Astrocytes co-express aquaporin-1,-4, and vascular endothelial growth factor in brain edema tissue associated with brain contusion

Introduction. Brain edema may be life threatening. The mechanisms underlying the development of traumatic brain edema are still unclear; however, mixed mechanisms including vasogenic, ischemic, and neurotoxic types of edema may be contributors. Recent studies indicate that astrocytes, aquaporins (AQPs; a protein family of water channels), and vascular endothelial growth factor (VEGF) may have important roles in the formation and resolution of brain edema. We studied the expression of AQPs and VEGF in the edematous brain. Methods. We investigated the expression of AQP1, AQP4, and vascular endothelial growth factor (VEGF) in contusional brain tissue surgically obtained from 6 patients. Glial fibrillary acidic protein (GFAP) was also stained to detect astrocytes and to clarify the location of those proteins. The specimens received immunohistological staining and 3-color immunofluorescent staining, and were observed using confocal laser scanning microscopy. Results. AQP1, AQP4, and VEGF were co-expressed in GFAP-positive astrocytes. AQP1 and AQP4 were expressed strongly in astrocytic end-feet. The astrocytes were located in the edematous tissue, and some cells surrounded cerebral capillaries. Conclusion. Our results suggest that AQP1, AQP4, and VEGF are induced in astrocytes located in and surrounding edematous tissue. Those astrocytes may regulate the water in- and out-flow in the injured tissue.