Jason Cooper’s research while affiliated with Rutgers, The State University of New Jersey and other places

Toxic protein aggregates can spread among neurons to promote human neurodegenerative disease pathology. We found that in C. elegans touch neurons intermediate filament proteins IFD-1 and IFD-2 associate with aggresome-like organelles and are required cell-autonomously for efficient production of neuronal exophers, giant vesicles that can carry aggregates away from the neuron of origin. The C. elegans aggresome-like organelles we identified are juxtanuclear, HttPolyQ aggregate-enriched, and dependent upon orthologs of mammalian aggresome adaptor proteins, dynein motors, and microtubule integrity for localized aggregate collection. These key hallmarks indicate that conserved mechanisms drive aggresome formation. Furthermore, we found that human neurofilament light chain (NFL) can substitute for C. elegans IFD-2 in promoting exopher extrusion. Taken together, our results suggest a conserved influence of intermediate filament association with aggresomes and neuronal extrusions that eject potentially toxic material. Our findings expand understanding of neuronal proteostasis and suggest implications for neurodegenerative disease progression.

C. elegans neurons under stress can produce giant vesicles, several microns in diameter, called exophers. Current models suggest that exophers are neuroprotective, providing a mechanism for stressed neurons to eject toxic protein aggregates and organelles. However, little is known of the fate of the exopher once it leaves the neuron. We found that exophers produced by mechanosensory neurons in C. elegans are engulfed by surrounding hypodermal skin cells and are then broken up into numerous smaller vesicles that acquire hypodermal phagosome maturation markers, with vesicular contents gradually degraded by hypodermal lysosomes. Consistent with the hypodermis acting as an exopher phagocyte, we found that exopher removal requires hypodermal actin and Arp2/3, and the hypodermal plasma membrane adjacent to newly formed exophers accumulates dynamic F-actin during budding. Efficient fission of engulfed exopher-phagosomes to produce smaller vesicles and degrade their contents requires phagosome maturation factors SAND-1/Mon1, GTPase RAB-35, the CNT-1 ARF-GAP, and microtubule motor associated GTPase ARL-8, suggesting a close coupling of phagosome fission and phagosome maturation. Lysosome activity was required to degrade exopher contents in the hypodermis but not for exopher-phagosome resolution into smaller vesicles. Importantly, we found that GTPase ARF-6 and effector SEC-10/Exocyst activity in the hypodermis, along with the CED-1 phagocytic receptor, is required for efficient production of exophers by the neuron. Our results indicate that the neuron requires specific interaction with the phagocyte for an efficient exopher response, a mechanistic feature potentially conserved with mammalian exophergenesis, and similar to neuronal pruning by phagocytic glia that influences neurodegenerative disease.

In human neurodegenerative diseases, toxic protein aggregates can spread between neurons to promote pathology. In the transparent genetic animal model C. elegans , stressed neurons can concentrate fluorescently tagged protein aggregates and organelles and extrude them in large, nearly soma-sized, membrane-bound vesicles called exophers that enter neighboring cells. C. elegans exophergenesis may occur by mechanisms analogous to those that enable aggregate spreading in the human brain in neurodegenerative disease. Here we report on aggresome-like biology in stressed C. elegans neurons that influences exophergenesis. We show that C. elegans intermediate filament proteins IFD-1 and IFD-2 can assemble into juxtanuclear structures with characteristics similar to mammalian aggresomes and document that these intermediate filaments are required cell autonomously for efficient exopher production. IFD- concentrating structures expand with age or neuronal stress level, can associate with neurotoxic polyglutamine expansion protein HttQ74, and depend upon orthologs of mammalian adapter proteins, dynein motors, and microtubule integrity for collection of aggregates into juxtanuclear compartments. IFD homolog human neurofilament light chain hNFL can substitute for C. elegans IFD-2 proteins in promoting exopher production, indicating conservation of the capacity of intermediate filaments to influence neuronal extrusion. In sum, we identify an unexpected requirement for specific intermediate filaments, counterparts of human biomarkers of neuronal injury and disease, and major components of Parkinsons disease Lewy bodies, in large vesicle extrusion from stressed neurons.

C. elegans neurons under stress can produce giant vesicles, several microns in diameter, called exophers. Current models suggest that exophers are neuroprotective, providing a mechanism for stressed neurons to eject toxic protein aggregates and organelles. However, little is known of the fate of the exopher once it leaves the neuron. We found that exophers produced by mechanosensory neurons in C. elegans are engulfed by surrounding hypodermal skin cells, and are then broken up into numerous smaller vesicles that acquire hypodermal phagosome maturation markers, with vesicular contents gradually degraded by hypodermal lysosomes. Consistent with the hypodermis acting as an exopher phagocyte, we found that the hypodermal plasma membrane adjacent to newly formed exophers surrounds the exopher and accumulates F-actin. Efficient fission of engulfed exopher-phagosomes to produce smaller vesicles and degrade their contents required phagosome maturation factors SAND-1/Mon1, GTPase RAB-35, the CNT-1 ARF-GAP, and microtubule motor associated GTPase ARL-8, suggesting a close coupling of phagosome fission and phagosome maturation. Lysosome activity was required to degrade exopher contents in the hypodermis but not for exopher-phagosome resolution into smaller vesicles. Importantly, we found that GTPase ARF-6 and effector SEC-10/Exocyst activity in the hypodermis, along with the CED-1 phagocytic receptor, is required for efficient production of exophers by the neuron. Our results indicate that the neuron requires specific interaction with the phagocyte for an efficient exopher response, a mechanistic feature potentially conserved with mammalian exophergenesis, and similar to neuronal pruning by phagocytic glia that influences neurodegenerative disease.

Significance In neurodegenerative disease, protein aggregates spread to neighboring cells to promote pathology. The in vivo regulation of toxic material transfer remains poorly understood, although mechanistic understanding should reveal previously unrecognized therapeutic targets. Proteostressed Caenorhabditis elegans neurons can concentrate protein aggregates and extrude them in membrane-encased vesicles called exophers. We identify specific systemic stress conditions that enhance exopher production, revealing stress-type, stress-level, and temporal constraints on the process. We identify three pathways that promote fasting-induced exophergenesis: lipid synthesis, FGF/RAS/MAPK, and EGF/RAS/MAPK. In establishing an initial molecular model for transtissue requirements for fasting-induced exopher elevation in neurons, we report molecular insights into the regulation of aggregate transfer biology, relevant to the fundamental mysteries of neurodegenerative disease.