Regulation of Lipid Catabolism by Autophagy in Neural Stem Cell of Tuberous Sclerosis Complex

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Tuberous sclerosis complex (TSC) is a genetic disorder affects as many as 50,000 people in US. TSC often affects brain by seizures, autism, intelligence instability and growth of noncancerous (benign) tumors. These defects persist in neonatal and adult brains of TSC patients. The mutations of Tsc1 or Tsc2 gene leading to the loss of their tumor suppressor functions to control the activity of mTORC1 underlie the pathogenesis of TSC. mTORC1 is an established master regulator of cellular homeostasis and stimulates the activity of translation but negatively regulate autophagy, a conserved catabolic process that degrades cytoplasmic constituents and organelles in the lysosome. Interestingly, ours recent findings revealed a higher autophagy activity in Tsc1-deficient cells under energy stress conditions, leading to establishment of a novel double conditional knockout (cKO) mouse model to delete TSC1 and FIP200 (Fak interaction protein of 200 KD, an essential component in autophagy induction complex) in postnatal neural stem cells (NSC). Using this unique model, we revealed the essential functions of autophagy to sustain high mTORC1 activity and in abnormal postnatal development of Tsc1-deficient NSC. In addition, we found that autophagy was required for mitochondria oxidative phosphorylation to resist energy-stress conditions, most likely providing free fatty acids to generate ATP from intracellular lipid storage. These pilot findings form the basis of our hypothesis that autophagy mediates the lipids degradation in Tsc1-deficient NSC for β-oxidation and ATP production to maintain their high mTORC1 activity, which provide a valuable metabolic target for TSC patients. In Aim1 of this proposal, we will exam the molecular and metabolic mechanisms of autophagy in lipid degradation and the functions of lipophagy to regulate signaling pathways for high mTORC1 activity, using primitive and differentiating NSC. In Aim2, we will use our newly developed FIP200 conditional knockin mouse which is defective in binding with Atg13 to generate Tsc1/Fip200 2cKI mice. This genetic tool will further clarify the mechanisms of lipophagy in Tsc1-deficient NSC. We will also adopt pharmacological methods to target autophagy mediated lipid catabolism to treat defects in postnatal Tsc1-deficient NSC. In Aim3, we will generate novel inducible mouse models to specifically deplete Tsc1 and Fip200 in postnatal NSC. We will also use these mouse models to treat existing SEN/SEGA, which is more clinically relevant, to complement studies in Aim2. At the end of these studies, we will expand our knowledge of pathogenesis in TSC-deficient NSC, identify candidate signaling pathways and metabolic alterations by hyperactivated mTORC1, and develop new therapeutic concepts for continued investigation in the treatment of brain development disorders in TSC patients.