ALS-Linked Mutations Enlarge TDP-43-Enriched Neuronal RNA Granules in the Dendritic Arbor

Abstract

Trans-activating response region (TAR) DNA-binding protein of 43 kDa (TDP-43) is an RNA-binding protein that is mutated in familial amyotrophic lateral sclerosis (ALS). Disease-linked mutations in TDP-43 increase the tendency of TDP-43 to aggregate, leading to a corresponding increase in formation of stress granules, cytoplasmic protein/RNA complexes that form in response to stress. Although the field has focused on stress granules, TDP-43 also forms other types of RNA granules. For example, TDP-43 is associated with RNA granules that are prevalent throughout the dendritic arbor in neurons. Because aggregation of TDP-43 is also important for the formation of these neuronal RNA granules, we hypothesized that disease-linked mutations might alter granule formation even in the absence of stress. We now report that ALS-linked mutations in TDP-43 (A315T and Q343R) increase the size of neuronal TDP-43 granules in the dendritic arbor of rat hippocampal neurons. The mutations correspondingly reduce the granule density, movement, and mobility of TDP-43 granules. Depolarization of rat hippocampal neurons with KCl stimulates TDP-43 granule migration into dendrites, but A315T and Q343R TDP-43 granules migrate shorter distances and into fewer dendrites than wild-type TDP-43. These findings highlight novel elements of TDP-43 biology that are affected by disease-linked mutations and suggest a neuronally selective mechanism through which TDP-43 mutations might elicit neuronal dysfunction.

Amyotrophic lateral sclerosis-linked mutations increase the viscosity of liquid-like TDP-43 RNP granules in neurons

“…We hypothesized that ALS-linked mutations, M337V (27,45) and G298S (46), in the LCS of TDP-43 would alter the liquid-like properties of axonal TDP-43 RNP granules and disrupt their function. Motile TDP-43 M337V and G298S granules display similar instantaneous velocities to motile TDP-43 WT granules but show less efficient transport, consistent with previous characterization of TDP-43 mutant motility (26,47). We noted that processive transport of motile TDP-43 mutant RNP granules is more often interrupted compared with TDP-43 WT granules; TDP-43 mutant processive runs frequently stall or halt completely upon interaction with another granule (Fig.…”

“…7F). In addition, we and others have observed that ALS-linked mutations disrupt TDP-43 RNP transport (26,47). These data suggest the altered viscoelastic properties of mutant TDP-43 granules may contribute to disease pathogenesis.…”

Linking RNA Dysfunction and Neurodegeneration in Amyotrophic Lateral Sclerosis

“…Disease-causing mutations in TARDBP reduce the density and mobility of these RNA particles and interfere with their transport into dendrites [20,51]. These results suggest that dysregulation of TDP43 or FUS through inherited mutations or acquired mislocalization might inhibit mRNA transport and localized translation, both of which are essential for proper neuronal function.…”

“…Within the nucleus, TDP43 has essential roles in RNA transcription, splicing, and stability [13,14,[47][48][49][50], and transports select mRNA to localized sites of translation within the cytoplasm [20,51,52]. In addition to its function in RNA trafficking, cytoplasmic TDP43 also helps regulate RNA translation and homeostasis by sequestering transcripts in RNA granules [53][54][55][56].…”

“…In addition to their roles in sequestering RNAs within stress granules, TDP43 and FUS shuttle RNA from the nucleus to the dendrites in an activity-dependent process [20,51,52,104]. Disease-causing mutations in TARDBP reduce the density and mobility of these RNA particles and interfere with their transport into dendrites [20,51].…”