Tendões são descritos como tecido conjuntivo denso modelado que inserem os músculos aos ossos. Sua principal função é servir como tecido de transição das forças contráteis geradas pelos músculos aos ossos, podendo assim gerar movimentos. Entre todos os tendões, o calcâneo é um dos mais frequentemente lesados. As lesões ocorrem principalmente em homens e são mais frequentes entre a terceira e quarta década de vida. Dentre os vários métodos de sutura existentes, do ponto de vista clínico, a de Kessler-Tajima com os nós entre os cotos é muito utilizada por evitar o estrangulamento da microcirculação. Após a cirurgia o paciente retorna ao trabalho após 85 dias, em média, podendo atingir até 270 dias. O objetivo do presente estudo foi testar a eficiência da aplicação da proteína biocompatível F1, uma proteína extraída a partir do látex natural da Hevea brasiliensis, sobre tendões lesados, buscando uma melhora no reparo, assim como, a influência da sutura-U e de Kessler-Tajima. Alterações musculares decorrentes da lesão no tendão também foram avaliadas. Para isso, utilizamos ratos Sprague Dawley machos de 3 meses, que foram submetidos a tenotomia completa, a lesão foi corrigida com ambas as suturas, seguido da aplicação da proteína e avaliados após duas e quatro semanas. As técnicas utilizadas para análises no tendão foram as de microscopia de luz, microscopia eletrônica de varredura e transmissão, bem como, a síntese de colágeno tipos I e III, TIMP-1 e 2, MMP-2 e 9 por western blot. Para analisar as alterações musculares, a expressão dos genes MuRF1 e Atrogin1 foram quantificadas por RT-qPCR, seguido de análises de contração muscular máxima e teste de fadiga. Os resultados sugerem uma melhora no reparo do tendão no grupo que utilizamos a sutura-U associada à proteína após quatro semanas, devido ao aumento na síntese de colágeno tipo I e a diminuição de MMP-9, assim como, a capacidade de contração muscular máxima retorna aos níveis do grupo controle. A sutura-U também influencia menos na fadiga muscular. / Tendons are described as dense modeled connective tissue which insert the muscles to the bones. Its main function is to serve as transition tissue of the contractile forces generated by muscles to the bones, and thus generate movements. Among all the tendons, the calcaneal is the most frequently injured one. The lesions occur mainly in men and are more frequent between the third and fourth decade of life. Among the several existing suture methods, from a clinical point of view, the Kessler-Tajima with the nodes between the stumps is used to a great extent in order to avoid the microcirculations strangling. After surgery, the patient returns to work after 85 days, on average, and can reach up to 270 days. The objective of this study was to test the efficiency of the application of biocompatible F1 protein, a protein extracted from natural latex from the Hevea brasiliensis, on injured tendons, seeking an improvement in the repair, as well as the influence of the suture-U and Kessler-Tajima. Muscle changes arising from the tendon injury were also evaluated. For this reason, Sprague Dawley male rats at 3 mounths-old were used, which underwent complete tenotomy, the lesion was corrected with both sutures, followed by the application of protein and evaluated after two and four weeks. The techniques used for analyzes in the tendon were the light microscopy, scanning electron microscopy and transmission, as well as the synthesis of collagen types I and III, TIMP-1, -2, MMP-2, and -9 by Western blot. In order to analyze the muscular alterations, the expression of genes MuRF1 and Atrogin1 were quantified by RT-qPCR, followed by analysis of maximum muscle contraction and fatigue testing. The results suggest an improvement in the tendon repair in the group that the suture-U was used associated with protein after four weeks, due to the increase in the synthesis of collagen type I and the decrease of MMP-9, as well as the ability of maximum muscle contraction to return to the levels of the control group. The suture-U also influences on less muscle fatigue.

Muscle loss from lack of activity is a serious issue for immobilized patients on Earth and in human spaceflight, where the low gravity environment prevents normal muscle activity. Simulating muscle loss in cultured cells is an important step in understanding how this condition occurs. This work evaluates different means of simulating muscle loss and selects the one that most closely mimics the cellular responses seen in animals and humans. To simulate the microgravity environment of spaceflight, mouse skeletal muscle cells were grown in a rotary cell culture system (RCCS). Growing the cells within a natural gelled substrate was compared against growing them on the surface of small plastic beads. Changes after culture under simulated microgravity were characterized by assessing proteins and genes known to change during muscle loss. The structure of the cells was also evaluated by microscopy. The mouse skeletal muscle cells grown on plastic beads in the RCCS had significant changes in multiple key genes associated with muscle loss and demonstrated physical characteristics expected of mature tissue in live animals. This model is a valuable platform for exploring muscle loss mechanisms and testing new drugs.

Les protéines SREBP-1 sont des facteurs de transcription connus pour leur rôle dans la régulation du métabolisme lipidique. Plus récemment des études faites in vitro (myotubes humains en culture primaire) et in vivo (muscle tibial de souris) ont montré que la surexpression de SREBP-1a ou SREBP-1c induit une atrophie musculaire et bloque la différenciation musculaire, en inhibant notamment l’expression des protéines structurales du muscle squelettique et des facteurs de la différenciation musculaire (MRFs). Les travaux de thèse présentés dans ce manuscrit ont eu pour but de décrypter le mécanisme de l’atrophie induite par SREBP-1 et de déterminer comment les protéines SIRT1 pourraient réguler ce facteur de transcription. L’atrophie musculaire résulte d’un déséquilibre entre la quantité de protéines synthétisées et dégradées. Dans nos études, nous montrons que SREBP-1 régule la synthèse protéique et la dégradation protéique, respectivement via le contrôle négatif de l’expression des MRFs et via le contrôle de l’expression des atrogènes, MuRF1 et Atrogin-1. Dans le muscle squelettique, nous démontrons que la désacétylase SIRT1 régule l’activité transcriptionnelle de SREBP-1. Les protéines SREBP-1 et SIRT1 étant toutes deux impliquées dans la régulation du métabolisme lipidique, nous mettons en évidence une nouvelle voie de signalisation reliant le métabolisme énergétique et nutritionnel avec l’activité transcriptionnelle de SREBP-1 dans le muscle. Étant donné le rôle de SIRT1 et SREBP-1 dans le métabolisme lipidique et musculaire, nous nous sommes intéressés au rôle des phospholipides et plus particulièrement des céramides dans la régulation de la masse musculaire.Nos études montrent que la régulation de la quantité de céramides par la cytokine TNFα régule la masse musculaire. Ainsi, nos travaux mettent en évidence de nouveaux liens entre le métabolisme lipidique et la régulation de la masse et du métabolisme musculaire. / SREBP-1 transcription factors are involved in lipid metabolism regulation. Recently, in vitro and in vivo studies have shown that SREBP-1a or SREBP-1c overexpression induce muscular atrophy and block muscular differentiation, notably by inhibiting structural proteins and Myogenics Regulatory Factors (MRFs) expression. The aims of this work are the mecanism determination of the muscular atrophy induced by SREBP-1 overexpression and the elucidation of the role of SIRT1 proteins on SREBP-1 regulation.The muscular atrophy results from an imbalance between the amount of synthesized and degraded proteins. In our studies, we shown that SREBP-1 regulates protein synthesis and protein degradation, respectively via a negative control of MRFs expression and via a control of atrogenes expression, MuRF1 and Atrogin-1. In skeletal muscle, we shown that SIRT1 desacetylase enzyme regulates SREBP-1 transcription activity. Because of SREBP-1 and SIRT1 proteins involvement in lipid metabolism regulation, our results suggest a new signalisation pathway linking energetic metabolism and SREBP-1 transcriptionnal activity in muscle. As SIRT1 and SREBP-1 have a role on lipid and muscular metabolism, we took an interest in phospholipids involvement and more specifically in ceramides involvement in muscle mass regulation. Our studies shown that the regulation of the amount of ceramids by the TNFα regulates muscle mass. Thus, our work allows to identify new links between lipid metabolism and muscle mass and metabolism regulation.

Les facteurs de transcription de la famille p53 dans l’atrophie musculaire - Implications dans la Sclérose Latérale Amyotrophique et la cachéxie. L’atrophie musculaire est un symptôme dangereux retrouvé dans plusieurs maladies. Dans la sclérose latérale amyotrophique (SLA), une maladie neuromusculaire rare, ainsi que dans le cancer (phénomène de cachexie), l’atrophie musculaire cause le décès des patients. Les facteurs de transcription de la famille p53 sont impliqués dans de nombreux processus cellulaires, faisant face à des situations de « stress » pour les cellules. Notamment, ils peuvent induire la mort cellulaire ou promouvoir la différentiation.Nous avons constaté, à partir de modèles cellulaire et animaux de SLA et cachéxie cancéreuse, que des membres de la famille p53 sont activés dans les muscles atrophiques. Cette activation entraine l’expression de gènes cibles impliqués dans la mort cellulaire. De manière intéressante, TAp73, mais surtout TAp63, sont capables d’activer la transcription d’un effecteur de l’atrophie musculaire appelé MuRF1, démontrant que la famille p53 peut participer activement à l’atrophie en induisant la dégradation des fibres musculaires.De plus, nous avons utilisé nos modèles animaux pour identifier une nouvelle approche contre l’atrophie musculaire. Ainsi, nous avons identifié un dérivé de tocophérol avec des propriétés thérapeutiques intéressantes. / The p53 family of transcription factors in muscular atrophy - Involvements in Amyotrophic Lateral Sclerosis and cachexia Muscular atrophy is a dangerous condition found in several diseases. In amyotrophic lateral sclerosis (ALS), a rare neuromuscular disease, as well as in cancer (phenomenon of cachexia), muscular atrophy can be fatal to patients.The transcription factors from the p53 family are involved in several cellular processes, facing cellular “stress” situations. Most notably, they can induce dell death or promote differentiation.We found, using cellular and mouse models of ALS and cachexia, that members of the p53 family are induced during muscular atrophy. This induction leads to the expression of canonnic target genes involved in cell death. Interestingly, TAp73, but especially TAp63, are able to activate the transcription of an effector or muscular atrophy called MuRF1. This proves that the p53 family cand participate in muscular atrophy by promoting the breakdown of muscle fibres.In addition, we used our mouse models to identifiy a new approach agains muscular atrophy.Indeed, we identified a derivative of tocopherol with interesting therapeutical proprieties.

Background About half of heart failure (HF) patients, while having preserved left ventricular function, suffer from diastolic dysfunction (so-called HFpEF). No specific therapeutics are available for HFpEF in contrast to HF where reduced ejection fractions (HFrEF) can be treated pharmacologically. Myocardial titin filament stiffening, endothelial dysfunction, and skeletal muscle (SKM) myopathy are suspected to contribute to HFpEF genesis. We previously described small molecules interfering with MuRF1 target recognition thereby attenuating SKM myopathy and dysfunction in HFrEF animal models. The aim of the present study was to test the efficacy of one small molecule (MyoMed-205) in HFpEF and to describe molecular changes elicited by MyoMed-205. - Methods Twenty-week-old female obese ZSF1 rats received the MuRF1 inhibitor MyoMed-205 for 12 weeks; a comparison was made to age-matched untreated ZSF1-lean (healthy) and obese rats as controls. LV (left ventricle) unction was assessed by echocardiography and by invasive haemodynamic measurements until week 32. At week 32, SKM and endothelial functions were measured and tissues collected for molecular analyses. Proteome-wide analysis followed by WBs and RT-PCR was applied to identify specific genes and affected molecular pathways. MuRF1 knockout mice (MuRF1-KO) SKM tissues were included to validate MuRF1-specificity. - Results By week 32, untreated obese rats had normal LV ejection fraction but augmented E/e′ ratios and increased end diastolic pressure and myocardial fibrosis, all typical features of HFpEF. Furthermore, SKM myopathy (both atrophy and force loss) and endothelial dysfunction were detected. In contrast, MyoMed-205 treated rats had markedly improved diastolic function, less myocardial fibrosis, reduced SKM myopathy, and increased SKM function. SKM extracts from MyoMed-205 treated rats had reduced MuRF1 content and lowered total muscle protein ubiquitination. In addition, proteomic profiling identified eight proteins to respond specifically to MyoMed-205 treatment. Five out of these eight proteins are involved in mitochondrial metabolism, dynamics, or autophagy. Consistent with the mitochondria being a MyoMed-205 target, the synthesis of mitochondrial respiratory chain complexes I + II was increased in treated rats. MuRF1-KO SKM controls also had elevated mitochondrial complex I and II activities, also suggesting mitochondrial activity regulation by MuRF1. - Conclusions MyoMed-205 improved myocardial diastolic function and prevented SKM atrophy/function in the ZSF1 animal model of HFpEF. Mechanistically, SKM benefited from an attenuated ubiquitin proteasome system and augmented synthesis/activity of proteins of the mitochondrial respiratory chain while the myocardium seemed to benefit from reduced titin modifications and fibrosis.

Les protéines SREBP-1 sont des facteurs de transcription connus pour leur rôle dans la régulation du métabolisme lipidique. Plus récemment des études faites in vitro (myotubes humains en culture primaire) et in vivo (muscle tibial de souris) ont montré que la surexpression de SREBP-1a ou SREBP-1c induit une atrophie musculaire et bloque la différenciation musculaire, en inhibant notamment l'expression des protéines structurales du muscle squelettique et des facteurs de la différenciation musculaire (MRFs). Les travaux de thèse présentés dans ce manuscrit ont eu pour but de décrypter le mécanisme de l'atrophie induite par SREBP-1 et de déterminer comment les protéines SIRT1 pourraient réguler ce facteur de transcription. L'atrophie musculaire résulte d'un déséquilibre entre la quantité de protéines synthétisées et dégradées. Dans nos études, nous montrons que SREBP-1 régule la synthèse protéique et la dégradation protéique, respectivement via le contrôle négatif de l'expression des MRFs et via le contrôle de l'expression des atrogènes, MuRF1 et Atrogin-1. Dans le muscle squelettique, nous démontrons que la désacétylase SIRT1 régule l'activité transcriptionnelle de SREBP-1. Les protéines SREBP-1 et SIRT1 étant toutes deux impliquées dans la régulation du métabolisme lipidique, nous mettons en évidence une nouvelle voie de signalisation reliant le métabolisme énergétique et nutritionnel avec l'activité transcriptionnelle de SREBP-1 dans le muscle. Étant donné le rôle de SIRT1 et SREBP-1 dans le métabolisme lipidique et musculaire, nous nous sommes intéressés au rôle des phospholipides et plus particulièrement des céramides dans la régulation de la masse musculaire.Nos études montrent que la régulation de la quantité de céramides par la cytokine TNFα régule la masse musculaire. Ainsi, nos travaux mettent en évidence de nouveaux liens entre le métabolisme lipidique et la régulation de la masse et du métabolisme musculaire.

Laing distal myopathy is inherited in an autosomal dominant manner usually before the age of five that initially involves the dorsiflexion in the ankles’ and in big toes to the finger extensors. Weakness of the flexor muscles in the neck is seen in most affected individuals and mild facial weakness is also often present. Hypertrophic or dilated cardiomyopathy, starting at birth to respectively second or third decade of life, is the symptom in the affected humans.This study performed on Drosophila melanogaster, has evaluated whether feeding MuRF1 enzyme (which has a similar role as ABBA enzyme) to Drosophila larvae, in different concentrations, will have a positive effect on the larvae’s muscular abilities through an analysis of their manifestation, the distance they manage to crawl and the time it takes for them to turn from a ventral up to dorsal up position.The result show no significant impact on larvae ability to turn or crawl between different groups fed with MuRF1 enzyme, nor between the two control groups, wild larvae and mutated larvae. Other studies have proven that there is a significant difference in muscular ability between wild and mutated larvae, so explanations to why this study did not manage to replicate these results were evaluated. The study found that how many days has passed since hatching has a significant impact on performance of turning and crawling for wild larvae that are not treated with enzyme.There are a number of improvement suggestions to the experimental design and the methodology to enable a proper evaluation of the research aim of this thesis. Future research on the topic should implement these and redo the experiments and measurements of this study. In addition, the quantity of larvae that reaches pupa stage should be captured to evaluate whether the MuRF1 enzyme has a positive impact on mutated larvae reaching pupation stage. The most important parts of the improvement proposals to measure the ability of larvae when they are about the same age, as this was proven with statistical significance to have an impact on crawling and turning.

Skeletal muscle atrophy can occur at any age and as a result of numerous physiological conditions and thus, it was necessary to better identify the molecular underpinnings of the atrophy cascade so that new therapeutic targets to treat muscle wasting might be identified. MuRF1 was first identified as a marker of skeletal muscle atrophy over a decade ago; however, recent work suggests that this E3 ubiquitin ligase may participate in muscle wasting by regulating the transcriptional activity of genes differentially expressed in response to muscle atrophy. Dusp4, a dual-specificity phosphatase and member of the MAPK cascade, is induced in response to neurogenic atrophy; however, this induction is significantly blunted in the MuRF1-null mice which are resistant to muscle atrophy. The research presented in this thesis aims to characterize the mechanism by which MuRF1 may transcriptionally regulate Dusp4 and characterizes the function of Dusp4 in skeletal muscle.

Det har forskats mycket på olika signalvägar i det mänskliga genomet, trotts detta finns det många frågetecken som kvarstår. Denna uppsats undersöker några av dem. Syfte: Undersöka förändringar i genuttryck och mRNA-nivåer för hypertrofi- (MRF4) translations- (5.8S & 18S) och proteolysreglerande gener (MuRF1 & GDF-8) efter en 10 veckor lång styrketräningsperiod hos kvinnor och män. Frågeställningar: (1) Finns det en förändring i total mängd RNA före och efter en 10 veckors styrketräningsintervention. (2) Finns det en förändring i uttryck av MRF4, 5.8S, 18S, MuRF1 samt GDF-8 efter en 10 veckors styrketräningsintervention. (3) Finns det en könsskillnad i förändringen av total mängd RNA samt aktivering av MRF4, 5.8S, 18S, MuRF1 och GDF-8 efter en 10 veckors styrketräningsintervention. Metod: Urvalet för analysen bestod av 16 otränade försökspersoner varav 8 var män och 8 var kvinnor. Försökspersonerna utförde unilateral styrketräning av nedre extremiteten under 10 veckor, under 2 av dessa veckor utfördes ocklusionsträning.  Träningsperiodiseringen var vågformig (70-90% av 1RM, 5-12 rep, 3 ggr/vecka). Muskelbiopsier togs i det arbetande benet före träningsperiodens start samt 3-7 dagar efter träningsperiodens avslut. Genuttryck analyserades med qPCR. Resultat: Det fanns ingen signifikant skillnad i förändring mellan män och kvinnors totala RNA eller genuttryck. Total RNA ökade signifikant (p<0,01) med 19,2 %. Kvinnorna hade en signifikant ökning (P<0,05) av RNA på 27,6 % medan männen hade en signifikant ökning (p<0,05) på 14 %. MRF4 hade en signifikant (P>0,05) procentuell ökning i genuttryck med 55,7 % och kvinnor för sig hade en signifikant (P>0,05) ökning på 64 %. GDF-8 ökade signifikant (P>0,05) med 55,5 % medan GAPDH ökade signifikant (P>0,05) för båda könen tillsammans med 70,6 % och för män med 87,8 %. MuRF1 och 5.8S hade inga signifikanta förändringar i genuttryck. Slutsats: Det verkar som att både män och kvinnor får en liknande procentuell förändring av total RNA och mRNA genuttryck 3-7 dagar efter en 10 veckors hypertrofistyrd styrketräningsperiod. För att mäta genuttryck av translationsgenen MRF4 verkar 3-7 dagar efter en 10 veckors styrketräningsperiod vara en tidpunkt då det fortfarande pågår hypertrofi av skelettmuskulaturen.  Av de proteolysreglerande generna GDF-8 och MuRF1 sågs en uppreglering av GDF-8 vilket skulle kunna vara ett tecken på att hypertrofin börjar hämmas. Ett oväntat fynd var att GAPDH visade sig vara olämplig som kontrollgen vid en styrketräningsintervention på 10 veckor och att 18S var väldigt stabil. Detta kan betyda att GAPDH inte skall användas vid längre styrketräningsinterventioner. / There have been much research on signaling pathways in the human genome, but there still remain many questions. This paper examines some of them. Aim: Investigate changes in gene expression and mRNA levels of hypertrophy (MRF4), translation (5.8S & 18S) and proteolysis regulating genes (GDF-8) after a 10-week strength training period in men and women. Research questions: (1) Is there a change in the total amount of RNA before and after a 10-week strength training intervention. (2) Is there a change in the expression of MRF4, 5.8S, 18S, Murf1 and GDF-8 after 10 weeks of strength training. (3) Is there a gender difference in the change of total RNA and the expression of MRF4, 5.8S, Murf1 and GDF-8 after a 10-week long strength training intervention. Method: The sample for analysis consisted of 16 untrained subjects, of whom 8 were men and 8 were women. The subjects performed unilateral resistance training of lower extremities for 10 weeks, during two of these weeks blood flow restriction training were performed. The training was undulating (70-90% of 1RM, 5-12 cord, 3 times / week). Muscle biopsies were taken from the working leg before the start and 3-7 days after the training period. Gene expression was analyzed by qPCR. Results: There was no significant gender difference in total RNA or gene expression. Total RNA was significantly increased (p <0.01) with 19.2 %. The women had a significant increase (P <0.05) of RNA at 27.6 %, while the men had a significant increase (p <0.05) at 14 %. MRF4 had a significant (P> 0.05) percentage increase in gene expression by 55.7 %, and women had a significant (P> 0.05) increase of 64 %. GDF-8 increased significantly (P> 0.05) with 55.5 %, while GAPDH increased significantly (P> 0.05) for both sexes with 70.6 % and for men with 87.8 %. Murf1 and 5.8S had no significant changes in gene expression. Conclusions: It seems that both men and women experience a similar percentage difference of total RNA and mRNA gene expression 3-7 days after a 10 weeks long strength training period. To measure the gene expression of MRF4 3-7 days after a 10-week weight-training period seems to be a time when there still is a anabolic responses in the skeletal muscle. Of the proteolysis regulating genes GDF-8 and Murf1 there was an upregulation of GDF-8, which could be a sign that the inhibition of hypertrophy started. An unexpected finding is that GAPDH was found to be unsuitable as a control gene at a strength training intervention at 10 weeks and rRNA 18S was very stable, which could mean that GAPDH should not be used as control gene in longer strength training studies.

Die Komposition der Skelettmuskulatur resultiert aus der fein abgestimmten Balance von Proteinauf- und Abbaumechanismen. Die Skelettmuskelatrophie kann in verschiedenen Situationen entstehen bzw. von diversen Krankheiten ausgelöst werden (Altern, Hunger, Krebs, Nervenschädigung, Kachexie) und ist meist die Folge von gesteigertem Proteinabbau, der die Proteinsynthese überwiegt. Der Muskelabbau ist physiologisch teilweise sinnvoll und dient der Notversorgung von lebenswichtigen Organen mit Lipiden, Aminosäuren und Glukose. Insgesamt ist eine funktionsfähige Muskulatur sehr wichtig, sowohl für Gesunde als auch Erkrankte, da bei Muskelatrophie auslösenden Erkrankungen das Gesamtüberleben wesentlich verringert ist und die Lebensqualität der Patienten enorm reduziert ist. Der Abbau von strukturellen Muskelproteinen wurde hauptsächlich dem Ubiquitin-Proteasom System zugeschrieben, dessen Regulation und von seinen einzelnen Enzymen muss genauestens verstanden sein, um in der Zukunft zielgerichtete Therapien entwickeln zu können. Eines der zentralen Enzyme in der Skelett- und Herzmuskelatrophie ist die E3 Ubiquitin Ligase MuRF1. In nahezu allen Modellen für Muskelatrophie wurde eine starke Zunahme der Expression von MuRF1 beschrieben. Betrachtet man die sehr zentrale Rolle von MuRF1 im UPS, dort vermittelt MuRF1 den Abbau von strukturellen Proteinen des Sarkomers, und der beobachteten starken Regulation bei diversen Atrophie-Modellen, wird klar, wie wichtig das Verständnis der transkriptionellen Regulation von MuRF1 selbst ist. In den letzten Jahren wurden bereits einige Transkriptionsfaktoren identifiziert, die an der Regulation von MuRF1 bei verschiedenen Atrophie-Modellen beteiligt sind, die Studien zeigten aber auch, dass noch nicht alle Modelle erklärt werden konnten. Um die verbleibenden Wissenslücken zu füllen, wurde in dieser Studie nach neuen transkriptionellen Regulatoren von MuRF1 gesucht und deren Beteiligung an bereits bekannten Signalwegen analysiert. / Skeletal muscle mass is permanently balanced as a result of fine tuned protein synthesis and degradation mechanisms. Skeletal muscle atrophy occurs when protein degradation exceeds protein synthesis, which happens in a variety of conditions, such as aging, starvation, cancer, cachexia or denervation. Degradation of muscle mass can sometimes be useful, e.g. as source for lipids, amino acids and glucose in case of critical malnutrition as well as several other physiological conditions. But a solid composition and thereby functional maintenance of muscles is necessary for healthy individuals as well as individuals suffering from atrophy releasing diseases as to retain their mobility and to preserve full heart functions. Since degradation of structural proteins in muscle tissue has been addressed mainly to the ubiquitin-proteasome-system, the regulation of the participating components needs to be understood in detail to develop constructive treatments and therapies for atrophy prevention. One of the key enzymes in skeletal and heart muscle atrophy is the E3 ubiquitin ligase MuRF1. Its expression levels and protein content was found to be elevated in almost every know atrophy model. MuRF1 is very critical for the muscles composition and thus their functional integrity, as it marks and initiates degradation of structural and contractile proteins via the UPS. Since MuRF1 plays a prominent role in muscle atrophy, its transcriptional regulation needs to be well understood to develop effective therapies for all the different atrophy models MuRF1 has been linked to. Several transcription factors have been identified to regulate MuRF1 at different ratios and in diverse atrophy models. Importantly, they do not explain all MuRF1 inducing events observed. To fill some of the remaining knowledge gaps, the studies aims were to find new transcriptional regulators for MuRF1 and to analyze potential involvements of the obtained candidates in pathways affecting skeletal muscle atrophy.