Using immunohistochemistry, we observed different
aquaporin expression patterns depending on localization:
aquaporin 4 and -1 were detected in infratentorial
subependymomas in the entire
tumor tissue. In contrast, supratentorial
subependymomas revealed
aquaporin 4 and -1 expression only in border areas of the
tumor. PCR analyses however showed no difference in
aquaporin 4 expression between all
subependymomas independent of localization but at higher levels than in normal brain. In contrast,
aquaporin 1 RNA levels were found to be higher only in infratentorial samples compared to supratentorial and normal brain samples. The reason for the different distribution pattern of
aquaporin 4 in
subependymomas still remains unclear. On the cellular level,
aquaporin 4 was redistributed on the surface of the
tumor cells, and in freeze fracture replicas no orthogonal arrays of particles were found. This was similar to our previous findings in malignant
glioblastomas. From these studies, we know that extracellular matrix molecules within the
tumor like
agrin and its receptor
alpha-dystroglycan are involved in forming orthogonal arrays of particles. In
subependymomas neither
agrin nor
alpha-dystroglycan were detected around blood vessels.
CONCLUSIONS: Taken together, we show in this study that in the benign
subependymomas aquaporins 1 and 4 are dramatically redistributed and upregulated. We speculate that extracellular environments of infra- and supratentorial
subependymomas are different and lead to different distribution patterns of
aquaporin 4 and -1.