gms | German Medical Science

Objective: Aquaporine-9 (AQP9) is one of thirteen known isoforms of the aquaporin channels group. For each isoform a distinct tissue distribution has been described. This integral group of proteins regulate the water transport through cell membranes. A vast amount of different functions has been described so far. AQP9 is expressed in astrocytes, subpopulations of neurons and endothelial cells of subpial blood vessels. It plays an important role in maintaining brain water homeostasis. Several authors report an involvement in the pathogenesis of malignant brain neoplasias by influencing migration and invasion of tumor cells and facilitating edema development. The aim of this study was to evaluate the AQP9 expression in malignant glioma and compare the expression between patients which did and did not receive steroids prior to surgery.

Method: Twenty-four Patients (n=24) with lesions suggestive for malignant glioma were operated in the Department of Neurosurgery, University Hospital of Münster. Total RNA was prepared from paraffin-embedded tissue. AQP9 mRNA expression was determined using quantitative real-time PCR using TaqMan gene expression assays. mRNA copy numbers were estimated from CT values, assuming that a single copy yields a CT value of 40 and that, in each cycle, the amount of PCR product is doubled.

Results: Histopathological examination showed sixteen (n=16) glioblastomas and nine lower graded gliomas. PCR analysis showed a significantly higher mRNA AQP9 expression in glioblastoma tissue (n=16) than in lower graded gliomas (n=9, p<0,001). Furthermore, AQP9 expression was lower in the steroid group (n=9) than in patients which did not receive steroids prior to surgery (n=15).

Conclusions: Steroids appear to have an effect on the expression of AQP9 in tumor cells. These findings support past reports, where AQP9 is stated as to be involved in the edema development in the surroundings of tumor cells. In addition, AQP9 expression was expressed significantly higher in glioblastoma compared to lower graded gliomas. Clinical significance as well as the role of AQP9 in tumor cells require further investigation.