells but not in neurons (Nielsen et al., 1997 1997 ; Rash et al., 1998 1998 ; Saadoun et al., 2002 2002 ). AQP4 is proposed to play an important role in water homeostasis in the brain and in formation of brain edema (Nielsen et al., 1997 1997 ). Recently, AQP4 expression has been investigated to clarify its role in the development of brain injury. It has been reported that AQP4 is increased at the injury site in rat traumatic brain injury (Sun et al., 2003 2003 ), and is up-regulated following non-traumatic brain injury such as stroke or water intoxication in rodents (Taniguchi et al., 2000 2000 ). In AQP4 gene knockout mice, there is less brain swelling 24 h after brain ischemia (Manley et al., 2000 2000 ). In a human brain autopsy study, AQP4 immunoreactivity was found increased after cerebral infarction (Aoki et al., 2003 2003 ). However, the expression characteristics of AQP4 in human traumatic brain injury are unknown. Furthermore, in human brains, AQP4 expression increases in edematous human astrocytomas, and there is significant correlation between up-regulation of AQP4 expression and breakdown of the blood-brain barrier (Aoki et al., 2003 2003 ; Saadoun et al., 2002 2002 ). Most malignant brain tumors, including gliomas and metastatic adenocarcinoma, are associated with considerable brain edema. Whether gliomas and metastatic adenocarcinoma activate astrocytes and increase AQP4 expression remains unknown. The aim of this study was to clarify the properties of AQP4 expression in human traumatic brain injury and brain tumors (astrocytoma, ganglioglioma and metastatic adenocarcinoma) using biopsy specimens from brain surgery. This may help determine the mechanisms responsible for brain edema associated with brain injury and brain tumors. MATERIALS AND METHODS 1 Patients 2 This study was approved by the ethics committee of the Second Affiliated Hospital, School of Medicine, Zhejiang University. Brain specimens were obtained from 17 patients (Nos. 3~19 in Table 1 1 ) who underwent brain surgery because of traumatic brain injury or brain tumors. Two relatively normal specimens were from patients with benign meningioma (No. 1 in Table 1 1 ) and hemorrhagic stroke in an early stage (No. 2 in Table 1 1 ). MRI or CT images were taken to evaluate brain edema. A neuropathologist without knowledge of the results described here examined the patients. The diagnosis of each brain tumor was established according to the usual criteria pertaining to the clinical MRI picture, appropriate laboratory data and biopsy findings. Astrocytomas and ganglioglioma were classified as low (I–II) or high grades (III–IV) according to the Daumas-Duport criteria (Table 1 1 ). NA: not applicable; ND: not detected; −: no expression, +: mild, ++: moderate, +++: strong Histology No. Age and sex Duration from onset Side Grade Adjacent to lesions Center of lesions Control –Benign meningioma 1 51 F NA L NA + ND –Hemorrhagic stroke 2 63 F 6 h L NA + ND 9 Traumatic brain injury 3 55 M 6 h R NA ND + 4 51 M 9 h L NA ND ++ 5 30 M 14 h R NA ND + 6 52 M 15 h R NA ND ++ 7 52 M 1 d R/L NA ND ++ 8 21 M 1 d R/L NA ND +++ 9 71 M 2.5 d R NA ND +++ 10 21 F 3 d L NA ND ++ 11 39 M 8 d R NA ND +++ 5 Astrocytoma 12 42 F NA L II +++ +++ 13 38 F NA R III +++ +++ 14 82 M NA L III–IV +++ ++ 15 64 M NA L II–III +++ ++ 16 29 F NA L II +++ ++ Ganglioglioma 17 52 M NA L II +++ +++ 2 Metastatic adenocarcinoma 18 55 M NA L NA +++ − 19 51 F NA R NA +++ − Materials 2 Primary antibody against AQP4 was purchased from Santa Crutz, USA. Anti-goat IgG biotinylated secondary antibodies, avidin biotin complex and diaminobenzidine tetrahydrochloride were purchased from Zymed, USA. Other reagents were commercial products with analytic purity. Histopathological examination and immunohistoc-hemistry 2 Brain tissues were fixed in 4% formaldehyde for 24~48 h and then embedded in paraffin. Six μm sections were cut and stained with hematoxylin and eosin (HE). Adjacent sections were incubated with a primary antibody against AQP4 (1:300) for 1 d at 4 °C. Sections were sequentially incubated with anti-goat IgG biotynylated secondary antibodies and avidin biotin complex. Sections were finally visualized with 0.01% diaminobenzidine tetrahydrochloride (DAB) and 0.005% H 2 O 2 in 50 mmol/L Tris-HCl, pH 7.6. To test the specificity of the immunohistochemical reaction, control sections were treated with normal goat serum instead of the primary antibody. Nuclei were counterstained by hematoxylin. RESULTS 1 AQP4 expression in non-edematous brain 2 No edema was found around the benign meningioma by using MRI (Fig. 1a 1a ), and HE staining showed normal structure (Fig. 1b 1b ). The brain specimen from the patient with hemorrhagic stroke in an early stage was similar (data not shown). AQP4 immunoreactivity (brown deposit) was detected over cell processes surrounding microvessels in these brain samples (Fig. 2a 2a and Nos. 1 and 2 in Table 1 1 ). AQP4 expression in traumatic brain injury 2 Brain edema was found in the area surrounding traumatic brain injury by using CT (Fig. 1c 1c ). HE staining suggested that neurons and glial were shrunken 15 h after traumatic brain injury (Fig. 1d 1d ). AQP4 expression showed no apparent change at the injury site 6~14 h after brain injury (Fig. 2b 2b and Table 1 1 ), but it was increased from 15 h and even more 8 d after brain injury (Figs. 2c–2f 2c–2f and Table 1 1 ). AQP4 expression in brain tumors 2 Brain edema was present around the tumors according to MRI (Fig. 1e 1e ), and HE staining showed high density of abnormal cells within astrocytomas (Fig. 1f 1f ). AQP4 expression in the brain tumors varied according to the kind of tumor. In astrocytomas and gangliogliomas, AQP4 immunoreactivity was increased both in the center of the tumors and adjacent areas (Figs. 3a–3d 3a–3d and Table 1 1 ). However, in metastatic adenocarcinoma, AQP4 immunoreactivity increased robustly around the tumor, but was not detected in the center of the tumor (Figs. 3e–3g 3e–3g and Table 1 1 . DISCUSSION 1 The main finding of this study was that AQP4 expression increased after traumatic brain injury, in peritumoral brain tissue and in the centers of tumors derived from brain tissue. In normal brain tissue, AQP4 was found around microvessels. This is consistent with its location in rat brain, in which AQP4 was detected on astrocyte foot processes adjacent to endothelial cells, and the basolateral membrane of ependymal cells by immunohistochemistry and immunoelectromicroscopy (Nielsen et al., 1997 1997 ; Rash et al., 1998 1998 ). Our finding demonstrate the characteristics of AQP4 expression in human brains, where AQP4 is expressed exclusively in astrocytes around vessels (Aoki et al., 2003 2003 ; Taniguchi et al., 2000 2000 ). We found that AQP4 expression gradually increased in human brains after traumatic brain injury, with some increase apparent 15 h after brain injury and an even greater increase 8 d after brain injury. This was consistent with that in a rat model in which AQP4 mRNA expression did not change at 1 or 4 h; but significantly increased at the site of injury and decreased in the area adjacent to the injury 24 h after traumatic brain injury (Sun et al., 2003 2003 ). As some injury properties of brain trauma and brain ischemia are similar (Leker and Shohami, 2002 2002 ), it is interesting to compare the two. In a rat brain ischemia model, AQP4 mRNA expression increased in the peri-infarcted cortex during the observation period (1~7 d, maximal on 3rd day) after middle cerebral artery occlusion, with the change being related to the generation and resolution of brain edema (Taniguchi et al., 2000 2000 ). Thus, it is possible that the increased expression of AQP4 at the injured site in traumatic brain injury might be involved in brain edema formation. Because only a small number samples were used and quantitative analysis was not performed in this study, the time dependence of AQP4 expression after traumatic brain injury remains unclear. In future studies it would be valuable to determine whether time dependent changes in AQP4 expression varies according to the location and severity of injury. We found that AQP4 expression in brain tumors increased but that pattern of increased expression was different depending on the kind of tumor. Expression of AQP4 in astrocytoma and ganglioglioma increased obviously at their centers and adjacent areas of the tumors. But in metastatic adenocarcinoma, increased AQP4 expression was seen only in areas adjacent to the tumor, and not in the center. This extends results in which AQP4 expression was simply described to be increased in metastatic adenocarcinoma (Saadoun et al., 2002 2002 ). Because AQP4 is expressed in astrocytes, the absence of AQP4 in the center of metastatic adenocarcinoma derived from lungs may be due to the lack of astrocytes. Since most brain tumors exhibit high vascular permeability and peritumoral edema (Verkman, 2002 2002 ), and AQP4 is believed to participate in the transport of water in brain tumors (Saadoun et al., 2002 2002 ), the increased AQP4 expression within or around brain tumors might result in edema of malignant brain tumors. 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Water and glycerol permeabilities of aquaporins 1-5 and MIP determined quantitatively by expression of epitope-tagged constructs in Xenopus oocytes We thank Prof. Chen Pei-Hui, Department of Pathology, Second Affiliated Hospital, School of Medicine, Zhejiang University, for his help in the analysis of brain sections. We also thank Dr. Steven A. Thomas at the Department of Pharmacology, University of Pennsylvania for critically reading and commenting on this manuscript. 10.1631/jzus.2005.B0033 Project supported by the National Natural Science Foundation of China (No. 30271498) and the National Basic Research Program (973) of China (No. G1999054000) 2004-07-10 2004-08-03 2004-12-20 2022-01-05 Copyright © 2005, Journal of Zhejiang University Science 2005 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 01 6B