Nuclear depletion of RNA-binding protein ELAVL3 (HuC) in sporadic and familial amyotrophic lateral sclerosis

Maria J. Rodriguez,John Ravits,Sandra Diaz-Garcia,Ruth Chia,Olubankole Aladesuyi Arogundade,Don Cleveland,Vivian I. Ko,Bryan J. Traynor,Sonia Vazquez-Sanchez

doi:10.1007/s00401-021-02374-4

Abstract

Amyotrophic lateral sclerosis is a progressive fatal neurodegenerative disease caused by loss of motor neurons and characterized neuropathologically in almost all cases by nuclear depletion and cytoplasmic aggregation of TDP-43, a nuclear RNA-binding protein (RBP). We identified ELAVL3 as one of the most downregulated genes in our transcriptome profiles of laser captured microdissection of motor neurons from sporadic ALS nervous systems and the most dysregulated of all RBPs. Neuropathological characterizations showed ELAVL3 nuclear depletion in a great percentage of remnant motor neurons, sometimes accompanied by cytoplasmic accumulations. These abnormalities were common in sporadic cases with and without intermediate expansions in ATXN2 and familial cases carrying mutations in C9orf72 and SOD1. Depletion of ELAVL3 occurred at both the RNA and protein levels and a short protein isoform was identified, but it is not related to a TDP-43-dependent cryptic exon in intron 3. Strikingly, ELAVL3 abnormalities were more frequent than TDP-43 abnormalities and occurred in motor neurons still with normal nuclear TDP-43 present, but all neurons with abnormal TDP-43 also had abnormal ELAVL3. In a neuron-like cell culture model using SH-SY5Y cells, ELAVL3 mislocalization occurred weeks before TDP-43 abnormalities were seen. We interrogated genetic databases, but did not identify association of ELAVL3 genetic structure with ALS. Taken together, these findings suggest that ELAVL3 is an important RBP in ALS pathogenesis acquired early and the neuropathological data suggest that it is involved by loss of function rather than cytoplasmic toxicity.

Highlights

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by adult-onset progressive motor impairments from degeneration of upper and lower motor neurons [5, 28, 58]
We focused our attention on candidate RNA-binding protein (RBP) and identified three that were abnormally expressed in both studies—downregulation of ELAVL3 and upregulation of HNRPA1 and NOL8
While it is well recognized that nuclear depletion and cytoplasmic aggregation of TDP43 do not occur in SOD1 ALS [37], surprisingly we found that 48% of 33 residual motor neurons examined in four SOD1 ALS nervous systems had nuclear depletion of ELAVL3 (Fig. 3g–i)

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by adult-onset progressive motor impairments from degeneration of upper and lower motor neurons [5, 28, 58]. The discovery of TDP-43, a nuclear RNA-binding protein (RBP), identified the importance of RNA biology in ALS pathogenesis and led to identification of several other RBPs including FUS [2, 33, 44], TAF15 [27, 55], hnRNPA1 [13, 16, 17, 26, 61], hnRNPA2B1 [29], EWS [42], and MATR3 [23] It is unclear how these RBPs contribute to pathogenesis and the debate has focused on loss of their nuclear functions highlighted neuropathologically by nuclear depletion and cytoplasm toxicity highlighted neuropathologically by cytoplasmic accumulation of inclusions and aggregations [4, 9, 18, 54, 57]

Methods

Results

Conclusion