(EN) Tumours are heterogeneous and consist of multiple populations of cells. The population of cells with tumour-initiating capability is known as cancer stem cells (CSC). Cells with increased stemness properties and elevated resistance to anti-cancer treatment have been shown to be highly affected upon decline of mitochondrial respiration, linking the concept of CSCs to deregulated bioenergetics. Consistently, functional electron transport chain (ETC) is crucial in tumorigenesis. Expression of HER2 oncogene, associated with resistance to treatment in breast cancer, has been connected with regulation of mitochondrial function. We therefore investigated the possibility that manipulation of mitochondrial bioenergetics via disruption of ETC eliminates the conventional therapy-resistant populations of tumour, such as CSCs and HER2high cells. We demonstrate that HER2high cells and tumours have increased complex I-driven respiration and increased assembly of respiratory supercomplexes (SC). These cells are highly sensitive to MitoTam, a novel mitochondria-targeted derivative of tamoxifen, acting as a CI inhibitor and SC disruptor. MitoTam was able to overcome resistance to tamoxifen, and to reduce the metastatic potential of HER2high cells. Higher sensitivity of HER2high cells to MitoTam is dependent on...

1 Abstract in English Mitochondrial electron transport chain (ETC) targeting shows a great promise in cancer therapy. However, why modern ETC-targeted compounds are tolerated on the organismal level and what are the molecular reasons for this tolerance remains unclear. Most somatic cells are in a non-proliferative state, and features associated with the ETC in quiescence might therefore contribute to specificity. Thus, we investigated the ETC status and the role of two major consequences of ETC blockade, reactive oxygen species (ROS) generation and inhibition of ATP production, in cell death induction in breast cancer cells and in proliferating and quiescent non-transformed cells. First, we characterised the effect of a newly developed ETC inhibitor mitochondria- targeted tamoxifen (MitoTam) in in vitro and in vivo tumour models of breast cancer with varying status of the Her2 oncogene. We document that Her2high cells and tumours have increased assembly of respiratory supercomplexes (SCs) and increased complex I-driven respiration in vitro and in vivo. They are also highly sensitive to MitoTam. Unlike the parental compound tamoxifen, MitoTam efficiently suppressed experimental Her2high tumours without systemic toxicity. Mechanistically, MitoTam inhibits complex I- driven respiration and disrupts respiratory...

Mood disorders are serious diseases. Nevertheless, their pathophysiology is not sufficiently clarified. Biological markers that would facilitate the diagnosis or successful prediction of pharmacotherapy are still being sought. The aim of the study was to find out whether mitochondrial functions are affected by antidepressants, mood stabilizers and depression. Our research is based on recent hypotheses of mood disorders, the advanced monoamine hypothesis, the neurotrophic hypothesis, and the mitochondrial dysfunction hypothesis. We assume that impaired function of mitochondria leads to neuronal damage and can be related to the origin of mood disorders. Effects of antidepressants and mood stabilizers on mitochondrial functions can be related to their therapeutic or side effects. In vitro effects of pharmacologically different antidepressants and mood stabilizers on the activities of mitochondrial enzymes were measured in mitochondria isolated from pig brains (in vitro model). Activity of monoamine oxidase (MAO) isoforms was determined radiochemically, activities of other mitochondrial enzymes were measured spectrophotometrically. Overall activity of the system of oxidative phosphorylation was measured electrochemically using high- resolution respirometry. Methods were modified to measure the same...

Mitochondria are essential organelles for most eukaryotic cells, containing intricate networks of numerous proteins. These include, among others, complexes I-IV of the electron transport chain. Being at the crossroads of the tricarboxylic acid cycle and the respiratory chain, mitochondrial complex II plays a key role in cellular metabolism. The protein complex, also known as succinate dehydrogenase, is capable of not only succinate oxidation and electron transfer but also contributes to the production of reactive oxygen species. Mitochondrial complex II consists of four subunits, SDHA-D, and four dedicated protein assembly factors SDHAF1-4 that participate in complex II biogenesis. Mutations and epigenetic modulations of genes coding for succinate dehydrogenase subunits or assembly factors are associated with pathological conditions such as neurodegenerative diseases, or may result in tumor formation. However, inborn complex-II-linked mitochondrial pathologies are rather understudied, compared to diseases with causative errors of other mitochondrial complexes, presumably due to the fact that none of complex II subunits is encoded in the mitochondrial genome. Recent studies have shown that impairment of mitochondrial complex II function or assembly leads to accumulation of alternative assembly forms...

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Psychopharmaca are a large group of drugs widely used not only in psychiatry. Their systemic administration affects both the main diagnosis and the organism as a whole. The subject of our experiments is the effect of psychopharmaca on the changes in mitochondrial functions, which is beneficial for understanding of molecular mechanisms of therapeutic and adverse effects of drugs. The aim of this thesis was to study the in vitro effects of selected drugs on the cell energy metabolism. Selected antipsychotics (chlorpromazine, levomepromazine, haloperidol, risperidone, ziprasidone, zotepine, aripiprazole, clozapine, olanzapine, and quetiapine), antidepressants (bupropion, fluoxetine, amitriptyline, imipramine) and mood stabilizers (lithium, valproate, valpromide, lamotrigine, carbamazepine) were tested. In vitro effects of selected psychopharmaca were measured on isolated pig brain mitochondria. The activities of citrate synthase (CS) and electron transport chain (ETC) complexes (I, II+III, IV) were measured spectrophotometrically. Drug-induced changes of mitochondrial respiration rates linked to complex I (supported by malate and pyruvate) and complex II (supported by succinate) were evaluated by high resolution respirometry. Complex I was significantly inhibited by lithium, carbamazepine, fluoxetine,...

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ATP synthase est une protéine essentielle associée à la membrane interne mitochondriale, qui synthétise l'ATP par couplage d’un transport de protons au travers de la membrane, en dissipant un gradient électrochimique de protons créé par la chaîne respiratoire. Cette réaction assure l’alimentation en énergie des processus biologiques cellulaires. Si la membrane mitochondriale se dépolarise, la réaction inverse d’hydrolyse d’ATP est rapidement bloquée par un inhibiteur soluble naturel de l’ATPase mitochondriale, IF1. Cette régulation efficace et réversible évite le gaspillage de l’énergie par la cellule. Chez la levure, IF1 est une petite protéine de 63 amino-acides. Elle se fixe sur l'une des trois interfaces catalytiques de l’ATP synthase et inhibe l’hydrolyse d’ATP. Bien que les structures cristallographiques des complexes F1-ATPase inhibés par IF1 aient été résolus, l'étape initiale de reconnaissance et celle du verrouillage d’IF1 restent peu claires au niveau moléculaire.Pendant ma thèse, nous nous sommes intéressés au mécanisme d’inhibition de l’ATPase par IF1. Par des analyses des structures disponibles et des alignements de séquence, nous avons sélectionné de nombreux résidus localisés dans différentes régions des sous-unités α et β de l'ATP synthase de Saccharomyces cerevisiae et susceptibles de participer au processus de fixation d'IF1. En utilisant le mutagenèse dirigée combinée à des experiences cinétiques, nous avons étudié les effects des mutations sur l’inhibition de l’ATP synthase par IF1 chez Saccharomyces cerevisiae. Dans ce travail, nous avons identifié des résidus ou motifs des sous-unités α et β de l’ATP synthase impliqués dans les étapes de reconaissance et/ou verrouillage d’IF1, ce qui nous permet de compléter les études structurales et d'esquisser un mécanisme de fixation d'IF1. / ATP synthase is an essential protein complex located in the mitochondrial inner membrane, which synthesize ATP by coupling to a rotary proton transport across the membrane at the expense of the electrochemical proton gradient created by the electron transport chain. This reaction guarantees the supply of energy to biological processes in a cell. When mitochondria get deenergized, i.e. the protomotive force across the mitochondrial inner membrane collapses, the ATP synthase switches from ATP synthesis to hydrolysis. This hydrolytic activity is then immediately prevented by a natural soluble mitochondrial ATPase inhibitor, IF1. This efficient reversible inhibition system protects cells from wasting energy. In yeast, IF1 is a small protein consisting of 63 amino acids. It binds to one of the three (αβ) catalytic interfaces of ATP synthase and thereby blocks the rotary catalysis. Although the crystal structure of the dead-end IF1 inhibited F1-ATPase complex has been resolved, IF1 initial binding and locking to ATPase still remain unclear events at the molecular level.During my thesis, we have been interested in the dynamic mechanism of ATPase inhibition by IF1. By means of analyses of published structures and protein sequence alignment, we selected numerous residues located in different regions of Saccharomyces cerevisiae ATP synthase α, β subunits, which might potentially paticipate in IF1 binding process. Using site-directed mutagenesis combined with kinetic experiments, we studied the effect of mutations of the selected candidates on the rate and extent of ATPase inhibition by IF1. In this way we identified residues or motifs in ATP synthase α, β subunits involved in IF1 recognition and/or locking steps, which allows complementing structural studies and drawing an outline of IF1 binding.