Les cassures double brin (CDB) de l’ADN sont des lésions dangereuses qui peuventêtre produites par des agents physiologiques et environnementaux. La réparation inefficace desCDB dans les cellules souches adultes (CSA), qui sont au sommet de la hiérarchie cellulaire,peut affecter leur capacité d’auto-renouvellement et également le processus de régénération.Le maintien de la stabilité génomique est fondamental et l’altération de ce processus accélèrele vieillissement et peut engendrer des cancers (cellules souches cancéreuses).Les CSA du muscle squelettique (cellules satellites, CS) sont responsables del’homéostasie et de la régénération musculaire. Après activation, les CS quiescentesprolifèrent, régénèrent les myofibres et reconstituent le pool, en s’auto-renouvelant.Ce projet de thèse a eu pour but d’étudier la réparation des CDB dans les CS et leursdescendants, au cours de la différenciation. Nous avons montré que les CS réparent les CDBplus efficacement et plus fidèlement que les cellules différenciées, avec l’implication du NHEJet de DNA-PK. Cette efficacité dépend plus de l’état de différenciation que de la proliférationet la niche a un impact mineur. De plus, des expériences avec des mutants de réparation,apoptose et différenciation suggèrent un mécanisme spécifique de réparation des CDB dans lesCS, qui pourrait être lié à l’architecture distincte de la chromatine de ces cellules. Ces étudesdevraient aider à comprendre comment le maintien de l’intégrité de l’ADN préserve le pooldes CS, influence la régénération et le vieillissement et protège de la carcinogenèse. / DNA double strand breaks (DSBs) are dangerous DNA lesions that are generated byphysiological and environmental DNA agents. Mismanagement of DSBs in adult stem cellsthat are at the top of the hierarchy generating the differentiated tissue, can affect their selfrenewalcapacity and the fate of their progeny. Maintenance of genome stability throughrobust DNA repair is fundamental for tissue regeneration, and impairment of this processaccelerates aging and may lead to cancers (cancer stem cells).Adult muscle stem cells (satellite cells, SCs) sustain skeletal muscle homeostasis andregeneration. Upon activation, quiescent SCs proliferate thereby regenerating muscle fibersand reconstituting the satellite cell pool by self-renewing.This thesis project aims to study DSB repair in SCs and their progeny, duringdifferentiation. We showed that muscle SCs repair DSBs more efficiently and, surprisingly,more accurately than differentiated cells by implicating NHEJ and DNA-PK. The repairefficiency is more a function of the differentiation status than of the replication status ofmyogenic cells, and the niche has a minor effect on the repair efficiency of SCs. Moreover,experiments with DSB repair, apoptosis and differentiation mutants suggest that SCs repairDSBs through a specific mechanism, that may be linked to the distinct chromatin architectureof these cells. These studies should help understanding how the maintenance of genomestability preserves SCs pool, influence regeneration and aging and protect fromcarcinogenesis.

During aging there is a decline in (MuSCs) and muscle regeneration, though the underlying reason is unknown. Interestingly, mitochondrial fragmentation is a common feature in aging, however, how this impacts MuSC function and maintenance has not been investigated. To address the effect of mitochondrial fragmentation in MuSCs, we generated a knockout mouse model using the Pax7CreERT2 inducible system to target deletion of the mitochondrial fusion protein Opa1 specifically within MuSCs (Opa1-KO). Analysis of MuSC function following muscle injury revealed a defect in the regenerative potential of Opa1-KO MuSCs. Moreover, following injury there was a substantial decrease in the number of MuSC in Opa1-KO animals with a concomitant increase in the number of committing cells, illustrating that loss of Opa1 drives MuSC towards commitment at the expense of self-renewal. Furthermore, loss of Opa1 in MuSCs alters the quiescence state, priming MuSCs for activation, as indicated by a reduction in quiescence-related genes, increased EdU incorporation, and enhanced cell cycle kinetics. To address the impact of mitochondrial dysfunction on muscle stem cell capacity, we generated a model of chronic Opa1 loss. Analysis of muscle stem cell function 3 months after Opa1 ablation revealed mitochondrial dysfunction and a defect in proliferation upon activation, leading to failed muscle regeneration. These data are the first to demonstrate a novel role for mitochondrial structure in the regulation of MuSC maintenance and regenerative capacity.

The objective of the study: To characterize stem cells isolated from mouse skeletal muscle and evaluate their regenerative potential to repair injured bone and articular cartilage in a mouse and rat animal model. The aims of the study: 1. Isolate MDSCs from mouse skeletal muscle, to determine their phenotypic characteristics and differentiation potential in vitro. 2. Evaluate osteogenic and chondrogenic regeneration capacity of MDSCs genetically engineered to express bone morphogenetic protein 4 (BMP4). 3. Evaluate osteogenic and chondrogenic differentiation potential of MDSCs-expressing BMP4 in vivo. 4. Investigate the possibility of MDSCs-expressing BMP4 and vascular endothelial growth factor (VEGF) to enhance bone repair. 5. Investigate the possibility of MDSCs-expressing BMP4 and anti-angiogenic factor sFlt1 to enhance articular cartilage repair. The brief overview of the study This investigation addresses important issues regarding: 1) stem cell isolation from skeletal muscle and their specific characteristics that enable us to identify these cells from other populations of stem cells in skeletal muscle; 2) the efficiency of muscle-derived stem cell-mediated bone and cartilage formation in vivo using retroviral vectors to express bone morpho-genetic protein 4 (BMP4); 3) the enhancement of osteogenic and chondrogenic potential of BMP4-secreting muscle-derived stem cells by addition of cells engineered to express vascular endothelial growth factor (VEGF) or its... [to full text] / Skeleto raumuo yra patogus ir lengvai prieinamas kamieninių ląstelių šaltinis. Satelitinės ląstelės, kurios kitaip vadinamos raumenų kamieninėmis ląstelėmis ir yra linkusios diferencijuoti miogenine linkme, dalyvauja raumens regeneracijoje ir gali savarankiškai atsinaujinti. Mūsų laboratorijoje izoliuotos raumeninės kilmės kamieninės ląstelės (RKKL) yra laikomos satelitinių ląstelių pirmtakėmis, tačiau nuo jų skiriasi. RKKL gali diferencijuoti ne tik miogenine linkme, bet ir kitomis linkmėmis (kauline, kremzline, riebalinio audinio, nervų, endotelio ir kraujodaros), ir joms yra būdinga ilgalaikė proliferacija, savarankiškas atsinaujinimas, privilegija imuninės sistemos atžvilgiu ir atsparumas oksidacijos sukeltam stresui. Šio darbo metu atlikti tyrimai atsako į labai svarbius klausimus, susijusius su: 1) RKKL išskyrimu ir jų specifinių savybių, leidžiančių šias ląsteles atskirti nuo kitų skeleto raumenų kamieninių ląstelių populiacijų, nustatymu; 2) genetiškai modifikuotų RKKL sukeliamo kaulų ir kremzlių formavimosi in vivo veiksmingumu, naudojant retroviruso vektorių kaulų morfogenezės baltymo 4 (BMP4) raiškai; 3) RKKL osteogeninio ir chondrogeninio pajėgumo stiprinimu, vienu metu naudojant ląsteles, išskiriančias BMP4, ir ląsteles, išskiriančias kraujagyslių endotelio augimo faktorių (VEGF) arba sFlt1. Šio tyrimo naujumas yra tas, jog iš esmės pirmą kartą parodyta, kad iš išgrynintų pelės skeleto raumenų ląstelių (PP6) populiacijos, išskirtos ląstelių sukibimo su... [toliau žr. visą tekstą]

Nous sommes sur le point de montrer que le muscle squelettique adulte contient une population de cellules souches capables de se différencier in vitro en cellules cardiaques présentant des battements automatiques. Ces cellules pulsantes différenciées en culture, possèdent toutes les caractéristiques d’un type de cellules spécialisées dans la conduction cardiaque : les cellules pacemaker du sinus atrial De même, lorsque ces cellules souches sont transplantées chez des souris mutantes qui présentent des troubles de la conduction cardiaque, elles sont retrouvées différentiées en cellules pacemaker dans le cœur et améliorent significativement les troubles du rythme de ces souris. Ces résultats indiquent qu’il est important d’isoler une population avec le même potentiel à partir du muscle squelettique humain étant donné le potentiel réparateur extrêmement prometteur de ces cellules souches adultes pour leur utilisation en thérapie cellulaire des dysfonctionnements du rythme cardiaque. Une analyse préliminaire sur le microcèbe, modèle primate, nous a d’ores et déjà permis de valider la différentiation in vitro des cellules souches dérivées du muscle squelettique en cellules pacemaker. / We show that adult multipotent Muscle-Derived Stem Cells (MDSC) have the ability to differentiate into cardiac pacemaker cells in vitro and in vivo. In vitro, differentiated beating pacemaker-like cells remain active for months and express all the markers of native cardiac pacemakers. They show both hyperpolarization-activated “funny” current (If) and b-adrenergic- and cholinergic-responsive spontaneous Ca2+ transients. In vivo, systemic injection of MDSC from wt muscle significantly improved heart rhythm in severely bradycardic mutant CaV1.3-/- mice. This functional recovery was accompanied by differentiation of donor-derived CaV1.3-expressing cells in the sinoatrial node. MDSC from the primate Microcebe revealed a similar ability to differentiate in vitro into functional pacemaker-like cells. MDSC thus represent a unique, non-tumorigenic and directly transplantable stem cell source shown to efficiently engraft in mutant mouse heart and correct human-mirrored severe rhythm disorders.

La transplantation de cellules souches de muscle possède un grand potentiel pour la réparation à long terme du muscle dystrophique. Cependant, la croissance ex vivo des cellules souches musculaires réduit de manière significative l'efficacité de leur greffe puisque le potentiel myogénique est considérablement réduit lors de la mise en culture. La voie de signalisation Notch a émergé comme un régulateur majeur des cellules souches musculaires (MuSCs) et il a également été décrit que la sur-activation de Notch est crucial pour le maintien du caractère souche des MuSC. Cette découverte pourrait être traduite comme un bénéfice thérapeutique potentiel. Des MuSCs murines ont été fraîchement isolées et ensemencées sur des boîtes de culture recouverte de Dll1-Fc, le domaine extracellulaire de Delta-like-1 est fusionné au fragment Fc humain, afin d'activer la voie de signalisation Notch et avec un IgG hu-main comme contrôle. Nous avons utilisé le rAAV afin d’exprimer le Dll1 spécifique-ment dans les muscles de souris. Les souris P3 ont été traitées avec de l’AAV pendant 3 semaines et 6 semaines afin d’étudier l'effet de Dll1 au cours du développement postnatal. Afin d’étudier le processus de régénération, l'AAV a également été injecté dans les muscles de souris mdx alors que les souris de type sauvage ont été utilisées comme contrôle. Un potentiel caractère souche supérieur (marquée avec le Pax7) est observé dans les cultures des MuSCs qui sont recouverte de Dll1-Fc par rapport à leurs homologues contrôles, par contre le taux de proliférer est réduit. Au cours du développement postnatal, la sur-activation de la voie de signalisation Notch par Dll1 sur les fibres musculaires a été en mesure d'élargir le pool des cellules Pax7+, cependant elle entraîne une diminution de la masse musculaire avec réduction de la taille des fibres et ceci sans affecter l'accumulation des myonuclei. Dans les MuSCs quiescentes (de type sauvage), la sur-activation de la voie de signalisation Notch ne présente pas de réel effet. La surexpression de Dll1 dans le muscle mdx a diminué la masse musculaire et agrandit le pool de cellules souches musculaires, ce-pendant le taux de régénération n'a pas été affecté. L’augmentation des MuSCs est attribuée à une différenciation entravée des cellules souches musculaires. En étudiant la stimulation de la voie de signalisation Notch dans les MuSCs à la fois in vitro et in vivo, nous démontrons que sur-activation de Notch préserve le caractère souche des cellules via l’inhibition de la prolifération et de la différenciation myogénique des MuSCs. / Muscle stem cell transplantation possesses great potential for long-term repair of dys-trophic muscle. However expansion of muscle stem cells ex vivo significantly reduces their engraftment efficiency since the myogenic potential is dramatically lost in culture. The Notch signaling pathway has emerged as a major regulator of muscle stem cells (MuSCs) and it has recently been discovered that high Notch activity is crucial for maintaining stemness in MuSCs. This feature might be exploited and developed into a novel therapeutic approach.Murine MuSCs were freshly isolated and seeded on culture vessels coated with Dll1-Fc, which fused Delta-like-1 extracellular domain with human Fc, to activate Notch sig-naling and with human IgG as a control. The rAAV gene delivery system was em-ployed to express Dll1 in murine muscles. P3 mice were treated with AAV for 3 weeks and 6 weeks to investigate the effect of Dll1 during postnatal development. To investi-gate the regeneration process, AAV were injected into mdx muscles whereas wild-type mice were used as control.Higher potential stemness (marked by Pax7 positivity) was observed in MuSCs grow-ing on a Dll1-Fc surface as compared to their counterparts on the control surface, while their proliferation rate was reduced. During postnatal development, overstimulation of Notch signaling by Dll1 on the mus-cle fibers was able to enlarge the Pax7+ cell pool, while also resulting in decreased muscle mass and smaller muscle fibers without affecting the accretion of myonuclei into the fiber. In quiescent (wild-type) MuSCs, overstimulation of Notch signaling did not have any discernible effect. Overexpression of Dll1 in mdx muscle decreased the muscle mass and enlarged the muscle stem cell pool, while muscle regeneration re-mained unaffected. By investigating Notch stimulation in MuSCs both in vitro and in vivo, we demonstrate that high Notch activity preserves stemness via inhibition of MuSCs proliferation and myogenic differentiation. Our findings point out that the Dll1 molecule, as a canonical Notch ligand, might have a therapeutic potential in cell-based therapies against muscu-lar dystrophies.

Pendant la régénération musculaire, les cellules souches musculaires (dites satellites) prolifèrent de manière symétrique et asymétrique. La ségrégation non aléatoire des brins d'ADN est un mécanisme associé à la division asymétrique, souvent en lien avec des destins cellulaires distincts. Quand ce phénomène apparaît et comment il est régulé durant la régénération musculaire sont des points clés sur lesquels je me suis focalisée durant ma thèse. Afin d'étudier le rôle de signaux extracellulaires dans les décisions du type de division, nous avons utilisé des micropatrons de motifs symétrique et asymétrique recouverts de matrice extracellulaire. Nous avons alors montré que les fréquences de divisions asymétriques peuvent être modulées selon la forme du motif. En outre, nous décrivons une fenêtre de temps in vivo au cours de la régénération musculaire où une sous population de cellules satellites peut passer d'une division symétrique à asymétrique. Une analyse transcriptionnelle de ces cellules a permis d'identifier des gènes candidats potentiellement impliqués dans la régulation de cette transition. Nous avons testé l'effet de quelques protéines associées à ces gènes incorporées dans des niches artificielles 2D. Des données préliminaires suggérèrent que des signaux extrinsèques (protéine de la matrice extracellulaire et rigidité du substrat) combinés à une signalisation intracellulaire peuvent réguler la balance entre prolifération et différentiation. L'ensemble de ces données de thèse montre l'importance d'un dialogue entre le microenvironnement et les signaux intracellulaires dans la régulation du comportement des cellules souches. / During muscle regeneration, muscle stem (satellite) cells proliferate symmetrically and asymmetrically. Non-random segregation of old and new template DNA strands (NRDS) is one mechanism associated with an asymmetric cell division, and this is often linked with distinct daughter cell fates. How this frequency is modulated and when during tissue remodelling are key questions that are the focus of my thesis project. To address the role of extrinsic cues in NRDS and cell fate decisions, we used micropatterns coated with extracellular matrix and designed with symmetric and asymmetric topological motifs. We show that the frequency of NRDS and transcription factors asymmetry (Pax7, stem; Myogenin, differentiated) can be modulated depending on the topology of the adhesion cues of the micropattern. Moreover, we show that a temporal switch occurs in vivo during early muscle regeneration from symmetric to asymmetric DNA segregation in a subpopulation of satellite cells. Gene expression profiling of symmetrically and asymmetrically dividing cells allowed the identification of candidate regulators that might impinge on this regulatory transition. Some candidate genes were assayed in a high throughput screen that was on 2D artificial stem-cell niches. Preliminary data show that extrinsic cues (ECM protein and substrate stiffness) combined with signalling pathways can regulate the balance between proliferation and differentiation in a context dependent manner. Taken together, this thesis project shows that the interplay between microenvironment and intracellular signalling impacts on the regulation of stem cell behaviour.

<p>Skeletal muscle takes up nearly 40% of total body mass, is critical for daily function by</p> <p>providing balance, supports breathing, movement, and energy expenditure. Preserving</p> <p>skeletal muscle can also significantly improve one’s quality by maintaining balance, movement</p> <p>and improving metabolic health [1, 2]. This becomes more imperative with age, as skeletal muscle mass naturally declines, and further compounds decline in quality of life and health [1, 2]. Thus, it is critical to understand the physiology of skeletal muscle and the underlying cellular and</p> <p>molecular mechanisms that contribute to normal function. Using mouse models to further our</p> <p>understanding, this dissertation leverages single-cell RNA-sequencing (scRNA-seq) to dissect the</p> <p>cellular and molecular underpinnings of skeletal muscle injury and repair. Specifically, chapter 1</p> <p>provides an overview of skeletal muscle structure, muscle regeneration, and the current state of</p> <p>scRNA-seq literature in muscle regeneration. In chapter 2, I will discuss the large-scale scRNAseq of regenerating muscle which identified dynamic population of resident and infiltrating cells. In chapter 3, I will discuss the potential immunomodulatory role of MuSCs and leveraging scRNAseq data to understand the cellular mechanisms that govern successful muscle regeneration. Finally, in chapter 4 I will discuss the role of the transcription factor Sox11, which was identified by scRNA-seq and was specific to differentiating MuSCs. Thus, this dissertation spans the cellular and molecular components of muscle regeneration.</p>

Duchenne Muscular Dystrophy (DMD) is a disorder caused by loss-of-function mutations in dystrophin, a critical protein that maintains muscle fiber integrity. Our lab discovered that dystrophin-deficient skeletal muscle stem cells, also known as satellite cells, cannot generate enough myogenic progenitors for proper muscle regeneration. Previously, we demonstrated that WNT7A, a protein expressed during muscle regeneration, stimulates symmetric division of satellite cells, and gives rise to two daughter satellite cells. Conversely, epidermal growth factor (EGF) induces asymmetric division, which generates one daughter satellite cell and one committed precursor cell. We aimed to investigate these satellite cell division mechanisms following WNT7A or EGF treatment in a human model using healthy and DMD-patient derived hiPSCs differentiated into the myogenic lineage. The presence of satellite-like cells was confirmed in both lines by their characteristic expression of PAX7 and other myogenic markers. Intriguingly, DMD-patient hiPSCs precociously differentiated compared to healthy control human induced pluripotent stem cells (hiPSCs). More notably, WNT7A treatment had a potent effect on the DMD differentiated cells. High content analysis revealed an expansion of the satellite-like cell pool as observed by a higher number of PAX7+ cells within the total population and gene expression analysis demonstrated a significant increase in global PAX7 expression. In contrast, EGF treatment reduced the number of PAX7+ cells and increased the proportion of MYOG+ cells within the myogenic population, indicating an increase in myogenic progenitors. Taken together, WNT7A and EGF can alter the myogenic differentiation program of healthy and DMD-patient derived hiPSCs by modulating the satellite-like cell division dynamics.

Les cassures double-brin (DSB) sont des dommages dangereux de l’ADN et représentent un facteur de risque pour la stabilité du génome. Le maintien de l'intégrité du génome est essentiel pour les cellules souches adultes, qui sont responsables de la régénération des tissus endommagés et de l'homéostasie tissulaire tout au long de la vie. La régénération musculaire chez l'adulte repose sur les cellules souches musculaires (cellules satellites, SCs) qui possèdent une remarquable capacité de réparation des DSB, mais dont le mécanisme sous-jacent reste inconnu. Ce projet de thèse consistait à étudier comment la différenciation musculaire est affectée lorsque la réparation des DSB est altérée, et quels sont le(s) mécanisme(s) et les conséquences de ce défaut de réparation sur la régénération musculaire. Au cours de cette étude, il est apparu de façon originale que les facteurs de réparation des DSB peuvent affecter la myogenèse, indépendamment de leur fonction dans la réparation de l'ADN. La présente étude a porté sur le rôle de la protéine kinase dépendante de l'ADN (DNA-PK), un facteur crucial pour la réparation non-homologue des DSBs (NHEJ), au cours de la différenciation musculaire chez la souris. L’étude a ciblé l'activation des SCs et la régénération musculaire in vitro et in vivo et a également abordé la régulation de cette kinase. Le rôle "canonique" de la DNA-PK, et donc du NHEJ, dans les SCs a également été étudié en présence de lésions de l'ADN radio-induites. Le rôle d’ATM, une kinase qui orchestre les réponses cellulaires aux DSB, a également été abordé dans le contexte de la régénération musculaire. Ces résultats confirment la notion émergente du rôle multifonctionnel des protéines de réparation de l’ADN dans d’autres processus physiologiques que la réparation elle-même, ce qui m’a également permis de réaliser une étude bibliographique. Ce travail i) identifie de nouveaux régulateurs de la myogenèse et ii) contribue à la compréhension de la résistance des cellules souches musculaires au stress génotoxique. Ces résultats pourraient avoir des implications dans l'amélioration des thérapies cellulaires de la dysfonction musculaire en agissant sur les régulateurs nouvellement découverts. / DNA double-strand breaks (DSBs) are dangerous DNA damages and a risk factor for genome stability. The maintenance of genome integrity is crucial for adult stem cells that are responsible for regeneration of damaged tissues and tissue homeostasis throughout life. Muscle regeneration in the adult relies on muscle stem cells (satellite cells, SCs) that have a remarkable DSB repair activity, but the underlying mechanism is not known. The aims of the present PhD project were to investigate how muscle differentiation is affected when DSB repair is impaired, and which are the mechanism(s) and the consequences on muscle regeneration. During this study, a novel possibility has arisen, namely that DSB repair factors affects myogenesis independently of their DNA repair activity, suggesting a novel function, not previously anticipated, of these factors. The present study has addressed the role of DNA-dependent protein kinase (DNA-PK), a crucial factor in non-homologous end-joining (NHEJ) repair of DSBs, in muscle differentiation in the mouse. Studies have targeted SC activation and muscle regeneration in vitro and in vivo and also addressed the regulation of this kinase. In parallel the more “canonical” role of DNA-PK, and thereby of NHEJ, has been investigated in SCs via radiation-induced DNA damage. The role of ATM, a kinase that orchestrates cellular responses to DSBs in muscle regeneration has also been addressed. These results support the emerging notion of multifunctional repair proteins in a variety of physiological processes beyond the repair process itself, on which I have conducted a bibliographical study. This work i) identifies novel regulators of myogenesis, and ii) helps understanding the resistance of muscle stem cells to genotoxic stress. It has potential implications for improving cellular therapies for muscle dysfunction by acting on the newly discovered regulators.

<p dir="ltr">Skeletal muscle accounts for 40% of total body weight and the homeostasis of muscle tissue is critical in maintaining proper body function. Skeletal muscle develops during the embryonic stages from the muscle progenitor cells derived from the dermomyotome structure. The myogenic progenitor cells contribute to the primary myogenesis by forming the primary myotubes which are the founding structures that the secondary myogenesis continues to build on. A portion of the myogenic progenitor cells makes up the adult muscle stem cells residing in homeostatic muscle tissue. The adult muscle stem cells contribute substantially for the adult muscle regeneration. Due to the significance of the muscle tissue and the importance of muscle stem cells, dysregulation of the muscle homeostasis or the muscle stem cell homeostasis will result in severe pathological conditions such as myopathy.</p><p dir="ltr">Mitochondria are cellular organelles that are responsible for generating energy needed for cellular processes, especially for muscle tissue where muscle contraction requires the presence of ATP. On the other hand, mitochondria also serve as signaling molecules and provide macromolecules for the biosynthesis. FAM210A (Family With Sequence Similarity 210 Member A) protein was shown to impact the lean mass of human subjects yet a detailed study on the effect of FAM210A in skeletal muscle was not performed, nor has the molecular mechanisms through which FAM210A function been elucidated. Therefore, I take on the task to unveil the function of FAM210A in muscle development, muscle homeostasis and muscle stem cell behavior by using a combination of mouse models with different myogenic promoters to target <i>Fam210a</i> at different developmental stages.</p><p dir="ltr">In the first part of the thesis, I investigated the role of FAM210A in post differentiation myofibers. Using the <i>Myl1</i>^<em>Cre</em> driven deletion of <i>Fam210a</i>, I found that <i>Fam210a</i>^<em>MKO</em> had normal development before 3 weeks of age, but the growth was stagnant from 4 weeks on, and the mice did not survive past 8 weeks of age. I found that the assembly of the ribosomes in the <i>Fam210a</i>^<em>MKO</em> was defective, leading to impaired translation which attenuated the muscle atrophy phenotype. I identified through proteomics that the mitochondrial autophagy and proteostatic control pathways were significantly induced yet mitochondrial organization and energetic proteins were downregulated. Metabolomics analysis showed that the signaling metabolite acetyl-CoA was increased in the <i>Fam210a</i>^<em>MKO</em> which led to increased protein acetylation, specifically, we showed that the ribosomal proteins were hyperacetylated, and that the acetylation increase was elicited by the <i>Fam210a</i>-null mitochondria.</p><p dir="ltr">In the second part of the thesis, I investigated the function of FAM210A in muscle progenitor cells. In the <i>FamMKO</i> mice, I found that deletion of <i>Fam210a</i> from embryonic myogenic progenitor cells led to developmental arrest and postnatal death at day 6. In the <i>FamPKO</i> mice, I found that <i>Fam210a</i> is needed for adult muscle stem cell to contribute to regeneration. Loss of <i>Fam210a</i> leads to the regenerative defects when the muscle was exposed to injury cues. We further showed that <i>Fam210a</i> deletion in muscle stem cells resulted in disruption of the proteostatic control over muscle stem cell activation, thereby forbidding the translational increase necessary to facilitate activation and proliferation. Furthermore, I showed that <i>Fam210a</i> deletion leads to excessive OPA1 cleavage, which contributes to the regenerative failure of muscle stem cells as fusion is required for the mitochondrial network remodeling during regeneration. Therefore, <i>Fam210a</i> safeguards the mitochondrial network and proteostasis during regeneration.</p><p dir="ltr">In summary, my studies characterized the functional contribution of FAM210A during embryonic muscle development, muscle mass maintenance and adult muscle stem cell homeostasis. The regulation of FAM210A in these three processes impinge on the translational regulation. My studies further demonstrated the importance of mitochondrial regulated protein translation in skeletal muscle and muscle stem cells.</p>