Pathophysiological insights into ACO2-related inherited disorders through combined functional and multi-omic analyses of ACO2 patient-derived fibroblasts

ACO2 encodes the mitochondrial aconitase, involved in the second step of the tricarboxylic acid cycle. ACO2 variants cause isolated dominant or recessive optic atrophy, characterized by the degeneration of the optic nerves and leading to vision loss with high clinical heterogeneity, which ranges from pauci-symptomatic to legally blind patients. ACO2 variants also cause rare severe syndromic presentations, like infantile cerebellar-retinal degeneration, characterized by developmental delay, truncal hypotonia, ataxia, seizures, optic atrophy and retinal degeneration.

As ACO2 pathophysiology still lacks proper characterization and no treatment is available for ACO2-related disorders, we combined a functional study with a multi-omic analysis of patient-derived fibroblasts carrying ACO2 variants. Here, we show that ACO2 variants decrease ACO2 protein levels, ACO2 and cytoplasmic ACO1 mRNA expression and mtDNA levels. Metabolomic analyses identified 14 discriminating metabolites involved in amino acid metabolism, TCA cycle, nucleotide and lipid metabolism.

Transcriptomic analyses disclosed a down-regulation of immunity-related pathways and an up-regulation of cell cycle-related pathways. These results provide new insights into the cellular impact of ACO2 deficiency beyond its primary role in the TCA cycle, and identify citrate accumulation as a crucial determinant in ACO2 physiopathology. We would like to thank the patients and their families for their participation, and the clinicians for their contribution to this study.

We would also like to thank the SCIAM (Service Commun d’Imageries et d’Analyses Microscopiques) and PACeM (Plateforme d’Analyse Cellulaire et Moléculaire) platforms. We are indebted to all the Mitolab team members for constant support and discussions. We acknowledge the institutional support from Angers University and University Hospital, the CNRS and Inserm, from the Ouvrir les Yeux and ACO2 Gene patient organizations, and the ANRT (Association Nationale de la Recherche et de la Technologie).

Univ Angers, MitoLab Team, MitoVasc Unit, UMR CNRS 6015, Inserm U1083, SFR ICAT, University Hospital of Angers, F-49000, Angers, France Cléis Beaulieu, Aymane Bouzidi, Ismail Gouiza, Naïg Gueguen, Valérie Desquiret-Dumas, Morgane Le Mao, Florence Pascaretti-Grizon, Adélie Mellinger, Nolwenn Bounaix, Delphine Prunier-Mirebeau, Salim Khiati, Marco Spinazzi, Arnaud Chevrollier, Olivier R. Baris & Guy Lenaers Association Ouvrir Les Yeux, 45 rue François Gauthier, 62300, Lens, France Department of Biochemistry and Molecular Biology, University Hospital of Tours, 2, Bd Tonnellé, 37044, Tours, France Metabolomic and Biochemical Analysis Facility, Us-61 Asb, Inserm, University of Tours, 37044, Tours, France Department of Biochemistry and Molecular Biolology, University Hospital of Angers, Angers, France Cinzia Bocca, Naïg Gueguen, Valérie Desquiret-Dumas & Delphine Prunier-Mirebeau Genetics Department, University Hospital of Angers, F-49000, Angers, France Genetics and Immuno-Cell Therapy Team, Mohammed First University, Oujda, Morocco Department of Internal and General Medicine, Haut-Anjou Hospital Center, 1, Quai Du Dr Lefèvre, 53200, Château-Gontier, France Neurology Department, University Hospital of Angers, Angers, France The authors declare no competing interests. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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