Increased expression of l-amino acid transporters in balloon cells of tuberous sclerosis

Abstract

Tuberous sclerosis complex (TSC) is a dysgenetic syndrome involved in multiple organs, and the pathognomonic cortical tuber act as an epileptic substrate. The amino acid transport system L (LAT) is a major nutrient transport system, and LAT1 is highly expressed in malignant tumors to support tumor cell growth. To study the life-long epilepsy from the cortical tuber, the expression of LAT1 in balloon cells and dysplastic neurons of the cortical tuber is investigated. LAT1 expression was investigated by LAT1 mRNA using reverse transcription-polymerase chain reaction and immunohistochemical staining with anti-human LAT1 antibody in nine patients with TSC and three control brains. LAT1 mRNA was detectable only in fresh-frozen tissues of TSC, and it was upregulated in the cortical tuber lesion. While the LAT1 immunopositivity of control brains was limited in the capillary endothelial cells in the gray matter, increased LAT1 immunopositivity was noted in balloon cells of the cortical tubers in addition to the capillary endothelial cells as shown in control brains. Linear and strong immunopositivity along the cell membrane and cytoplasm of the balloon cells, and weakly granular immunopositivity in their cytoplasm were noted. Increased expression of LAT1 in the balloon cells is important for the active transport of large neutral amino acids into the balloon cells, and that the biologic process may play an important role in the active protein synthesis with metabolic maintenance of balloon cells in cortical tubers of patients with TSC.