TFEB-Mediated Autophagosome-Lysosome Fusion Enhancement in Aged Neuronal Synapses

Age-related synaptic dysfunction is characterized by accumulation of damaged organelles and misfolded proteins due to compromised autophagy-lysosomal pathway efficiency. While TFEB activation increases lysosomal biogenesis, the critical bottleneck in aged synapses may be the impaired fusion between autophagosomes and lysosomes rather than lysosomal abundance alone. This hypothesis proposes that TFEB activation specifically enhances autophagosome-lysosome fusion machinery by upregulating SNARE proteins (STX17, SNAP29, VAMP8) and Rab7 GTPase activity at synaptic terminals. In aged synapses, accumulated oxidative damage disrupts the microtubule network and reduces Rab7-RILP complex formation, preventing efficient autophagosome trafficking to lysosomes. TFEB transcriptionally upregulates not only lysosomal genes but also fusion machinery components, restoring the spatial coupling between autophagosome formation and lysosomal degradation. The intervention would involve targeted TFEB activation through small molecule agonists or optogenetic approaches specifically at synaptic compartments, where the fusion deficit is most pronounced. Evidence would focus on measuring fusion events using dual-fluorescence LC3-LAMP1 assays, monitoring Rab7 activation states, and quantifying SNARE complex formation in aged vs young synaptic preparations. Success would be demonstrated by restored autophagic flux rates, reduced accumulation of p62/SQSTM1 aggregates, and improved synaptic transmission efficiency in aged neurons following TFEB activation.