RESUMO
The peroxisome proliferator-activated receptor γ coactivator-1α (Ppargc1a) gene encodes several PGC-1α isoforms that regulate mitochondrial bioenergetics and cellular adaptive processes. Expressing specific PGC-1α isoforms in mice can confer protection in different disease models. This SnapShot summarizes how regulation of Ppargc1a transcription, splicing, translation, protein stability, and activity underlies its multifaceted functions. To view this SnapShot, open or download the PDF.
Assuntos
Regulação da Expressão Gênica , Mitocôndrias , Animais , Biologia , Metabolismo Energético , Camundongos , Mitocôndrias/genética , Mitocôndrias/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/genética , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/metabolismo , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismoRESUMO
Depression is a debilitating condition with a profound impact on quality of life for millions of people worldwide. Physical exercise is used as a treatment strategy for many patients, but the mechanisms that underlie its beneficial effects remain unknown. Here, we describe a mechanism by which skeletal muscle PGC-1α1 induced by exercise training changes kynurenine metabolism and protects from stress-induced depression. Activation of the PGC-1α1-PPARα/δ pathway increases skeletal muscle expression of kynurenine aminotransferases, thus enhancing the conversion of kynurenine into kynurenic acid, a metabolite unable to cross the blood-brain barrier. Reducing plasma kynurenine protects the brain from stress-induced changes associated with depression and renders skeletal muscle-specific PGC-1α1 transgenic mice resistant to depression induced by chronic mild stress or direct kynurenine administration. This study opens therapeutic avenues for the treatment of depression by targeting the PGC-1α1-PPAR axis in skeletal muscle, without the need to cross the blood-brain barrier.
Assuntos
Depressão/prevenção & controle , Cinurenina/metabolismo , Músculo Esquelético/enzimologia , Estresse Psicológico/complicações , Fatores de Transcrição/metabolismo , Animais , Barreira Hematoencefálica , Depressão/metabolismo , Perfilação da Expressão Gênica , Humanos , Ácido Cinurênico , Camundongos , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/metabolismo , PPAR alfa/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Condicionamento Físico Animal , Condicionamento Físico Humano , Transaminases/metabolismo , Fatores de Transcrição/genéticaRESUMO
Exercise training benefits many organ systems and offers protection against metabolic disorders such as obesity and diabetes. Using the recently identified isoform of PGC1-α (PGC1-α4) as a discovery tool, we report the identification of meteorin-like (Metrnl), a circulating factor that is induced in muscle after exercise and in adipose tissue upon cold exposure. Increasing circulating levels of Metrnl stimulates energy expenditure and improves glucose tolerance and the expression of genes associated with beige fat thermogenesis and anti-inflammatory cytokines. Metrnl stimulates an eosinophil-dependent increase in IL-4 expression and promotes alternative activation of adipose tissue macrophages, which are required for the increased expression of the thermogenic and anti-inflammatory gene programs in fat. Importantly, blocking Metrnl actions in vivo significantly attenuates chronic cold-exposure-induced alternative macrophage activation and thermogenic gene responses. Thus, Metrnl links host-adaptive responses to the regulation of energy homeostasis and tissue inflammation and has therapeutic potential for metabolic and inflammatory diseases.
Assuntos
Tecido Adiposo Marrom/metabolismo , Fatores de Crescimento Neural/metabolismo , Animais , Glucose/metabolismo , Interleucina-13/metabolismo , Interleucina-4/metabolismo , Fígado/metabolismo , Macrófagos/metabolismo , Camundongos , Camundongos Transgênicos , Músculo Esquelético/metabolismo , Fatores de Crescimento Neural/genética , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Termogênese , Fatores de Transcrição/genéticaRESUMO
PGC-1α is a transcriptional coactivator induced by exercise that gives muscle many of the best known adaptations to endurance-type exercise but has no effects on muscle strength or hypertrophy. We have identified a form of PGC-1α (PGC-1α4) that results from alternative promoter usage and splicing of the primary transcript. PGC-1α4 is highly expressed in exercised muscle but does not regulate most known PGC-1α targets such as the mitochondrial OXPHOS genes. Rather, it specifically induces IGF1 and represses myostatin, and expression of PGC-1α4 in vitro and in vivo induces robust skeletal muscle hypertrophy. Importantly, mice with skeletal muscle-specific transgenic expression of PGC-1α4 show increased muscle mass and strength and dramatic resistance to the muscle wasting of cancer cachexia. Expression of PGC-1α4 is preferentially induced in mouse and human muscle during resistance exercise. These studies identify a PGC-1α protein that regulates and coordinates factors involved in skeletal muscle hypertrophy.
Assuntos
Proteínas de Choque Térmico/metabolismo , Músculo Esquelético/metabolismo , Condicionamento Físico Animal , Treinamento Resistido , Transativadores/metabolismo , Fatores de Transcrição/metabolismo , Adiposidade , Animais , Glucose/metabolismo , Humanos , Hipertrofia , Fator de Crescimento Insulin-Like I/metabolismo , Camundongos , Camundongos Transgênicos , Dados de Sequência Molecular , Fibras Musculares Esqueléticas/metabolismo , Miostatina/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Isoformas de Proteínas/metabolismoRESUMO
Skeletal muscle atrophy is a morbidity and mortality risk factor that happens with disuse, chronic disease, and aging. The tissue remodeling that happens during recovery from atrophy or injury involves changes in different cell types such as muscle fibers, and satellite and immune cells. Here, we show that the previously uncharacterized gene and protein Zfp697 is a damage-induced regulator of muscle remodeling. Zfp697/ZNF697 expression is transiently elevated during recovery from muscle atrophy or injury in mice and humans. Sustained Zfp697 expression in mouse muscle leads to a gene expression signature of chemokine secretion, immune cell recruitment, and extracellular matrix remodeling. Notably, although Zfp697 is expressed in several cell types in skeletal muscle, myofiber-specific Zfp697 genetic ablation in mice is sufficient to hinder the inflammatory and regenerative response to muscle injury, compromising functional recovery. We show that Zfp697 is an essential mediator of the interferon gamma response in muscle cells and that it functions primarily as an RNA-interacting protein, with a very high number of miRNA targets. This work identifies Zfp697 as an integrator of cell-cell communication necessary for tissue remodeling and regeneration.
Assuntos
Músculo Esquelético , Proteínas de Ligação a RNA , Animais , Camundongos , Músculo Esquelético/metabolismo , Músculo Esquelético/patologia , Proteínas de Ligação a RNA/metabolismo , Proteínas de Ligação a RNA/genética , Humanos , Inflamação/metabolismo , Inflamação/patologia , Inflamação/genética , Camundongos Knockout , Atrofia Muscular/metabolismo , Atrofia Muscular/genética , Atrofia Muscular/patologia , MicroRNAs/genética , MicroRNAs/metabolismo , Camundongos Endogâmicos C57BL , Interferon gama/metabolismoRESUMO
Within the intestine, the human G protein-coupled receptor (GPCR) GPR35 is involved in oncogenic signaling, bacterial infections, and inflammatory bowel disease. GPR35 is known to be expressed as two distinct isoforms that differ only in the length of their extracellular N-termini by 31 amino acids, but detailed insights into their functional differences are lacking. Through gene expression analysis in immune and gastrointestinal cells, we show that these isoforms emerge from distinct promoter usage and alternative splicing. Additionally, we employed optical assays in living cells to thoroughly profile both GPR35 isoforms for constitutive and ligand-induced activation and signaling of 10 different heterotrimeric G proteins, ligand-induced arrestin recruitment, and receptor internalization. Our results reveal that the extended N-terminus of the long isoform limits G protein activation yet elevates receptor-ß-arrestin interaction. To better understand the structural basis for this bias, we examined structural models of GPR35 and conducted experiments with mutants of both isoforms. We found that a proposed disulfide bridge between the N-terminus and extracellular loop 3, present in both isoforms, is crucial for constitutive G13 activation, while an additional cysteine contributed by the extended N-terminus of the long GPR35 isoform limits the extent of agonist-induced receptor-ß-arrestin2 interaction. The pharmacological profiles and mechanistic insights of our study provide clues for the future design of isoform-specific GPR35 ligands that selectively modulate GPR35-transducer interactions and allow for mechanism-based therapies against, for example, inflammatory bowel disease or bacterial infections of the gastrointestinal system.
Assuntos
Receptores Acoplados a Proteínas G , Regulação Alostérica , Cisteína/química , Dissulfetos/química , Proteínas de Ligação ao GTP/química , Humanos , Doenças Inflamatórias Intestinais/metabolismo , Ligantes , Isoformas de Proteínas/química , Isoformas de Proteínas/metabolismo , Receptores Acoplados a Proteínas G/química , Receptores Acoplados a Proteínas G/metabolismo , beta-Arrestinas/metabolismoRESUMO
Skeletal muscle cells contain hundreds of myonuclei within a shared cytoplasm, presenting unique challenges for regulating gene expression. Certain transcriptional programs (e.g., postsynaptic machinery) are segregated to specialized domains, while others (e.g., contractile proteins) do not show spatial confinement. Furthermore, local stimuli, such as denervation, can induce transcriptional responses that are propagated along the muscle cells. Regulated transport of nuclear proteins (e.g., transcription factors) between myonuclei represents a potential mechanism for coordinating gene expression. However, the principles underlying the transport of nuclear proteins within multinucleated cells remain poorly defined. Here we used a mosaic transfection model to create myotubes that contained exactly one myonucleus expressing a fluorescent nuclear reporter and monitored its distribution among all myonuclei. We found that the transport properties of these model nuclear proteins in myotubes depended on molecular weight and nuclear import rate, as well as on myotube width. Interestingly, muscle hypertrophy increased the transport of high molecular weight nuclear proteins, while atrophy restricted the transport of smaller nuclear proteins. We have developed a mathematical model of nuclear protein transport within a myotube that recapitulates the results of our in vitro experiments. To test the relevance to nuclear proteins expressed in skeletal muscle, we studied the transport of two transcription factors-aryl hydrocarbon receptor nuclear translocator and sine oculis homeobox 1-and found that their distributions were similar to the reporter proteins with corresponding molecular weights. Together, these results define a set of variables that can be used to predict the spatial distributions of nuclear proteins within a myotube.
Assuntos
Músculo Esquelético/metabolismo , Mioblastos/metabolismo , Proteínas Nucleares/metabolismo , Animais , Células Cultivadas , Proteínas de Homeodomínio/química , Proteínas de Homeodomínio/metabolismo , Cinética , Camundongos , Fibras Musculares Esqueléticas/química , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/química , Mioblastos/química , Proteínas Nucleares/química , Transporte Proteico , Receptores de Hidrocarboneto Arílico/química , Receptores de Hidrocarboneto Arílico/metabolismoRESUMO
BACKGROUND: Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) acts as a transcriptional coactivator and regulates mitochondrial function. Various isoforms are generated by alternative splicing and differentially regulated promoters. In the heart, total PGC-1α deficiency knockout leads to dilatative cardiomyopathy, but knowledge on the complexity of cardiac isoform expression of PGC-1α remains sparse. Thus, this study aims to generate a reliable dataset on cardiac isoform expression pattern by long-read mRNA sequencing, followed by investigation of differential regulation of PGC-1α isoforms under metabolic and ischemic stress, using high-fat-high-sucrose-diet-induced obesity and a murine model of myocardial infarction. RESULTS: Murine (C57Bl/6J) or human heart tissue (obtained during LVAD-surgery) was used for long-read mRNA sequencing, resulting in full-length transcriptomes including 58,000 mRNA isoforms with 99% sequence accuracy. Automatic bioinformatic analysis as well as manual similarity search against exonic sequences leads to identification of putative coding PGC-1α isoforms, validated by PCR and Sanger sequencing. Thereby, 12 novel transcripts generated by hitherto unknown splicing events were detected. In addition, we postulate a novel promoter with homologous and strongly conserved sequence in human heart. High-fat diet as well as ischemia/reperfusion (I/R) injury transiently reduced cardiac expression of PGC-1α isoforms, with the most pronounced effect in the infarcted area. Recovery of PGC-1α-isoform expression was even more decelerated when I/R was performed in diet-induced obese mice. CONCLUSIONS: We deciphered for the first time a complete full-length transcriptome of the murine and human heart, identifying novel putative PGC-1α coding transcripts including a novel promoter. These transcripts are differentially regulated in I/R and obesity suggesting transcriptional regulation and alternative splicing that may modulate PGC-1α function in the injured and metabolically challenged heart.
Assuntos
Isquemia Miocárdica , Transcriptoma , Processamento Alternativo , Animais , Humanos , Camundongos , Isquemia Miocárdica/genética , Obesidade/genética , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/genética , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/metabolismo , Isoformas de Proteínas/genética , RNA Mensageiro/metabolismoRESUMO
Administration of branched-chain amino acids (BCAA) has been suggested to enhance mitochondrial biogenesis, including levels of PGC-1α, which may, in turn, alter kynurenine metabolism. Ten healthy subjects performed 60 min of dynamic one-leg exercise at â¼70% of Wmax on two occasions. They were in random order supplied either a mixture of BCAA or flavored water (placebo) during the experiment. Blood samples were collected during exercise and recovery, and muscle biopsies were taken from both legs before, after, and 90 and 180 min following exercise. Ingestion of BCAA doubled their concentration in both plasma and muscle while causing a 30%-40% reduction (P < 0.05 vs. placebo) in levels of aromatic amino acids in both resting and exercising muscle during 3-h recovery period. The muscle concentration of kynurenine decreased by 25% (P < 0.05) during recovery, similar in both resting and exercising leg and with both supplements, although plasma concentration of kynurenine during recovery was 10% lower (P < 0.05) when BCAA were ingested. Ingestion of BCAA reduced the plasma concentration of kynurenic acid by 60% (P < 0.01) during exercise and recovery, whereas the level remained unchanged with placebo. Exercise induced a three- to fourfold increase (P < 0.05) in muscle content of PGC-1α1 mRNA after 90 min of recovery under both conditions, whereas levels of KAT4 mRNA and protein were unaffected by exercise or supplement. In conclusion, the reduction of plasma levels of kynurenine and kynurenic acid caused by BCAA were not associated with any changes in the level of muscle kynurenine, suggesting that kynurenine metabolism was altered in tissues other than muscle.
Assuntos
Aminoácidos de Cadeia Ramificada/administração & dosagem , Exercício Físico/fisiologia , Cinurenina/sangue , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Consumo de Oxigênio/efeitos dos fármacos , Adulto , Feminino , Humanos , Cinurenina/metabolismo , Masculino , Consumo de Oxigênio/fisiologia , Adulto JovemRESUMO
The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD+ levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ectopically expressed NDUFA4L2 caused a ~20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD+ , which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.
Assuntos
Complexo I de Transporte de Elétrons/metabolismo , Hipóxia/fisiopatologia , Mitocôndrias/metabolismo , Músculo Esquelético/patologia , Atrofia Muscular/patologia , Animais , Proliferação de Células , Complexo I de Transporte de Elétrons/genética , Feminino , Camundongos , Camundongos Endogâmicos C57BL , Músculo Esquelético/metabolismo , Atrofia Muscular/metabolismo , Espécies Reativas de OxigênioRESUMO
BACKGROUND: Mitochondrial dysfunction is a common feature of aging, neurodegeneration, and metabolic diseases. Hence, mitotherapeutics may be valuable disease modifiers for a large number of conditions. In this study, we have set up a large-scale screening platform for mitochondrial-based modulators with promising therapeutic potential. RESULTS: Using differentiated human neuroblastoma cells, we screened 1200 FDA-approved compounds and identified 61 molecules that significantly increased cellular ATP without any cytotoxic effect. Following dose response curve-dependent selection, we identified the flavonoid luteolin as a primary hit. Further validation in neuronal models indicated that luteolin increased mitochondrial respiration in primary neurons, despite not affecting mitochondrial mass, structure, or mitochondria-derived reactive oxygen species. However, we found that luteolin increased contacts between mitochondria and endoplasmic reticulum (ER), contributing to increased mitochondrial calcium (Ca2+) and Ca2+-dependent pyruvate dehydrogenase activity. This signaling pathway likely contributed to the observed effect of luteolin on enhanced mitochondrial complexes I and II activities. Importantly, we observed that increased mitochondrial functions were dependent on the activity of ER Ca2+-releasing channels inositol 1,4,5-trisphosphate receptors (IP3Rs) both in neurons and in isolated synaptosomes. Additionally, luteolin treatment improved mitochondrial and locomotory activities in primary neurons and Caenorhabditis elegans expressing an expanded polyglutamine tract of the huntingtin protein. CONCLUSION: We provide a new screening platform for drug discovery validated in vitro and ex vivo. In addition, we describe a novel mechanism through which luteolin modulates mitochondrial activity in neuronal models with potential therapeutic validity for treatment of a variety of human diseases.
Assuntos
Retículo Endoplasmático/efeitos dos fármacos , Luteolina/farmacologia , Mitocôndrias/efeitos dos fármacos , Neurônios/metabolismo , Animais , Linhagem Celular Tumoral , Avaliação Pré-Clínica de Medicamentos , Retículo Endoplasmático/metabolismo , Ensaios de Triagem em Larga Escala , Humanos , Camundongos , Mitocôndrias/metabolismo , Neurônios/efeitos dos fármacos , Transdução de SinaisRESUMO
Microfluidic-based technologies enable the development of cell culture systems that provide tailored microenvironmental inputs to mammalian cells. Primary myoblasts can be induced to differentiate into multinucleated skeletal muscle cells, myotubes, which are a relevant model system for investigating skeletal muscle metabolism and physiology in vitro. However, it remains challenging to differentiate primary myoblasts into mature myotubes in microfluidics devices. Here we investigated the effects of integrating continuous (solid) and intermittent (dashed) walls in microfluidic channels as topological constraints in devices designed to promote the alignment and maturation of primary myoblast-derived myotubes. The topological constraints caused alignment of the differentiated myotubes, mimicking the native anisotropic organization of skeletal muscle cells. Interestingly, dashed walls facilitated the maturation of skeletal muscle cells, as measured by quantifying myotube cell area and the number of nuclei per myotube. Together, our results suggest that integrating dashed walls as topographic constraints in microfluidic devices supports the alignment and maturation of primary myoblast-derived myotubes.
Assuntos
Dispositivos Lab-On-A-Chip , Fibras Musculares Esqueléticas/citologia , Mioblastos/citologia , Animais , Diferenciação Celular , Células Cultivadas , Camundongos , Músculo Esquelético/citologiaRESUMO
Tryptophan catabolism through the kynurenine pathway generates a variety of bioactive metabolites. Physical exercise can modulate kynurenine pathway metabolism in skeletal muscle and thus change the concentrations of select compounds in peripheral tissues and in the central nervous system. Here we review recent advances in our understanding of how exercise alters tryptophan-kynurenine metabolism in muscle and its subsequent local and distal effects. We propose that the effects of kynurenine pathway metabolites on skeletal muscle, adipose tissue, immune system, and the brain suggest that some of these compounds could qualify as exercise-induced myokines. Indeed, some of the more recently discovered biological activities for kynurenines include many of the best-known benefits of exercise: improved energy homeostasis, promotion of an anti-inflammatory environment, and neuroprotection. Finally, by considering the tissue expression of the different membrane and cytosolic receptors for kynurenines, we discuss known and potential biological activities for these tryptophan metabolites.
Assuntos
Sistema Nervoso Central/metabolismo , Cinurenina/metabolismo , Redes e Vias Metabólicas/fisiologia , Músculo Esquelético/metabolismo , Encéfalo/metabolismo , Encéfalo/fisiologia , Sistema Nervoso Central/fisiologia , Exercício Físico/fisiologia , Homeostase/genética , Homeostase/fisiologia , Humanos , Sistema Imunitário/metabolismo , Sistema Imunitário/fisiologia , Cinurenina/genética , Metabolismo/fisiologia , Músculo Esquelético/fisiologia , PPAR gama/genética , Triptofano/metabolismoRESUMO
PGC-1α is a transcriptional coactivator that powerfully regulates many pathways linked to energy homeostasis. Specifically, PGC-1α controls mitochondrial biogenesis in most tissues but also initiates important tissue-specific functions, including fiber type switching in skeletal muscle and gluconeogenesis and fatty acid oxidation in the liver. We show here that S6 kinase, activated in the liver upon feeding, can phosphorylate PGC-1α directly on two sites within its arginine/serine-rich (RS) domain. This phosphorylation significantly attenuates the ability of PGC-1α to turn on genes of gluconeogenesis in cultured hepatocytes and in vivo, while leaving the functions of PGC-1α as an activator of mitochondrial and fatty acid oxidation genes completely intact. These phosphorylations interfere with the ability of PGC-1α to bind to HNF4α, a transcription factor required for gluconeogenesis, while leaving undisturbed the interactions of PGC-1α with ERRα and PPARα, factors important for mitochondrial biogenesis and fatty acid oxidation. These data illustrate that S6 kinase can modify PGC-1α and thus allow molecular dissection of its functions, providing metabolic flexibility needed for dietary adaptation.
Assuntos
Gluconeogênese/fisiologia , Mitocôndrias/metabolismo , Proteínas Quinases S6 Ribossômicas/metabolismo , Fatores de Transcrição/metabolismo , Animais , Linhagem Celular , Células HEK293 , Humanos , Camundongos , Camundongos Endogâmicos BALB CRESUMO
Cancer-cachexia (CC) is a wasting condition directly responsible for 20-40% of cancer-related deaths. The mechanisms controlling development of CC-induced muscle wasting are not fully elucidated. Most investigations focus on the postcachectic state and do not examine progression of the condition. We recently demonstrated mitochondrial degenerations precede muscle wasting in time course progression of CC. However, the extent of muscle perturbations before wasting in CC is unknown. Therefore, we performed global gene expression analysis in CC-induced muscle wasting to enhance understanding of intramuscular perturbations across the development of CC. Lewis lung carcinoma (LLC) was injected into the hind-flank of C57BL6/J mice at 8 wk of age with tumor allowed to develop for 1, 2, 3, or 4 wk and compared with PBS-injected control. Muscle wasting was evident at 4 wk LLC. RNA sequencing of gastrocnemius muscle samples showed widespread alterations in LLC compared with PBS animals with largest differences seen in 4 wk LLC, suggesting extensive transcriptomic alterations concurrent to muscle wasting. Commonly altered pathways included: mitochondrial dysfunction and protein ubiquitination, along with other less studied processes in this condition regulating transcription/translation and cytoskeletal structure. Current findings present novel evidence of transcriptomic shifts and altered cellular pathways in CC-induced muscle wasting.
Assuntos
Caquexia/genética , Fibras Musculares Esqueléticas/patologia , Atrofia Muscular/genética , Transcriptoma/genética , Animais , Caquexia/patologia , Carcinoma Pulmonar de Lewis/genética , Carcinoma Pulmonar de Lewis/patologia , Progressão da Doença , Perfilação da Expressão Gênica/métodos , Camundongos , Camundongos Endogâmicos C57BL , Mitocôndrias/genética , Mitocôndrias/patologia , Atrofia Muscular/patologiaRESUMO
High-intensity interval training (HIIT) is a time-efficient way of improving physical performance in healthy subjects and in patients with common chronic diseases, but less so in elite endurance athletes. The mechanisms underlying the effectiveness of HIIT are uncertain. Here, recreationally active human subjects performed highly demanding HIIT consisting of 30-s bouts of all-out cycling with 4-min rest in between bouts (≤3 min total exercise time). Skeletal muscle biopsies taken 24 h after the HIIT exercise showed an extensive fragmentation of the sarcoplasmic reticulum (SR) Ca(2+) release channel, the ryanodine receptor type 1 (RyR1). The HIIT exercise also caused a prolonged force depression and triggered major changes in the expression of genes related to endurance exercise. Subsequent experiments on elite endurance athletes performing the same HIIT exercise showed no RyR1 fragmentation or prolonged changes in the expression of endurance-related genes. Finally, mechanistic experiments performed on isolated mouse muscles exposed to HIIT-mimicking stimulation showed reactive oxygen/nitrogen species (ROS)-dependent RyR1 fragmentation, calpain activation, increased SR Ca(2+) leak at rest, and depressed force production due to impaired SR Ca(2+) release upon stimulation. In conclusion, HIIT exercise induces a ROS-dependent RyR1 fragmentation in muscles of recreationally active subjects, and the resulting changes in muscle fiber Ca(2+)-handling trigger muscular adaptations. However, the same HIIT exercise does not cause RyR1 fragmentation in muscles of elite endurance athletes, which may explain why HIIT is less effective in this group.
Assuntos
Cálcio/metabolismo , Exercício Físico/fisiologia , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Retículo Sarcoplasmático/metabolismo , Adulto , Animais , Atletas , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Fibras Musculares Esqueléticas/fisiologia , Resistência Física , Espécies Reativas de Oxigênio/metabolismo , RecreaçãoRESUMO
Endurance and resistance exercise training induces specific and profound changes in the skeletal muscle transcriptome. Peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α) coactivators are not only among the genes differentially induced by distinct training methods, but they also participate in the ensuing signaling cascades that allow skeletal muscle to adapt to each type of exercise. Although endurance training preferentially induces PGC-1α1 expression, resistance exercise activates the expression of PGC-1α2, -α3, and -α4. These three alternative PGC-1α isoforms lack the arginine/serine-rich (RS) and RNA recognition motifs characteristic of PGC-1α1. Discrete functions for PGC-1α1 and -α4 have been described, but the biological role of PGC-1α2 and -α3 remains elusive. Here we show that different PGC-1α variants can affect target gene splicing through diverse mechanisms, including alternative promoter usage. By analyzing the exon structure of the target transcripts for each PGC-1α isoform, we were able to identify a large number of previously unknown PGC-1α2 and -α3 target genes and pathways in skeletal muscle. In particular, PGC-1α2 seems to mediate a decrease in the levels of cholesterol synthesis genes. Our results suggest that the conservation of the N-terminal activation and repression domains (and not the RS/RNA recognition motif) is what determines the gene programs and splicing options modulated by each PGC-1α isoform. By using skeletal muscle-specific transgenic mice for PGC-1α1 and -α4, we could validate, in vivo, splicing events observed in in vitro studies. These results show that alternative PGC-1α variants can affect target gene expression both quantitatively and qualitatively and identify novel biological pathways under the control of this system of coactivators.
Assuntos
Processamento Alternativo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/metabolismo , Animais , Células Cultivadas , Sequência Conservada , Éxons , Regulação da Expressão Gênica , Redes Reguladoras de Genes , Camundongos , Camundongos Transgênicos , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/química , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo/genética , Regiões Promotoras Genéticas , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Estabilidade Proteica , Receptores de Esteroides/química , Receptores de Esteroides/genética , Receptores de Esteroides/metabolismoRESUMO
Peroxisome proliferator-activated receptor gamma coactivator 1-alpha 4 (PGC-1α4) is a protein isoform derived by alternative splicing of the PGC1α mRNA and has been shown to promote muscle hypertrophy. We show here that G protein-coupled receptor 56 (GPR56) is a transcriptional target of PGC-1α4 and is induced in humans by resistance exercise. Furthermore, the anabolic effects of PGC-1α4 in cultured murine muscle cells are dependent on GPR56 signaling, because knockdown of GPR56 attenuates PGC-1α4-induced muscle hypertrophy in vitro. Forced expression of GPR56 results in myotube hypertrophy through the expression of insulin-like growth factor 1, which is dependent on Gα12/13 signaling. A murine model of overload-induced muscle hypertrophy is associated with increased expression of both GPR56 and its ligand collagen type III, whereas genetic ablation of GPR56 expression attenuates overload-induced muscle hypertrophy and associated anabolic signaling. These data illustrate a signaling pathway through GPR56 which regulates muscle hypertrophy associated with resistance/loading-type exercise.
Assuntos
Regulação da Expressão Gênica/fisiologia , Fibras Musculares Esqueléticas/metabolismo , Proteínas Musculares/metabolismo , Condicionamento Físico Animal , Receptores Acoplados a Proteínas G/biossíntese , Transdução de Sinais/fisiologia , Animais , Colágeno Tipo III/biossíntese , Hipertrofia/metabolismo , Fator de Crescimento Insulin-Like I/biossíntese , Masculino , Camundongos , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Fatores de Transcrição/metabolismoRESUMO
Physical exercise has emerged as an alternative treatment for patients with depressive disorder. Recent animal studies show that exercise protects from depression by increased skeletal muscle kynurenine aminotransferase (KAT) expression which shifts the kynurenine metabolism away from the neurotoxic kynurenine (KYN) to the production of kynurenic acid (KYNA). In the present study, we investigated the effect of exercise on kynurenine metabolism in humans. KAT gene and protein expression was increased in the muscles of endurance-trained subjects compared with untrained subjects. Endurance exercise caused an increase in plasma KYNA within the first hour after exercise. In contrast, a bout of high-intensity eccentric exercise did not lead to increased plasma KYNA concentration. Our results show that regular endurance exercise causes adaptations in kynurenine metabolism which can have implications for exercise recommendations for patients with depressive disorder.
Assuntos
Exercício Físico/fisiologia , Ácido Cinurênico/sangue , Músculo Esquelético/fisiologia , Condicionamento Físico Humano/fisiologia , Resistência Física/fisiologia , Transaminases/metabolismo , Humanos , Masculino , Condicionamento Físico Humano/métodos , Regulação para Cima/fisiologia , Adulto JovemRESUMO
KEY POINTS: Transcriptional co-activator PGC-1α1 has been shown to regulate energy metabolism and to mediate metabolic adaptations in pathological and physiological cardiac hypertrophy but other functional implications of PGC-1α1 expression are not known. Transgenic PGC-1α1 overexpression within the physiological range in mouse heart induces purposive changes in contractile properties, electrophysiology and calcium signalling but does not induce substantial metabolic remodelling. The phenotype of the PGC-1α1 transgenic mouse heart recapitulates most of the functional modifications usually associated with the exercise-induced heart phenotype, but does not protect the heart against load-induced pathological hypertrophy. Transcriptional effects of PGC-1α1 show clear dose-dependence with diverse changes in genes in circadian clock, heat shock, excitability, calcium signalling and contraction pathways at low overexpression levels, while metabolic genes are recruited at much higher PGC-1α1 expression levels. These results imply that the physiological role of PGC-1α1 is to promote a beneficial excitation-contraction coupling phenotype in the heart. ABSTRACT: The transcriptional coactivator PGC-1α1 has been identified as a central factor mediating metabolic adaptations of the heart. However, to what extent physiological changes in PGC-1α1 expression levels actually contribute to the functional adaptation of the heart is still mostly unresolved. The aim of this study was to characterize the transcriptional and functional effects of physiologically relevant, moderate PGC-1α1 expression in the heart. In vivo and ex vivo physiological analysis shows that expression of PGC-1α1 within a physiological range in mouse heart does not induce the expected metabolic alterations, but instead induces a unique excitation-contraction (EC) coupling phenotype recapitulating features typically seen in physiological hypertrophy. Transcriptional screening of PGC-1α1 overexpressing mouse heart and myocyte cultures with higher, acute adenovirus-induced PGC-1α1 expression, highlights PGC-1α1 as a transcriptional coactivator with a number of binding partners in various pathways (such as heat shock factors and the circadian clock) through which it acts as a pleiotropic transcriptional regulator in the heart, to both augment and repress the expression of its target genes in a dose-dependent fashion. At low levels of overexpression PGC-1α1 elicits a diverse transcriptional response altering the expression state of circadian clock, heat shock, excitability, calcium signalling and contraction pathways, while metabolic targets of PGC-1α1 are recruited at higher PGC-1α1 expression levels. Together these findings demonstrate that PGC-1α1 elicits a dual effect on cardiac transcription and phenotype. Further, our results imply that the physiological role of PGC-1α1 is to promote a beneficial EC coupling phenotype in the heart.