Eukaryotic Translation Initiation Factor 5A (eIF5A) Regulates Mitochondrial Protein Import by Alleviating Ribosome Stalling at the TIM50 Translocase mRNA

Core Concepts

Eukaryotic translation initiation factor 5A (eIF5A) is essential for alleviating ribosome stalling at the polyproline-rich region of the TIM50 mRNA, which encodes a key receptor subunit of the mitochondrial inner membrane translocase. Depletion of eIF5A leads to reduced Tim50 protein levels, compromised mitochondrial protein import, and activation of the mitochondrial protein import stress response.

Abstract

The content describes how eIF5A, a conserved translation factor, regulates mitochondrial function by controlling the translation of the TIM50 mRNA, which encodes a crucial receptor subunit of the mitochondrial inner membrane translocase complex.
Key highlights:

Depletion of eIF5A leads to a general down-regulation of mitochondrial proteins, including components of the oxidative phosphorylation (OXPHOS) system and TCA cycle enzymes.
This down-regulation occurs at the translational level, as eIF5A depletion causes reduced ribosome association with mRNAs encoding mitochondrial proteins.
The TIM50 mRNA, which contains a polyproline-rich region, is identified as a direct target of eIF5A. Removal of the polyproline stretch rescues the translation of TIM50 mRNA in the eIF5A mutant.
Depletion of eIF5A leads to ribosome stalling at the polyproline region of the TIM50 mRNA, resulting in reduced Tim50 protein levels and compromised mitochondrial protein import.
The reduced mitochondrial protein import upon eIF5A depletion activates the mitochondrial protein import stress response, leading to the accumulation of mitochondrial precursor proteins in cytosolic aggregates.
Restoring Tim50 levels by removing the polyproline region alleviates the mitochondrial import stress response, but does not fully rescue the mitochondrial dysfunction caused by eIF5A depletion, suggesting additional mechanisms by which eIF5A regulates mitochondrial function.

Stats

Depletion of eIF5A leads to a 3-fold reduction in the synthesis of Tim50 protein at the restrictive temperature.
Removing the polyproline stretch in Tim50 rescues its protein synthesis in the eIF5A mutant at the restrictive temperature.
The time required for translating a wild-type TIM50 mRNA is significantly increased (from 2 minutes to 4 minutes) in the eIF5A mutant at the restrictive temperature, indicating ribosome stalling.
Removal of the polyproline stretch in Tim50 restores the translation time to the wild-type level in the eIF5A mutant.

Quotes

"eIF5A promotes the translation elongation between amino acids known to be poor substrates for the formation of peptide bonds that may stall translation, such as polyproline motifs but also combinations of proline, glycine, and charged amino acids."
"Through the alleviation of ribosome stalling of TIM50 mRNA and thus, modulation of Tim50 protein levels, eIF5A specifically controls the import and translocation of mitochondrial proteins."
"Removal of the polyprolines from Tim50 rescues the mitochondrial import stress response, as well as the translation of oxidative phosphorylation reporter genes in an eIF5A loss of function."

Key Insights Distilled From

eIF5A controls mitoprotein import by relieving ribosome stalling at the TIM50 translocase mRNA

by Barba-Aliaga... at www.biorxiv.org 12-19-2023

https://www.biorxiv.org/content/10.1101/2023.12.19.572290v1

Deeper Inquiries

How might the eIF5A-dependent regulation of Tim50 translation be integrated with other mechanisms that link eIF5A to mitochondrial function

The eIF5A-dependent regulation of Tim50 translation can be interconnected with various mechanisms that link eIF5A to mitochondrial function. One possible integration point is through the broader impact of eIF5A on mitochondrial protein synthesis. eIF5A is known to promote translation elongation at specific sequences, such as polyprolines, which are common in mitochondrial proteins. By facilitating the translation of these proteins, eIF5A plays a crucial role in maintaining the proper levels of mitochondrial proteins, including Tim50. This direct effect on protein synthesis can influence the overall mitochondrial function by ensuring the timely and efficient production of key components involved in mitochondrial processes.
Furthermore, the regulation of Tim50 translation by eIF5A may intersect with the mitochondrial import machinery. Tim50 is a critical component of the TIM23 complex, which is responsible for the translocation of proteins into the mitochondrial inner membrane. By controlling the translation of Tim50, eIF5A can impact the efficiency of mitochondrial protein import. Any disruption in Tim50 synthesis due to eIF5A depletion can lead to import defects and the accumulation of misfolded proteins in the cytosol, triggering stress responses and affecting overall mitochondrial function.
Additionally, eIF5A has been implicated in other mitochondrial processes beyond protein synthesis and import. It has been shown to influence mitochondrial respiration rates and membrane potential, indicating a broader role in mitochondrial function. The regulation of Tim50 translation by eIF5A may be just one piece of the puzzle, with potential crosstalk with other eIF5A-mediated mechanisms that contribute to mitochondrial homeostasis and cellular health.

What are the potential implications of the eIF5A-mediated regulation of mitochondrial protein import in the context of human diseases associated with mitochondrial dysfunction

The eIF5A-mediated regulation of mitochondrial protein import has significant implications for human diseases associated with mitochondrial dysfunction. Mitochondria play a crucial role in energy production, metabolism, and cell signaling, and any disruption in mitochondrial function can have profound effects on cellular health and disease development. In conditions where mitochondrial protein import is compromised, such as neurodegenerative disorders, metabolic diseases, and aging-related conditions, the eIF5A-dependent control of Tim50 translation could be a critical factor.
For example, in neurodegenerative diseases like Parkinson's and Alzheimer's, mitochondrial dysfunction and impaired protein import have been implicated in disease progression. The accumulation of misfolded proteins in the cytosol due to import defects can lead to cellular stress and toxicity, contributing to neuronal damage and degeneration. By modulating the translation of Tim50 and other mitochondrial proteins, eIF5A could potentially influence the severity and progression of these diseases.
Furthermore, in metabolic disorders where mitochondrial function is compromised, such as diabetes and obesity, the eIF5A-mediated regulation of mitochondrial protein import could impact cellular energy metabolism and overall metabolic health. Dysregulation of mitochondrial protein import can disrupt metabolic pathways and contribute to metabolic imbalances seen in these conditions. Targeting eIF5A or the Tim50 translation pathway could offer novel therapeutic strategies for mitigating mitochondrial dysfunction and improving metabolic outcomes in these diseases.

Could modulating eIF5A activity or the polyproline region of Tim50 be a potential therapeutic strategy for diseases with compromised mitochondrial protein import

Modulating eIF5A activity or targeting the polyproline region of Tim50 could indeed be a potential therapeutic strategy for diseases characterized by compromised mitochondrial protein import. By understanding the critical role of eIF5A in regulating Tim50 translation and mitochondrial protein import, researchers could explore interventions that enhance eIF5A function or specifically target the translation of Tim50 to restore proper mitochondrial function.
One approach could involve developing small molecules or compounds that enhance eIF5A activity or stabilize its interaction with ribosomes, promoting the efficient translation of Tim50 and other mitochondrial proteins. By boosting eIF5A-mediated translation elongation, the import of mitoproteins could be improved, reducing the accumulation of misfolded proteins and alleviating mitochondrial stress responses.
Alternatively, targeting the polyproline region of Tim50 could offer a more specific strategy to prevent ribosome stalling and enhance the synthesis of Tim50. By modifying the proline-rich sequence or developing inhibitors that prevent stalling at this region, the translation of Tim50 could be optimized, leading to improved mitochondrial protein import and overall mitochondrial function.
Overall, modulating eIF5A activity or targeting the Tim50 translation pathway represents a promising avenue for developing novel therapeutics aimed at addressing mitochondrial dysfunction in various diseases and conditions associated with impaired protein import and mitochondrial stress.