Illuminating Endocytic Organelles with pH-Resposive [sic] Nanomaterials

Endosomes, lysosomes and related catabolic organelles are a dynamic continuum of vacuolar structures that impact a number of key cell physiological processes that include protein/lipid metabolism, nutrient sensing and cell survival. To support quantitative investigation of these processes in living cells, we have developed a library of ultra-pH sensitive (UPS) fluorescent nanoparticles with chemical properties that allow fine-scale, multiplexed, spatial-temporal perturbation and quantification of catabolic organelle maturation at single organelle resolution. Deployment in cells enabled quantification of the proton accumulation rate in endosomes; illumination of previously unrecognized regulatory mechanisms coupling pH transitions to endosomal coat protein exchange; discovery of distinct pH thresholds required for mTORC1 activation by free amino acids versus proteins; broad-scale characterization of the consequence of endosomal pH transitions on cellular metabolomic profiles; and functionalization of a context-specific metabolic vulnerability in lung cancer cells. These biological applications benchmarked the robustness and adaptability of this nanotechnology-enabled 'detect and perturb' strategy. As a translational application, we leveraged the technology in high-throughput screening assays that successfully identified chemical agents in the promotion of autophagolysosomal activity through TFEB activation. Formulation of these compounds in liver-tropic biodegradable, biocompatible nanoparticles conferred hepatoprotection against diet-induced steatosis in murine models and prolonged survival in Caenorhabditis elegans. These results highlight the therapeutic potential of small-molecule TFEB activators to ameliorate metabolic syndrome and extend lifespan.