The cell possesses a number of vital mechanisms to respond to different stressors. Mitochondria are dynamic organelles which undergo constant changes in length, transport and inner membrane structure and curvature. Invaginations of this inner membrane, cristae, have been known to respond to the energetic state of mitochondria, but the regulation of these changes as well as the consequences thereof remain undetermined. We find that Optic Atrophy 1 (OPA1), a protein involved in inner membrane fusion and cristae maintenance during cell death, can respond to the energetic state of mitochondria and the cell. Moreover, OPA1-dependent changes in cristae structure are required for resistance to starvation induced cell death, proper functioning of the electron transport chain, for growth in galactose media and for maintenance of ATP synthase assembly. Interestingly, we demonstrate that select members of the mitochondrial solute carriers (SLC25A) interact with OPA1 and affect the response of OPA1 to substrate levels. Taken together, we propose an SLC25A-dependent role for OPA1 in sensing energy substrate availability and responding to alter cristae, bioenergetics and cellular survival. We also identified KIAA0664 as a novel OPA1-interacting protein, describe its subcellular localization and investigate its role in mitochondrial fusion and in mitochondrial localization. Finally, since both known carriers of mitochondrial glutathione were demonstrated to interact with OPA1, we investigated the role of OPA1 in cellular glutathione redox. OPA1 depleted cells demonstrated both increased total cellular glutathione and a shift in redox to its reduced form. The role of OPA1 in glutathione levels and redox ratios required GTPase activity, but surprisingly not fusion. Since glutathione is a master regulator of reactive oxygen species detoxification, these findings may shed light on the role of OPA1 in ROS-induced cell death pathways.

La dynamique et la distribution mitochondriale sont essentielles pour l’homéostasie énergétique cellulaire. CLUH est une protéine indispensable à la distribution mitochondriale, dont la déplétion provoque une agrégation mitochondriale périnucléaire. Afin de comprendre le rôle de CLUH dans le métabolisme cellulaire, nous avons généré des cellules knockout CLUH par la méthode CRISPR-cas9. Nos résultats montrent que l’agrégation mitochondriale est associée à la diminution de la taille cellulaire et à la réduction quantitative des complexes de la chaîne respiratoire, menant ainsi à des défauts de la phosphorylation oxydative. Cette déficience énergétique est due à la perturbation de la traduction mitochondriale, et provoque un shift métabolique vers la glycolyse. Le profil métabolique des cellules KO montre un dysfonctionnement du cycle de Krebs et une altération de l’oxydation des acides gras. Dans ce sens, nous avons déterminé une fonction cruciale de CLUH dans le couplage de la distribution mitochondriale au contrôle de l’état cellulaire énergétique et métabolique. Pour approfondir l’analyse de la fonction de CLUH, nous avons effectué une étude de prédiction des domaines fonctionnels in silico, et avons identifié cinq domaines évolutivement conservés au sein de la séquence primaire de CLUH. De plus, nous démontrons que CLUH oligomérise en tétramères et en octomères, qui sont déstabilisés par l’expression ectopique de formes tronquées de CLUH dépourvues des domaines Clu-Nou TPR, par un effet dominant négatif. En résumé, nos résultats montrent l’importance de CLUH dans le maintien de l’homéostasie métabolique cellulaire, et une régulation potentielle de ses fonctions par oligomérisation. / Mitochondrial dynamics and distribution are critical insupplying ATP in response to energy demands. CLUHis a highly conserved protein involved in mitochondrial distribution, whose dysfunction leads to mitochondrial clustering around the nucleus. To gain insight into the role of CLUH in cellular metabolism, we generated CLUH knockout cells using CRISPR/Cas9. We show that mitochondrial clustering is associated with a smaller cell size and with decreased abundance of respiratory complexes, resulting in OXPHOS defects. This energetic impairment was found to be due to the alteration of mitochondrial translation, leading to a metabolic shift towards glucose dependency. Metabolomic profiling by mass spectrometry disclosed a dysfunctional Krebs cycle and an alteration of fatty acidoxidation. Thus, we established a clear function of CLUH in coupling mitochondrial distribution to the control of cellular energetic and metabolic status. To further analyze CLUH function, we performed in silico the prediction of the functional domains of this protein, disclosing 5 evolutionary conserved domains within the CLUH primary sequence. We reveal an oligomerization of CLUH into tetramers and octamers, and show a dominant negative effect associated to the expression of CLUH truncated forms missing Clu-N or TPR domains. Taken together, our studies reveal the importance of CLUH in maintaining cellular metabolism homeostasis and the potential regulation of its function through oligomerization.