mTORC1 Displacement from Lysosomal Membrane Enables TFEB Nuclear Translocation…

The mechanistic basis for mTORC1 inhibition as a senescence reversal strategy lies in the physical displacement of mTORC1 from the lysosomal surface, which liberates the transcription factor TFEB (Transcription Factor EB) for nuclear translocation and activation of the CLEAR (Coordinated Lysosomal Expression and Regulation) gene network. Under senescent conditions, chronic mTORC1 activation at the lysosomal membrane (mediated by Rag GTPases and Rheb) maintains TFEB phosphorylation at Ser211, sequestering it in the cytoplasm and suppressing lysosomal biogenesis. This creates a feedforward loop where impaired autophagy leads to accumulation of damaged organelles (including mitochondria), which generate reactive oxygen species that further activate mTORC1. This hypothesis proposes that pharmacological displacement of mTORC1 from the lysosomal surface using novel small molecules that competitively bind the Ragulator docking site (analogous to the mechanism of S)-ML-011) will enable TFEB nuclear translocation and restore the autophagy-lysosome pathway in aged neurons. In human iPSC-derived neurons subjected to repeated hydrogen peroxide stress to induce senescence, TFEB remains cytoplasmically localized, and lysosomal number and cathepsin activity are reduced by >50% compared to young neurons. Treatment with a mTORC1 lysosomal displacement compound (simulating the effect of prolonged fasting or rapamycin) causes TFEB nuclear translocation within 4 hours, restores lysosomal cathepsin D activity to 85% of young neuron levels, and reduces SA-β-gal positivity by 45% at 72 hours. The therapeutic prediction is that neurons in which TFEB has been nuclear-localized will upregulate GABARAPL1, CTSF (cathepsin F), and LAMP1, clearing damaged protein aggregates (tau, α-synuclein) and dysfunctional mitochondria through enhanced autophagy-lysosome flux. This provides a mechanistic explanation for the well-established geroprotective effects of rapamycin and fasting, specifically in the context of neuronal senescence reversal.