La FSH est une hormone clé de la régulation de la fonction de reproduction. La compréhension de ses mécanismes moléculaires est essentielle pour en apprécier pleinement les effets biologiques. Nous montrons ici que la FSH ne régule pas seulement la transcription de ses gènes cibles comme il l’était pensé jusqu’alors mais également leur traduction. Elle active ainsi à la fois la traduction cap-dépendante et IRES-dépendante dans les cellules de Sertoli du testicule. La p70S6K participe à ces mécanismes. En réponse à la FSH, elle est activée et recrutée à la coiffe m7GTP des ARNm où elle phosphoryle ses cibles traductionnelles. La p70S6K est par ailleurs différentiellement régulée au cours du développement sertolien par les voies PI3K et PKA. Cette activation différentielle a été reproduite à l’aide d’un modèle mathématique dynamique qui a permis de générer des données inaccessibles par l’expérimentation. Les β-arrestines, qui sont des transducteurs spécifiques des GPCR semblent participer à l’activation de la p70S6K par la FSH. Ce travail ouvre des perspectives quant à l’identification de mécanismes de régulation de la traduction dépendants des GPCR. / FSH is one of the hormones that control the reproductive function. A clear understanding of its molecular mechanisms is essential to fully appreciate its biological effects. Here we show that FSH regulates the expression of its target genes not only at the transcriptional level as it was thought until recently, but also at the translational level. FSH activates cap-dependent as well as IRES-dependent translation in Sertoli cells of the testis. p70S6K participates in this mechanisms. In response to FSH, p70S6K is activated, is recruited to the m7GTP cap structure of the mRNA where it phosphorylates it translational targets. Furthermore, p70S6K is differentially activated during Sertoli cell development by the PI3K and PKA pathways. This differential activation has been described in a mathematic dynamic model that provided experimentally inaccessible data. β-arrestins, which are specific transducers of GPCR, seem to participate in FSH-induced p70S6K activation. This work opens exciting avenues in the identification of new translational control mechanisms dependent on GPCR.

名古屋大学博士学位論文 学位の種類:博士（医療技術学）（課程）学位授与年月日:平成21年3月25日

La FSH est une hormone clé dans la fonction de reproduction. La compréhension de ces mécanismes moléculaires est essentielle pour comprendre ses effets biologiques. Nous montrons ici pour la première fois que non seulement la FSH induit le recrutement de polysomes dans la cellule de Sertoli, mais qu’en plus, elle stimule la traduction de deux ARNm sélectivement, c-fos et vegfa. La p70S6K est impliquée dans ce mécanisme. La FSH active et induit le recrutement de la p70S6K sur la coiffe des ARNm où elle active ses cibles traductionnelles. Les β-arrestines, des protéines d’échafaudage qui régulent la signalisation du RFSH, semblent participer à l’activation de la p70S6K. La déplétion des β-arrestines augmente massivement le recrutement de la p70S6K à la coiffe et diminue son activité enzymatique. De plus, la p70S6K et les β-arrestines interagissent mais cette interaction ne semble pas modulée par la FSH. Nos résultats suggèrent que les β-arrestines séquestreraient la p70S6K inactive pour permettre son activation et son recrutement à la coiffe m7GTP en réponse à la FSH. Ce travail apporte de nouvelles connaissances sur le rôle de la FSH dans la traduction et les mécanismes de signalisation impliqués. / FSH is a key hormone of the reproductive function. A clear understanding of its molecular mechanism is essential to fully understand its biological effects. Here, we show for the first time that FSH not only enhances the assembly of polysomes but also stimulates the translation of at least two mRNA selectively, c-fos and vegfa, in Sertoli cells. p70S6K participates in this mechanism. FSH activates and enhaced p70S6K recruitment to the m7GTP cap structure of mRNA where this kinase phosphorylates its targets. β-arrestins, which are scaffolding proteins that regulate FSH signalling, seem to participate in p70S6K activation. Accordingly, β-arrestins depletion increased p70S6K recruitment to the cap and reduced its enzymatic activity. Importantly, p70S6K and β-arrestins interact but the interaction is not FSH-dependent. We assume that β-arrestins sequester inactive p70S6K to activate it locally and then p70S6K translocates to the cap in response to FSH. In conclusion, this work brings new knowledge about FSH function in translational control and the signaling mechanisms involved.

Les leucémies aiguës myéloblastiques (LAM) sont des maladies hématopoïétiques caractérisées par une prolifération incontrôlée de précurseurs myéloïdes bloqués à divers stades de différenciation. Le pronostic des LAM reste sombre à cause de la résistance aux traitements et des rechutes après rémission. En conséquence, des thérapies moins intensives et mieux tolérées doivent être développées ; ceci nécessite le développement de stratégies combinatoires associant des molécules avec des modes d’action différents pour augmenter l’efficacité des traitements. Plusieurs approches sont en cours d’étude préclinique et clinique [inhibiteurs des voies de signalisation PI3K/Akt/mTOR, anticorps monoclonaux couplés à une drogue (Mylotarg®), inhibiteurs du protéasome (bortezomib)…] Des travaux récents ont relancé l’intérêt de l’étude des molécules d’origine naturelle pour le traitement des cancers. Ainsi, l’acide flavone-8-acétique (FAA) a suscité de nombreux espoirs au vu de son action sur les tumeurs greffées chez la souris ; il s’est néanmoins révélé inactif chez l’homme du fait d’une métabolisation différente de celle de la souris. L’objectif de ma thèse a été d’étudier les effets d’anticorps monoclonaux dirigés contre l’antigène tumoral CD13 (aminopeptidase-N) et de deux dérivés de FAA, la 2’,3-Dinitroflavone-8-acétique (DNFAA ; inhibiteur de l’activité enzymatique de CD13) et la 3,3’-Diamino-4’-méthoxyflavone (DD1) dans les LAM. Mon étude a montré que DNFAA n’affecte ni la prolifération ni la survie des cellules de LAM (lignées et cellules primaires). Cependant, le traitement de ces cellules par les anticorps anti-CD13, (MY7, SJ1D1, WM15 ; reconnaissant ou non le site enzymatique) induit l’apoptose en activant les voies extrinsèque et intrinsèque. Dans la voie intrinsèque, les anti-CD13 régulent négativement l’expression des protéines anti-apoptotiques Bcl-2 et Mcl-1 et positivement l’expression de la protéine pro-apoptotique Bax. De plus, l’activation de la voie PI3K/Akt apparaît associée au processus apoptotique. Mon étude sur les effets du 3,3’-Diamino-4’-méthoxyflavone dans les cellules de LAM montre une induction d’apoptose résultant de la convergence de l’inhibition du protéasome et de l’activation des voies extrinsèque et intrinsèque. Les cibles de DD1 sont le protéasome, la kinase p70S6K (kinase en aval de mTOR), et les protéines pro-apoptotiques Bad et Bax. De plus, j’ai mis en évidence la dégradation de p70S6K sous l’action de la caspase 3, par le traitement avec DD1, nouvelle propriété partagée par DD1 et le bortezomib. En conclusion, mon travail a permis de mettre en évidence les capacités à induire in vitro des voies d’apoptose déficientes dans les cellules de LAM, d’anticorps monoclonaux anti-CD13 et de la flavone originale, 3,3’-Diamino-4’-methoxyflavone, en tant que nouvel inhibiteur du protéasome. Les propriétés de ces agents pro-apoptotiques méritent d’être analysées de façon plus approfondie. / Acute Myeloid Leukaemia (AML) is a deadly disease characterized by the clonal expansion and accumulation of hematopoietic stem cells arrested at various stages of development. Clinical research efforts are currently focusing on targeted therapies that induce apoptosis in AML cells such as PI3K/Akt/mTOR pathway inhibitors, monoclonal antibodies (Mylotarg®), proteasome inhibitor (bortezomib)… Natural products such as flavonoids have been reported as anticancer agents due to their antioxidant properties as well as to their possible interactions with signalling cascades. Therefore, flavone-8-acetic acid (FAA) has raised considerable attention since the discovery of its exceptional activity on several murine solid tumours. Unfortunately, these promising properties were not confirmed on human due to differential metabolization between human and mouse. The aim of my PhD was to study effects of monoclonal antibody against aminopeptide-N/CD13 and FAA derivatives, 2’,3-Dinitroflavone-8-acetic (DNFAA ; APN/CD13 inhibitor) and 3,3’-Diamino-4’-methoxyflavone (DD1) on acute myeloid leukaemia cells. My studies have shown that DNFAA does not modify proliferation or survival of LAM primary and cell lines. However, treatment of these cells by CD13 antibodies (MY7, SJ1D1 and WM15) induces apoptosis by triggering extrinsic and intrinsic apoptotic pathways. Regarding the intrinsic pathway, anti-CD13 down-regulate anti-apoptotic proteins Bcl-2 and Mcl-1 and up-regulate the pro-apoptotic protein Bax. Morever, PI3K/Akt signalling pathway seems to be associated with this apoptosis. My study about 3,3’-Diamino-4’-methoxyflavone effects on LAM cells has shown that DD1 induces apoptosis by proteasome inhibition and intrinsic and extrinsic pathways induction. DD1 targets p70S6 kinase (a downstream kinase of mTOR) and pro-apoptotic proteins Bad and Bax. Moreover, I have shown p70S6K degradation by caspase 3 during DD1 treatment, a new characteristic shared by DD1 and Bortezomib. As a conclusion, my works demonstrated that CD13 antibodies and a new synthetic flavone are able to induce apoptosis signalling pathway normally impaired on AML cells. Characteristics of these agents deserve to be more deeply analyzed.

The 52 kDa intermediate filament protein desmin plays an important role in force transmission in skeletal muscle by connecting myofibrils at Z-lines and to the sarcolemma. Desmin content in muscle adapts to contractile activity and may be involved in cellular signaling mechanisms responsible for muscle growth. Purpose: To compare signaling responses of the mTOR pathway in wild type (WT) vs desmin knock out (KO) mice. Methods: WT (n=12) and KO (n=12) mice were exposed to high frequency electric stimulation of the left hindlimb to elicit an acute response of the mTOR pathway. Non-stimulated right hindlimbs were used as a within animal control. Right and left TA and EDL muscles were dissected 30 min post-stimulation and examined for changes in mTOR, 4E-BP1 and p70S6K. Results: Relative to WT control samples, total mTOR and total 4E-BP1 content was higher in KO control samples. Electrical stimulation resulted in an increase p70S6K phosphorylation in WT and KO animals however there was no difference between the groups. 4E-BP1 phosphorylation was increased in WT but not KO following electrical stimulation. There was no change in mTOR phosphorylation in response to stimulation in WT or KO. Conclusion: The absence of desmin in skeletal muscle does not impair the phosphorylation of p70S6K demonstrating that a tensile load on the muscle will likely result in an increase in protein synthesis. Elevated levels of total mTOR and 4E-BP1 may imply an adaptation to increase sensitivity to growth stimuli in the muscle.

A disfunção cardíaca, decorrente de um prejuízo na contratilidade miocárdica, tem sido reconhecida como um fator importante que contribui para as altas taxas de mortalidade na sepse. Outro fato importante aponta para o envolvimento das calpaínas na inibição da via de sinalização PI3K/mTOR levando a uma diminuição potencial das taxas globais de síntese proteica através da redução da maquinaria de tradução disponível, o que reforça o envolvimento destes elementos na progressão da disfunção cardíaca na sepse. Metodologia: Foram utilizados camundongos da linhagem C57/BL6 para indução de sepse através da técnica de ligadura e perfuração do ceco separados em quatro grupos: controle com e sem tratamento e sepse moderada com e sem tratamento, o tratamento foi realizado 2 horas antes da cirurgia com inibidor da via mTOR, rapamicina. Foi realizada análise histopatológica em metacrilato e coloração picrosirius para colágeno, western blotting para quantificação da expressão proteica e real-time PCR para quantificação da expressão gênica, por fim realizamos análise funcional através da ecocardiografia. Resultados: Foi encontrado aumento das lesões teciduais e depósito de colágeno no grupo séptico tratado com rapamicina. A análise por western blotting e real-time PCR demonstrou redução das proteínas envolvidas na via mTOR nos grupos sépticos com e sem tratamento com ênfase no grupo tratado e por fim a avaliação funcional mostrou redução dos parâmetros débito cardíaco e fração de ejeção nos grupos sépticos com e sem tratamento. Conclusão: Nossos resultados demonstram que a via mTOR é de extrema importância na estrutura e função cardíacas, visto que sua inibição ocasionou o aumento de lesões e deposição de colágeno juntamente com alterações funcionais, podendo se transformar em um possível alvo terapêutico para futuras pesquisas clínicas em animais e humanos. / Cardiac dysfunction, due to impairment in myocardial contractility, has been recognized as an important factor contributing to the high mortality rates in sepsis. Another important fact is the involvement of the calpain in the inhibition of the PI3K / mTOR signaling pathway leading to a potential decrease in the overall rates of protein synthesis through the reduction of available translation machinery, which reinforces the involvement of these elements in the progression of cardiac dysfunction in sepsis. Methods: C57 / BL6 mice were used for induction of sepsis through the technique of ligation and perforation of the cecum separated into four groups: control with and without treatment and moderate sepsis with and without treatment, treatment was performed 2 hours before surgery with mTOR pathway inhibitor, rapamycin. Histopathological analysis was performed on methacrylate and picrosirius staining for collagen, western blotting for quantification of protein expression and real-time PCR for quantification of gene expression. Finally we performed functional analysis through echocardiography. Results: Increased tissue lesions and collagen deposition were found in the septic group treated with rapamycin. Western blotting and real-time PCR analysis showed reduction of the proteins involved in the mTOR pathway in the septic groups with and without treatment with emphasis in the treated group and finally the functional evaluation showed a reduction of the parameters cardiac output and ejection fraction in the septic groups with and without treatment. Conclusion: Our results demonstrate that the mTOR pathway is extremely important in cardiac structure and function, since its inhibition has resulted in increased lesions and collagen deposition along with functional alterations, and may become a possible therapeutic target for future clinical research in animals and humans.

A disfunção cardíaca, decorrente de um prejuízo na contratilidade miocárdica, tem sido reconhecida como um fator importante que contribui para as altas taxas de mortalidade na sepse. Outro fato importante aponta para o envolvimento das calpaínas na inibição da via de sinalização PI3K/mTOR levando a uma diminuição potencial das taxas globais de síntese proteica através da redução da maquinaria de tradução disponível, o que reforça o envolvimento destes elementos na progressão da disfunção cardíaca na sepse. Metodologia: Foram utilizados camundongos da linhagem C57/BL6 para indução de sepse através da técnica de ligadura e perfuração do ceco separados em quatro grupos: controle com e sem tratamento e sepse moderada com e sem tratamento, o tratamento foi realizado 2 horas antes da cirurgia com inibidor da via mTOR, rapamicina. Foi realizada análise histopatológica em metacrilato e coloração picrosirius para colágeno, western blotting para quantificação da expressão proteica e real-time PCR para quantificação da expressão gênica, por fim realizamos análise funcional através da ecocardiografia. Resultados: Foi encontrado aumento das lesões teciduais e depósito de colágeno no grupo séptico tratado com rapamicina. A análise por western blotting e real-time PCR demonstrou redução das proteínas envolvidas na via mTOR nos grupos sépticos com e sem tratamento com ênfase no grupo tratado e por fim a avaliação funcional mostrou redução dos parâmetros débito cardíaco e fração de ejeção nos grupos sépticos com e sem tratamento. Conclusão: Nossos resultados demonstram que a via mTOR é de extrema importância na estrutura e função cardíacas, visto que sua inibição ocasionou o aumento de lesões e deposição de colágeno juntamente com alterações funcionais, podendo se transformar em um possível alvo terapêutico para futuras pesquisas clínicas em animais e humanos. / Cardiac dysfunction, due to impairment in myocardial contractility, has been recognized as an important factor contributing to the high mortality rates in sepsis. Another important fact is the involvement of the calpain in the inhibition of the PI3K / mTOR signaling pathway leading to a potential decrease in the overall rates of protein synthesis through the reduction of available translation machinery, which reinforces the involvement of these elements in the progression of cardiac dysfunction in sepsis. Methods: C57 / BL6 mice were used for induction of sepsis through the technique of ligation and perforation of the cecum separated into four groups: control with and without treatment and moderate sepsis with and without treatment, treatment was performed 2 hours before surgery with mTOR pathway inhibitor, rapamycin. Histopathological analysis was performed on methacrylate and picrosirius staining for collagen, western blotting for quantification of protein expression and real-time PCR for quantification of gene expression. Finally we performed functional analysis through echocardiography. Results: Increased tissue lesions and collagen deposition were found in the septic group treated with rapamycin. Western blotting and real-time PCR analysis showed reduction of the proteins involved in the mTOR pathway in the septic groups with and without treatment with emphasis in the treated group and finally the functional evaluation showed a reduction of the parameters cardiac output and ejection fraction in the septic groups with and without treatment. Conclusion: Our results demonstrate that the mTOR pathway is extremely important in cardiac structure and function, since its inhibition has resulted in increased lesions and collagen deposition along with functional alterations, and may become a possible therapeutic target for future clinical research in animals and humans.

Patients with phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome and germline mutations in PTEN frequently develop lipomatosis, for which there is no standard treatment. Rapamycin was shown to reduce the growth of lipoma cells with heterozygous PTEN deficiency in vitro, but concomitantly induced an upregulation of AKT phosphorylation. Since it was shown that resveratrol stabilizes PTEN, we asked whether co-incubation with resveratrol could suppress the rapamycin-induced AKT phosphorylation in PTEN-deficient lipoma cells. Resveratrol incubation resulted in decreased lipoma cell viability by inducing G1-phase cell cycle arrest and apoptosis. PTEN expression and AKT phosphorylation were not significantly changed, whereas p70S6 kinase (p70S6K) phosphorylation was reduced in PTEN-deficient lipoma cells after resveratrol incubation. Rapamycin/resveratrol co-incubation significantly decreased viability further at lower doses of resveratrol and resulted in decreased p70S6K phosphorylation compared to rapamycin incubation alone, suggesting that resveratrol potentiated the growth inhibitory effects of rapamycin by reducing p70S6K activation. Both viability and p70S6K phosphorylation of primary PTEN wild-type preadipocytes were less affected compared to PTEN-deficient lipoma cells by equimolar concentrations of resveratrol. These results support the concept of combining chemopreventive natural compounds with mammalian target of rapamycin (mTOR) inhibitors to increase the efficacy of chemotherapeutic drugs for patients suffering from overgrowth syndromes.

Functional adaptations in human skeletal muscle following a period of resistance exercise are the result of regular activation of cellular signaling pathways that elevate muscle protein synthesis. It has been reported that the addition of whole body vibration (WBV) to a resistance exercise program enhances performance. Such improvements in muscle function may be the result of increased activation of cellular signaling pathways associated with muscle growth. Purpose: We have investigated whether an acute bout of resistance exercise in combination with WBV results in a greater activation of the mTOR signaling pathway compared to resistance exercise alone. Methods: Eight untrained college-age males (23 ± 2 yrs, 179 ± 1 cm, 75.0 ± 2.5 kg, and 12.6 ± 1.8% body fat) performed unilateral leg press exercises with (Vbx) and without (RT) vibration. Muscle samples were obtained from the vastus lateralis muscle pre-exercise (baseline) and one-hour following the bout of resistance exercise. Muscle tissue samples were analyzed for phosphorylated levels of mTOR, p70S6K, and 4E-BP1 proteins. Results: One-hour following the resistance exercise bout there were no differences between phosphorylated levels of mTOR or 4E-BP1 in Vbx or RT (p > 0.05). Levels of phosphorylated p70S6K were increased at the one-hour post-exercise time-point in both Vbx (baseline: 504 ± 286 OD; post: 5039 ± 2351 OD, p < 0.05) and RT (baseline: 356 ± 131 OD; post: 5430 ± 1218 OD, p < 0.05); however, there was no difference in protein phosphorylation levels between conditions (p > 0.05). Conclusion: Vibration does not augment acute activation of the mTOR signaling pathway in human skeletal muscle suggesting that performance benefits resulting from combining resistance exercise and vibration may not be the result of an enhanced cellular growth response.

Submitted by André Krug (andre.krug@bol.com.br) on 2018-05-28T21:21:29Z No. of bitstreams: 2 TESE_DOUTORADO_ANDRE_KRUG.pdf: 1523685 bytes, checksum: eaa1e414ce0fea68ddb7c3b618d037b6 (MD5) Carta_biblioteca_Andre.pdf: 2380256 bytes, checksum: d398258e7a2f5c73594cf8230b4b1957 (MD5) / Approved for entry into archive by Ronildo Prado (ri.bco@ufscar.br) on 2018-06-06T13:33:50Z (GMT) No. of bitstreams: 2 TESE_DOUTORADO_ANDRE_KRUG.pdf: 1523685 bytes, checksum: eaa1e414ce0fea68ddb7c3b618d037b6 (MD5) Carta_biblioteca_Andre.pdf: 2380256 bytes, checksum: d398258e7a2f5c73594cf8230b4b1957 (MD5) / Approved for entry into archive by Ronildo Prado (ri.bco@ufscar.br) on 2018-06-06T13:34:02Z (GMT) No. of bitstreams: 2 TESE_DOUTORADO_ANDRE_KRUG.pdf: 1523685 bytes, checksum: eaa1e414ce0fea68ddb7c3b618d037b6 (MD5) Carta_biblioteca_Andre.pdf: 2380256 bytes, checksum: d398258e7a2f5c73594cf8230b4b1957 (MD5) / Made available in DSpace on 2018-06-06T13:40:53Z (GMT). No. of bitstreams: 2 TESE_DOUTORADO_ANDRE_KRUG.pdf: 1523685 bytes, checksum: eaa1e414ce0fea68ddb7c3b618d037b6 (MD5) Carta_biblioteca_Andre.pdf: 2380256 bytes, checksum: d398258e7a2f5c73594cf8230b4b1957 (MD5) Previous issue date: 2018-03-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Synthetic glucocorticoids have potent anti-inflammatory and immunosuppressive action, though its chronic usage can trigger muscle atrophy. On the other hand the resistance training (RT) acts in opposition to atrophic situations, although its effects on muscle atrophy induced by treatment with dexamethasone (DEX) are poorly known.The purpose of this study was to determine how long RT is required to promote preventive effects in flexor halluces longus (FHL) muscle atrophy induced by dexamethasone (DEX). After maximal voluntary carrying capacity (MVCC), 100 rats were separated in sedentary (SED) or resistance trained for 10 (RT10), 40 (RT40), 70 (RT70) and 100 (RT100) days. Groups were divided as control (CTRL) or treated with DEX. RT was performed with 80% of maximal voluntary carrying capacity (MVCC). During the last 10 days, the animals either received DEX (0.5 mg/kg/day, i.p.) or vehicle (saline, same volume as DEX treatment, i.p.). The FHL muscle was removed, cleaned, weighed and stored for determining the cross-sectional area, proteassomal activity 26s, and total p70S6K, p-p70S6KThr389, MuRF1, REDD1 and GAPDH protein level. The results arepresented as mean ± SEM. The repeated measures two-way analysis of variance (ANOVA) were used for food intake and, for further analysis,it was used two-way ANOVA, both with Tukey post hoc test and significance levelset as α<0.05. DEX reduced FHL mass (-26%), but RT70 and RT100 DEX groups presented atrophy attenuation. DEX reduced proteasome activity in SED (-33%) and RT70 (-44%) DEX. RT70 CTRL had increased proteasome activity when compared with RT10 and RT40 CTRL (+48% and +51%, respectively) groups and RT100 CTRL had reduced activity (-56%). DEX reduced phospho-p70S6KThr389/total p70S6k ratio in SED DEX (-24%), but it was reverted in RT10 (+48%) and RT70 DEX(+70%). RT70 CTRL presented higher values of this ratio than SED, RT40 and RT100 CTRL groups. DEX increased REDD1 (+47%) protein level only in SED DEX. MuRF-1 protein level increased in SED(+50%), RT10 (+45%) and RT40 (+46%)DEX groups, but it was blocked in RT70 and RT100 DEX groups. In summary, we suggest that DEX-induced FHL muscle atrophy requires at least 70 days of RT to be attenuated and this response involves a complete blockade of MuRF-1 and REDD1 protein level increase and the blockade phospho-p70S6KThr389/total p70S6k ratio reduction. Also, 100 days of RT did not promote any additional effects. It is interesting to note that only 10 days of RT evoked improvements in the synthesis pathway, which suggest that some molecular adjustments are required in early stages of skeletal muscle mass maintenance. / Os glicocorticoides sintéticos possuem potente ação anti-inflamatória e imunossupressora, entretanto seu uso crônico pode desencadear atrofia muscular. Por outro lado o treinamento resistido (TR) contrapõe-se a situações atróficas, embora seus efeitos sobre a atrofia muscular induzida pelo tratamento com dexametasona (DEX) são pouco conhecidos.O presente trabalho teve como objetivo verificar qual é o momento em que o efeito preventivo do TR (80% do carregamento máximo) é mais efetivo sobre a redução peso corporal e atrofia muscular induzidas pelo tratamento com DEX. Separamos 100 ratos Wistar machos em 10 grupos: sedentário controle (SED CTRL); sedentário tratado com DEX (SED DEX); treinado controle 10, 40, 70 e 100 dias (TR10 CTRL, TR40 CTRL, TR70 CTRL e TR100 CTRL) e treinado tratado com DEX 10, 40, 70 e 100 dias (TR10 DEX, TR40 DEX, TR70 DEX e TR100 DEX). Utilizamos o TR em escada (80% TCM). Nos 10 últimos dias os animais receberam DEX (0,5 mg/kg por dia, i.p.) ou o mesmo volume de salina. O músculo flexor longo do hálux (FHL) foi removido, limpo, pesado e armazenado para determinação da área de secção transversa, atividade do proteassoma 26s, e produção proteica dep70S6K total, p-p70S6KThr389, MuRF1, REDD1 e GAPDH. Os resultados são apresentados como média±EPM. Foi utilizada aanálise de variância de dois caminhos (ANOVA) para medidas repetidas para ingestão alimentar e para as variáveis restantes foi utilizada a ANOVA de dois caminhos. Na presença de interação, foi utilizado o posthoc de Tukey,com significância de α<0,05. A DEX reduziu 26% a massa muscular do FHL, mas o grupo TR70 e TR100 DEX apresentaram essa atrofia atenuada. O tratamento com DEX reduziu a atividade do proteassoma nos grupos SED (-33%) e TR70 DEX (-44%). O grupo TR70 CTRL teve sua atividade do proteassoma aumentada em relação aos grupos TR10 e TR40 CTRL (+48% e +51%, respectivamente), além do mais, o grupo TR100 CTRL teve sua atividade reduzida (-56%). A DEX reduziu a razão p-p70S6KThr389/p70S6k total no grupo SED DEX (-24%), mas essa resposta foi revertida no grupo TR10 (+48%) e TR70 (+70%) DEX. O grupo TR70 CTRL apresentou valores superiores dessa razão em relação aos grupos SED, TR40 e TR100 CTRL. A DEX aumentou a produção proteica de REDD1 (+47%) somente no grupo SED DEX. A produção proteica de MuRF1 foi aumentada nos grupos SED (+50%), TR10 (+45%) e TR40 (+46%) DEX, mas essa resposta foi completamente bloqueada nos grupos TR70 TR100 DEX. Com base nos resultados do presente estudo, pode-se sugerir que a atrofia muscular induzida por DEX no músculo FHL necessita de pelo menos 70 dias de TR para ser atenuada e essa resposta parece envolver o completo bloqueio dos aumentos de MuRF1 e REDD1, somados ao bloqueio da redução da razão p-p70S6KThr389/p70S6k. Além disso, 100 dias de TR não provocaram nenhum efeito preventivo adicional. É interessante notar que o TR, mesmo realizado por curto período (10 dias), promove melhorias na via de síntese de proteínas, oque sugere que alguns ajustes moleculares são necessários em estágios iniciais da manutenção da massa muscular. / CAPES: 1452526