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1.
J Appl Physiol (1985) ; 128(2): 286-295, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-31944890

RESUMO

Leucine (Leu) and its metabolite ß-hydroxy-ß-methylbutyrate (HMB) stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent protein synthesis in the skeletal muscle of neonatal pigs. This study aimed to determine whether HMB and Leu utilize common nutrient-sensing mechanisms to activate mTORC1. In study 1, neonatal pigs were fed one of five diets for 24 h: low protein (LP), high protein (HP), or LP supplemented with 4 (LP+HMB4), 40 (LP+HMB40), or 80 (LP+HMB80) µmol HMB·kg body wt-1·day-1. In study 2, neonatal pigs were fed for 24 h: LP, LP supplemented with Leu (LP+Leu), or HP diets delivering 9, 18, and 18 mmol Leu·kg body wt-1·day-1, respectively. The upstream signaling molecules that regulate mTORC1 activity were analyzed. mTOR phosphorylation on Ser2448 and Ser2481 was greater in LP+HMB40, LP+HMB80, and LP+Leu than in LP and greater in HP than in HMB-supplemented groups (P < 0.05), whereas HP and LP+Leu were similar. Rheb-mTOR complex formation was lower in LP than in HP (P < 0.05), with no enhancement by HMB or Leu supplementation. The Sestrin2-GATOR2 complex was more abundant in LP than in HP and was reduced by Leu (P < 0.05) but not HMB supplementation. RagA-mTOR and RagC-mTOR complexes were higher in LP+Leu and HP than in LP and HMB groups (P < 0.05). There were no treatment differences in RagB-SH3BP4, Vps34-LRS, and RagD-LRS complex abundances. Phosphorylation of Erk1/2 and TSC2, but not AMPK, was lower in LP than HP (P < 0.05) and unaffected by HMB or Leu supplementation. Our results demonstrate that HMB stimulates mTORC1 activation in neonatal muscle independent of the leucine-sensing pathway mediated by Sestrin2 and the Rag proteins.NEW & NOTEWORTHY Dietary supplementation with either leucine or its metabolite ß-hydroxy-ß-methylbutyrate (HMB) stimulates protein synthesis in skeletal muscle of the neonatal pig. Our results demonstrate that both leucine and HMB stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) phosphorylation in neonatal muscle. This leucine-stimulated process involves dissociation of the Sestrin2-GATOR2 complex and increased binding of Rag A/C to mTOR. However, HMB's activation of mTORC1 is independent of this leucine-sensing pathway.

2.
J Nutr ; 150(1): 22-30, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31518419

RESUMO

BACKGROUND: Rapid growth of skeletal muscle in the neonate requires the coordination of protein deposition and myonuclear accretion. During this developmental stage, muscle protein synthesis is highly sensitive to amino acid supply, especially Leu, but we do not know if this is true for satellite cells, the source of muscle fiber myonuclei. OBJECTIVE: We examined whether dietary protein restriction reduces myonuclear accretion in the neonatal pig, and if any reduction in myonuclear accretion is mitigated by restoring Leu intake. METHODS: Neonatal pigs (1.53 ± 0.2 kg) were fitted with jugular vein and gastric catheters and fed 1 of 3 isoenergetic milk replacers every 4 h for 21 d: high protein [HP; 22.5 g protein/(kg/d); n= 8]; restricted protein [RP; 11.2 g protein/(kg/d); n= 10]; or restricted protein with Leu [RPL; 12.0 g protein/(kg/d); n= 10]. Pigs were administered 5-bromo-2'-deoxyuridine (BrdU; 15 mg/kg) intravenously every 12 h from days 6 to 8. Blood was sampled on days 6 and 21 to measure plasma Leu concentrations. On day 21, pigs were killed and the longissimus dorsi (LD) muscle was collected to measure cell morphometry, satellite cell abundance, myonuclear accretion, and insulin-like growth factor (IGF) system expression. RESULTS: Compared with HP pigs, postprandial plasma Leu concentration in RP pigs was 37% and 47% lower on days 6 and 21, respectively (P < 0.05); Leu supplementation in RPL pigs restored postprandial Leu to HP concentrations. Dietary protein restriction reduced LD myofiber cross-sectional area by 21%, satellite cell abundance by 35%, and BrdU+ myonuclear abundance by 25% (P < 0.05); Leu did not reverse these outcomes. Dietary protein restriction reduced LD muscle IGF2 expression by 60%, but not IGF1 or IGF1R expression (P < 0.05); Leu did not rescue IGF2 expression. CONCLUSIONS: Satellite cell abundance and myonuclear accretion in neonatal pigs are compromised when dietary protein intake is restricted and are not restored with Leu supplementation.

3.
Nat Commun ; 10(1): 5364, 2019 12 02.
Artigo em Inglês | MEDLINE | ID: mdl-31792207

RESUMO

DNA methylation regulates cell type-specific gene expression. Here, in a transgenic mouse model, we show that deletion of the gene encoding DNA methyltransferase Dnmt3a in hypothalamic AgRP neurons causes a sedentary phenotype characterized by reduced voluntary exercise and increased adiposity. Whole-genome bisulfite sequencing (WGBS) and transcriptional profiling in neuronal nuclei from the arcuate nucleus of the hypothalamus (ARH) reveal differentially methylated genomic regions and reduced expression of AgRP neuron-associated genes in knockout mice. We use read-level analysis of WGBS data to infer putative ARH neural cell types affected by the knockout, and to localize promoter hypomethylation and increased expression of the growth factor Bmp7 to AgRP neurons, suggesting a role for aberrant TGF-ß signaling in the development of this phenotype. Together, these data demonstrate that DNA methylation in AgRP neurons is required for their normal epigenetic development and neuron-specific gene expression profiles, and regulates voluntary exercise behavior.


Assuntos
Metilação de DNA , Neurônios/metabolismo , Condicionamento Físico Animal , Adiposidade , Animais , Comportamento Animal , Proteína Morfogenética Óssea 7/genética , Proteína Morfogenética Óssea 7/metabolismo , DNA (Citosina-5-)-Metiltransferases/genética , DNA (Citosina-5-)-Metiltransferases/metabolismo , Feminino , Hipotálamo/citologia , Hipotálamo/metabolismo , Masculino , Camundongos , Camundongos Knockout , Transdução de Sinais
4.
Am J Physiol Endocrinol Metab ; 317(5): E839-E851, 2019 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-31503514

RESUMO

Postnatal growth of lean mass is commonly blunted in preterm infants and may contribute to short- and long-term morbidities. To determine whether preterm birth alters the protein anabolic response to feeding, piglets were delivered at term or preterm, and fractional protein synthesis rates (Ks) were measured at 3 days of age while fasted or after an enteral meal. Activation of signaling pathways that regulate protein synthesis and degradation were determined. Relative body weight gain was lower in preterm than in term. Gestational age at birth (GAB) did not alter fasting plasma glucose or insulin, but when fed, plasma insulin and glucose rose more slowly, and reached peak value later, in preterm than in term. Feeding increased Ks in longissimus dorsi (LD) and gastrocnemius muscles, heart, pancreas, and kidney in both GAB groups, but the response was blunted in preterm. In diaphragm, lung, jejunum, and brain, feeding increased Ks regardless of GAB. Liver Ks was greater in preterm than term and increased with feeding regardless of GAB. In all tissues, changes in 4EBP1, S6K1, and PKB phosphorylation paralleled changes in Ks. In LD, eIF4E·eIF4G complex formation, phosphorylation of TSC2, mTOR, and rpS6, and association of mammalian target of rapamycin (mTOR1) complex with RagA, RagC, and Rheb were increased by feeding and blunted by prematurity. There were no differences among groups in LD protein degradation markers. Our results demonstrate that preterm birth reduces weight gain and the protein synthetic response to feeding in muscle, pancreas, and kidney, and this is associated with blunted insulin- and/or amino acid-induced translation initiation signaling.


Assuntos
Animais Recém-Nascidos , Ingestão de Alimentos , Biossíntese de Proteínas , Transdução de Sinais , Animais , Peso ao Nascer , Glicemia/metabolismo , Feminino , Idade Gestacional , Rim/metabolismo , Músculo Esquelético/metabolismo , Fenômenos Fisiológicos da Nutrição , Pâncreas/metabolismo , Suínos , Serina-Treonina Quinases TOR/metabolismo , Ganho de Peso
5.
J Physiol ; 597(7): 1855-1872, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30730556

RESUMO

KEY POINTS: Impaired growth during fetal life can reprogramme heart development and increase the risk for long-term cardiovascular dysfunction. It is uncertain if the developmental window during which the heart is vulnerable to reprogramming as a result of inadequate nutrition extends into the postnatal period. We found that adult female mice that had been undernourished only from birth to 3 weeks of age had disproportionately smaller hearts compared to males, with thinner ventricle walls and more mononucleated cardiomyocytes. In females, but not males, cardiac diastolic function, and heart rate responsiveness to adrenergic stimulation were limited and maximal exercise capacity was compromised. These data suggest that the developmental window during which the heart is vulnerable to reprogramming by inadequacies in nutrient intake may extend into postnatal life and such individuals could be at increased risk for a cardiac event as a result of strenuous exercise. ABSTRACT: Adults who experienced undernutrition during critical windows of development are at increased risk for cardiovascular disease. The contribution of cardiac function to this increased disease risk is uncertain. We evaluated the effect of a short episode of postnatal undernutrition on cardiovascular function in mice at the whole animal, organ, and cellular levels. Pups born to control mouse dams were suckled from birth to postnatal day (PN) 21 on dams fed either a control (20% protein) or a low protein (8% protein) isocaloric diet. After PN21 offspring were fed the same control diet until adulthood. At PN70 V ̇ O 2 , max was measured by treadmill test. At PN80 cardiac function was evaluated by echocardiography and Doppler analysis at rest and following ß-adrenergic stimulation. Isolated cardiomyocyte nucleation and Ca2+ transients (with and without ß-adrenergic stimulation) were measured at PN90. Female mice that were undernourished and then refed (PUN), unlike male mice, had disproportionately smaller hearts and their exercise capacity, cardiac diastolic function, and heart rate responsiveness to adrenergic stimulation were limited. A reduced left ventricular end diastolic volume, impaired early filling, and decreased stored energy at the beginning of diastole contributed to these impairments. Female PUN mice had more mononucleated cardiomyocytes; under resting conditions binucleated cells had a functional profile suggestive of increased basal adrenergic activation. Thus, a brief episode of early postnatal undernutrition in the mouse can produce persistent changes to cardiac structure and function that limit exercise/functional capacity and thereby increase the risk for the development of a wide variety of cardiovascular morbidities.

6.
Annu Rev Anim Biosci ; 7: 309-335, 2019 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-30388025

RESUMO

Skeletal muscle growth during the early postnatal period is rapid in the pig and dependent on the capacity of muscle to respond to anabolic and catabolic stimuli. Muscle mass is driven by the balance between protein synthesis and degradation. Among these processes, muscle protein synthesis in the piglet is exceptionally sensitive to the feeding-induced postprandial changes in insulin and amino acids, whereas muscle protein degradation is affected only during specific catabolic states. The developmental decline in the response of muscle to feeding is associated with changes in the signaling pathways located upstream and downstream of the mechanistic target of rapamycin protein complex. Additionally, muscle growth is supported by an accretion of nuclei derived from satellite cells. Activated satellite cells undergo proliferation, differentiation, and fusion with adjacent growing muscle fibers. Enhancing early muscle growth through modifying protein synthesis, degradation, and satellite cell activity is key to maximizing performance, productivity, and lifelong pig health.


Assuntos
Músculo Esquelético/crescimento & desenvolvimento , Suínos/crescimento & desenvolvimento , Animais , Animais Recém-Nascidos/crescimento & desenvolvimento , Modelos Animais , Proteínas Musculares/biossíntese , Músculo Esquelético/metabolismo , Células Satélites de Músculo Esquelético/citologia , Transdução de Sinais , Suínos/metabolismo , Serina-Treonina Quinases TOR/metabolismo
7.
Am J Clin Nutr ; 108(4): 830-841, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-30239549

RESUMO

Background: Orogastric tube feeding is indicated in neonates with an impaired ability to ingest food normally and can be administered with an intermittent bolus or continuous feeding schedule. Objectives: The objectives were to 1) compare the long-term effect of continuous with intermittent feeding on growth using the newborn pig as a model, 2) determine whether feeding frequency alters lean tissue and fat mass gain, and 3) identify the signaling mechanisms by which protein deposition is controlled in skeletal muscle in response to feeding frequency. Design: Neonatal pigs were fed the same amount of a balanced formula by orogastric tube either as an intermittent bolus meal every 4 h (INT) or as a continuous infusion (CON). Body composition was assessed at the start and end of the study by dual-energy X-ray absorptiometry, and hormone and substrate profiles, muscle mass, protein synthesis, and indexes of nutrient and insulin signaling were measured after 21 d. Results: Body weight, lean mass, spine length, and skeletal muscle mass were greater in the INT group than in the CON group. Skeletal muscle fractional protein synthesis rates were greater in the INT group after a meal than in the CON group and were associated with higher circulating branched-chain amino acid and insulin concentrations. Skeletal muscle protein kinase B (PKB) and ribosomal protein S6 kinase phosphorylation and eukaryotic initiation factor (eIF) 4E-eIF4G complex formation were higher, whereas eIF2α phosphorylation was lower in the INT group than in the CON group, indicating enhanced activation of insulin and amino acid signaling to translation initiation. Conclusions: These results suggest that when neonates are fed the same amounts of nutrients as intermittent meals rather than continuously there is greater lean growth. This response can be ascribed, in part, to the pulsatile pattern of amino acids, insulin, or both induced by INT, which enables the responsiveness of anabolic pathways to feeding to be sustained chronically in skeletal muscle.


Assuntos
Composição Corporal/fisiologia , Compartimentos de Líquidos Corporais/fisiologia , Comportamento Alimentar/fisiologia , Proteínas Musculares/metabolismo , Músculo Esquelético/fisiologia , Biossíntese de Proteínas , Ganho de Peso/fisiologia , Tecido Adiposo/metabolismo , Aminoácidos/sangue , Animais , Animais Recém-Nascidos/crescimento & desenvolvimento , Compartimentos de Líquidos Corporais/metabolismo , Ingestão de Energia , Fator de Iniciação 2 em Eucariotos/metabolismo , Fator de Iniciação 4E em Eucariotos/metabolismo , Feminino , Humanos , Recém-Nascido , Insulina/sangue , Músculo Esquelético/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Quinases S6 Ribossômicas/metabolismo , Transdução de Sinais , Coluna Vertebral/crescimento & desenvolvimento , Suínos
8.
Cell Rep ; 24(1): 197-208, 2018 07 03.
Artigo em Inglês | MEDLINE | ID: mdl-29972780

RESUMO

Maintenance of skeletal muscle mass requires a dynamic balance between protein synthesis and tightly controlled protein degradation by the calpain, autophagy-lysosome, and ubiquitin-proteasome systems (proteostasis). Several sensing and gene-regulatory mechanisms act together to maintain this balance in response to changing conditions. Here, we show that deletion of the highly conserved Rbfox1 and Rbfox2 alternative splicing regulators in adult mouse skeletal muscle causes rapid, severe loss of muscle mass. Rbfox deletion did not cause a reduction in global protein synthesis, but it led to altered splicing of hundreds of gene transcripts, including capn3, which produced an active form of calpain3 protease. Rbfox knockout also led to a reduction in autophagy flux, likely producing a compensatory increase in general protein degradation by the proteasome. Our results indicate that the Rbfox-splicing factors are essential for the maintenance of skeletal muscle mass and proteostasis.


Assuntos
Calpaína/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Músculo Esquelético/patologia , Proteostase , Fatores de Processamento de RNA/metabolismo , Animais , Autofagia , Metabolismo Energético , Deleção de Genes , Glucose/metabolismo , Camundongos Endogâmicos C57BL , Camundongos Knockout , Força Muscular , Resistência Física , Transcriptoma/genética
10.
Artigo em Inglês | MEDLINE | ID: mdl-29991029

RESUMO

Skeletal myogenesis begins in the embryo with proliferation and differentiation of muscle progenitor cells that ultimately fuse to form multinucleated myofibers. After midgestation, muscle growth occurs through hypertrophy of these myofibers. The most rapid growth phase occurs in the perinatal period, resulting in the expansion of muscle mass from 25% of lean mass at birth to 40-45% at maturity. These 2 phases of muscle growth are regulated by distinct molecular mechanisms engaged by extracellular cues and intracellular signaling pathways and regulatory networks they activate. Nutrients influence muscle growth by both providing the necessary substrates and eliciting extracellular cues which regulate the signal transduction pathways that control the anabolic processes of the fibers. The uniquely large capacity of immature myofibers for hypertrophy is enabled by a heightened capacity and sensitivity of protein synthesis to feeding-induced changes in plasma insulin and amino acids, and the ability to expand their myonuclear population through proliferation of muscle precursor cells (satellite cells). With maturation, satellite cells become quiescent, limiting myonuclear accretion, and the capacity of the muscles for protein anabolism progressively diminishes. Therefore, the early developmental phases represent critical windows for muscle growth which, if disrupted, result in muscle mass deficits that are unlikely to be entirely recoverable.


Assuntos
Músculo Esquelético/embriologia , Músculo Esquelético/crescimento & desenvolvimento , Fenômenos Fisiológicos da Nutrição/fisiologia , Fatores Etários , Aminoácidos/sangue , Animais , Diferenciação Celular , Feminino , Desenvolvimento Fetal/fisiologia , Transtornos da Nutrição Fetal/fisiopatologia , Humanos , Hipertrofia , Lactente , Transtornos da Nutrição do Lactente/fisiopatologia , Fenômenos Fisiológicos da Nutrição do Lactente/fisiologia , Recém-Nascido , Insulina/sangue , Desenvolvimento Muscular/fisiologia , Fibras Musculares Esqueléticas/citologia , Fibras Musculares Esqueléticas/fisiologia , Proteínas Musculares/biossíntese , Assistência Perinatal , Gravidez
12.
Nutrients ; 10(5)2018 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-29786674

RESUMO

Hepatic steatosis is a hallmark feature of kwashiorkor malnutrition. However, the pathogenesis of hepatic steatosis in kwashiorkor is uncertain. Our objective was to develop a mouse model of childhood undernutrition in order to test the hypothesis that feeding a maize vegetable diet (MVD), like that consumed by children at risk for kwashiorkor, will cause hepatic steatosis which is prevented by supplementation with choline. A MVD was developed with locally sourced organic ingredients, and fed to weanling mice (n = 9) for 6 or 13 days. An additional group of mice (n = 4) were fed a choline supplemented MVD. Weight, body composition, and liver changes were compared to control mice (n = 10) at the beginning and end of the study. The MVD resulted in reduced weight gain and hepatic steatosis. Choline supplementation prevented hepatic steatosis and was associated with increased hepatic concentrations of the methyl donor betaine. Our findings show that (1) feeding a MVD to weanling mice rapidly induces hepatic steatosis, which is a hallmark disturbance of kwashiorkor; and that (2) hepatic steatosis associated with feeding a MVD is prevented by choline supplementation. These findings support the concept that insufficient choline intake may contribute to the pathogenesis of hepatic steatosis in kwashiorkor.


Assuntos
Colina/administração & dosagem , Suplementos Nutricionais , Fígado Gorduroso/prevenção & controle , Kwashiorkor/dietoterapia , Fígado/patologia , Zea mays , Ração Animal , Fenômenos Fisiológicos da Nutrição Animal , Animais , Colina/metabolismo , Modelos Animais de Doenças , Ingestão de Alimentos , Metabolismo Energético/genética , Fígado Gorduroso/genética , Fígado Gorduroso/metabolismo , Fígado Gorduroso/patologia , Feminino , Regulação da Expressão Gênica , Kwashiorkor/genética , Kwashiorkor/metabolismo , Kwashiorkor/patologia , Metabolismo dos Lipídeos/genética , Fígado/metabolismo , Masculino , Camundongos , Estado Nutricional , Fatores de Tempo , Transcrição Genética , Ganho de Peso
13.
Amino Acids ; 50(7): 943-959, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29728917

RESUMO

The objective of this study was to determine if enteral leucine or branched-chain amino acid (BCAA) supplementation increases muscle protein synthesis in neonates who consume less than their protein and energy requirements, and whether this increase is mediated via the upregulation of the mechanistic target of rapamycin complex 1 (mTORC1) pathway or the decrease in muscle protein degradation signaling. Neonatal pigs were fed milk replacement diets containing reduced energy and protein (R), R supplemented with BCAA (RBCAA), R supplemented with leucine (RL), or complete protein and energy (CON) at 4-h intervals for 9 (n = 24) or 21 days (n = 22). On days 9 and 21, post-prandial plasma amino acids and insulin were measured at intervals for 4 h; muscle protein synthesis rate and activation of mTOR-related proteins were determined at 120 min post-feeding in muscle. For all parameters measured, the effects of diet were not different between day 9 or day 21. Compared to CON and R, plasma leucine and BCAA were higher (P ≤ 0.01) in RL- and RBCAA-fed pigs, respectively. Body weight gain, protein synthesis, and activation of S6 kinase (S6K1), 4E-binding protein (4EBP1), and eukaryotic initiation factor 4 complex (eIF4E·eIF4G) were decreased in RBCAA, RL, and R relative to CON (P < 0.01). RBCAA and RL upregulated (P ≤ 0.01) S6K1, 4EBP1, and eIF4E·eIF4G compared to R. In conclusion, when protein and energy are restricted, both leucine and BCAA supplementation increase mTOR activation, but do not enhance skeletal muscle protein synthesis and muscle growth in neonatal pigs.


Assuntos
Aminoácidos de Cadeia Ramificada/farmacologia , Ração Animal , Leucina/farmacologia , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Animais , Animais Recém-Nascidos , Suínos
14.
J Endocrinol ; 234(2): 187-200, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28533420

RESUMO

Insulin-like growth factors (IGFs) and myostatin have opposing roles in regulating the growth and size of skeletal muscle, with IGF1 stimulating, and myostatin inhibiting, growth. However, it remains unclear whether these proteins have mutually dependent, or independent, roles. To clarify this issue, we crossed myostatin null (Mstn-/-) mice with mice overexpressing Igf1 in skeletal muscle (Igf1+) to generate six genotypes of male mice; wild type (Mstn+/+ ), Mstn+/-, Mstn-/-, Mstn+/+:Igf1+, Mstn+/-:Igf1+ and Mstn-/-:Igf1+ Overexpression of Igf1 increased the mass of mixed fibre type muscles (e.g. Quadriceps femoris) by 19% over Mstn+/+ , 33% over Mstn+/- and 49% over Mstn-/- (P < 0.001). By contrast, the mass of the gonadal fat pad was correspondingly reduced with the removal of Mstn and addition of Igf1 Myostatin regulated the number, while IGF1 regulated the size of myofibres, and the deletion of Mstn and Igf1+ independently increased the proportion of fast type IIB myosin heavy chain isoforms in T. anterior (up to 10% each, P < 0.001). The abundance of AKT and rpS6 was increased in muscles of Mstn-/-mice, while phosphorylation of AKTS473 was increased in Igf1+mice (Mstn+/+:Igf1+, Mstn+/-:Igf1+ and Mstn-/-:Igf1+). Our results demonstrate that a greater than additive effect is observed on the growth of skeletal muscle and in the reduction of body fat when myostatin is absent and IGF1 is in excess. Finally, we show that myostatin and IGF1 regulate skeletal muscle size, myofibre type and gonadal fat through distinct mechanisms that involve increasing the total abundance and phosphorylation status of AKT and rpS6.


Assuntos
Regulação da Expressão Gênica/fisiologia , Fator de Crescimento Insulin-Like I/metabolismo , Músculo Esquelético/fisiologia , Miostatina/metabolismo , Tecido Adiposo/fisiologia , Animais , Genótipo , Fator de Crescimento Insulin-Like I/genética , Masculino , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Miostatina/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo
15.
J Endocrinol ; 232(3): 561-572, 2017 03.
Artigo em Inglês | MEDLINE | ID: mdl-28096434

RESUMO

Perinatal skeletal muscle growth rates are a function of protein and myonuclear accretion. Precocious exposure of the fetus to glucocorticoids (GLC) in utero impairs muscle growth. Reduced muscle protein synthesis rates contribute to this response, but the consequences for myonuclear hyperplasia are unknown. To test the hypothesis that blunting of Pax7+ muscle progenitor cell proliferative activity by GLC in vivo also contributes to reduced fetal muscle growth, pregnant rats were administered dexamethasone (DEX: 1 mg/L drinking water) from embryonic day (ED) 13 to ED21. Their responses were compared to pair-fed (PF) and ad libitum-fed controls (CON). Bromodeoxyuridine (BrdU) was administered before delivery to measure myonuclear accretion. Fetal hind limb and diaphragm muscles were collected at term and analyzed for myofiber cross-sectional area (CSA), total and BrdU+ myonuclei, Pax7+ nuclei, MyoD and myogenin protein and mRNA abundance and myosin heavy chain (MyHC) isoform composition. Mean fiber CSA, myonuclei/myofiber and Pax7+ nuclei/myofiber ratios were reduced in DEX compared to those in CON and PF muscles; CSA/myonucleus, BrdU+/total myonuclei and BrdU+ myonuclei/Pax7+ nuclei were similar among groups. Myogenin abundance was reduced and MyHC-slow was increased in DEX fetuses. The data are consistent with GLC inhibition of muscle progenitor cell proliferation limiting satellite cell and myonuclear accretion. The response of PF-fed compared to CON muscles indicated that decreased food consumption by DEX dams contributed to the smaller myofiber CSA but did not affect Pax7+ nuclear accretion. Thus, the effect on satellite cell reserve and myonuclear number also contributes to the blunting of fetal muscle growth by GLC.


Assuntos
Proliferação de Células/efeitos dos fármacos , Dexametasona/farmacologia , Glucocorticoides/farmacologia , Fibras Musculares Esqueléticas/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/metabolismo , Células Satélites de Músculo Esquelético/efeitos dos fármacos , Animais , Feminino , Fibras Musculares Esqueléticas/metabolismo , Miogenina/metabolismo , Cadeias Pesadas de Miosina/metabolismo , Fatores de Transcrição Box Pareados/metabolismo , Gravidez , Ratos , Células Satélites de Músculo Esquelético/metabolismo
16.
PLoS One ; 12(1): e0170127, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28099477

RESUMO

Offspring of murine dams chronically fed a protein-restricted diet have an increased risk for metabolic and neurobehavioral disorders. Previously we showed that adult offspring, developmentally exposed to a chronic maternal low-protein (MLP) diet, had lower body and hind-leg muscle weights and decreased liver enzyme serum levels. We conducted energy expenditure, neurobehavioral and circadian rhythm assays in male offspring to examine mechanisms for the body-weight phenotype and assess neurodevelopmental implications of MLP exposure. C57BL/6J dams were fed a protein restricted (8%protein, MLP) or a control protein (20% protein, C) diet from four weeks before mating until weaning of offspring. Male offspring were weaned to standard rodent diet (20% protein) and single-housed until 8-12 weeks of age. We examined body composition, food intake, energy expenditure, spontaneous rearing activity and sleep patterns and performed behavioral assays for anxiety (open field activity, elevated plus maze [EPM], light/dark exploration), depression (tail suspension and forced swim test), sociability (three-chamber), repetitive (marble burying), learning and memory (fear conditioning), and circadian behavior (wheel-running activity during light-dark and constant dark cycles). We also measured circadian gene expression in hypothalamus and liver at different Zeitgeber times (ZT). Male offspring from separate MLP exposed dams had significantly greater body fat (P = 0.03), less energy expenditure (P = 0.004), less rearing activity (P = 0.04) and a greater number of night-time rest/sleep bouts (P = 0.03) compared to control. MLP offspring displayed greater anxiety-like behavior in the EPM (P<0.01) but had no learning and memory deficit in fear-conditioning assay (P = 0.02). There was an effect of time on Per1, Per 2 and Clock circadian gene expression in the hypothalamus but not on circadian behavior. Thus, transplacental and early developmental exposure of dams to chronic MLP reduces food intake and energy expenditure, increases anxiety like behavior and disturbs sleep patterns but not circadian rhythm in adult male offspring.


Assuntos
Ansiedade/etiologia , Ritmo Circadiano/fisiologia , Dieta com Restrição de Proteínas/efeitos adversos , Metabolismo Energético , Sono/fisiologia , Tecido Adiposo , Animais , Comportamento Animal , Ritmo Circadiano/genética , Feminino , Expressão Gênica , Hipotálamo/fisiologia , Fígado/fisiologia , Masculino , Fenômenos Fisiológicos da Nutrição Materna , Camundongos Endogâmicos C57BL
17.
Elife ; 52016 06 21.
Artigo em Inglês | MEDLINE | ID: mdl-27328325

RESUMO

Many postnatal onset neurological disorders such as autism spectrum disorders (ASDs) and intellectual disability are thought to arise largely from disruption of excitatory/inhibitory homeostasis. Although mouse models of Rett syndrome (RTT), a postnatal neurological disorder caused by loss-of-function mutations in MECP2, display impaired excitatory neurotransmission, the RTT phenotype can be largely reproduced in mice simply by removing MeCP2 from inhibitory GABAergic neurons. To determine what role excitatory signaling impairment might play in RTT pathogenesis, we generated conditional mouse models with Mecp2 either removed from or expressed solely in glutamatergic neurons. MeCP2 deficiency in glutamatergic neurons leads to early lethality, obesity, tremor, altered anxiety-like behaviors, and impaired acoustic startle response, which is distinct from the phenotype of mice lacking MeCP2 only in inhibitory neurons. These findings reveal a role for excitatory signaling impairment in specific neurobehavioral abnormalities shared by RTT and other postnatal neurological disorders.


Assuntos
Expressão Gênica , Proteína 2 de Ligação a Metil-CpG/genética , Proteína 2 de Ligação a Metil-CpG/metabolismo , Doenças do Sistema Nervoso/genética , Doenças do Sistema Nervoso/patologia , Neurônios/fisiologia , Animais , Proteína 2 de Ligação a Metil-CpG/deficiência , Camundongos
18.
Am J Physiol Endocrinol Metab ; 310(11): E1072-84, 2016 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-27143558

RESUMO

Many low-birth weight infants are at risk for poor growth due to an inability to achieve adequate protein intake. Administration of the amino acid leucine stimulates protein synthesis in skeletal muscle of neonates. To determine the effects of enteral supplementation of the leucine metabolite ß-hydroxy-ß-methylbutyrate (HMB) on protein synthesis and the regulation of translation initiation and degradation pathways, overnight-fasted neonatal pigs were studied immediately (F) or fed one of five diets for 24 h: low-protein (LP), high-protein (HP), or LP diet supplemented with 4 (HMB4), 40 (HMB40), or 80 (HMB80) µmol HMB·kg body wt(-1)·day(-1) Cell replication was assessed from nuclear incorporation of BrdU in the longissimus dorsi (LD) muscle and jejunum crypt cells. Protein synthesis rates in LD, gastrocnemius, rhomboideus, and diaphragm muscles, lung, and brain were greater in HMB80 and HP and in brain were greater in HMB40 compared with LP and F groups. Formation of the eIF4E·eIF4G complex and S6K1 and 4E-BP1 phosphorylation in LD, gastrocnemius, and rhomboideus muscles were greater in HMB80 and HP than in LP and F groups. Phosphorylation of eIF2α and eEF2 and expression of SNAT2, LAT1, MuRF1, atrogin-1, and LC3-II were unchanged. Numbers of BrdU-positive myonuclei in the LD were greater in HMB80 and HP than in the LP and F groups; there were no differences in jejunum. The results suggest that enteral supplementation with HMB increases skeletal muscle protein anabolism in neonates by stimulation of protein synthesis and satellite cell proliferation.


Assuntos
Suplementos Nutricionais , Proteínas Musculares/biossíntese , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Biossíntese de Proteínas/efeitos dos fármacos , Valeratos/administração & dosagem , Administração Oral , Animais , Animais Recém-Nascidos , Relação Dose-Resposta a Droga , Nutrição Enteral , Feminino , Masculino , Músculo Esquelético/citologia , Biossíntese de Proteínas/fisiologia , Células Satélites de Músculo Esquelético/citologia , Células Satélites de Músculo Esquelético/efeitos dos fármacos , Células Satélites de Músculo Esquelético/metabolismo , Suínos , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/fisiologia
19.
FASEB J ; 30(7): 2541-8, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-27033262

RESUMO

Previous rodent studies have shown that maternal voluntary exercise during pregnancy leads to metabolic changes in adult offspring. We set out to test whether maternal voluntary exercise during pregnancy also induces persistent changes in voluntary physical activity in the offspring. Adult C57BL/6J female mice were randomly assigned to be caged with an unlocked (U) or locked (L) running wheel before and during pregnancy. Maternal running behavior was monitored during pregnancy, and body weight, body composition, food intake, energy expenditure, total cage activity, and running wheel activity were measured in the offspring at various ages. U offspring were slightly heavier at birth, but no group differences in body weight or composition were observed at later ages (when mice were caged without access to running wheels). Consistent with our hypothesis, U offspring were more physically active as adults. This effect was observed earlier in female offspring (at sexual maturation). Remarkably, at 300 d of age, U females achieved greater fat loss in response to a 3-wk voluntary exercise program. Our findings show for the first time that maternal physical activity during pregnancy affects the offspring's lifelong propensity for physical activity and may have important implications for combating the worldwide epidemic of physical inactivity and obesity.-Eclarinal, J. D., Zhu, S., Baker, M. S., Piyarathna, D. B., Coarfa, C., Fiorotto, M. L., Waterland, R. A. Maternal exercise during pregnancy promotes physical activity in adult offspring.


Assuntos
Comportamento Materno/fisiologia , Atividade Motora/fisiologia , Condicionamento Físico Animal/fisiologia , Animais , Feminino , Abrigo para Animais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Gravidez , Fatores Sexuais
20.
Am J Physiol Endocrinol Metab ; 310(8): E699-E713, 2016 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-26884386

RESUMO

Neonatal pigs are used as a model to study and optimize the clinical treatment of infants who are unable to maintain oral feeding. Using this model, we have shown previously that pulsatile administration of leucine during continuous feeding over 24 h via orogastric tube enhanced protein synthesis in skeletal muscle compared with continuous feeding alone. To determine the long-term effects of leucine pulses, neonatal piglets (n = 11-12/group) were continuously fed formula via orogastric tube for 21 days, with an additional parenteral infusion of either leucine (CON + LEU; 800 µmol·kg-1·h-1) or alanine (CON + ALA) for 1 h every 4 h. The results show that body and muscle weights and lean gain were ∼25% greater, and fat gain was 48% lower in CON + LEU than CON + ALA; weights of other tissues were unaffected by treatment. Fractional protein synthesis rates in longissimus dorsi, gastrocnemius, and soleus muscles were ∼30% higher in CON + LEU compared with CON + ALA and were associated with decreased Deptor abundance and increased mTORC1, mTORC2, 4E-BP1, and S6K1 phosphorylation, SNAT2 abundance, and association of eIF4E with eIF4G and RagC with mTOR. There were no treatment effects on PKB, eIF2α, eEF2, or PRAS40 phosphorylation, Rheb, SLC38A9, v-ATPase, LAMTOR1, LAMTOR2, RagA, RagC, and LAT1 abundance, the proportion of polysomes to nonpolysomes, or the proportion of mRNAs encoding rpS4 or rpS8 associated with polysomes. Our results demonstrate that pulsatile delivery of a leucine supplement during 21 days of continuous enteral feeding enhances lean growth by stimulating the mTORC1-dependent translation initiation pathway, leading to protein synthesis in skeletal muscle of neonates.


Assuntos
Leucina/farmacologia , Proteínas Musculares/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Biossíntese de Proteínas/efeitos dos fármacos , Alanina/farmacologia , Sistema A de Transporte de Aminoácidos/efeitos dos fármacos , Sistema A de Transporte de Aminoácidos/metabolismo , Animais , Animais Recém-Nascidos , Músculos do Dorso , Suplementos Nutricionais , Nutrição Enteral , Infusões Parenterais , Leucina/administração & dosagem , Alvo Mecanístico do Complexo 1 de Rapamicina , Alvo Mecanístico do Complexo 2 de Rapamicina , Complexos Multiproteicos/efeitos dos fármacos , Complexos Multiproteicos/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Fosforilação/efeitos dos fármacos , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/metabolismo , Proteínas Quinases S6 Ribossômicas 90-kDa/efeitos dos fármacos , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Proteínas Ribossômicas/efeitos dos fármacos , Proteínas Ribossômicas/genética , Sus scrofa , Suínos , Serina-Treonina Quinases TOR/efeitos dos fármacos , Serina-Treonina Quinases TOR/metabolismo
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