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J Anim Sci ; 98(11)2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33259597


Feeding ractopamine (RAC), a ß-adrenergic agonist (BAA), to pigs increases type IIB muscle fiber type-specific protein and mRNA expression. However, increases in the abundance of these fast-twitch fiber types occur with other forms of muscle hypertrophy and thus BAA-induced changes in myosin heavy chain (MyHC) composition may simply be associated with increased muscle growth known to occur in response to BAA feeding. The objective of this study was to determine whether RAC feeding could change the MyHC gene expression in the absence of maximal muscle growth. Pigs were fed either an adequate diet that supported maximal muscle hypertrophy or a low nutrient diet that limited muscle growth. RAC was included in diets at 0 or 20 mg/kg for 1, 2, or 4 wk. Backfat depth was less (P < 0.05) in pigs fed the low nutrient diet compared with the adequate diet but was not affected by RAC. Loin eye area was greater (P < 0.05) in pigs fed an adequate diet plus RAC at 1 wk but did not differ among remaining pigs. At 2 and 4 wk, however, pigs fed the adequate diet had greater loin eye areas (P < 0.05) than pigs fed the low nutrient diet regardless of RAC feeding. Gene expression of the MyHC isoforms, I, IIA, IIX, and IIB, as well as glycogen synthase, citrate synthase, ß 1-adrenergic receptor (AR), and ß 2-AR were determined in longissimus dorsi (LD) and red (RST) and white (WST) portions of the semitendinosus muscles. MyHC type I gene expression was not altered by RAC or diet. Feeding RAC decreased (P < 0.01) MyHC type IIA gene expression in all muscles, but to a greater extent in WST and LD. MyHC type IIX gene expression was lower (P < 0.05) in WST and LD muscles in response to RAC but was not altered in RST muscles. RAC increased (P < 0.05) MyHC type IIB gene expression in all muscles, but to a greater extent in RST. ß 1-AR gene expression was unaffected by RAC or diet, whereas the expression of the ß 2-AR gene was decreased (P < 0.001) by RAC. No significant RAC * diet interactions were observed in gene expression in this study, indicating that RAC altered MyHC and ß 2-AR gene expression in porcine skeletal muscles independent of growth.

Músculo Esquelético , Fenetilaminas , Animais , Expressão Gênica , Cadeias Pesadas de Miosina/genética , Fenetilaminas/farmacologia , Suínos
Dev Biol ; 402(1): 72-80, 2015 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-25794679


Each skeletal muscle contains a fixed ratio of fast and slow myofibers that are distributed in a stereotyped pattern to achieve a specific motor function. How myofibers are specified during development and regeneration is poorly understood. Here we address this question using transgenic reporter mice that indelibly mark the myofiber lineages based on activation of fast or slow myosin. Lineage tracing indicates that during development all muscles have activated the fast myosin gene Myl1, but not the slow myosin gene Myh7, which is activated in all slow but a subset of fast myofibers. Similarly, most nascent myofibers do not activate Myh7 during fast muscle regeneration, but the ratio and pattern of fast and slow myofibers are restored at the completion of regeneration. At the single myofiber level, most mature fast myofibers are heterogeneous in nuclear composition, manifested by mosaic activation of Myh7. Strikingly, Myh7 is activated in a subpopulation of proliferating myoblasts that co-express the myogenic progenitor marker Pax7. When induced to differentiate, the Myh7-activated myoblasts differentiate more readily than the non-activated myoblasts, and have a higher tendency, but not restricted, to become slow myotubes. Together, our data reveal significant nuclear heterogeneity within a single myofiber, and challenge the conventional view that myosin genes are only expressed after myogenic differentiation. These results provide novel insights into the regulation of muscle fiber type specification.

Regulação da Expressão Gênica no Desenvolvimento , Fibras Musculares de Contração Lenta/metabolismo , Músculos/citologia , Músculos/metabolismo , Mioblastos/citologia , Cadeias Pesadas de Miosina/metabolismo , Animais , Cardiotoxinas/química , Diferenciação Celular , Núcleo Celular/metabolismo , Separação Celular , Células Cultivadas , Citometria de Fluxo , Genes Reporter , Proteínas de Fluorescência Verde/metabolismo , Camundongos , Camundongos Transgênicos , Músculo Esquelético/metabolismo , Músculos/patologia , Miosinas/química , Fator de Transcrição PAX7/metabolismo , Regeneração , Células Satélites de Músculo Esquelético/citologia
Anim Sci J ; 81(5): 586-93, 2010 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-20887312


Our objective was to determine sensitivity of myostatin null (MN) mice to obesity induction by dietary or genetic means. To induce dietary obesity, 3-week-old wild type (WT) and MN mice were fed diets with 60% calories (HF) or 10% calories from fat (LF) for 4 weeks. MN mice did gain body fat on the HF diet but to a lesser extent than WT mice. Body weight and fat content was similar in MN mice fed HF and LF diets. To induce genetic obesity, the MN mutation was incorporated into leptin db/db (DB) mice generating mice homozygous for each mutation (MNDB). Nine-week-old MNDB mice were obese, similar to DB mice. Body weight, body fat content, fat pad weight and adipocyte size were all increased in MNDB mice compared to MN and WT mice and were quite similar to DB mice. However, fasting blood glucose, an indicator of insulin resistance and diabetes, was reduced in MNDB mice compared to DB mice. These results indicate that MN mice gain less body fat than WT on a HF diet, but the MN mutation does not alter fat accumulation caused by DB mutation. Thus, MN mice are not always resistant to obesity development.

Miostatina/deficiência , Obesidade/etiologia , Obesidade/genética , Animais , Dieta , Gorduras na Dieta/administração & dosagem , Camundongos , Camundongos Knockout
Am J Physiol Cell Physiol ; 296(5): C1040-8, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19295173


The signal transduction cascades that maintain muscle mass remain to be fully defined. Herein, we report that inhibition of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling in vitro decreases myotube size and protein content after 3-day treatment with a MEK inhibitor. Neither p38 nor JNK inhibitors had any effect on myotube size or morphology. ERK1/2 inhibition also upregulated gene transcription of atrogin-1 and muscle-specific RING finger protein 1 and downregulated the phosphorylation of Akt and its downstream kinases. Forced expression of enhanced green fluorescent protein-tagged MAPK phosphatase 1 (MKP-1) in soleus and gastrocnemius muscles decreased both fiber size and reporter activity. This atrophic effect of MKP-1 was time dependent. Analysis of the reporter activity in vivo revealed that the activities of nuclear factor-kappaB and 26S proteasome were differentially activated in slow and fast muscles, suggesting muscle type-specific mechanisms may be utilized. Together, these findings suggest that MAPK signaling is necessary for the maintenance of skeletal muscle mass because inhibition of these signaling cascades elicits muscle atrophy in vitro and in vivo.

Sistema de Sinalização das MAP Quinases/fisiologia , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Músculo Esquelético/metabolismo , Atrofia Muscular/metabolismo , Animais , Células Cultivadas , Fosfatase 1 de Especificidade Dupla/metabolismo , Genes Reporter , Masculino , Proteína Quinase 1 Ativada por Mitógeno/genética , Proteína Quinase 3 Ativada por Mitógeno/genética , Fibras Musculares de Contração Rápida/enzimologia , Fibras Musculares de Contração Rápida/patologia , Fibras Musculares de Contração Lenta/enzimologia , Fibras Musculares de Contração Lenta/patologia , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Músculo Esquelético/patologia , Atrofia Muscular/patologia , NF-kappa B/metabolismo , Fosforilação/fisiologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Ratos , Ratos Sprague-Dawley , Proteínas Ligases SKP Culina F-Box/genética , Proteínas Ligases SKP Culina F-Box/metabolismo , Proteínas com Motivo Tripartido , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo
FASEB J ; 22(8): 2990-3000, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18417546


Skeletal muscle is composed of diverse fiber types, yet the underlying molecular mechanisms responsible for this diversification remain unclear. Herein, we report that the extracellular signal-regulated kinase (ERK) 1/2 pathway, but not p38 or c-Jun NH(2)-terminal kinase (JNK), is preferentially activated in fast-twitch muscles. Pharmacological blocking of ERK1/2 pathway increased slow-twitch fiber type-specific reporter activity and repressed those associated with the fast-twitch fiber phenotype in vitro. Overexpression of a constitutively active ERK2 had an opposite effect. Inhibition of ERK signaling in cultured myotubes increased slow-twitch fiber-specific protein accumulation while repressing those characteristic of fast-twitch fibers. Overexpression of MAP kinase phosphatase-1 (MKP1) in mouse and rat muscle fibers containing almost exclusively type IIb or IIx fast myosin heavy chain (MyHC) isoforms induced de novo synthesis of the slower, more oxidative type IIa and I MyHCs in a time-dependent manner. Conversion to the slower phenotype was confirmed by up-regulation of slow reporter gene activity and down-regulation of fast reporter activities in response to forced MKP1 expression in vivo. In addition, activation of ERK2 signaling induced up-regulation of fast-twitch fiber program in soleus. These data suggest that the MAPK signaling, most likely the ERK1/2 pathway, is necessary to preserve the fast-twitch fiber phenotype with a concomitant repression of slow-twitch fiber program.

Sistema de Sinalização das MAP Quinases , Fibras Musculares de Contração Rápida/metabolismo , Fibras Musculares de Contração Lenta/metabolismo , Músculo Esquelético/metabolismo , Animais , Linhagem Celular , Fosfatase 1 de Especificidade Dupla/genética , Fosfatase 1 de Especificidade Dupla/metabolismo , Eletroporação , Flavonoides/farmacologia , Expressão Gênica , Genes Reporter , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Sistema de Sinalização das MAP Quinases/genética , Masculino , Camundongos , Camundongos Endogâmicos ICR , Proteína Quinase 1 Ativada por Mitógeno/antagonistas & inibidores , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/antagonistas & inibidores , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Fibras Musculares de Contração Rápida/efeitos dos fármacos , Fibras Musculares de Contração Lenta/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , Ratos , Ratos Sprague-Dawley , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Transfecção