Stressed Lysosome: Theoretical Model of Late Endosomal and Lysosomal pH Regulationapplied to Single and Mixed Stress Conditions

Lysosomes are important organelles of eukaryotic cells required for autophagy, endocytosis, protection against pathogens, maintenance of metabolic balance and cell signaling. A model of ion homeostasis and synchronised, interdependent operation of ion transporters in the lysosome allows one to predict the response to external influences and to design and interpret experiments correctly. Especially, with the advent of organelle rhodopsin optogenetics, there is a great need to predict cellular outcomes after light-driven specific ion transport in lysosomes and other organelles. At present, there are no models of lysosomal ion balance that fully match the current experimental data and allow simulation the organelle’s response to stress. Here we present an interactive model that provides near-lysosomal ion concentrations and adequate stress responses. The model is stable to lysosome maturation, transient organelle swelling, membrane permeabilization, deacidification by vATPase inhibition or additional proton efflux, accumulation of weakly basic, “proton sponge”-like cationic amphiphilic drug (CAD) in the lysosome. The model shows that at least one of the functions of lysosomal calcium could be attributed to the stress signal of organelle deacidification. As a major advance, our simulation provides the possibility to have the lysosome under mixed stress conditions. In addition to suggesting the dynamics of the stress response, the model also allows to study of purely selective effects, which can be experimentally induced using optogenetics. Understanding the mechanisms of stable, stress-resistant functioning of the lysosome provides ideas for the invention of anti-disease and anti-aging interventions.