Amyotrophic lateral sclerosis caused by TARDBP mutations: from genetics to TDP-43 proteinopathy

Abstract

Mutations in the TARDBP gene, which encodes the TDP-43 protein, account for only 3-5% of familial cases of amyotrophic lateral sclerosis and less than 1% of cases that are apparently idiopathic. However, the discovery of neuronal inclusions of TDP-43 as the neuropathological hallmark in the majority of cases of amyotrophic lateral sclerosis has transformed our understanding of the pathomechanisms underlying neurodegeneration. An individual TARDBP mutation can cause phenotypic heterogeneity. Most mutations lie within the C-terminus of the TDP-43 protein. In pathological conditions, TDP-43 is mislocalised from the nucleus to the cytoplasm, where it can be phosphorylated, cleaved, and form insoluble aggregates. This mislocalisation leads to dysfunction of downstream pathways of RNA metabolism, proteostasis, mitochondrial function, oxidative stress, axonal transport, and local translation. Biomarkers for TDP-43 dysfunction and targeted therapies are being developed, justifying cautious optimism for personalised medicine approaches that could rescue the downstream effects of TDP-43 pathology.

Figure 1. TDP-43 neuropathology in patients with amyotrophic lateral sclerosis

(A) Morphologically distinct pTDP-43 aggregates. Representative photomicrographs (magnification 40x) from the anterior horn of the cervical spinal cord of patients with amyotrophic lateral sclerosis (as described by Spence et al⁴¹) and a healthy control individual. Neuronal TDP-43 pathology is heterogeneous and prominent glial pathology can be also detected. Orange arrowheads indicate glia with TDP-43 pathology and white dotted lines show nuclear outlines. (B) Nuclear TDP-43^APT pathology. Representative photomicrographs (magnification 40x) from the anterior horn of the cervical spinal cord of patients with ALS (as described by Spence et al,⁴¹) showing that neuronal and glial nuclear pathology can be detected by use of sensitive techniques, such as RNA aptamers that stain pathological TDP-43 and can capture a wider range of aggregation than classical antibody staining, including nuclear aggregation.⁴¹ Orange arrowheads indicate glia with TDP-43 pathology. TDP-43^APT=RNA aptamers that stain pathological TDP-43.

Figure 2. Cellular phenotypes caused by TARDBP mutations

LLPS=liquid liquid phase separation. Originally created in BioRender. Balendra, R. et al. (2025) https://BioRender.com/l72h400.

Figure 3. Therapeutic approaches for TDP-43 pathology

A variety of approaches have been used in animal and in vitro models to target TDP-43. (A) Antibody-based therapies against TDP-43 have been investigated in cell and rodent models.^{132−134,135} (B) Small molecules, such as auranofin,¹³⁶ chelethryne,¹³⁶ or rTRD01 and nTRD22,^137,138 or bait RNA oligonucleotides¹⁰¹ can inhibit TDP-43 self-interaction or aberrant phase transition in cell and in vivo models. (C) Small molecules can reduce stress granule formation in cell models, including those induced by TDP-43^139,140 (D) Reducing the levels of ataxin-2 using antisense oligonucleotides¹⁴¹ or RNA-targeting CRISPR effectors¹⁴² ameliorates disease in cell and rodent models, but thus far, this strategy has not been clinically translated. (E) Small molecules can increase clearance of TDP-43^143,144 or reduce levels of TDP-43,^145−148, in some cases through an unknown mechanism, in cells and rodent models. A degron gene therapy vector (a protein sequence that can be recognised by E3 ubiquitin ligase, leading to protein degradation through the ubiquitin-proteasome system) also reduces TDP-43 levels and improves TDP-43 pathology in mouse disease models.¹⁰⁰ Small molecules can also reduce the nuclear export of TDP-43.^107,149 (F) Small molecules modulating levels of TDP-43 with post-translational modifications are effective in cell and rodent disease models^139,150,151 and could be developed to target post-translational modifications directly. (G) Utilising TDP-43’srole inrepressingcrypticexons, a TDP-REG therapeutic construct encoding a TDP-43/Raver1 fusion protein can be expressed only in diseased cells, including in a mouse model, leading to rescue of splicing changes.⁹⁹ (H) Approaches to modulate downstream effects of TDP-43 pathology are being tested in a clinical trial (NCT05633459). LLPS=liquid-liquid phase separation. Originally created in BioRender. Balendra, R. et al (2025) https://BioRender.com/q62k493.