Biology subjects

Reutenauer, L.

Publications and source records attributed to Reutenauer, L..

3 recordsLinked to original sources

bioRxiv2025

Partial Bypass of Frataxin Deficiency by ISCU M141I Restores Cytosolic and Nuclear FeS Cluster Assembly

Iron-sulfur (Fe-S) clusters are essential cofactors required for the activity of numerous proteins involved in fundamental cellular processes, including DNA replication, metabolism and mitochondrial respiration. In eukaryotes, Fe-S cluster biogenesis is initiated in mitochondria by the ISC machinery, which assembles iron and sulfur, delivered by a cysteine desulfurase, onto the scaffold protein ISCU. Frataxin (FXN), a key regulator of this pathway, enhances Fe-S production by accelerating persulfide transfer to ISCU. FXN is essential in eukaryotes, and its loss results in "petite" phenotype in yeast, senescence in dividing mammalian cells and embryonic lethality in mice. Interestingly, in yeast, a methionine to isoleucine substitution at position 141 of the scaffold protein Isu1 can bypass the requirement of FXN. To test whether this bypass mechanism is conserved in mammals, we introduced the equivalent M141I substitution into the endogenous Iscu gene in murine fibroblasts carrying a conditional Fxn allele using CRISPR-Cas9. We show that the ISCU M141I variant enables cell survival in the absence of FXN, preventing cell cycle arrest and decreasing baseline DNA damage. However, these FXN-null survivor clones exhibit slower proliferation, persistent mitochondrial dysfunction and defective mitochondrial Fe-S cluster proteins. In contrast, nuclear and cytosolic Fe-S proteins are preserved, as is cellular iron homeostasis. Importantly, the ISCU M141I variant delays, but does not fully rescue, embryonic lethality in Fxn-deficient mice. Altogether, our results reveal a previously unrecognized compartment-specific rescue of Fe-S cluster dependent processes by the ISCU M141I variant in mammalian cells, raising for the first time the possibility of compartmental regulation of Fe-S cluster biogenesis.

cell biology↗

bioRxiv2025

Characterization of a COQ8A-ataxia mouse model with E548K single-site mutation: distinct and comparable findings relative to a loss-of-function mutation

COQ8A-ataxia, also known as autosomal recessive cerebellar ataxia type 2 (ARCA2), is a rare mitochondrial disorder caused by biallelic mutations in COQ8A, a gene encoding for a mitochondrial protein critical for coenzyme Q (CoQ) biosynthesis. Although there is no clear genotype-phenotype correlation in patients, loss-of function variants generally produce a cerebellar-restricted phenotype, while missense mutations are more frequently associated with multisystemic symptoms. The COQ8AE551K variant has been reported at the homozygous state in individuals with early-onset disease and widespread systemic involvement. This study aimed to characterize the new Coq8aE548K knocking mouse model, equivalent to the human E551K variant, and compare its phenotype to the complete Coq8a-/- knockout mouse. Based on human data and preliminary data in the zebrafish, we hypothesized that the Coq8aE548K knocking would present a more pronounced phenotype than the constitutive knockout. Contrary to our initial hypothesis, mice homozygous for the Coq8aE548K allele exhibited no significant motor or cognitive impairments, nor muscle phenotype. Biochemically, the knocking Coq8aE548K mutation led to variable instability of the COQ8AE548K protein and reduced expression of proteins in the CoQ biosynthesis pathway, such as COQ5 and COQ7 in both cerebellum and muscle, similarly to the constitutive knockout. Despite this, mitochondrial function and tissue architecture remained intact, suggesting preserved cellular resilience. These findings highlight the complexity of genotype-phenotype correlations in COQ8A-related ataxia and provides a tool for investigating sub-threshold mitochondrial dysfunction.

cell biology↗

bioRxiv2020

High levels of frataxin overexpression leads to mitochondrial and cardiac toxicity in mouse models

Friedreich ataxia (FA) is currently an incurable inherited mitochondrial disease caused by reduced levels of frataxin (FXN). Cardiac dysfunction is the main cause of premature death in FA. AAV-mediated gene therapy constitutes a promising approach for FA, as demonstrated in cardiac and neurological mouse models. While the minimal therapeutic level of FXN protein to be restored and biodistribution have recently been defined for the heart, it is unclear if FXN overexpression could be harmful. Indeed, depending on the vector delivery route and dose administrated, the resulting FXN protein level could reach very high levels in the heart, cerebellum, or in off-target organs such as the liver. The present study demonstrates safety of FXN cardiac overexpression up to 9-fold the normal endogenous level, but significant toxicity to the mitochondria and heart above 20-fold. We show gradual severity with increasing FXN overexpression, ranging from subclinical cardiotoxicity to left ventricle dysfunction. This appears to be driven by impairment of mitochondria respiratory chain, ultrastructure and homeostasis, which lead to myofilaments alteration, cell death and fibrosis. Overall, this study underlines the need, during the development of gene therapy approaches, to consider appropriately vector potency, long term safety and biomarkers to monitor such events.

bioengineering↗