Intermediate filaments associate with aggresome-like structures in proteostressed C. elegans neurons and influence large vesicle extrusions as exophers

Abstract

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.

Podocyte exopher-formation as a novel pathomechanism in membranous nephropathy

“…We identified the ubiquitously expressed 14-3-3 chaperone-like protein 48 as an exopher-identifying protein. 14-3-3 abundance was high and ‘aggregate-like’ in patient and experimental exophers, and 14-3-3 aggregates were observed at juxtanuclear areas of exopher-formation in podocytes, corroborating the recently published involvement of 14-3-3 in neuronal exopher-formation 20 . In podocytes, 14-3-3 is a known synaptopodin interacting protein 49 , playing a role in the downstream function of cyclosporin A 49 .…”

“…To this end, 14-3-3 represented the most discerning marker in huIgG4 + -EVs. This is of interest, as 14-3-3 protein was recently shown to be required for exopher-formation in C. elegans neurons 20 . In comparison to nephrotic non-MN patients, huIgG4 + -EVs isolated from MN-patient urines contained abundant podocyte proteins such as THSD7A, PLA 2 R1, Nephrin, Podocin, and α-Actinin-4 by immunoblot or by immunofluorescence ( Fig.…”

“…In patients, MN-associated (autoantibody + /antigen + ) EVs fulfilled important features of exophers. As such, morphological criteria (extrusion from apical membranes especially from the juxtanuclear area as stalked large vesicles; expression of a characteristic set of EV markers) 18,20,21 , dynamic criteria (enhanced release by proteotoxic stress, reuptake by cells along the nephron) 18,27,34 , and molecular criteria (abundance of cell-specific and disease-associated proteins, presence of organelles) 18,35,22 establish them as a hitherto unrecognized podocyte-derived urinary EV form. They are distinct from migrasomes 36 , a large EV-type forming at tips and intersections of retraction fibers of migrating cells 37 .…”

“…Exophers represent a novel type of extracellular vesicle (EV) recently discovered in Caenorhabditis elegans neurons 18 and body wall muscles 19 . Exophers extrude from juxtanuclear plasma membrane areas 20 as long nanotubules which can reach up to 4 µm in diameter at the distal end 21 . In C. elegans , exopher-formation depends on cellular stressors 17,24 and mechanistically involves the delivery of cargo to aggresome-like organelles 20 .…”

“…Exophers extrude from juxtanuclear plasma membrane areas 20 as long nanotubules which can reach up to 4 µm in diameter at the distal end 21 . In C. elegans , exopher-formation depends on cellular stressors 17,24 and mechanistically involves the delivery of cargo to aggresome-like organelles 20 . Exopher-like processes have morphologically been reported in mammalian systems and are thought to represent a protective strategy to remove proteotoxic protein aggregates 21,27 and dysfunctional organelles such as mitochondria 22,24 .…”