CARM1 and skeletal muscle atrophy / Coactivator-associated arginine methyltransferase 1 (CARM1) is emerging as an important player in skeletal muscle biology. We sought to elucidate the role of CARM1 in mediating muscle mass and function, as well as in the induction and progression of the muscle atrophy program. To this end, we engineered CARM1 skeletal muscle-specific knockout (mKO) mice and employed distinct, but complementary models of muscle atrophy, including neurogenic muscle disuse, food deprivation, and the sarcopenia of aging. CARM1 mKO resulted in reduced muscle mass and myofiber cross-sectional area concomitant with dysregulated autophagic and atrophic signaling, which indicates the requirement of CARM1 for the maintenance of muscle biology. Interestingly, CARM1 deletion mitigated the progression of both denervation- and fasting-induced skeletal muscle atrophy as compared to wild-type (WT) mice. Key mechanistic findings revealed that CARM1 interacts with the master neuromuscular regulator AMPK and attenuates the expression and activity of its downstream autophagy and atrophy networks. Surprisingly, both male and female mKO mice have a significantly shorter lifespan versus their WT littermates, revealed by a ~50% reduction in survival at 22-months-old, which is equivalent to ~70 years-old in humans. As such, we observed significantly reduced functional outcomes of integrative physiology in old mKO mice compared to old WT animals, such as strength and motor performance. Taken together, these results indicate that skeletal muscle CARM1 is indispensable for maintaining muscle mass, function, and lifespan. Targeting the interplay between CARM1 and AMPK may offer a viable therapeutic strategy for combating life-limiting muscle wasting conditions. / Thesis / Doctor of Philosophy (PhD) / While muscle wasting and weakness remains a widespread issue, the mechanisms that control muscle atrophy are not entirely understood. Previous evidence suggests that coactivator-associated arginine methyltransferase 1 (CARM1) regulates skeletal muscle remodeling. However, the role of CARM1 during muscle atrophy is unknown. Therefore, the purpose of this work was to investigate the function of CARM1 during muscle wasting. We generated mice with CARM1 deleted in skeletal muscle and studied the impact of CARM1 deficiency on the loss of skeletal muscle mass during muscle disuse, food deprivation, and aging. We found that CARM1 is required to maintain muscle mass under basal conditions. Interestingly, knocking out CARM1 in muscle attenuated the progression of denervation- and fasting-induced atrophy. However, CARM1 deletion in muscle resulted in lower muscle strength and a reduced lifespan. CARM1 deficiency did not prevent aging-induced muscle loss. Overall, these findings advance our understanding of CARM1 in skeletal muscle biology.

Skeletal muscle atrophy is a common, debilitating consequence of muscle disuse, malnutrition, critical illness, musculoskeletal conditions, neurological disease, cancer, and organ failure. Despite its prevalence, little is known about the molecular pathogenesis of this devastating condition due in large part to an incomplete understanding of the molecular mechanisms that drive the atrophy process. In previous studies, we identified the transcription factor ATF4 as a critical mediator of skeletal muscle atrophy. We found that ATF4 is necessary and sufficient for skeletal muscle atrophy during limb immobilization. However, ATF4 mKO mice were only partially protected from skeletal muscle atrophy during limb immobilization, indicating the existence of another pro-atrophy factor that acts independently of the ATF4 pathway. Using mouse models, we identify p53 as this ATF4-independent factor. We show that skeletal muscle atrophy increases p53 expression in skeletal muscle fibers. In addition, overexpression of p53 causes skeletal muscle atrophy. Further, p53 mKO mice are partially resistant to muscle atrophy during limb immobilization. Taken together, these data indicate that like ATF4, p53 is sufficient and required for skeletal muscle atrophy during limb immobilization. Importantly, overexpression of p53 induces muscle atrophy in the absence of ATF4, whereas ATF4-mediated muscle atrophy does not require p53. Furthermore, overexpression of p53 and ATF4 induces greater muscle atrophy than p53 or ATF4 alone. Moreover, skeletal muscle lacking both p53 and ATF4 is more resistant to skeletal muscle atrophy than muscle lacking either p53 or ATF4 alone. Taken together, these data indicate that p53 and ATF4 mediate distinct and additive mechanisms to skeletal muscle atrophy. However, the precise mechanism by which p53 and ATF4 cause skeletal muscle atrophy remained unclear. Using genome-wide expression arrays, we identify p21 as a skeletal muscle mRNA that is highly induced by p53 and ATF4 during limb immobilization. Further, overexpression of p21 causes skeletal muscle atrophy. In addition, p21 is required for muscle atrophy due to limb immobilization, p53, and ATF4. Collectively, these results identify p53 and ATF4 as critical and complementary mediators of skeletal muscle atrophy during limb immobilization, and discover p21 as an essential downstream mediator of the p53 and ATF4 pathways.

Skeletal muscle (SM) atrophy complicates many illnesses, diminishing quality of life and increasing disease morbidity, health resource utilization and health care costs. In animal models of muscle atrophy, loss of SM mass results predominantly from ubiquitin-mediated proteolysis and ubiquitin ligases are the key enzymes that catalyze protein ubiquitination. We have previously shown that ubiquitin ligase Nedd4-1 is up-regulated in a rodent model of denervation-induced SM atrophy and the constitutive expression of Nedd4-1 is sufficient to induce myotube atrophy in vitro, suggesting an important role for Nedd4-1 in the regulation of muscle mass. In this study we generate a Nedd4-1 SM specific-knockout mouse and demonstrate that the loss of Nedd4-1 partially protects SM from denervation-induced atrophy confirming a regulatory role for Nedd4-1 in the maintenance of muscle mass in vivo. Nedd4-1 did not signal downstream through its known substrates Notch-1, MTMR4 or FGFR1, suggesting a novel substrate mediates Nedd4-1’s induction of SM atrophy.

Skeletal muscle is defined to be atrophic in osteoporosis models and therefore is a potential target tissue for osteoporosis research. The aim of this longitudinal randomized controlled interdisciplinary study was to analyze the functional, histological, ultra-structral and molecular changes and the role of cachectic muscle atrophy inducer TNF-alpha in the skeletal muscles of the ovariectomized (OVX) rat model which mimics postmenopausal osteoporosis. Female Sprague-Dawley rats were randomly assigned to the control, the OVX and the OVX+10&amp / #956 / g/g/week TNF-alpha antagonist (Remicade) treated OVX-TNF groups. Maximum isometric and tetanic-twitch amplitudes were lower than the control group in the OVX group. Maximum isometric twitch amplitudes recovered in the fast-twitch extensor digitorum longus (EDL) muscles but not in the slow-twitch soleus muscles in the OVX-TNF group. The decrease in tetanic-twitch amplitudes recovered in the OVX-TNF group in both muscle types. Splitting and size variations of fibers, central nuclei and well-preserved overall ultrastructure were noted in the OVX and the OVX-TNF groups. Slow-twitch Type I fiber percentage, areas and diameters increased in EDL muscles of the OVX and the OVX-TNF group comparing to the control group. p65 and MyoD immune-labeling increased in OVX group whereas MyoD and C-Rel increased and p50 decreased in OVX-TNF group. Expressions of 61 genes and 42 unidentified transcripts were significantly different between the control, the OVX and the OVX-TNF groups. To sum up TNF-alpha has a role in skeletal muscle dysfunction in OVX rats and TNF-alpha antagonist administration recovered it. But this modulation was not sufficient for total structural recovery.

Skeletal muscle (SM) atrophy complicates many illnesses, diminishing quality of life and increasing disease morbidity, health resource utilization and health care costs. In animal models of muscle atrophy, loss of SM mass results predominantly from ubiquitin-mediated proteolysis and ubiquitin ligases are the key enzymes that catalyze protein ubiquitination. We have previously shown that ubiquitin ligase Nedd4-1 is up-regulated in a rodent model of denervation-induced SM atrophy and the constitutive expression of Nedd4-1 is sufficient to induce myotube atrophy in vitro, suggesting an important role for Nedd4-1 in the regulation of muscle mass. In this study we generate a Nedd4-1 SM specific-knockout mouse and demonstrate that the loss of Nedd4-1 partially protects SM from denervation-induced atrophy confirming a regulatory role for Nedd4-1 in the maintenance of muscle mass in vivo. Nedd4-1 did not signal downstream through its known substrates Notch-1, MTMR4 or FGFR1, suggesting a novel substrate mediates Nedd4-1’s induction of SM atrophy.

Skeletal muscle atrophy is a debilitating condition caused by pathological conditions including cancer cachexia, disuse and denervation. Disuse atrophy is characterized by reduction in fiber size, fiber-type change and induction of markers of atrophy such as MuRF1 and Fn14. Recent studies have focused on understanding the fundamental role of signalling pathways and the proteolytic system in response to muscle atrophy. Unfortunately the exact mechanisms behind atrophy remain poorly understood. I recently demonstrated that cIAP1 and/or cIAP2 proteins are critical regulators of NF-kB activation, which has been shown to be involved in skeletal muscle atrophy. Here, I used genetic and pharmacological means to investigate the role of cIAP1 in a denervation-induced skeletal muscle atrophy model. Interestingly, I found that upon denervation loss of cIAP1 rescues muscle fiber size, prevents fiber-type changing and inhibits the expression of MuRF1 and Fn14. Moreover, treatment of mice with Smac mimetic compounds (SMC), a novel class of small molecule IAP antagonists, showed successful knockdown of cIAP1 in muscle and protects against denervation-induced muscle atrophy. Taken together, these data reveal that cIAP1 is both a novel mediator of skeletal muscle atrophy and an important therapeutic target.

No description available.

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A miopatia esquelética em doenças sistêmicas é um importante preditor de mortalidade e prognóstico em diversas síndromes, incluindo a insuficiência cardíaca. Os danos músculo-esqueléticos em situações de comprometimento cardíaco são descritos pela literatura há décadas, entretanto, nenhum recurso farmacológico proposto até o momento mostrou-se eficiente em reverter esses prejuízos, ressaltando o papel do treinamento físico aeróbio. Apesar dos inegáveis benefícios desta terapia adjuvante no tratamento da insuficiência cardíaca, muito pouco se sabe sobre a intensidade de exercício capaz de otimizar os ganhos promovidos por esta intervenção. Dado isso, nesse estudo avaliamos a eficácia do treinamento físico aeróbio em alta intensidade na musculatura esquelética em ratos submetidos ao infarto do miocárdio, comparando-a com protocolo isocalórico realizado em intensidade moderada. Observamos que os animais infartados apresentaram alterações patológicas na musculatura esquelética, similarmente ao observado em pacientes com IC, como prejuízos em enzimas metabólicas fundamentais, atrofia muscular, perturbação da homeostase redox e ativação do complexo proteassomal 26S. Ambos os protocolos de treinamento físico aeróbio foram capazes de aprimorar substancialmente a capacidade funcional e potência aeróbia máxima nos animais infartados, prevenindo a queda da atividade máxima das enzimas hexoquinase e citrato sintase, restaurando a morfologia da musculatura esquelética e aumentando a distribuição de fibras musculares do tipo I, o que foi acompanhado por melhora do balanço redox e redução da atividade do complexo proteassomal 26S. Apesar do treinamento físico aeróbio em alta intensidade ter proporcionado resultados superiores ao protocolo de intensidade moderada em relação a capacidade funcional dos animais, as adaptações músculo-esqueléticas às diferentes intensidades de TFA apresentaram-se muito semelhantes / Impaired skeletal muscle performance in systemic diseases is shown to strongly predict mortality and long-term prognosis in a wide variety of syndromes, including heart failure. The clinical picture of skeletal muscle damage in cardiac situations has been described for decades. However, no pharmacological strategy proposed so far was shown to effectively prevent the onset of skeletal myopathy, reinforcing the role of aerobic exercise training in counteracting such phenomenon. Despite the well-known benefits of exercise training in sets of cardiac dysfunction, very little is known about the optimal exercise intensity to elicit maximal outcomes. Therefore, in the present study we compared the effects of high-intensity aerobic exercise training with those of an isocaloric moderate-intensity protocol on skeletal muscle adaptations in infarcted rats. Our data suggest that infarcted rats presented signs of skeletal myopathy resembling those observed in HF patients, such as metabolic enzymes impairment, skeletal muscle atrophy, disrupted redox balance and proteasomal overactivation. Here we show that both high- and moderate-intensity aerobic exercise training were able to substantially increase aerobic capacity in infarcted rats, preventing the decay of citrate synthase and hexokinase maximal activities, reestablishing normal skeletal muscle morphology to a healthy profile and increasing the number of type I muscle fibers. Such outcomes were accompanied by an improved redox balance and reduced proteasomal activity in skeletal muscle. Even though high-intensity aerobic interval training was superior to moderate-intensity in improving functional capacity, the observed adaptations in skeletal muscle were remarkably similar between the protocols. Therefore, our data allow us to conclude that high-intensity and moderate-intensity aerobic exercise training equally prevent skeletal myopathy induced by myocardial infarction in rats

A miopatia esquelética em doenças sistêmicas é um importante preditor de mortalidade e prognóstico em diversas síndromes, incluindo a insuficiência cardíaca. Os danos músculo-esqueléticos em situações de comprometimento cardíaco são descritos pela literatura há décadas, entretanto, nenhum recurso farmacológico proposto até o momento mostrou-se eficiente em reverter esses prejuízos, ressaltando o papel do treinamento físico aeróbio. Apesar dos inegáveis benefícios desta terapia adjuvante no tratamento da insuficiência cardíaca, muito pouco se sabe sobre a intensidade de exercício capaz de otimizar os ganhos promovidos por esta intervenção. Dado isso, nesse estudo avaliamos a eficácia do treinamento físico aeróbio em alta intensidade na musculatura esquelética em ratos submetidos ao infarto do miocárdio, comparando-a com protocolo isocalórico realizado em intensidade moderada. Observamos que os animais infartados apresentaram alterações patológicas na musculatura esquelética, similarmente ao observado em pacientes com IC, como prejuízos em enzimas metabólicas fundamentais, atrofia muscular, perturbação da homeostase redox e ativação do complexo proteassomal 26S. Ambos os protocolos de treinamento físico aeróbio foram capazes de aprimorar substancialmente a capacidade funcional e potência aeróbia máxima nos animais infartados, prevenindo a queda da atividade máxima das enzimas hexoquinase e citrato sintase, restaurando a morfologia da musculatura esquelética e aumentando a distribuição de fibras musculares do tipo I, o que foi acompanhado por melhora do balanço redox e redução da atividade do complexo proteassomal 26S. Apesar do treinamento físico aeróbio em alta intensidade ter proporcionado resultados superiores ao protocolo de intensidade moderada em relação a capacidade funcional dos animais, as adaptações músculo-esqueléticas às diferentes intensidades de TFA apresentaram-se muito semelhantes / Impaired skeletal muscle performance in systemic diseases is shown to strongly predict mortality and long-term prognosis in a wide variety of syndromes, including heart failure. The clinical picture of skeletal muscle damage in cardiac situations has been described for decades. However, no pharmacological strategy proposed so far was shown to effectively prevent the onset of skeletal myopathy, reinforcing the role of aerobic exercise training in counteracting such phenomenon. Despite the well-known benefits of exercise training in sets of cardiac dysfunction, very little is known about the optimal exercise intensity to elicit maximal outcomes. Therefore, in the present study we compared the effects of high-intensity aerobic exercise training with those of an isocaloric moderate-intensity protocol on skeletal muscle adaptations in infarcted rats. Our data suggest that infarcted rats presented signs of skeletal myopathy resembling those observed in HF patients, such as metabolic enzymes impairment, skeletal muscle atrophy, disrupted redox balance and proteasomal overactivation. Here we show that both high- and moderate-intensity aerobic exercise training were able to substantially increase aerobic capacity in infarcted rats, preventing the decay of citrate synthase and hexokinase maximal activities, reestablishing normal skeletal muscle morphology to a healthy profile and increasing the number of type I muscle fibers. Such outcomes were accompanied by an improved redox balance and reduced proteasomal activity in skeletal muscle. Even though high-intensity aerobic interval training was superior to moderate-intensity in improving functional capacity, the observed adaptations in skeletal muscle were remarkably similar between the protocols. Therefore, our data allow us to conclude that high-intensity and moderate-intensity aerobic exercise training equally prevent skeletal myopathy induced by myocardial infarction in rats