The mechanism of nuclear autophagy

项目总结

Project Summary Over the last 10 years, the lysosome-mediated degradation pathway macroautophagy has gained prominence in the study of aging-related disorders and extension of lifespan. Macroautophagy is an essential cellular pathway responsible for the elimination of cytosolic proteins, lipids and organelles, and as such, the field has focused upon the role of macroautophagy in clearing protein aggregates or dysfunctional organelles (such as mitochondria) that specifically accumulate in the cytoplasm. Increasingly however, protein accumulation and organelle dysfunction are observed to occur within the nucleus, apparently shielded from cytoplasmic processes by the double-membraned nuclear envelope. Furthermore, links between aging and nuclear envelope structural defects are emerging, including nuclear envelopathies caused by mutations in the envelope scaffolding lamins and associated integral inner nuclear membrane proteins. How the cell responds to these nuclear insults is not well understood, but there is emerging evidence that components of the nuclear envelope and the nucleus are subject to macroautophagy-dependent turnover. Thus, it is clear that we must refocus our attention on how nuclear quality control is executed and specifically on the mechanism(s) that governs nuclear content turnover in cytoplasmic autophagosomes. Thus, in this proposal, we focus on the fundamental question of how cytoplasmic autophagy machinery and nuclear envelope remodeling are coordinated. Using S. cerevisiae, where discovery of the molecular machinery driving nuclear autophagy is the most mature and where we have generated substantial preliminary and recently published data, we will test an exciting “outside-in” model of nucleophagy. This model invokes a novel translumenal bridge that spans the nuclear envelope membranes and connects the cytosol to the nucleus. This proposal will thus fully define the molecular components that make up this nucleophagy pathway and place these factors within an ultrastructural timeline. Elements of this pathway will then be reconstituted using fully engineered in vitro systems in order to collectively provide critical molecular insight into the key membrane remodeling events necessary to remove nuclear contents while maintaining nuclear integrity. With the completion of this project, we will further our mechanistic understanding of a key underappreciated macroautophagic process and open doors to define how nuclear autophagy can impact aging-impaired proteostasis.