- Email: [email protected]
Can variation in aquaporin 4 gene be associated with different outcomes in traumatic brain edema?
Neuroscience Letters 426 (2007) 133–134
Can variation in aquaporin 4 gene be associated with different outcomes in traumatic brain edema? Ricardo R. Romeiro a , Marco A. Romano-Silva b , Luiz De Marco b , Antonio L. Teixeira Jr. c , Humberto Correa d,∗ a
Emergency Unit, Hospital Jo˜ao XXIII, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil b Department of Pharmacology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil c Department of Internal Medicine, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil d Department of Mental Health, Faculty of Medicine, Universidade Federal de Minas Gerais, Av. Alfredo Balena 190, Belo Horizonte 30130-100, Brazil Received 13 July 2007; accepted 5 September 2007
Abstract In traumatic brain injury (TBI), cerebral edema and hemorrhage are factors involved in the determination of the clinical presentation and outcome. The aquaporin 4 (AQP4) water channel is abundant in mammalian brain and there is a growing body of evidence suggesting that this protein plays a major role in the control of water flow within the central nervous system. Previous studies examined the influence of genetic variants in cerebral edema of TBI. However, to our knowledge, there are no previous studies of molecular variations of the AQP4 gene and its association with TBI. Thus, we sought to investigate if the clinical presentation and outcome of TBI could be influenced by the presence of mutations on exon 4 of the AQP4 gene. One hundred and two patients were enrolled in this study. A neurologist assessed the clinical severity at admission according to the GCS followed by a brain computer tomography (CT) scan. Then, DNA was extracted from blood cells and exon 4 of the AQP4 gene amplified by the polymerase chain reaction and directly sequenced. On discharge, GOS was assigned by a neurologist blind to the CGS on admission. We did not find any variation in exon 4 of the AQP4 gene in our considerable large sample. Despite this negative result, there is a strong biological rationale for the involvement of AQP4 gene in brain edema regulation and, as consequence, in TBI. Therefore, further studies should be performed, including the assessment of the other three exons of the AQP4 gene. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Head trauma; Brain edema; Aquaporin 4
The last decade brought new data about how water passes through different brain membranes via protein-forming channels, named aquaporins, which are involved in the redistribution of water in brain tissue [1]. One of those proteins is aquaporin 4 (AQP4), the predominant aquaporin in the central nervous system. There is now a growing body of experimental evidence suggesting that AQP4 plays a major role in the control of water flow within the central nervous system and that it is implicated in the generation and resolution of different forms of experimentally induced brain edema [2,3]. In traumatic brain injury (TBI), cerebral edema and hemorrhage have a crucial impact on morbidity and mortality, increasing intracranial pressure and impairing cerebral perfusion
∗
Corresponding author. Tel.: +55 31 32489785; fax: +55 31 32489785. E-mail address: [email protected] (H. Correa).
0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.09.004
and oxygenation. Previous studies have examined the influence of genetic variants in these parameters of TBI [6,4]. An association between the presence of interleukin-1RN (IL1RN, interleukin 1 receptor antagonist, MIM *147679) allele 2 and posttraumatic brain hemorrhage. Furthermore there was also a trend for a significant association between IL1RN allele 2 and lower Glasgow Coma Scale (GCS) score at presentation and higher Glasgow Outcome Scale (GOS) [4]. Based on this data we sought to investigate if the clinical presentation and outcome of TBI could be influenced by the presence of mutations on AQP4 gene, since we hypothesize that mutations in this gene could be associated with a non-functional or less-functional protein resulting in different clinical presentation of cerebral edema and influencing morbidity and mortality. The AQP4 gene is located on chromosome 18q11.2-12.1 and has four coding exons. The C-terminal exon 4 is of particular interest since in this region there are phosphory-
134
R.R. Romeiro et al. / Neuroscience Letters 426 (2007) 133–134
lation sites (Ser276 , Tyr277 ) that could be associated with water permeability, and also a C-terminal Ser-Ser-Val sequence (Ser-Ser-Val) which is a characteristic binding motif for PDZ domains found in scaffolding proteins such as ␣-syntrophin [3]. In addition, it has been previously described in exon 4 a non-synonymous polymorphism (rs3906956) in Met278Thr, which could be potentially associated with changes in protein function. The study was approved by the local ethical committee and by the National Council of Ethic in Research. An informed consent was provided by all included patients. One hundred and two consecutive patients, all males (mean ± S.D. age [range], 26.9 ± 7.1 [14–48]) with TBI who were admitted to the Emergency Unit of the Hospital Jo˜ao XXIII were enrolled in this study. A neurologist assessed the clinical severity at admission according to the GCS. Then a brain computer tomography (CT) scan was performed. The Marshall Classification was used to score the severity of TBI based on the CT scan [7]. A blood sample was collected and DNA extracted. Exon 4 of the AQP4 gene was amplified by the polymerase chain reaction (primers available on request). All products were analyzed by electrophoresis on 6.5% polyacrylamide gel followed by silver staining, purified using the GFX PCR DNA and Gel Band Purification Kit (Amersham Biosciences, Piscataway, NJ), and sequenced on the ABI PRISM 310 Genetic Analyzer (Applied Biosystems, Foster City, CA) in duplicate, both forward and reverse directions. Just before the individual patient was discharged, GOS was assigned by a neurologist blind to the CGS on admission. The median with interquartile range values of GCS, Marshall’s score and GOS were, respectively, 12 [7–13], 2 [2–3] and 5 [1–5]. The mean ± S.E. days of hospital stay were 19.7 ± 3.1. The mortality rate of our sample was 25.5%. We did not find any molecular variation in exon 4 of the AQP4 gene in our sample. Even the previously described allelic variant rs3906956 was not present in any subject. Hence no correlation could be established between AQP4 genetic variability and TBI presentation and outcome. We assessed a population that was rather representative concerning the ethnic background (Caucasian and afro-
descendents). Furthermore, our sample (102 subjects) is large enough to allow us to suggest that an eventual mutation in exon4 (if it exists) is probably rare in the general population and is of low concern in terms of public health. Despite our result, there is a strong biological rationale for the involvement of AQP4 gene in brain edema regulation and, as consequence, in TBI. AQP4 knock-out mice are protected from cytotoxic brain edema, however, they show aggravated vasogenic brain edema [8]. In addition, AQP4 was found to play a major role in astroglial cell migration and neural excitability [9,5]. Therefore, further studies should be performed, including the assessment of the other exons of the AQP4 gene, to better define the role of this gene in determining clinical presentation and outcome following TBI. References [1] M. Amiry-Moghaddam, O.P. Ottersen, The molecular basis of water transport in the brain, Nat. Rev. Neurosci. 4 (2003) 991–1001. [2] M. Amiry-Moghaddan, D.S. Frydenlund, O.P. Ottersen, Anchoring of aquaporine-4 in brain: molecular mechanisms and implications for the physiology and pathophysiology of water transport, Neuroscience 129 (2004) 997–1008. [3] E. Gunnarson, M. Zelenina, A. Aperia, Regulation of brain aquaporins, Neuroscience 129 (2004) 945–953. [4] G.M. Hadjigeorgiou, K. Paterakis, E. Dardiotis, M. Dardioti, K. Aggelakis, A. Tasiou, G. Xiromerisiou, A. Komnos, E. Zintzaras, N. Scarmeas, A. Papadimitriou, A. Karantanas, IL1-RN and IL-1B gene polymorphisms and cerebral hemorrhagic events after traumatic brain injury, Neurology 65 (2005) 1077–1082. [5] J. Hu, A.S. Verkman, Increased migration and metastatic potential of tumor cells expressing aquaporin water channels, FASEB J. 20 (2006) 1892– 1894. [6] I. Liaquat, L.T. Dunn, J.A.R. Nicoll, G.M. Teasdale, J.D. Norrie, Effect of apolipoprotein E genotype on hematoma volume after trauma, J. Neurosurg. 96 (2002) 90–96. [7] L.F. Marshall, S.B. Marshall, M.R. Klauber, M.B. Clark, H.M. Eisenberg, J.A. Jane, T.G. Luerssen, A. Marmarou, M.A. Foulkes, A new classification of head injury based on computerized tomography, J. Neurosurg. 75 (1991) 14–20. [8] M.C. Papadopoulos, A.S. Verkman, Aquaporin-4 and brain edema, Pediatr. Nephrol. 6 (2007) 778–784. [9] S. Saadoun, M.C. Papadopoulos, M. Hara-Chikuma, A.S. Verkman, Impairment of angiogenesis and cell migration by targeted aquaporin-1 gene disruption, Nature 434 (2005) 786–792.
Can variation in aquaporin 4 gene be associated with different outcomes in traumatic brain edema? Ricardo R. Romeiro a , Marco A. Romano-Silva b , Luiz De Marco b , Antonio L. Teixeira Jr. c , Humberto Correa d,∗ a
Emergency Unit, Hospital Jo˜ao XXIII, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil b Department of Pharmacology, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil c Department of Internal Medicine, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil d Department of Mental Health, Faculty of Medicine, Universidade Federal de Minas Gerais, Av. Alfredo Balena 190, Belo Horizonte 30130-100, Brazil Received 13 July 2007; accepted 5 September 2007
Abstract In traumatic brain injury (TBI), cerebral edema and hemorrhage are factors involved in the determination of the clinical presentation and outcome. The aquaporin 4 (AQP4) water channel is abundant in mammalian brain and there is a growing body of evidence suggesting that this protein plays a major role in the control of water flow within the central nervous system. Previous studies examined the influence of genetic variants in cerebral edema of TBI. However, to our knowledge, there are no previous studies of molecular variations of the AQP4 gene and its association with TBI. Thus, we sought to investigate if the clinical presentation and outcome of TBI could be influenced by the presence of mutations on exon 4 of the AQP4 gene. One hundred and two patients were enrolled in this study. A neurologist assessed the clinical severity at admission according to the GCS followed by a brain computer tomography (CT) scan. Then, DNA was extracted from blood cells and exon 4 of the AQP4 gene amplified by the polymerase chain reaction and directly sequenced. On discharge, GOS was assigned by a neurologist blind to the CGS on admission. We did not find any variation in exon 4 of the AQP4 gene in our considerable large sample. Despite this negative result, there is a strong biological rationale for the involvement of AQP4 gene in brain edema regulation and, as consequence, in TBI. Therefore, further studies should be performed, including the assessment of the other three exons of the AQP4 gene. © 2007 Elsevier Ireland Ltd. All rights reserved. Keywords: Head trauma; Brain edema; Aquaporin 4
The last decade brought new data about how water passes through different brain membranes via protein-forming channels, named aquaporins, which are involved in the redistribution of water in brain tissue [1]. One of those proteins is aquaporin 4 (AQP4), the predominant aquaporin in the central nervous system. There is now a growing body of experimental evidence suggesting that AQP4 plays a major role in the control of water flow within the central nervous system and that it is implicated in the generation and resolution of different forms of experimentally induced brain edema [2,3]. In traumatic brain injury (TBI), cerebral edema and hemorrhage have a crucial impact on morbidity and mortality, increasing intracranial pressure and impairing cerebral perfusion
∗
Corresponding author. Tel.: +55 31 32489785; fax: +55 31 32489785. E-mail address: [email protected] (H. Correa).
0304-3940/$ – see front matter © 2007 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2007.09.004
and oxygenation. Previous studies have examined the influence of genetic variants in these parameters of TBI [6,4]. An association between the presence of interleukin-1RN (IL1RN, interleukin 1 receptor antagonist, MIM *147679) allele 2 and posttraumatic brain hemorrhage. Furthermore there was also a trend for a significant association between IL1RN allele 2 and lower Glasgow Coma Scale (GCS) score at presentation and higher Glasgow Outcome Scale (GOS) [4]. Based on this data we sought to investigate if the clinical presentation and outcome of TBI could be influenced by the presence of mutations on AQP4 gene, since we hypothesize that mutations in this gene could be associated with a non-functional or less-functional protein resulting in different clinical presentation of cerebral edema and influencing morbidity and mortality. The AQP4 gene is located on chromosome 18q11.2-12.1 and has four coding exons. The C-terminal exon 4 is of particular interest since in this region there are phosphory-
134
R.R. Romeiro et al. / Neuroscience Letters 426 (2007) 133–134
lation sites (Ser276 , Tyr277 ) that could be associated with water permeability, and also a C-terminal Ser-Ser-Val sequence (Ser-Ser-Val) which is a characteristic binding motif for PDZ domains found in scaffolding proteins such as ␣-syntrophin [3]. In addition, it has been previously described in exon 4 a non-synonymous polymorphism (rs3906956) in Met278Thr, which could be potentially associated with changes in protein function. The study was approved by the local ethical committee and by the National Council of Ethic in Research. An informed consent was provided by all included patients. One hundred and two consecutive patients, all males (mean ± S.D. age [range], 26.9 ± 7.1 [14–48]) with TBI who were admitted to the Emergency Unit of the Hospital Jo˜ao XXIII were enrolled in this study. A neurologist assessed the clinical severity at admission according to the GCS. Then a brain computer tomography (CT) scan was performed. The Marshall Classification was used to score the severity of TBI based on the CT scan [7]. A blood sample was collected and DNA extracted. Exon 4 of the AQP4 gene was amplified by the polymerase chain reaction (primers available on request). All products were analyzed by electrophoresis on 6.5% polyacrylamide gel followed by silver staining, purified using the GFX PCR DNA and Gel Band Purification Kit (Amersham Biosciences, Piscataway, NJ), and sequenced on the ABI PRISM 310 Genetic Analyzer (Applied Biosystems, Foster City, CA) in duplicate, both forward and reverse directions. Just before the individual patient was discharged, GOS was assigned by a neurologist blind to the CGS on admission. The median with interquartile range values of GCS, Marshall’s score and GOS were, respectively, 12 [7–13], 2 [2–3] and 5 [1–5]. The mean ± S.E. days of hospital stay were 19.7 ± 3.1. The mortality rate of our sample was 25.5%. We did not find any molecular variation in exon 4 of the AQP4 gene in our sample. Even the previously described allelic variant rs3906956 was not present in any subject. Hence no correlation could be established between AQP4 genetic variability and TBI presentation and outcome. We assessed a population that was rather representative concerning the ethnic background (Caucasian and afro-
descendents). Furthermore, our sample (102 subjects) is large enough to allow us to suggest that an eventual mutation in exon4 (if it exists) is probably rare in the general population and is of low concern in terms of public health. Despite our result, there is a strong biological rationale for the involvement of AQP4 gene in brain edema regulation and, as consequence, in TBI. AQP4 knock-out mice are protected from cytotoxic brain edema, however, they show aggravated vasogenic brain edema [8]. In addition, AQP4 was found to play a major role in astroglial cell migration and neural excitability [9,5]. Therefore, further studies should be performed, including the assessment of the other exons of the AQP4 gene, to better define the role of this gene in determining clinical presentation and outcome following TBI. References [1] M. Amiry-Moghaddam, O.P. Ottersen, The molecular basis of water transport in the brain, Nat. Rev. Neurosci. 4 (2003) 991–1001. [2] M. Amiry-Moghaddan, D.S. Frydenlund, O.P. Ottersen, Anchoring of aquaporine-4 in brain: molecular mechanisms and implications for the physiology and pathophysiology of water transport, Neuroscience 129 (2004) 997–1008. [3] E. Gunnarson, M. Zelenina, A. Aperia, Regulation of brain aquaporins, Neuroscience 129 (2004) 945–953. [4] G.M. Hadjigeorgiou, K. Paterakis, E. Dardiotis, M. Dardioti, K. Aggelakis, A. Tasiou, G. Xiromerisiou, A. Komnos, E. Zintzaras, N. Scarmeas, A. Papadimitriou, A. Karantanas, IL1-RN and IL-1B gene polymorphisms and cerebral hemorrhagic events after traumatic brain injury, Neurology 65 (2005) 1077–1082. [5] J. Hu, A.S. Verkman, Increased migration and metastatic potential of tumor cells expressing aquaporin water channels, FASEB J. 20 (2006) 1892– 1894. [6] I. Liaquat, L.T. Dunn, J.A.R. Nicoll, G.M. Teasdale, J.D. Norrie, Effect of apolipoprotein E genotype on hematoma volume after trauma, J. Neurosurg. 96 (2002) 90–96. [7] L.F. Marshall, S.B. Marshall, M.R. Klauber, M.B. Clark, H.M. Eisenberg, J.A. Jane, T.G. Luerssen, A. Marmarou, M.A. Foulkes, A new classification of head injury based on computerized tomography, J. Neurosurg. 75 (1991) 14–20. [8] M.C. Papadopoulos, A.S. Verkman, Aquaporin-4 and brain edema, Pediatr. Nephrol. 6 (2007) 778–784. [9] S. Saadoun, M.C. Papadopoulos, M. Hara-Chikuma, A.S. Verkman, Impairment of angiogenesis and cell migration by targeted aquaporin-1 gene disruption, Nature 434 (2005) 786–792.