Researchers Uncover Key Regulators in Neurodegenerative Protein Synthesis

Research conducted by a team at Science Tokyo has identified critical translation factors that play a significant role in the abnormal protein synthesis associated with neurodegenerative disorders. The study, published in the journal Nucleic Acids Research, focuses on the C9orf72 gene, which is frequently implicated in both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD).

Using a human cell-free translation system, the researchers reconstructed the aberrant translation process linked to the mutated C9orf72 gene. This work revealed that translation initiation factors eIF1A and eIF5B serve as key repressors, acting at distinct checkpoints to suppress the synthesis of toxic proteins that contribute to neuronal damage.

Neurodegenerative disorders, including ALS and FTD, present major challenges in modern medicine. The causes of these diseases vary, but many inherited cases are attributed to the abnormal repetition of DNA sequences. Such genetic defects can lead to a cellular process known as repeat-associated non-AUG (RAN) translation, which deviates from traditional protein synthesis methods. Unlike standard processes that begin at an AUG codon, RAN translation initiates from non-AUG codons, producing toxic proteins that accumulate in neurons.

Despite understanding the existence of these toxic proteins, the specific regulators governing RAN translation have remained largely unexplored. Traditional research methods rely on whole living cells, which often introduce indirect cellular responses that can obscure the results. To address this gap, Professor Hideki Taguchi and his team employed a bottom-up approach to identify these critical regulators.

“Our goal was to understand the potential regulators of RAN translation using a bottom-up screening approach,” Taguchi stated, outlining the motivation behind the investigation.

The researchers utilized the innovative human factor-based reconstituted translation system, known as human PURE, developed by scientists from the University of Hyogo. This system accurately reproduces the C9orf72-mediated RAN translation process outside of living cells, allowing for a focused examination of non-AUG initiation mechanisms.

Through systematic screening, the research team discovered that eIF1A and eIF5B act as repressors of RAN translation. They confirmed that these factors maintain tighter control over non-canonical translation initiation at two separate checkpoints. Specifically, eIF1A restricts C9-RAN translation during the scanning phase by promoting accurate start codon selection. In contrast, eIF5B reinforces translational control in the post-scanning phase, during the assembly of ribosomal subunits.

“The successful in vitro reconstitution of abnormal protein synthesis enabled us to elucidate the mechanisms of action of eIF1A and eIF5B in detail,” Taguchi noted.

The researchers expanded their findings by validating their results within human cells. They demonstrated that both eIF1A and eIF5B repress RAN translation through independent and additive mechanisms. Notably, their experiments revealed that when cells experience stress, C9-RAN translation tends to increase. However, this increase was completely negated in the absence of eIF1A, underscoring its critical role in the enhancement of C9-RAN during the integrated stress response.

By identifying eIF1A and eIF5B as essential regulators, this study enhances the understanding of the mechanisms underlying ALS and FTD. “These newfound insights provide a foundation for developing technologies aimed at controlling RAN translation, which could lead to novel therapeutic strategies for neurodegenerative diseases,” Taguchi expressed, conveying optimism for future research endeavors.

The detailed findings of this research represent a significant step forward in the quest to unravel the complexities of neurodegenerative disorders and may pave the way for innovative treatment options.