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Abberant neuronal Wnt activation causes defective TDP43 localization

ABSTRACT: Conserved neuropathologies across multiple neurodegenerative diseases have identified shared causal pathways for neurodegeneration. One pathway involves the RNA-binding protein TDP-43, whose nuclear exclusion and cytoplasmic accumulation are established drivers of neurodegeneration. TDP-43 mislocalization is attributed to defective nucleocytoplasmic transport (NCT), but the underlying mechanisms are unclear. The vertebrate-specific six-transmembrane enzyme, Glycerophosphodiester phosphodiesterase 2 (GDE2 or GDPD5), cleaves the glycosylphosphatidylinositol (GPI)-anchor that tethers some proteins to the membrane. Here, we show that loss of GDE2 leads to aberrant sustained activation of canonical Wnt signaling in adult neurons, which is sufficient to cause NCT and nuclear pore abnormalities and the nuclear exclusion of TDP-43. GDE2 disruption coincides with TDP-43 nuclear exclusion in postmortem tissue from patients with Amyotrophic Lateral Sclerosis (ALS), and neuronal Wnt signaling is erroneously activated in Drosophila and induced human spinal neuronal (iSN) models of ALS. Wnt knockdown in Drosophila ALS models mitigates cell death, while pharmacological inhibition of Wnt activation in iSNs from ALS patients rescues mRNA levels of known TDP-43 splicing targets. Our study identifies GDE2 as a critical regulator of Wnt signaling in adult neurons and highlights Wnt pathway activation as a previously unappreciated mechanism contributing to NCT and TDP-43 abnormalities in disease.

ORGANISM(S): Mus musculus

PROVIDER: GSE246462 | GEO | 2024/09/27

REPOSITORIES: GEO

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Project description:Aims: Loss of nuclear TDP-43 characterises sporadic and most familial forms of amyotrophic lateral sclerosis (ALS). TDP-43 (encoded by TARDBP) has multiple roles in RNA processing. We aimed to determine whether 1) RNA splicing dysregulation is present in lower motor neurons in ALS and in a motor neuron-like cell model, and 2) TARDBP mutations (mtTARDBP) are associated with aberrant RNA splicing using patient-derived fibroblasts. Methods: Affymetrix exon arrays were used to study mRNA expression and splicing in lower motor neurons obtained by laser capture microdissection of autopsy tissue from individuals with sporadic ALS and TDP-43 proteinopathy. Findings were confirmed by qRT-PCR and in NSC34 motor neuronal cells following shRNA-mediated TDP-43 depletion. Exon arrays and immunohistochemistry were used to study mRNA splicing and TDP-43 expression in fibroblasts from patients with mtTARDBP-associated, sporadic and mutant SOD1-associated ALS. Results: We found altered expression of spliceosome components in motor neurons and widespread aberrations of mRNA splicing that specifically affected genes involved in ribonucleotide binding. This was confirmed in TDP-43 depleted NSC34 cells. Fibroblasts with mtTARDBP showed loss of nuclear TDP-43 protein and demonstrated similar changes in splicing and gene expression, that were not present in fibroblasts from patients with sporadic or SOD1-related ALS. Conclusion: Loss of nuclear TDP-43 is associated with RNA processing abnormalities in ALS motor neurons, patient-derived cells with mtTARDBP, and following artificial TDP-43 depletion, suggesting that splicing dysregulation directly contributes to disease pathogenesis. Key functional pathways affected include those central to RNA metabolism. RNA was extracted from fibroblasts grown from neurologically healthy controls (n=6) and 3 groups of patients with ALS: 1) sporadic cases (n=6); 2) cases due to mutations of SOD1 (n=4); 3) cases due to mutations of TARDBP (n=3). The three ALS groups were compared to the controls.

Project description:Aims: Loss of nuclear TDP-43 characterises sporadic and most familial forms of amyotrophic lateral sclerosis (ALS). TDP-43 (encoded by TARDBP) has multiple roles in RNA processing. We aimed to determine whether 1) RNA splicing dysregulation is present in lower motor neurons in ALS and in a motor neuron-like cell model, and 2) TARDBP mutations (mtTARDBP) are associated with aberrant RNA splicing using patient-derived fibroblasts. Methods: Affymetrix exon arrays were used to study mRNA expression and splicing in lower motor neurons obtained by laser capture microdissection of autopsy tissue from individuals with sporadic ALS and TDP-43 proteinopathy. Findings were confirmed by qRT-PCR and in NSC34 motor neuronal cells following shRNA-mediated TDP-43 depletion. Exon arrays and immunohistochemistry were used to study mRNA splicing and TDP-43 expression in fibroblasts from patients with mtTARDBP-associated, sporadic and mutant SOD1-associated ALS. Results: We found altered expression of spliceosome components in motor neurons and widespread aberrations of mRNA splicing that specifically affected genes involved in ribonucleotide binding. This was confirmed in TDP-43 depleted NSC34 cells. Fibroblasts with mtTARDBP showed loss of nuclear TDP-43 protein and demonstrated similar changes in splicing and gene expression, that were not present in fibroblasts from patients with sporadic or SOD1-related ALS. Conclusion: Loss of nuclear TDP-43 is associated with RNA processing abnormalities in ALS motor neurons, patient-derived cells with mtTARDBP, and following artificial TDP-43 depletion, suggesting that splicing dysregulation directly contributes to disease pathogenesis. Key functional pathways affected include those central to RNA metabolism. RNA was extracted from lower motor neurons obtained by laser capture microdissection from autopsy material from neurologically healthy controls (n=6) and cases of sporadic ALS (n=3) and ALS due to C9ORF72 mutations (n=3).

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Abberant neuronal Wnt activation causes defective TDP43 localization

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