Differential toxicity of TAR DNA‐binding protein 43 isoforms depends on their submitochondrial localization in neuronal cells

Abstract

TAR DNA-binding protein 43 (TDP-43) is an RNA-binding protein and a major component of protein aggregates found in amyotrophic lateral sclerosis and several other neurodegenerative diseases. TDP-43 exists as a full-length protein and as two shorter forms of 25 and 35 kDa. Full-length mutant TDP-43s found in amyotrophic lateral sclerosis patients re-localize from the nucleus to the cytoplasm and in part to mitochondria, where they exert a toxic role associated with neurodegeneration. However, induction of mitochondrial damage by TDP-43 fragments is yet to be clarified. In this work, we show that the mitochondrial 35 kDa truncated form of TDP-43 is restricted to the intermembrane space, while the full-length forms also localize in the mitochondrial matrix in cultured neuronal NSC-34 cells. Interestingly, the full-length forms clearly affect mitochondrial metabolism and morphology, possibly via their ability to inhibit the expression of Complex I subunits encoded by the mitochondrial-transcribed mRNAs, while the 35 kDa form does not. In the light of the known differential contribution of the full-length and short isoforms to generate toxic aggregates, we propose that the presence of full-length TDP-43s in the matrix is a primary cause of mitochondrial damage. This in turn may cause oxidative stress inducing toxic oligomers formation, in which short TDP-43 forms play a major role.

Disease-modifying effects of metabolic perturbations in ALS/FTLD

“…Indeed, there is evidence to suggest that TDP-43 regulates glycolysis in hepatocellular carcinoma cell lines [ 131 ], and one study demonstrated that the abnormal localization of TDP-43 to mitochondria in cells from ALS/FTLD patients leads to the disassembly of the respiratory chain complex I and impairs mitochondrial oxidative phosphorylation [ 181 ]. This has been corroborated by two more studies showing a pathological displacement of TDP-43, or its N- and C-terminal fragments, in mitochondria leading to impairment of mitochondrial functioning [ 34 , 153 ]. Hyperglycemia could counteract this by providing more substrate (glucose) for cellular glucose metabolism, thereby partially replenishing the ATP deficit.…”

TDP-43-Mediated Toxicity in HEK293T Cells: A Fast and Reproducible Protocol To Be Employed in the Search of New Therapeutic Options against Amyotrophic Lateral Sclerosis

“…Despite our data, impaired mitochondrial function was shown to be closely related to ALS pathophysiology (Muyderman and Chen, 2014). Mitochondrial dysfunction is another toxic effect mediated by TDP-43 according to independent reports [23,24], and TDP-43 colocalization in the mitochondria seems to be essential for this deleterious effect [25,26].…”

Histaminergic transmission slows progression of amyotrophic lateral sclerosis

“…Evaluation of mitochondrial bioenergetics was performed by Seahorse XF96 Extracellular Flux Analyzer (Seahorse Bioscience‐Agilent, USA). Multiple parameters of mitochondrial function were measured with Stimulus XF Stress Test Kit (Seahorse Bioscience) . Briefly, differentiated NSC‐34 cells were seeded (7 × 10 4 cells/well) into micro‐lysine‐coated XF96 microplates and incubated overnight in 5% CO 2 , 37 °C.…”