Dysregulation of Acid Ceramidase-mediated Sphingolipid Metabolism Contributes to Tumor Progression in Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is disorder of multi-system benign neoplasia in the brain, heart, kidneys and lungs. Lymphangioleiomyomatosis (LAM) is a progressive pulmonary disease affecting exclusively women. Both are caused by mutations in TSC1 and TSC2, resulting in mTORC1 hyperactivation. Single cell RNA sequencing of LAM lungs identified activation of genes in the sphingolipid pathway. Independent validation studies showed that acid ceramidase (ASAH1) and dihydroceramide desaturase (DEGS1), key enzyme for regulating sphingolipid and ceramide metabolism, were significantly increased in TSC2-null cells, and their expression and activity were rapamycin-insensitive. TSC2 negatively regulated the biosynthesis of tumorigenic sphingolipids. Suppression of ASAH1 by shRNA or the inhibitor ARN14976 (17a) markedly decreased the viability of TSC2-null cells. In vivo, 17a significantly decreased the growth of Tsc2-null cell derived mouse xenografts. When combined with rapamycin, 17a more strongly inhibited the progression of renal cystadenomas in Tsc2+/- mice than either agent alone, evaluated by pathology and MRI. Collectively, our studies identify a rapamycin-insensitive disorder of sphingolipid metabolism in TSC2-null cells and tumors and validate the novel hypothesis that TSC2 regulates sphingolipid production and action via ASAH1. Targeting aberrant sphingolipid metabolism pathways may have therapeutic value in TSC and LAM, and possibly in mTORC1-hyperactive neoplasms.