title: Amyotrophic lateral sclerosis-linked mutations increase the viscosity of liquid-like TDP-43 RNP granules in neurons.
abstract: Ribonucleoprotein (RNP) granules are enriched in specific RNAs and RNA-binding proteins (RBPs) and mediate critical cellular processes. Purified RBPs form liquid droplets in vitro through liquid-liquid phase separation and liquid-like non-membrane-bound structures in cells. Mutations in the human RBPs TAR-DNA binding protein 43 (TDP-43) and RNA-binding protein FUS cause amyotrophic lateral sclerosis (ALS), but the biophysical properties of these proteins have not yet been studied in neurons. Here, we show that TDP-43 RNP granules in axons of rodent primary cortical neurons display liquid-like properties, including fusion with rapid relaxation to circular shape, shear stress-induced deformation, and rapid fluorescence recovery after photobleaching. RNP granules formed from wild-type TDP-43 show distinct biophysical properties depending on axonal location, suggesting maturation to a more stabilized structure is dependent on subcellular context, including local density and aging. Superresolution microscopy demonstrates that the stabilized population of TDP-43 RNP granules in the proximal axon is less circular and shows spiculated edges, whereas more distal granules are both more spherical and more dynamic. RNP granules formed by ALS-linked mutant TDP-43 are more viscous and exhibit disrupted transport dynamics. We propose these altered properties may confer toxic gain of function and reflect differential propensity for pathological transformation.
authors.affiliation: Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.|Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Pallavi P
authors.initials: PP
authors.lastname: Gopal
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.|Neuroscience Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Nirschl
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.|Neuroscience Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Eva
authors.identifier: 0000-0001-9570-442X
authors.initials: E
authors.lastname: Klinman
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104; holzbaur@mail.med.upenn.edu.|Neuroscience Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Erika L F
authors.initials: EL
authors.lastname: Holzbaur
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000737:chemistry / Q000378:metabolism; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D009046:Motor Neurons / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D014783:Viscosity
chemical_list: D004268:DNA-Binding Proteins; D012261:Ribonucleoproteins; C000598624:TARDBP protein, human; C000627100:Tardbp protein, rat
keywords: TDP-43; amyotrophic lateral sclerosis; liquid droplets; neurons; ribonucleoprotein granules