Beta-adrenergic receptor-adenylate cyclase alterations during the postnatal development of skeletal muscle

The postnatal development of mammalian skeletal muscle is associated with an increased capacity for glycogenolysis. In the present study rabbit skeletal muscle underwent a 7-fold increase in glycogen synthase and glycogen phosphorylase activity over the postnatal period of 0--8 weeks. An enriched fraction of sarcolemma was prepared from neonatal and adult muscle to examine the development of the beta-adrenergic receptor-adenylate cyclase system. Adult membranes possessed a 2-fold greater Na+K+(Mg2+)-ATPase activity and a 6--8 fold greater sodium fluoride- and epinephrine-stimulated adenylate cyclase activity. The activation ratio (effector activity/basal activity) increased 2--3 fold for epinephrine and sodium fluoride in adult sarcolemma. The activation by catecholamines conformed to the physiological beta 2 type response with isoproterenol (1.8 . 10(-8) M) > epinephrine (1.1 . 10(-7) M) > norinephrine (3.2 . 10(-6) M). In contrast, binding studies employing (-)-[3H]dihydroalprenolol showed little difference between neonatal and adult membranes with respect to (1) number of binding sites, (2) equilibrium dissociation constant and (3) displacement of (-)-[3H]dihydroalprenolol by catecholamine agonists. Protein and lipid components of the sarcolemma were also modified during development. Neonatal membranes possessed two glycopeptides of Mr 80000 and 86000, whereas in the adult only a single Mr 113000 species was evident. The total lipid phosphorus and phospholipid composition was unchanged during development. The content of linoleic acid increased approx. 3-fold during development in the phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine phospholipids. The cholesterol content of adult membranes was decreased by 29% compared to neonatal membranes.     

β-adrenegic receptor-adenylate cyclase alterations during the postnatal development of skeletal muscle

The postnatal development of mammalian skeletal muscle is associated with an increased capacity for glycogenolysis. In the present study rabbit skeletal muscle underwent a 7-fold increase in glycogen synthase and glycogen phosphorylase activity over the postnatal period of 0–8 weeks. An enriched fraction of sarcolemma was prepared from neonatal and adult muscle to examine the development of the β-adrenergic receptor-adenylate cyclase system. Adult membranes possessed a 2-fold greater Na⁺K⁺(Mg²⁺)-ATPase activity and a 6–8-fold greater sodium fluoride- and epinephrine-stimulated adenylate cyclase activity. The activation ratio (effector activity/basal activity) increased 2–3-fold for epinephrine and sodium fluoride in adult sarcolemma. The activation by catecholamines conformed to the physiological β₂ type response with isoproterenol (1.8 · 10^?8 M) > epinephrine (1.1 · 10^?7 M) > norinephrine (3.2 · 10^?6 M). In contrast, binding studies employing (?)-[³H] dihydroalprenolol showed little difference between neonatal and adult membranes with respect to (1) number of binding sites, (2) equilibrium dissociation constant and (3) displacement of (?)-[³H]dihydroalprenolol by catecholamine agonists.Protein and lipid components of the sarcolemma were also modified during development. Neonatal membranes possessed two glycopeptides of M_r 80 000 and 86 000, whereas in the adult only a single M_r 133 000 species was evident. The total lipid phosphorus and phospholipid composition was unchanged during development. The content of linoleic acid increased approx. 3-fold during development in the phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine phospholipids. The cholesterol content of adult membranes was decreased by 29% compared to neonatal membranes.     

Diversification of the myofibrillar M-band in rat skeletal muscle during postnatal development

Summary The fine structure of the M-band in soleus (SOL) and extensor digitorum longus (EDL) muscles in newborn and four-week-old rats was studied using electron-microscopic techniques. In newborn rats, all myotubes and fibres in both muscles had an identical myofibrillar appearance. A five-line M-band pattern was seen in longitudinal sections and distinct M-bridges in cross-sections. The Z-discs were of medium width. On the other hand, in four-week-old rats, different muscle fibre types were observed on the basis of their myofibrillar pattern. In SOL two fibre types were distinguished in longitudinal sections. One had a four-line M-band pattern and very broad Z-discs, whereas the other type had five lines in the M-band and broad Z-discs. In EDL, three different myofibrillar patterns were observed. The M-bands were composed of three, four or five lines. Fibres had either thin, broad or medium Z-disc widths, respectively. In cross-sections of the SOL muscle one group of fibres showed indistinct M-bridges, whereas distinct M-bridges were seen in the other fibres and in all observed EDL muscle fibres. We conclude that initially there seems to be a single intrinsic program for M-band genesis; this program becomes modified upon the induction of functionally differentiated fibres.     

Underestimated contribution of skeletal muscle in ornithine metabolism during mouse postnatal development

Ornithine aminotransferase (l-ornithine 2-oxoacid aminotransferase, OAT) is widely expressed in organs, but studies in mice have focused primarily on the intestine, kidney and liver because of the high OAT-specific activity in these tissues. This study aimed to investigate OAT activity in adult mouse tissues to assess the potential contribution to ornithine metabolism and to determine OAT control during postnatal development. OAT activity was widely distributed in mouse tissues. Sexual dimorphism was observed for most tissues in adults, with greater activity in females than in males. The contribution of skeletal muscles to total OAT activity (34 % in males and 27 % in females) was the greatest (50 %) of the investigated tissues in pre-weaned mice and was similar to that of the liver in adults. OAT activity was found to be regulated in a tissue-specific manner during postnatal development in parallel with large changes in the plasma testosterone and corticosterone levels. After weaning, OAT activity markedly increased in the liver but dropped in the skeletal muscle and adipose tissue. Anticipating weaning for 3 days led to an earlier reduction of OAT activity in skeletal muscles. Orchidectomy in adults decreased OAT activity in the liver but increased it in skeletal muscle and adipose tissue. We concluded that the contribution of skeletal muscle to mouse ornithine metabolism may have been underestimated. The regulation of OAT in skeletal muscles differs from that in the liver. The present findings suggest important and tissue-specific metabolic roles for OAT during postnatal development in mice.     

Diaphragm muscle fatigue resistance during postnatal development.

Changes in the contractile and fatigue properties of the cat diaphragm muscle were examined during the first 6 wk of postnatal development. Both twitch contraction time and half-relaxation time decreased progressively with age. Correspondingly, the force-frequency curve was shifted to the left early in development compared with adults. The ratio of peak twitch force to maximum tetanic force decreased with age. Fatigue resistance of the diaphragm was highest at birth and then progressively decreased with age. At birth, most diaphragm muscle fibers stained darkly for myofibrillar adenosinetriphosphatase after alkaline preincubation and thus would be classified histochemically as type II. During subsequent postnatal development, the proportion of type I fibers (lightly stained for adenosinetriphosphatase) increased while the number of type II fibers declined. At birth, type I fibers were larger than type II fibers. The size of both fiber types increased with age, but the increase in cross-sectional area was greater for type II fibers. On the basis of fiber type proportions and mean cross-sectional areas, type I fibers contributed 15% of total muscle mass at birth and 25% in adults. Thus postnatal changes in diaphragm contractile and fatigue properties cannot be attributed to changes in the relative contribution of histochemically classified type I and II fibers. However, the possibility that these developmental changes in diaphragm contractile and fatigue properties correlated with the varying contractile protein composition of muscle fibers was discussed.     

Expression of fibroblast growth factor family during postnatal skeletal muscle hypertrophy

The potential role of the fibroblast growth factor (FGF) familyduring stretch-induced postnatal skeletal muscle hypertrophy wasanalyzed by using an avian wing-weighting model. After 2 or 11 days ofweighted stretch, anterior latissimus dorsi (ALD) muscles were, onaverage, 34 (P < 0.01) and 85%(P < 0.01) larger, respectively, than unweighted ALD control muscles. By using quantitative RT-PCR, FGF-1 mRNA expression was found to be significantly decreased in ALDmuscles stretched for 2 or 11 days. In contrast, FGF-4 and FGF-10 mRNAexpression was significantly increased 2 days after initiation ofstretch. FGF-2, FGF-10, fibroblast growth factor receptor 1, andFREK mRNA expression was significantly increased at 11 days poststretch. Increases in FGF-2 and FGF-4 protein could bedetected throughout the myofiber periphery after 11 days of stretch. Ona cellular level, FGF-2 and FGF-4 proteins were differentiallylocalized. This differential expression pattern and proteinlocalization of the FGF family in response to stretch-induced hypertrophy suggest distinct roles for individual FGFs during thepostnatal hypertrophy process.

     

Dynamics of muscle fibre growth during postnatal mouse development

Background  

Postnatal growth in mouse is rapid, with total skeletal muscle mass increasing several-fold in the first few weeks. Muscle growth can be achieved by either an increase in muscle fibre number or an increase in the size of individual myofibres, or a combination of both. Where myofibre hypertrophy during growth requires the addition of new myonuclei, these are supplied by muscle satellite cells, the resident stem cells of skeletal muscle.     

Cellular heterogeneity during vertebrate skeletal muscle development

Although skeletal muscles appear superficially alike at different anatomical locations, in reality there is considerably more diversity than previously anticipated. Heterogeneity is not only restricted to completely developed fibers, but is clearly apparent during development at the molecular, cellular and anatomical level. Multiple waves of muscle precursors with different features appear before birth and contribute to muscular diversification. Recent cell lineage and gene expression studies have expanded our knowledge on how skeletal muscle is formed and how its heterogeneity is generated. This review will present a comprehensive view of relevant findings in this field.     

Sequential maturation of skeletal muscle groups during postnatal ontogenesis of rats]

Experiments were conducted on rats during the early postnatal period; a study was made of the membrane potential (MP) establishment of the fibers of the skeletal muscles of the neck, the anterior and the posterior limbs. At birth the most mature were the muscles of the neck, and the least -- the muscles of the posterior limb. Establishment of the stationary MP level in the muscles of the neck occurred during the first week after birth, in the muscles of the anterior limbs -- by the 10th-12th day, and of the posterior limbs -- by the 15th-20th day. The order of maturation of various groups of the skeletal muscles was associated with the peculiarities of the neuro-trophic influences at various age periods. Muscles of the neck were characterized at all the developmental stages by a rhythmic low-frequency electromyographic activity. In the muscles of the limbs the rhythmic electromyographic activity was transformed into the discharge high-frequency activity by the period of termination of increase of the MP of the muscles.     

Satellite cell proliferation and differentiation during postnatal growth of porcine skeletal muscle

Age-related changes in satellitecell proliferation and differentiation during rapid growth of porcineskeletal muscle were examined. Satellite cells were isolated fromhindlimb muscles of pigs at 1, 7, 14, and 21 wk of age (4 animals/agegroup). Satellite cells were separated from cellular debris by usingPercoll gradient centrifugation and were adsorbed to glass coverslipsfor fluorescent immunostaining. Positive staining for neural celladhesion molecule (NCAM) distinguished satellite cells from nonmyogeniccells. The proportion of NCAM-positive cells (satellite cells) inisolates decreased from 1 to 7 wk of age. Greater than 77% ofNCAM-positive cells were proliferating cell nuclear antigen positive atall ages studied. Myogenin-positive satellite cells decreased from 30%at 1 wk to 14% at 7 wk of age and remained at constant levels thereafter. These data indicate that a high percentage of satellite cells remain proliferative during rapid postnatal muscle growth. Thereduced proportion of myogenin-positive cells during growth may reflecta decrease in the proportion of differentiating satellite cells oraccelerated incorporation of myogenin-positive cells into myofibers.

     

Identification of secreted proteins during skeletal muscle development

The differentiation program of skeletal muscle cells is exquisitely sensitive to secreted proteins. We developed a strategy to maximize the discovery of secreted proteins, using mass spectrometry-based proteomics, from cultured muscle cells, C2C12, grown in a serum-free medium. This strategy led to the identification of 80 nonredundant proteins, of which 27 were secretory proteins that were identified with a minimum of two tryptic peptides. A number of the identified secretory proteins are involved in extracellular matrix remodeling, cellular proliferation, migration, and signaling. A putative network of proteins involving matrix metalloproteinase 2, SPARC, and cystatin C that all interact with TGFbeta signaling has been postulated to contribute toward a functional role in the myogenic differentiation program.     

Fiber-type proportions in mammalian soleus muscle during postnatal development

We analyzed the fiber-type composition of the soleus muscle in rats and mice to determine whether the adult proportion of fiber types is fixed soon after birth or whether it changes during postnatal maturation. We examined muscles from animals varying in age from 1 week to 1 year using monoclonal antibodies that distinguish between fast and slow isoforms of myosin heavy chains. In cross sections of unfixed muscle containing profiles of all myofibers in the muscle, we counted the fibers that stained with antibodies to fast myosin, and in adjacent sections, those that stained positive with an antibody to slow myosin. We also counted the total number of fibers in each section. Rat soleus contained about 2500 myofibers, and mouse about 1000 at all ages studied, suggesting that myogenesis ceases in soleus by 1 week after birth or sooner. In mouse soleus, the relative proportions of fibers staining positive with fast and slow myosin antibodies were similar at all ages studied, about 60%–70% being fast and 30%–40% slow. In rat soleus, however, the proportions of fast antibody-positive and slow antibody-positive fibers changed dramatically during postnatal maturation. At 1 week after birth, about 50% of rat soleus fibers stained with fast myosin antibodies, whereas between 1 and 2 months this value fell to about 10%. In mouse, about 10% of fibers at 1 week, but none at 1 year, reacted with both fast and slow antibodies, whereas in rat, fewer than 3% bound both antibodies to a significant degree at 1 week. It is puzzling why, in rat soleus, the majority of apparently fast fibers present at 1 week is converted to a slow phenotype, whereas in mouse soleus the predominant change appears to be the suppression of fast myosin expression in a subset of fibers that expresses both myosin types at 1 week. It is possible that this may be related to differences in size and the amount of body growth between these two species.     

MicroRNA transcriptome profiles during swine skeletal muscle development

Background

Dietary polyunsaturated fatty acids (PUFA), in particular the long chain marine fatty acids docosahexaenoic (DHA) and eicosapentaenoic (EPA), are linked to many health benefits in humans and in animal models. Little is known of the molecular response to DHA and EPA of the small intestine, and the potential contribution of this organ to the beneficial effects of these fatty acids. Here, we assessed gene expression changes induced by DHA and EPA in the wildtype C57BL/6J murine small intestine using whole genome microarrays and functionally characterized the most prominent biological process.

Results

The main biological process affected based on gene expression analysis was lipid metabolism. Fatty acid uptake, peroxisomal and mitochondrial beta-oxidation, and omega-oxidation of fatty acids were all increased. Quantitative real time PCR, and -in a second animal experiment- intestinal fatty acid oxidation measurements confirmed significant gene expression differences and showed in a dose-dependent manner significant changes at biological functional level. Furthermore, no major changes in the expression of lipid metabolism genes were observed in the colon.

Conclusion

We show that marine n-3 fatty acids regulate small intestinal gene expression and increase fatty acid oxidation. Since this organ contributes significantly to whole organism energy use, this effect on the small intestine may well contribute to the beneficial physiological effects of marine PUFAs under conditions that will normally lead to development of obesity, insulin resistance and diabetes.