Roles for Rab7 in Endocytic Trafficking and in Response to Endo-lysosomal Stress

Intracellular endosomal trafficking controls the balance between protein degradation in lysosomes and protein synthesis, i.e. proteostasis, but also many of the cellular signaling pathways that emanate from activated receptors after endocytosis. The quality control of endosomes and lysosomes is essential to maintaining faithful endocytic trafficking, signaling, and degradation. Many diseases, including lysosomal storage disorders, neurodegenerative diseases and ischemia-reperfusion injury directly perturb lysosomal membranes or their function. Endosomal trafficking, sorting, and motility are coordinated by the Rab family of small GTPases whose function as molecular switches direct activity at endosomal membranes through effector proteins. Rab7 is particularly important in the coordination of the degradative functions of the pathway at late endosomes and lysosomes. However, the contributions of Rab7 in the context of endo-lysosomal stress and quality control pathways are currently not known. Within this dissertation, we explore Rab7 driven mechanisms of quality control to pH neutralizing stress. We uncover mechanistic connections between Rab7 activation and endosomal V-ATPase assembly in immortalized and primary cell models. In neurons, in which spatiotemporal regulation of endosomal trafficking is particularly challenging due to their enormous size and complex architecture, we have elucidated novel roles for Rab7 in the regulation of retrograde dendritic trafficking in response to stress. Finally, using Rab7-knockout models, we have uncovered new nodes of key Rab7 activity in endosomal trafficking. Together, this work contributes to our broader understanding of the fundaments of Rab7-driven membrane trafficking and uncovers new roles for Rab7 in endo-lysosomal quality control measures, which are broadly relevant to a multitude of pathologic processes and important for therapeutic considerations.