AQP4 and glioma: In line with the evolving model of aquaporin function in glioma-induced brain edema are mRNA and protein expression studies in human brain tumor specimens that show the highest expression levels of AQP4 in pilocytic astrocytomas WHO grade I and grade IV glioblastomas, both tumor types with a high degree of BBB remodeling and angiogenesis, with a progressive increase in expression levels from WHO grade II to IV [270].