Evidence for increased myofibrillar mobility in desmin-null mouse skeletal muscle

2002 ◽  
Vol 205 (3) ◽  
pp. 321-325
Author(s):  
Sameer B. Shah ◽  
Fong-Chin Su ◽  
Kimberly Jordan ◽  
Derek J. Milner ◽  
Jan Fridén ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Quantitative Estimation ◽  
Horizontal Displacement ◽  
Radial Force ◽  
Null Mouse ◽  
Force Transmission ◽  
Wild Type ◽  
Functional Roles ◽  
Fifth Toe ◽  
Knockout Animals

SUMMARY Quantitative electron microscopy was used to characterize the longitudinal mobility of myofibrils during muscle extension to investigate the functional roles of skeletal muscle intermediate filaments. Extensor digitorum longus fifth toe muscles from wild-type (+/+) and desmin-null (des –/–) animals were passively stretched to varying lengths, and the horizontal displacement of adjacent Z-disks in neighboring myofibrils (Δxmyo) and average sarcomere length (SL) were calculated. At short SL (<2.20 μm), wild-type and desmin-null Δxmyo were not significantly different, although there was a trend towards greater Z-disk misalignment in muscles from knockout animals (Δxmyo 0.34±0.04 μm versus 0.22±0.09 μm; P>0.2; means ± s.e.m.). However, at higher SL (>2.90 μm), muscles from knockout animals displayed a dramatically increased Δxmyo relative to wild-type muscles (0.49±0.10 μm versus 0.25±0.07 μm; P<0.05). The results, which establish a maximum extension of the desmin network surrounding the Z-disk, provide what we believe to be the first quantitative estimation of the functional limits of the desmin intermediate filament system in the presence of an intact myofibrillar lattice. The existence of a limit on the extension of desmin suggests a mechanism for the recruitment of desmin into a network of force transmission, whether as a longitudinal load bearer or as a component in a radial force-transmission system.

scholarly journals Influences of Desmin and Keratin 19 on Passive Biomechanical Properties of Mouse Skeletal Muscle

2012 ◽  
Vol 2012 ◽  
pp. 1-12 ◽  
Author(s):  
Sameer B. Shah ◽  
James M. Love ◽  
Andrea O'Neill ◽  
Richard M. Lovering ◽  
Robert J. Bloch
Keyword(s):  
Skeletal Muscle ◽  
Structural Connectivity ◽  
Structural Response ◽  
Biomechanical Properties ◽  
Force Transmission ◽  
Wild Type ◽  
Additional Insight ◽  
Keratin 19 ◽  
Keratin Intermediate Filaments ◽  
Insight Into

In skeletal muscle fibers, forces must be transmitted between the plasma membrane and the intracellular contractile lattice, and within this lattice between adjacent myofibrils. Based on their prevalence, biomechanical properties and localization, desmin and keratin intermediate filaments (IFs) are likely to participate in structural connectivity and force transmission. We examined the passive load-bearing response of single fibers from the extensor digitorum longus (EDL) muscles of young (3 months) and aged (10 months) wild-type, desmin-null, K19-null, and desmin/K19 double-null mice. Though fibers are more compliant in all mutant genotypes compared to wild-type, the structural response of each genotype is distinct, suggesting multiple mechanisms by which desmin and keratin influence the biomechanical properties of myofibers. This work provides additional insight into the influences of IFs on structure-function relationships in skeletal muscle. It may also have implications for understanding the progression of desminopathies and other IF-related myopathies.

The α1- and α2-isoforms of Na-K-ATPase play different roles in skeletal muscle contractility

2001 ◽  
Vol 281 (3) ◽  
pp. R917-R925 ◽  
Author(s):  
Suiwen He ◽  
Daniel A. Shelly ◽  
Amy E. Moseley ◽  
Paul F. James ◽  
J. Howard James ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Muscle Contraction ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Wild Type ◽  
Muscle Contractility ◽  
Functional Roles ◽  
Skeletal Muscle Contraction ◽  
Contractile Parameters

The Na-K-ATPase, which maintains the Na+ and K+ gradients across the plasma membrane, can play a major role in modulation of skeletal muscle contractility. Although both α1- and α2-isoforms of the Na-K-ATPase are expressed in skeletal muscle, the physiological significance of these isoforms in contractility is not known. Evaluation of the contractile parameters of mouse extensor digitorum longus (EDL) was carried out using gene-targeted mice lacking one copy of either the α1- or α2-isoform gene of the Na-K-ATPase. The EDL muscles from heterozygous mice contain approximately one-half of the α1- or α2-isoform, respectively, which permits differentiation of the functional roles of these isoforms. EDL from the α1 +/− mouse shows lower force compared with wild type, whereas that from the α2 +/− mouse shows greater force. The different functional roles of these two isoforms are further demonstrated because inhibition of the α2-isoform with ouabain increases contractility of α1 +/−EDL. These results demonstrate that the Na-K-ATPase α1- and α2-isoforms may play different roles in skeletal muscle contraction.

scholarly journals Sarcomere number regulation maintained after immobilization in desmin-null mouse skeletal muscle

2001 ◽  
Vol 204 (10) ◽  
pp. 1703-1710 ◽  
Author(s):  
S.B. Shah ◽  
D. Peters ◽  
K.A. Jordan ◽  
D.J. Milner ◽  
J. Friden ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Knockout Mice ◽  
Tibialis Anterior ◽  
Null Mouse ◽  
Wild Type ◽  
Optimal Arrangement ◽  
Hindlimb Muscles ◽  
Muscle Changes ◽  
Sarcomere Number

The serial sarcomere number of skeletal muscle changes in response to chronic length perturbation. The role of the intermediate filament desmin in regulating these changes was investigated by comparing the architectural adaptations of the tibialis anterior, extensor digitorum longus (EDL) and soleus from wild-type mice with those of homozygous desmin knockout mice after hindlimb immobilization. After 28 days, serial sarcomere number increased significantly in the lengthened wild-type tibialis anterior (by approximately 9 %) and EDL (by approximately 17 %). Surprisingly, muscles from desmin knockout mice also experienced significant serial remodeling, with the serial sarcomere number of the tibialis anterior increasing by approximately 10 % and that of the EDL by approximately 27 %. A consistent result was observed in the shortened soleus: a significant decrease in sarcomere number was observed in the muscles from both wild-type (approximately 26 %) and knockout (approximately 12 %) mice. Thus, although desmin is not essential for sarcomerogenesis or sarcomere subtraction in mouse hindlimb muscles, the results do suggest subtle differences in the nature of sarcomere number adaptation. We speculate that desmin may play a role in regulating the optimal arrangement of sarcomeres within the muscle or in sensing the magnitude of the immobilization effect itself.

Negative impact of tissue inhibitor of metalloproteinase-3 null mutation on lung structure and function in response to sepsis

2003 ◽  
Vol 285 (6) ◽  
pp. L1222-L1232 ◽  
Author(s):  
Erica L. Martin ◽  
Brent Z. Moyer ◽  
M. Cynthia Pape ◽  
Barry Starcher ◽  
Kevin J. Leco ◽  
...  
Keyword(s):  
Negative Impact ◽  
Cecal Ligation ◽  
Lung Compliance ◽  
Tissue Inhibitor Of Metalloproteinase ◽  
Tissue Inhibitors Of Metalloproteinases ◽  
Wild Type ◽  
Gelatinase Activity ◽  
Lung Structure ◽  
And Function ◽  
Knockout Animals

Matrix metalloproteinases (MMPs) are degradative enzymes, which act to remodel tissue. Their activity is regulated by the tissue inhibitors of metalloproteinases (TIMPs). An imbalance in the degradation/inhibition activities has been associated with many diseases, including sepsis. We have previously shown that TIMP-3 knockout animals develop spontaneous, progressive air space enlargement. The objectives of this study were to determine the effects of a septic lung stress induced by cecal ligation and perforation (CLP) on lung function, structure, pulmonary surfactant, and inflammation in TIMP-3 null mice. Knockout and wild-type animals were randomized to either sham or CLP surgery, allowed to recover for 6 h, and then euthanized. TIMP-3 null animals exposed to sham surgery had a significant increase in lung compliance when compared with sham wild-type mice. Additionally, the TIMP-3 knockout mice showed a significant increase in compliance following CLP. Rapid compliance changes were accompanied by significantly decreased collagen and fibronectin levels and increased gelatinase (MMP-2 and -9) abundance and activation. Additionally, in situ zymography showed increased airway-associated gelatinase activity in the knockout animals enhanced following CLP. In conclusion, exposing TIMP-3 null animals to sepsis rapidly enhances the phenotypic abnormalities of these mice, due to increased MMP activity induced by CLP.

Insulin promotes glycogen synthesis in the absence of GSK3 phosphorylation in skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. E28-E35 ◽  
Author(s):  
Michale Bouskila ◽  
Michael F. Hirshman ◽  
Jørgen Jensen ◽  
Laurie J. Goodyear ◽  
Kei Sakamoto
Keyword(s):  
Skeletal Muscle ◽  
Glucose Uptake ◽  
Muscle Glycogen ◽  
Glycogen Content ◽  
Glycogen Synthase ◽  
Glycogen Synthesis ◽  
Wild Type ◽  
Muscle Glycogen Synthesis ◽  
Mutant Forms

Insulin promotes dephosphorylation and activation of glycogen synthase (GS) by inactivating glycogen synthase kinase (GSK) 3 through phosphorylation. Insulin also promotes glucose uptake and glucose 6-phosphate (G-6- P) production, which allosterically activates GS. The relative importance of these two regulatory mechanisms in the activation of GS in vivo is unknown. The aim of this study was to investigate if dephosphorylation of GS mediated via GSK3 is required for normal glycogen synthesis in skeletal muscle with insulin. We employed GSK3 knockin mice in which wild-type GSK3α and -β genes are replaced with mutant forms (GSK3α/βS21A/S21A/S9A/S9A), which are nonresponsive to insulin. Although insulin failed to promote dephosphorylation and activation of GS in GSK3α/βS21A/S21A/S9A/S9Amice, glycogen content in different muscles from these mice was similar compared with wild-type mice. Basal and epinephrine-stimulated activity of muscle glycogen phosphorylase was comparable between wild-type and GSK3 knockin mice. Incubation of isolated soleus muscle in Krebs buffer containing 5.5 mM glucose in the presence or absence of insulin revealed that the levels of G-6- P, the rate of [14C]glucose incorporation into glycogen, and an increase in total glycogen content were similar between wild-type and GSK3 knockin mice. Injection of glucose containing 2-deoxy-[3H]glucose and [14C]glucose also resulted in similar rates of muscle glucose uptake and glycogen synthesis in vivo between wild-type and GSK3 knockin mice. These results suggest that insulin-mediated inhibition of GSK3 is not a rate-limiting step in muscle glycogen synthesis in mice. This suggests that allosteric regulation of GS by G-6- P may play a key role in insulin-stimulated muscle glycogen synthesis in vivo.

AMP kinase is not required for the GLUT4 response to exercise and denervation in skeletal muscle

2004 ◽  
Vol 287 (4) ◽  
pp. E739-E743 ◽  
Author(s):  
Burton F. Holmes ◽  
David B. Lang ◽  
Morris J. Birnbaum ◽  
James Mu ◽  
G. Lynis Dohm
Keyword(s):  
Skeletal Muscle ◽  
Dominant Negative ◽  
Treadmill Running ◽  
Wild Type ◽  
Α Subunit ◽  
Ampk Activity ◽  
Denervated Muscles ◽  
Amp Activated Protein Kinase ◽  
Response To Exercise

An acute bout of exercise increases muscle GLUT4 mRNA in mice, and denervation decreases GLUT4 mRNA. AMP-activated protein kinase (AMPK) activity in skeletal muscle is also increased by exercise, and GLUT4 mRNA is increased in mouse skeletal muscle after treatment with AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside(AICAR). These findings suggest that AMPK activation might be responsible for the increase in GLUT4 mRNA expression in response to exercise. To investigate the role of AMPK in GLUT4 regulation in response to exercise and denervation, transgenic mice with a mutated AMPK α-subunit (dominant negative; AMPK-DN) were studied. GLUT4 did not increase in AMPK-DN mice that were treated with AICAR, demonstrating that muscle AMPK is inactive. Exercise (two 3-h bouts of treadmill running separated by 1 h of rest) increased GLUT4 mRNA in both wild-type and AMPK-DN mice. Likewise, denervation decreased GLUT4 mRNA in both wild-type and AMPK-DN mice. GLUT4 mRNA was also increased by AICAR treatment in both the innervated and denervated muscles. These data demonstrate that AMPK is not required for the response of GLUT4 mRNA to exercise and denervation.

Treadmill running causes significant fiber damage in skeletal muscle of KATP channel-deficient mice

2005 ◽  
Vol 22 (2) ◽  
pp. 204-212 ◽  
Author(s):  
M. Thabet ◽  
T. Miki ◽  
S. Seino ◽  
J.-M. Renaud
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Treadmill Running ◽  
Wild Type ◽  
Connective Tissues ◽  
Fiber Damage ◽  
Hindlimb Muscles ◽  
Skeletal Muscle Fibers ◽  
And Function ◽  
Deficient Mice

Although it has been suggested that the ATP-sensitive K+ (KATP) channel protects muscle against function impairment, most studies have so far given little evidence for significant perturbation in the integrity and function of skeletal muscle fibers from inactive mice that lack KATP channel activity in their cell membrane. The objective was, therefore, to test the hypothesis that KATP channel-deficient skeletal muscle fibers become damaged when mice are subjected to stress. Wild-type and KATP channel-deficient mice (Kir6.2−/− mice) were subjected to 4–5 wk of treadmill running at either 20 m/min with 0° inclination or at 24 m/min with 20° uphill inclination. Muscles of all wild-type mice and of nonexercised Kir6.2−/− mice had very few fibers with internal nuclei. After 4–5 wk of treadmill running, there was little evidence for connective tissues and mononucleated cells in Kir6.2−/− hindlimb muscles, whereas the number of fibers with internal nuclei, which appear when damaged fibers are regenerated by satellite cells, was significantly higher in Kir6.2−/− than wild-type mice. Between 5% and 25% of the total number of fibers in Kir6.2−/− extensor digitum longus, plantaris, and tibialis muscles had internal nuclei, and most of such fibers were type IIB fibers. Contrary to hindlimb muscles, diaphragms of Kir6.2−/− mice that had run at 24 m/min had few fibers with internal nuclei, but mild to severe fiber damage was observed. In conclusion, the study provides for the first time evidence 1) that the KATP channels of skeletal muscle are essential to prevent fiber damage, and thus muscle dysfunction; and 2) that the extent of fiber damage is greater and the capacity of fiber regeneration is less in Kir6.2−/− diaphragm muscles compared with hindlimb muscles.

Lower skeletal muscle mass in male transgenic mice with muscle-specific overexpression of myostatin

2003 ◽  
Vol 285 (4) ◽  
pp. E876-E888 ◽  
Author(s):  
Suzanne Reisz-Porszasz ◽  
Shalender Bhasin ◽  
Jorge N. Artaza ◽  
Ruoqing Shen ◽  
Indrani Sinha-Hikim ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Transgenic Mice ◽  
Muscle Mass ◽  
Skeletal Muscle Mass ◽  
Fluorescent Protein ◽  
Male Mice ◽  
Wild Type ◽  
Specific Expression ◽  
Muscle Weight ◽  
Myostatin Gene

Mutations in the myostatin gene are associated with hypermuscularity, suggesting that myostatin inhibits skeletal muscle growth. We postulated that increased tissue-specific expression of myostatin protein in skeletal muscle would induce muscle loss. To investigate this hypothesis, we generated transgenic mice that overexpress myostatin protein selectively in the skeletal muscle, with or without ancillary expression in the heart, utilizing cDNA constructs in which a wild-type (MCK/Mst) or mutated muscle creatine kinase (MCK-3E/Mst) promoter was placed upstream of mouse myostatin cDNA. Transgenic mice harboring these MCK promoters linked to enhanced green fluorescent protein (EGFP) expressed the reporter protein only in skeletal and cardiac muscles (MCK) or in skeletal muscle alone (MCK-3E). Seven-week-old animals were genotyped by PCR of tail DNA or by Southern blot analysis of liver DNA. Myostatin mRNA and protein, measured by RT-PCR and Western blot, respectively, were significantly higher in gastrocnemius, quadriceps, and tibialis anterior of MCK/Mst-transgenic mice compared with wild-type mice. Male MCK/Mst-transgenic mice had 18–24% lower hind- and forelimb muscle weight and 18% reduction in quadriceps and gastrocnemius fiber cross-sectional area and myonuclear number (immunohistochemistry) than wild-type male mice. Male transgenic mice with mutated MCK-3E promoter showed similar effects on muscle mass. However, female transgenic mice with either type of MCK promoter did not differ from wild-type controls in either body weight or skeletal muscle mass. In conclusion, increased expression of myostatin in skeletal muscle is associated with lower muscle mass and decreased fiber size and myonuclear number, decreased cardiac muscle mass, and increased fat mass in male mice, consistent with its role as an inhibitor of skeletal muscle mass. The mechanism of gender specificity remains to be clarified.

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