Cellular toxicity induced by the 26‐kDa fragment and amyotrophic lateral sclerosis‐associated mutant forms of TAR DNA‐binding protein 43 in human embryonic stem cell‐derived motor neurons

Abstract

Aims: Amyotrophic lateral sclerosis (ALS) results in the selective loss of motor neurons within several years of disease onset; however, the molecular mechanisms behind ALS pathogenesis remain largely unknown. Among the genes responsible for familial ALS, mutations in TAR DNA-binding protein 43 (TDP-43) have been identified. The present study evaluated the cytotoxicity of TDP-43 fragments and ALS-associated mutants against human embryonic stem cell-derived motor neurons. Methods: Magnetofection was used to investigate the mortality rates of motor neurons after forced expression of TDP-43 C-terminal fragments and ALS-associated TDP-43 missense mutants. Results: Neither wild-type TDP-43 nor the 35-kDa fragment induced cell death. However, the 26-kDa fragment, which forms insoluble aggregates in the motor neurons of ALS patients, showed significant cytotoxicity, similar to mutant forms of TDP-43, including p.A315T and p.A382T. Hence, a motor neuron-specific neurotoxic function might be attributed to both the 26-kDa fragment and the TDP-43 mutants. Thus, 26kDa C-terminal fragment was considered to play an important role in ALS pathology, but alterations in adenosine deaminase acting on RNA 2 (ADAR2) expression, an enzyme accountable for GluA2 (AMPA receptor subunit 2) mRNA editing insufficiency in sporadic ALS, did not lead to alterations in the expression of the 26-kDa fragment. Conclusions: This is the first report showing the influence of specific ALS-associated factors on the mortality of motor neurons through the manipulation of gene expression. The motor neuron disease model described herein might prove useful for the identification of novel pathogenic factors and neuroprotective agents for the treatment of ALS.

The cleavage pattern of TDP-43 determines its rate of clearance and cytotoxicity

“…The amount of LDH released from the dead cells was quantified by measuring the absorbance at 560 nm. The viability of hESC-derived motor neurons was quantified as described previously 42 with modifications. In brief, 5-6 days after transduction, the cells were first labelled with SNAP-Cell Star 505 for 30 min at 37°C.…”

The long non-coding RNA nuclear-enriched abundant transcript 1_2 induces paraspeckle formation in the motor neuron during the early phase of amyotrophic lateral sclerosis

“…Wild-type (WT) TDP-43 and FUS/TLS are predominantly observed in the nucleus by immunostaining [8,9]. Besides full-length WT TDP-43, 35-kDa and 18–26-kDa C-terminal fragments are produced via caspase-dependent and -independent pathways [8,10]. The 26-kDa C-terminal TDP-43 fragment aggregated insolubly in the cytoplasm of ALS motor neurons with ubiquitination and phosphorylation [11,12].…”