Protein aggregation is centrally implicated in the pathogenesis of most late-onset neurodegenerative disorders, including Alzheimer?s disease. Aggregating proteins disrupt intracellular functions and can spread outside of neurons to compromise neighboring cells. Internal anti-aggregation controls available to neurons for maintaining proteostasis include chaperone activity, autophagy/lysosomal degradation, and proteasome- mediated degradation. My project is distinct in focusing on a mechanism for external aggregate elimination. We discovered, and have begun to characterize, a previously unknown capacity of C. elegans adult neurons to extrude large (~5M) vesicles that include deleterious cell contents. We call these extruded vesicles exophers. Introduction of proteostasis challenges via inhibiting chaperone expression, autophagy, or the proteasome, or by over-expressing aggregating proteins like human Alzheimer's disease A?1-42, expanded polyglutamine Q128 protein, or high concentration mCherry, increases exopher production from the affected neurons. Aggregated protein can be preferentially segregated into exophers over soluble protein, which remains behind in the neuronal soma. Neurons that make exophers reflect less functional damage from proteotoxic transgene products as compared to those that do not, revealing an apparently neuroprotective activity of exopher-genesis. Some exopher contents can later turn up in remote cells, confirming extrusion. Our initial studies suggest that the early stages of exopher-genesis have mechanistic similarities to the formation of mammalian aggresomes. My project will extend preliminary work that identified cytoskeletal genes required to form exophers. I will: 1) test genetic and mechanistic similarities to aggresome formation; 2) use genetic and cell biological approaches to define the pathway by which microtubules, dynein motors, actin and intermediate filaments mediate the dynamic collection and elimination of aggregating proteins as exophers. My project will identify new genes required for producing exophers, and probe molecular and cellular mechanisms by which several exopher-genesis suppressors contribute to the process of exopher formation. I will also determine whether exopher formation initiates with via a mechanism similar to mammalian aggresome formation and better reveal how cells sort toxic contents. We postulate that exopher-genesis occurs by a mechanism that is conserved from C. elegans to humans. Since we must understand all proteostasis strategies in order to identify targets for neurodegenerative disease, my work on a novel neuroprotective mechanism is likely to have high health relevance and importance in the field.
My proposed studies use the considerable experimental advantages of the simple animal model C. elegans to address basic biology of high relevance to understanding neurodegenerative disease mechanisms. I have discovered that neurons can throw out neurotoxic trash, transferring potentially deleterious materials out to neighboring cells for remote handling. The study of how aggregating proteins are selected for extrusion and transferred will provide insight into novel pathology mechanisms relevant to a broad range of neurodegenerative diseases including Alzheimer?s disease, and the work has potential to inspire design of novel therapeutic approaches.
| Arnold, Meghan Lee; Melentijevic, Ilija; Smart, Anna Joelle et al. (2018) Q&A: Trash talk: disposal and remote degradation of neuronal garbage. BMC Biol 16:17 |
