The myogenic regulatory factor MRF4 is highly expressed in adult skeletal muscle but its function is unknown. Here we show that Mrf4 knockdown in adult muscle induces hypertrophy and prevents ...denervation-induced atrophy. This effect is accompanied by increased protein synthesis and widespread activation of muscle-specific genes, many of which are targets of MEF2 transcription factors. MEF2-dependent genes represent the top-ranking gene set enriched after Mrf4 RNAi and a MEF2 reporter is inhibited by co-transfected MRF4 and activated by Mrf4 RNAi. The Mrf4 RNAi-dependent increase in fibre size is prevented by dominant negative MEF2, while constitutively active MEF2 is able to induce myofibre hypertrophy. The nuclear localization of the MEF2 corepressor HDAC4 is impaired by Mrf4 knockdown, suggesting that MRF4 acts by stabilizing a repressor complex that controls MEF2 activity. These findings open new perspectives in the search for therapeutic targets to prevent muscle wasting, in particular sarcopenia and cachexia.
The on-target pioneer factors Ascl1 and Myod1 are sequence-related but induce two developmentally unrelated lineages-that is, neuronal and muscle identities, respectively. It is unclear how these two ...basic helix-loop-helix (bHLH) factors mediate such fundamentally different outcomes. The chromatin binding of Ascl1 and Myod1 was surprisingly similar in fibroblasts, yet their transcriptional outputs were drastically different. We found that quantitative binding differences explained differential chromatin remodelling and gene activation. Although strong Ascl1 binding was exclusively associated with bHLH motifs, strong Myod1-binding sites were co-enriched with non-bHLH motifs, possibly explaining why Ascl1 is less context dependent. Finally, we observed that promiscuous binding of Myod1 to neuronal targets results in neuronal reprogramming when the muscle program is inhibited by Myt1l. Our findings suggest that chromatin access of on-target pioneer factors is primarily driven by the protein-DNA interaction, unlike ordinary context-dependent transcription factors, and that promiscuous transcription factor binding requires specific silencing mechanisms to ensure lineage fidelity.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Myonuclei transcriptionally regulate muscle fibers during homeostasis and adaptation to exercise. Their subcellular location and quantity are important when characterizing phenotypes of myopathies, ...the effect of treatments, and understanding the roles of satellite cells in muscle adaptation and muscle "memory." Difficulties arise in identifying myonuclei due to their proximity to the sarcolemma and closely residing interstitial cell neighbors. We aimed to determine to what extent (pericentriolar material-1) PCM1 is a specific marker of myonuclei in vitro and in vivo. Single isolated myofibers and cross sections from mice and humans were studied from several models including wild-type and Lamin A/C mutant mice after functional overload and damage and recovery in humans following forced eccentric contractions. Fibers were immunolabeled for PCM1, Pax7, and DNA. C2C12 myoblasts were also studied to investigate changes in PCM1 localization during myogenesis. PCM1 was detected at not only the nuclear envelope of myonuclei in mature myofibers and in newly formed myotubes but also centrosomes in proliferating myogenic precursors, which may or may not fuse to join the myofiber syncytium. PCM1 was also detected in nonmyogenic nuclei near the sarcolemma, especially in regenerating areas of the
mouse and damaged human muscle. Although PCM1 is not completely specific to myonuclei, the impact that PCM1+ macrophages and interstitial cells have on myonuclei counts would be small in healthy muscle. PCM1 may prove useful as a marker of satellite cell dynamics due to the distinct change in localization during differentiation, revealing satellite cells in their quiescent (PCM1-), proliferating (PCM1+ centrosome), and prefusion states (PCM1+ nuclear envelope).
Human Endogenous Retroviruses (HERVs) are fossil viruses that composes 8% of the human genome and plays several important roles in human physiology, including muscle repair/myogenesis. It is believed ...that inflammation may also regulate HERV expression, and therefore may contribute in the muscle repair, especially after training exercise. Hence, this study aimed to assess the level of HERVs expression and inflammation profile in practitioners' resistance exercises after an acute strength training session.
Healthy volunteers were separated in regular practitioners of resistance exercise training group (REG, n = 27) and non-trained individuals (Control Group, n = 20). All individuals performed a strength exercise section. Blood samples were collected before the exercise (T0) and 45 minutes after the training session (T1). HERV-K (HML1-10) and W were relatively quantified, cytokine concentration and circulating microparticles were assessed.
REG presented higher level of HERV-W expression (~2.5 fold change) than CG at T1 (p<0.01). No difference was observed in the levels of HERV-K expression between the groups as well as the time points. Higher serum TNF-α and IL-10 levels were verified post-training session in REG and CG (p<0.01), and in REG was found a positive correlation between the levels of TNF-α at T1 and IL-10 at T0 (p = 0.01). Finally, a lower endothelial microparticle percentage was observed in REG at T1 than in T0 (p = 0.04).
REG individuals exhibited a significant upregulation of HERV-W and modulation of inflammatory markers when compared to CG. This combined effect could potentially support the process of skeletal muscle repair in the exercised individuals.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Nuclear pore complexes (NPCs) are multiprotein channels connecting the nucleus with the cytoplasm. NPCs have been shown to have tissue-specific composition, suggesting that their function can be ...specialized. However, the physiological roles of NPC composition changes and their impacts on cellular processes remain unclear. Here we show that the addition of the Nup210 nucleoporin to NPCs during myoblast differentiation results in assembly of an Mef2C transcriptional complex required for efficient expression of muscle structural genes and microRNAs. We show that this NPC-localized complex is essential for muscle growth, myofiber maturation, and muscle cell survival and that alterations in its activity result in muscle degeneration. Our findings suggest that NPCs regulate the activity of functional gene groups by acting as scaffolds that promote the local assembly of tissue-specific transcription complexes and show how nuclear pore composition changes can be exploited to regulate gene expression at the nuclear periphery.
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•Nucleoporin Nup210 is required for myofiber maturation, survival, and muscle growth•Nup210 recruits Mef2C to the nuclear periphery during myogenic differentiation•Nup210/Mef2C regulate the expression of muscle genes and miRNAs at nuclear pores•Nuclear pores act as scaffolds for the assembly of specific transcription complexes
Nup210 is a tissue-specific nuclear pore complex component with a role in myogenic differentiation. Raices, Bukata et al. show in zebrafish and mammalian myoblasts that Nup210 regulates myofiber maturation, growth, and survival by promoting assembly of a Mef2C-dependent transcription complex at nuclear pores to regulate muscle structural and miRNA genes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Brown and beige fat dissipate chemical energy in the form of heat through uncoupling protein-1 (Ucp1) on the mitochondrial inner membrane as well as through the other pathways, while white fat ...generally stores energy in the form of lipid. Stimulating development and/or function of brown fat is highly anticipated as a novel strategy for the treatment of obesity and its complications including type 2 diabetes. Previously, we identified a transcription factor nuclear factor I-A (NFIA) as a crucial regulator of brown fat. NFIA binds to and activates the brown-fat-specific enhancers even before differentiation and later facilitates the binding of PPARgamma (peroxisome proliferator-activated receptor gamma—a master transcription factor of adipogenesis), to control the brown fat gene program. Here we show that the C-terminal 17 amino acid residues of NFIA (which we call pro#3 domain) are required for the transcriptional activity of NFIA. Full-length NFIA—but not deletion mutant lacking pro#3 domain—rescued impaired Pparg expression and adipogenesis in NFIA-knockout cells. However, the deletion mutant still binds to Myod1 enhancer to represses Myod1 expression via competition with KLF5 in terms of enhancer binding, leading to suppression of myogenic gene program. Therefore, the negative effect of NFIA on the myogenic gene program is, at least partly, independent of the positive effect on Pparg expression and its downstream adipogenic gene program. Overall, our results uncover multiple ways of action of NFIA to ensure optimal regulation of brown adipocyte differentiation.
Disclosure
Y. Hiraike: Research Support; Self; Daiichi Sankyo, Daiichi Sankyo, Novo Nordisk Inc., Novo Nordisk Inc. H. Waki: Research Support; Self; Astellas Pharma Inc., Novartis Pharma K.K., Ono Pharmaceutical Co., Ltd., Takeda Science Foundation, The Cell Science Research Foundation. Speaker’s Bureau; Self; AstraZeneca K.K., AstraZeneca K.K., Chugai Pharmaceutical Co., Ltd., Daiichi Sankyo, Kyowa Hakko Kirin Co., Ltd., Nippon Boehringer Ingelheim Co. Ltd., Novo Nordisk Inc., Ono Pharmaceutical Co., Ltd., Sanofi K.K. K. Miyake: Research Support; Self; NTT DOCOMO, INC. M. Oguchi: None. T. Yamauchi: Research Support; Self; AeroSwitch, Asahi Mutual Life Insurance Company, Astellas Pharma Inc., AstraZeneca K.K., Boehringer Ingelheim International GmbH, Daiichi Sankyo Company, Limited, Kowa Pharmaceutical company,limited., Kyowa Hakko Kirin Co., Ltd., Merck Sharp & Dohme Corp., Mitsubishi Corporation Life Sciences Limited, Mitsubishi Tanabe Pharma Corporation, Novartis Pharma K.K., Novo Nordisk Inc., NTT Docomo Inc., Ono Pharmaceutical Co., Ltd., Sanofi K.K., Sanwa Kagaku Kenkyusho, Shionogi & Co., Ltd., Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited, TOSOH CORPORATION. Other Relationship; Self; Covidien Japan Inc. (Medtronic Japan Co., Ltd.), Eli Lilly Japan K.K., Johnson & Johnson, Kissei Pharmaceutical Co., Ltd. T. Kadowaki: Research Support; Self; Astellas Pharma Inc., Daiichi Sankyo, Mitsubishi Tanabe Pharma Corporation, MSD Corporation, Novartis Pharma K.K., Novo Nordisk Pharma Ltd., Ono Pharmaceutical Co., Ltd., Sanofi, Sumitomo Dainippon Pharma Co., Ltd., Takeda Pharmaceutical Company Limited. Speaker’s Bureau; Self; Abbott, Astellas Pharma Inc., AstraZeneca K.K., Boehringer Ingelheim Pharmaceuticals, Inc., Cosmic Corporation, Daiichi Sankyo, Eli Lilly Japan K.K., FUJIFILM, Kowa Company, Ltd., Kyowa Hakko Kirin Co., Ltd., Medscape Education, Medtronic, Mitsubishi Tanabe Pharma Corporation, MSD Corporation, NIPRO Medical Corporation, Novartis Pharma K.K., Novo Nordisk Pharma Ltd., Ono Pharmaceutical Co., Ltd., Sanofi, Sanwa Kagaku Kenkyusho, Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Co., Ltd., Takeda Pharmaceutical Company Limited, Terumo Medical Corporation. Other Relationship; Self; Asahi Mutual Life Insurance.
The outstanding regenerative capacity of skeletal muscle is attributed to the resident muscle stem cell termed satellite cell. Satellite cells are essential for skeletal muscle regeneration as they ...ultimately provide the myogenic precursors that rebuild damaged muscle tissue. Satellite cells characteristically are a heterogeneous population of stem cells and committed progenitor cells. Delineation of cellular hierarchy and understanding how lineage fate choices are determined within the satellite cell population will be invaluable for the advancement of muscle regenerative therapies.
Duchenne muscular dystrophy (DMD) is a devastating and debilitating muscle degenerative disease affecting 1 in every 3,500 male births worldwide. DMD is progressive and fatal; accumulated weakening ...of the muscle tissue leads to an inability to walk and eventual loss of life due to respiratory and cardiac failure. Importantly, there remains no effective cure for DMD. DMD is caused by defective expression of the DMD gene, which encodes for dystrophin, a component of the dystrophin glycoprotein complex. In muscle fibers, this protein complex plays a critical role in maintaining muscle membrane integrity. Emerging studies have shown that muscle stem cells, which are adult stem cells responsible for muscle repair, are also affected in DMD. DMD muscle stem cells do not function as healthy muscle stem cells, and their impairment contributes to disease progression. Deficiencies in muscle stem cell function include impaired establishment of cell polarity leading to defective asymmetric stem cell division, reduced myogenic commitment, impaired differentiation, altered metabolism, and enhanced entry into senescence. Altogether, these findings indicate that DMD muscle stem cells are dysfunctional and have impaired regenerative potential. Although recent advances in adeno-associated vector and antisense oligonucleotide-mediated mechanisms for gene therapy have shown clinical promise, the current therapeutic strategies for muscular dystrophy do not effectively target muscle stem cells and do not address the deficiencies in muscle stem cell function. Here, we discuss the merits of restoring endogenous muscle stem cell function in degenerating muscle as a viable regenerative medicine strategy to mitigate DMD.
Leg muscle ischemia in patients with peripheral artery disease (PAD) leads to alterations in skeletal muscle morphology and reduced leg strength. We tested the hypothesis that exposure to heat ...therapy (HT) would improve skeletal muscle function in a mouse model of ischemia-induced muscle damage. Male 42-wk-old C57Bl/6 mice underwent ligation of the femoral artery and were randomly assigned to receive HT (immersion in a water bath at 37°C, 39°C, or 41°C for 30 min) or a control intervention for 3 wk. At the end of the treatment, the animals were anesthetized and the soleus and extensor digitorum longus (EDL) muscles were harvested for the assessment of contractile function and examination of muscle morphology. A subset of animals was used to examine the impact of a single HT session on the expression of genes involved in myogenesis and the regulation of muscle mass. Relative soleus muscle mass was significantly higher in animals exposed to HT at 39°C compared with the control group (control: 0.36 ± 0.01 mg/g versus 39°C: 0.40 ± 0.01 mg/g,
= 0.024). Maximal absolute force of the soleus was also significantly higher in animals treated with HT at 37°C and 39°C (control: 274.7 ± 6.6 mN; 37°C: 300.1 ± 7.7 mN; 39°C: 299.5 ± 10 mN,
< 0.05). In the soleus, but not the EDL muscle, a single session of HT enhanced the mRNA expression of myogenic factors as well as of both positive and negative regulators of muscle mass. These findings suggest that the beneficial effects of HT are muscle specific and dependent on the treatment temperature in a model of PAD.
This is the first study to comprehensively examine the impact of temperature and muscle fiber type composition on the adaptations to repeated heat stress in a model of ischemia-induced muscle damage. Exposure to heat therapy (HT) at 37°C and 39°C, but not at 41°C, improved force development of the isolated soleus muscle. These results suggest that HT may be a practical therapeutic tool to restore muscle mass and strength in patients with peripheral artery disease.
Myocardial infarction (MI)-induced heart failure (HF) is commonly accompanied with profound effects on skeletal muscle. With the process of MI-induced HF, perturbations in skeletal muscle contribute ...to muscle atrophy. Exercise is viewed as a feasible strategy to prevent muscle atrophy. The aims of this study were to investigate whether exercise could alleviate MI-induced skeletal muscle atrophy via insulin-like growth factor 1 (IGF-1) pathway in mice. Male C57/BL6 mice were used to establish the MI model and were divided into three groups: sedentary MI group (MI), MI with aerobic exercise group, and MI with resistance exercise group; sham-operated group was used as control. Exercise-trained animals were subjected to 4 wk of aerobic exercise (AE) or resistance exercise (RE). Cardiac function, muscle weight, myofiber size, levels of IGF-1 signaling and proteins related to myogenesis, protein synthesis, and degradation and apoptosis in gastrocnemius muscle were detected. H
O
-treated C2C12 cells were intervened with recombinant human IGF-1, IGF-1 receptor (IGF-1R) inhibitor NVP-AEW541, and PI3K inhibitor LY294002 to explore the mechanism. Exercises upregulated the IGF-1/IGF-1R-phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling; increased the expressions of Pax7, myogenic regulatory factors (MRFs), and protein synthesis; and reduced protein degradation and cell apoptosis in MI mice. In vitro, IGF-1 upregulated the levels of Pax7, MRFs, mTOR, and P70S6K; reduced MuRF1 and MAFbx; and inhibited cell apoptosis via IGF-1R-PI3K/Akt pathway. AE and RE, safely and effectively, alleviate skeletal muscle atrophy by regulating the levels of myogenesis, protein degradation, and cell apoptosis in mice with MI via activating IGF-1/IGF-1R-PI3K/Akt signaling pathway.
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