Skeletal Muscle Characterization of Japanese Quail Line Selectively Bred for Lower Body Weight as an Avian Model of Delayed Muscle Growth with Hypoplasia

This study was designed to extensively characterize the skeletal muscle development in the low weight (LW) quail selected from random bred control (RBC) Japanese quail in order to provide a new avian model of impaired and delayed growth in physically normal animals. The LW line had smaller embryo and body weights than the RBC line in all age groups (P<0.05). During 3 to 42 d post-hatch, the LW line exhibited approximately 60% smaller weight of pectoralis major muscle (PM), mainly resulting from lower fiber numbers compared to the RBC line (P<0.05). During early post-hatch period when myotubes are still actively forming, the LW line showed impaired PM growth with prolonged expression of Pax7 and lower expression levels of MyoD, Myf-5, and myogenin (P<0.05), likely leading to impairment of myogenic differentiation and consequently, reduced muscle fiber formation. Additionally, the LW line had delayed transition of neonatal to adult myosin heavy chain isoform, suggesting delayed muscle maturation. This is further supported by the finding that the LW line continued to grow unlike the RBC line; difference in the percentages of PMW to body weights between both quail lines diminished with increasing age from 42 to 75 d post-hatch. This delayed muscle growth in the LW line is accompanied by higher levels of myogenin expression at 42 d (P<0.05), higher percentage of centered nuclei at 42 d (P<0.01), and greater rate of increase in fiber size between 42 and 75 d post-hatch (P<0.001) compared to the RBC line. Analysis of physiological, morphological, and developmental parameters during muscle development of the LW quail line provided a well-characterized avian model for future identification of the responsible genes and for studying mechanisms of hypoplasia and delayed muscle growth.     

Beef palatability and its relationship with protein degradation and muscle fibre type profile in longissimus thoracis in Alentejana breed from divergent growth pathways

The traditional beef production in the South of Portugal is based on a discontinuous growth (DG) system that requires lower external inputs and could enhance meat quality and financial returns to cattle producers. This system allows farmers to take advantage of the bull’s compensatory growth when the pasture is abundant and finishes the cattle on concentrates for 2 to 3 months before slaughter. The fast gain rate before slaughter could be a valuable strategy to improve tenderness and to reduce its inconsistency in beef production. Therefore, the aim of this study was to evaluate the effects of production system (continuous growth (CG) v. DG) on longissimus thoracis muscle properties from Alentejana bulls. In total, 40 Alentejana male calves were allocated to two distinct feeding regimes: in the CG system, animals were fed concentrate plus hay and slaughtered at 18 months of age, whereas in the DG system, animals were fed on hay until 15 months of age and then fed the same diet provided to the CG group until 24 months of age. The DG system had a positive impact on meat tenderness (P<0.001) and global acceptability (P<0.001). DG bulls had greater fibre cross-sectional area (CSA) of glycolytic fibres (P<0.05) and relative area of the muscle (RA) occupied by type IIX fibres (P<0.01) and greater levels of α-actinin (P<0.05) and myosin light chain 2 (P<0.01) proteins, and pH_24h (P<0.01) than CG bulls. The latter had greater CSA of type I (P<0.05) and type IIA (P<0.01) and greater RA of type IIA (P<0.05) and oxidative (P<0.05) than CG bulls. The compensatory growth production system had a positive impact on meat tenderness and global acceptability, overcoming the negative effects of slaughter of the bulls at a later age. The DG beef system could be a worthwhile strategy of beef production in Mediterranean areas due to the low-quality pasture in summer.     

Spatial fiber type distribution in normal human muscle Histochemical and tensiomyographical evaluation

The variability of fiber type distribution in nine limb muscles was examined with histochemical and tensiomyographical (TMG) methods in two groups of 15 men aged between 17 and 40 years. The aim of this study was to determine the extent to which the relative occurrence of different fiber types and subtypes varies within human limb muscles in function to depth and to predict fiber type proportions with a non-invasive TMG method.The distribution of different fiber types varied within the muscles, as a function of depth, with a predominance of type 2b fibers at the surface and type 1 fibers in deeper regions of the muscle. For all the analyzed muscles the contraction times measured at stimulus intensity 10% of supramaximal stimulus (10% MS) were significantly (p<0.05) shorter than the contraction times measured at 50% of supramaximal stimulus intensity (50% MS). The Pearson's correlation coefficient between percentage of type 1 muscle fibers measured at the surface of the muscle and contraction time at 10% MS, obtained by TMG was statistically significant (r=0.76,P<0.01). Also the Pearson's correlation coefficient between percentage of type 1 muscle fibers measured in the deep region of the muscle and contraction time at 50% MS obtained by TMG was also statistically significant (r=0.90,P<0.001).These findings suggest that the contraction time obtained by TMG may be useful for non-invasive examining of muscle fiber types spatial distribution in humans.     

The rearing system modulates biochemical and histological differences in loin and ham muscles between Basque and Large White pigs

Conventional pork production, based on highly selected breeds for growth efficiency and carcass leanness, is generally considered to decrease pork quality. In contrast, non-selected breeds produced in extensive systems are associated with high pork quality, which is generally attributed to higher intramuscular fat (IMF) content and less glycolytic muscle metabolism. The present study aimed to determine biochemical, histological and quality traits of loin and ham muscles of pigs from selected Large White (LW) and local French, non-selected Basque (B) breeds. Pigs were reared in a conventional indoor (C, slatted floor), alternative (A, indoor bedding and outdoor area) or extensive system (E, free range, B pigs only). A total of 100 castrated males were produced in 2 replicates, each containing 5 groups of 10 pigs based on breed and system: LWC, LWA, BC, BA and BE. The glycolytic longissimus muscle (LM) and semimembranosus muscle (SM), and the deep red (RSTM) and superficial white (WSTM) portions of semitendinosus muscle (STM) were studied at 145 kg BW. Overall, breed induced stronger effects on muscle traits than the rearing system, among which the E system induced greater changes. The lower muscle growth of B pigs was associated with fewer muscle fibers and a smaller cross-sectional area (CSA) of glycolytic fibers (P < 0.01). The SM was less glycolytic and more oxidative in B than in LW pigs (P < 0.001). The WSTM followed a similar trend, with a larger relative area of type I fibers in B pigs. In contrast, the LM and RSTM were more oxidative in LW pigs. B pigs had higher IMF content and ultimate pH in all muscles, along with lower glycolytic potential, less light and redder meat in the LM and SM (P < 0.001). Compared to the C system, the A system induced only a shift towards a more oxidative metabolism in the LM and a smaller fiber CSA in the RSTM of LW pigs (P < 0.05), without influencing pork quality traits. Compared to BC pigs, BE pigs had a more oxidative and less glycolytic muscle metabolism, along with higher ultimate pH, lower lightness and redder meat (P < 0.01), but similar IMF content. Overall, results indicate that influences of breed and rearing system on muscle properties depend on muscle type, and that IMF content and fiber-type composition are unrelated traits that can be modified independently by genetic or rearing factors.     

Skeletal muscle is protected from disuse in hibernating dauria ground squirrels

The purpose of this study is to test the hypothesis that muscle fibers are protected from undue atrophy in hibernating dauria ground squirrels (Spermophilus dauricus, Brandt). Muscle mass, fiber cross sectional area (CSA, video analysis) and fiber type distribution (m-ATPase staining) were determined in extensor digitorum longus (EDL) muscle from non-hibernating control animals (Pre-H), from animals who hibernated for one (H1) or two (H2) months, and from animals 2-4 days after arousal (Post-H; N = 8 each). Muscle wet weight decreased less than body weight in hibernating animals, resulting in a steady increase in muscle-to-body mass ratio (+ 37% in Post-H compared to Pre-H, p < 0.001). In the Pre-H group, Type I (6.3 ± 2.0%) and II (93.7 ± 2.0%) fiber CSAs were 1719 ± 201 and 2261 ± 287 μm², respectively. There was a tendency (n.s.) of larger CSA of type I in hibernators compared to pre-H. In the Post-H group, fiber CSA and type distribution were not different from Pre-H. We are the first to report data on EDL fiber type distribution and confirm a protective effect that prevents muscle atrophy in spite of prolonged disuse during hibernation in dauria ground squirrels.     

Genomic variants associated with the number and diameter of muscle fibers in pigs as revealed by a genome-wide association study

Muscle fiber characteristics comprise a set of complex traits that influence the mea quality and lean meat production of livestock. However, the genetic and biological mechanisms regulating muscle fiber characteristics are largely unknown in pigs. Based on a genome-wide association study (GWAS) performed on 421 Large White × Min pig F2 individuals presenting well-characterized phenotypes, this work aimed to detect genome variations and candidate genes for five muscle fiber characteristics: percentage of type I fibers (FIB1P), percentage of type IIA fibers (FIB2AP), percentage of type IIB fibers (FIB2BP), diameter of muscle fibers (DIAMF) and number of muscle fibers per unit area (NUMMF). The GWAS used the Illumina Porcine SNP60K genotypic data, which were analyzed by a mixed model. Seven and 10 single nucleotide polymorphisms (SNPs) were significantly associated with DIAMF and NUMMF, respectively (P < 1.10E-06); no SNP was significantly associated with FIB1P, FIB2AP or FIB2B. For DIAMF, the significant SNPs on chromosome 4 were located in the previously reported quantitative trait loci (QTL) interval. Because the significant SNPs on chromosome 6 were not mapped in the previously reported QTL interval, a putative novel QTL was suggested for this locus. None of the previously reported QTL intervals on chromosomes 6 and 14 harbored significant SNPs for NUMMF; thus, new potential QTLs on these two chromosomes are suggested in the present work. The most significant SNPs associated with DIAMF (ALGA0025682) and NUMMF (MARC0046984) explained 12.02% and 11.59% of the phenotypic variation of these traits, respectively. In addition, both SNPs were validated as associated with DIAMF and NUMMF in Beijing Black pigs (P < 0.01). Some candidate genes or non-coding RNAs, such as solute carrier family 44 member 5 and miR-124a-1 for DIAMF, and coiled-coil serine rich protein 2 for NUMMF, were identified based on their close location to the significant SNPs. This study revealed some genome-wide association variants for muscle fiber characteristics, and it provides valuable information to discover the genetic mechanisms controlling these traits in pigs.     

Alanine metabolism in skeletal muscle in tissue culture

Alanine production by skeletal muscle in tissue culture was studied using an established myogenic line (L₆) of rat skeletal muscle cells. Correlation analyses were performed on rates of metabolism of alanine, glucose, lactate and pyruvate over incubation periods up to 96 h. Alanine production did not correlate significantly with glucose utilization (r = 0.24, P < 0.20). Alanine production, however, did correlate with lactate production (r = 0.72, P < 0.0005) as well as medium (r = 0.50, P < 0.025) and intracellular (r = 0.85, P < 0.0005) pyruvate concentrations. The intercepts of the latter two correlation analyses indicated that when medium or cell pyruvate fell below 0.28 mM or 1 nmol/mg protein, respectively, net alanine consumption occurred. Alanine synthesis also correlated (r = 0.71, P < 0.0005) with the percent change in the cell mass action ratio for the sum of the alanine and aspartate aminotransferase reactions, i.e., [alanine] [malate]/[aspartate] [lactate]. These results suggest that alanine production is not necessarily linked to the rate of glucose utilization but rather to pyruvate overflow above a critical intracellular level; under conditions of pyruvate overflow, alanine synthesis is driven by the tendency to establish equilibrium between metabolites of the linked amino acid transaminases in skeletal muscle.     

Skeletal muscle weakness in osteogeneis imperfecta mice

Exercise intolerance, muscle fatigue and weakness are often-reported, little-investigated concerns of patients with osteogenesis imperfecta (OI). OI is a heritable connective tissue disorder hallmarked by bone fragility resulting primarily from dominant mutations in the proα1(I) or proα2(I) collagen genes and the recently discovered recessive mutations in post-translational modifying proteins of type I collagen. In this study we examined the soleus (S), plantaris (P), gastrocnemius (G), tibialis anterior (TA) and quadriceps (Q) muscles of mice expressing mild (+/oim) and moderately severe (oim/oim) OI for evidence of inherent muscle pathology. In particular, muscle weight, fiber cross-sectional area (CSA), fiber type, fiber histomorphology, fibrillar collagen content, absolute, relative and specific peak tetanic force (P_o, P_o/mg and P_o/CSA respectively) of individual muscles were evaluated. Oim/oim mouse muscles were generally smaller, contained less fibrillar collagen, had decreased P_o and an inability to sustain P_o for the 300-ms testing duration for specific muscles; +/oim mice had a similar but milder skeletal muscle phenotype. +/oim mice had mild weakness of specific muscles but were less affected than their oim/oim counterparts which demonstrated readily apparent skeletal muscle pathology. Therefore muscle weakness in oim mice reflects inherent skeletal muscle pathology.     

Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure

Delp, Michael D., Changping Duan, John P. Mattson, andTimothy I. Musch. Changes in skeletal muscle biochemistry and histology relative to fiber type in rats with heart failure.J. Appl. Physiol. 83(4):1291-1299, 1997.One of the primary consequences of leftventricular dysfunction (LVD) after myocardial infarction is adecrement in exercise capacity. Several factors have been hypothesizedto account for this decrement, including alterations in skeletal musclemetabolism and aerobic capacity. The purpose of this study was todetermine whether LVD-induced alterations in skeletal muscle enzymeactivities, fiber composition, and fiber size are1) generalized in muscles orspecific to muscles composed primarily of a given fiber type and2) related to the severity of theLVD. Female Wistar rats were divided into three groups: sham-operatedcontrols (n = 13) and rats withmoderate (n = 10) and severe(n = 7) LVD. LVD was surgicallyinduced by ligating the left main coronary artery and resulted inelevations (P < 0.05) in leftventricular end-diastolic pressure (sham, 5 ± 1 mmHg; moderate LVD,11 ± 1 mmHg; severe LVD, 25 ± 1 mmHg). Moderate LVDdecreased the activities of phosphofructokinase (PFK) and citratesynthase in one muscle composed of type IIB fibers but did not modifyfiber composition or size of any muscle studied. However, severe LVDdiminished the activity of enzymes involved in terminal and-oxidation in muscles composed primarily of type I fibers, type IIAfibers, and type IIB fibers. In addition, severe LVD induced areduction in the activity of PFK in type IIB muscle, a 10% reductionin the percentage of type IID/X fibers, and a corresponding increase inthe portion of type IIB fibers. Atrophy of type I fibers, type IIAfibers, and/or type IIB fibers occurred in soleus and plantarismuscles of rats with severe LVD. These data indicate that rats withsevere LVD after myocardial infarction exhibit1) decrements in mitochondrialenzyme activities independent of muscle fiber composition,2) a reduction in PFK activity in type IIB muscle, 3) transformationof type IID/X to type IIB fibers, and4) atrophy of type I, IIA, and IIBfibers.

     

Influence of complete spinal cord injury on skeletal muscle within 6mo of injury

This study examined the influence of spinal cord injury (SCI) onaffected skeletal muscle. The right vastus lateralis muscle wasbiopsied in 12 patients as soon as they were clinically stable (average6 wk after SCI), and 11 and 24 wk after injury. Samples were also takenfrom nine able-bodied controls at two time points 18 wk apart. Surfaceelectrical stimulation (ES) was applied to the left quadriceps femorismuscle to assess fatigue at these same time intervals. Biopsies wereanalyzed for fiber type percent and cross-sectional area (CSA), fibertype-specific succinic dehydrogenase (SDH) and -glycerophosphatedehydrogenase (GPDH) activities, and myosin heavy chainpercent. Controls showed no change in any variable overtime. Patients showed 27-56% atrophy(P = 0.000) of type I, IIa, andIIax+IIx fibers from 6 to 24 wk after injury, resulting in fiber CSAapproximately one-third that of controls. Their fiber type specific SDHand GPDH activities increased (P  0.001) from 32 to 90% over the 18 wk, thereby approaching or surpassing control values. The relative CSA of type I fibers and percentage of myosin heavy chain type I did not change. There wasapparent conversion among type II fiber subtypes; type IIa decreasedand type IIax+IIx increased (P  0.012). Force loss during ES did not change over time for either groupbut was greater (P = 0.000) for SCIpatients than for controls overall (27 vs. 9%). The results indicatethat vastus lateralis muscle shows marked fiber atrophy, no change inthe proportion of type I fibers, and a relative independence ofmetabolic enzyme levels from activation during the first 24 wk afterclinically complete SCI. Over this time, quadriceps femoris muscleshowed moderately greater force loss during ES in patients than incontrols. It is suggested that the predominant response of mixed humanskeletal muscle within 6 mo of SCI is loss of contractile protein.Therapeutic interventions could take advantage of this to increasemuscle mass.

     

Lower limb skeletal muscle function after 6wk of bed rest

Berg, H. E., L. Larsson, and P. A. Tesch. Lower limbskeletal muscle function after 6 wk of bed rest. J. Appl. Physiol. 82(1): 182-188, 1997.Force,electromyographic (EMG) activity, muscle mass, and fibercharacteristics were studied in seven healthy men before and after 6 wkof bed rest. Maximum voluntary isometric and concentric knee extensortorque decreased (P < 0.05)uniformly across angular velocities by 25-30% after bed rest.Maximum quadricep rectified EMG decreased by 19 ± 23%, whereassubmaximum (100-Nm isometric action) EMG increased by 44 ± 28%.Knee extensor muscle cross-sectional area (CSA), assessed by usingmagnetic resonance imaging, decreased by 14 ± 4%. Maximum torqueper knee extensor CSA decreased by 13 ± 9%. Vastus lateralis fiberCSA decreased 18 ± 14%. Neither type I, IIA, and IIB fiberpercentages nor their relative proportions of myosin heavy chain (MHC)isoforms were altered after bed rest. Because the decline in strengthcould not be entirely accounted for by decreased muscle CSA, it issuggested that the strength loss is also due to factors resulting indecreased neural input to muscle and/or reduced specifictension of muscle, as evidenced by a decreased torque/EMG ratio.Additionally, it is concluded that muscle unloading in humans does notinduce important changes in fiber type or MHC composition or in vivomuscle contractile properties.

     

Contrasting cellularity on fat deposition in the subcutaneous adipose tissue and longissimus lumborum muscle from lean and fat pigs under dietary protein reduction

The production of pork with high amounts of intramuscular fat (IMF) without an increase in subcutaneous fat is highly desirable for the pig industry and consumers. Herein, we question the impact of dietary protein reduction (18% v. 13%) on fat deposition in the subcutaneous adipose tissue (SAT) and longissimus lumborum (LL) muscle using genetically diverse pigs for body fatness (lean v. fat). A clear effect of genotype was observed on plasma insulin (P=0.004) and leptin (P<0.001), as well as on backfat thickness (P<0.001), with the fat pigs having higher values. Accordingly, IMF was higher in the fat pigs, when compared with their lean counterparts (P=0.003), which was supported by enlarged adipocytes (P<0.001). The area of lipid droplets within the LL fibres (P=0.039) and extramyocellular lipids number (P=0.017) were increased in pigs fed reduced protein diets, regardless of genotype, which is consistent with higher levels of plasma triacylglycerols (P=0.002). The gene-expression pattern of lipogenic factors in the SAT was distinct from the LL muscle. In the SAT, PPARG expression was similar among genotypes (P>0.05), whereas in the LL muscle it was higher in the lean pigs (P=0.023), especially when fed on low protein diet (P=0.057). The CEBPA and FABP4 mRNA levels were increased in the SAT of fat pigs (P<0.001), without changes in the LL muscle (P>0.05). The influence of diet on FABP4 expression in the SAT was dependent on pig’s genetic background (P=0.005). In conclusion, fat deposition was clearly influenced by genotype and, to a lesser extent, by dietary protein level, the SAT being more sensitive than the LL muscle. One can speculate that the pathways involved in lipid metabolism are downregulated in intramuscular adipocytes when compared with SAT fat cells. This result might be a direct consequence of the relatively low proportion of adipocytes found in the LL muscle.     

Interrelationships of myofibrillar ATPase activity and metabolic properties of myosin heavy chain-based fibre types in rat skeletal muscle

 Myofibrillar ATPase (mATPase), succinate dehydrogenase (SDH) and α-glycerophosphate dehydrogenase (GPD) activities and cross-sectional area (CSA) were measured in fibres of rat medial gastrocnemius muscle using quantitative histochemistry. The same fibres were typed immunohistochemically using monoclonal antibodies specific to selected myosin heavy chain (MHC) isoforms. The values of mATPase, SDH, GPD and CSA formed a continuum, but significant differences in mean values were observed among fibre types of presumed homogeneous MHC content. Type I fibres had the lowest mATPase activity, followed in rank order by type IIA<type IID/X<type IIB. Type IIA fibres had the highest SDH activity, followed in rank order by type IID/X>type I>type IIB. The mean GPD activity was consistently ranked according to fibre type such that type IIB>type IID/X >type IIA>type I. Type IIA fibres were the smallest, type IIB fibres were the largest and types I and IID/X were of intermediate size. Significant interrelationships between mATPase, SDH, GPD and CSA values were found on a fibre-to-fibre basis. Consequently, discrimination of fibres according to their MHC content was possible on the basis of their mATPase, SDH, GPD and CSA profiles. These intrafibre interrelationships suggest that the MHC isoform is associated with phenotypic differences in contractile, metabolic and size properties of muscle fibre types. Accepted: 30 November 1998     

Lack of skeletal muscle hypertrophy in very aged male Fischer 344 x Brown Norway rats.

To examine the effect of extreme old age on muscle plasticity, 6- (adult) and 36-mo-old (old) male Fischer 344 x Brown Norway hybrid rats underwent bilateral surgical ablation of the gastrocnemius muscle to functionally overload (OV) the fast-twitch plantaris muscle for 8 wk. Plantaris muscle wet weight, muscle cross-sectional area (CSA), and average fiber CSA decreased by 44, 42, and 40%, respectively, in old compared with adult rats, and peak isometric tetanic tension decreased by 83%. Compared with muscles in age-matched controls, plantaris muscle mass increased by 53% and type I, IIA, and IIX/IIB CSA increased by 91, 76, and 103%, respectively, in adult-OV rats, but neither wet mass nor fiber CSA increased in old-OV rats. OV decreased type I, IIA, and IIX/IIB mean fiber CSA by 31, 35, and 30%, respectively, in old-OV rats. Collectively, our data indicate that in extreme old age the plantaris muscle undergoes significant loss of mass, fiber CSA, and contractile function, as well as its capacity to undergo hypertrophy in response to a chronic increase in mechanical load.     

Evidence for ACTN3 as a Speed Gene in Isolated Human Muscle Fibers

Purpose

To examine the effect of α-actinin-3 deficiency due to homozygosity for the ACTN3 577X-allele on contractile and morphological properties of fast muscle fibers in non-athletic young men.

Methods

A biopsy was taken from the vastus lateralis of 4 RR and 4 XX individuals to test for differences in morphologic and contractile properties of single muscle fibers. The cross-sectional area of the fiber and muscle fiber composition was determined using standard immunohistochemistry analyses. Skinned single muscle fibers were subjected to active tests to determine peak normalized force (P₀), maximal unloading velocity (V₀) and peak power. A passive stretch test was performed to calculate Young’s Modulus and hysteresis to assess fiber visco-elasticity.

Results

No differences were found in muscle fiber composition. The cross-sectional area of type II_a and II_x fibers was larger in RR compared to XX individuals (P<0.001). P₀ was similar in both groups over all fiber types. A higher V₀ was observed in type II_a fibers of RR genotypes (P<0.001) but not in type I fibers. The visco-elasticity as determined by Young’s Modulus and hysteresis was unaffected by fiber type or genotype.

Conclusion

The greater V₀ and the larger fast fiber CSA in RR compared to XX genotypes likely contribute to enhanced whole muscle performance during high velocity contractions.     

Quantifying differences in the material properties of the fiber regions of the pectoralis major using ultrasound shear wave elastography

The sternocostal and clavicular regions of the pectoralis major are independently harvested to provide shoulder stability, but surgical decision making does not consider the biomechanical consequences that disinsertion of one fiber region over the other has on shoulder function. Differences in material properties between the fiber regions could influence which tissue is more optimal for surgical harvesting. The current study utilized ultrasound shear wave elastography (SWE) to investigate whether the in vivo material properties differ between the fiber regions. Shear wave velocities (SWVs) were collected from the sternocostal and clavicular fiber regions of the pectoralis major from ten healthy young male participants. Participants produced isometric shoulder torques of varying magnitudes (passive, 15%, and 30% MVC) and directions (horizontal and vertical adduction). Four shoulder positions encompassing different vertical abduction and external rotation angles were examined. One-way ANOVAs tested the hypotheses that differences in SWVs during rest existed between the fiber regions as a function of shoulder position, and differences in SWVs during contraction existed as a function of shoulder position and torque direction. In all shoulder positions, the clavicular region exhibited greater SWVs during rest than the sternocostal region (P < 0.001). In shoulder positions that did not include external rotation, the clavicular region exhibited greater SWVs during contraction when producing horizontal adduction torques (P < 0.001), while the sternocostal region exhibited greater SWVs during contraction when producing vertical adduction torques at 30% MVC (P < 0.01). Our results suggest that each fiber region of the pectoralis major provides unique contributions to passive and active shoulder function.     

Aldosterone up‐regulates 12‐ and 15‐lipoxygenase expression and LDL oxidation in human vascular smooth muscle cells

Several lines of evidence suggest that aldosterone excess may have detrimental effects in the cardiovascular system, independent of its interaction with the renal epithelial cells. Here we examined the possibility that aldosterone modulates 12‐ and/or 15‐lipoxygenase (LO) expression/activity in human vascular smooth muscle cells (VSMC), in vitro, thereby potentially contributing to both vascular reactivity and atherogenesis. Following 24 h treatment of VSMC with aldosterone (1 nmol/L), there was a ～2‐fold increase in the generation rate of 12 hydroxyeicosatetraenoic acid (12‐HETE), 70% increase in platelet type 12‐LO mRNA expression (P < 0.001) along with a ～3‐fold increase in 12‐LO protein expression, which were blocked by the mineralocorticoid receptor (MR) antagonists spironolactone (100 nmol/L) and eplerelone (100 nmol/ml). Additionally, aldosterone (1 nmol/L; 24 h) increased the production of 15‐HETE (50%; P < 0.001) and the expression of 15‐LO type 2 mRNA (50%; P < 0.05) (in VSMC). Aldosterone also increased the 12‐ and 15‐LO type 2 mRNA expression in a line of human aortic smooth muscle cells (T/G HA‐VSMC) (60% and 50%, respectively). Aldosterone‐induced 12‐ and 15‐LO type 2 mRNA expressions were blocked by the EGF‐receptor antagonist AG 1478 and by the MAPK‐kinase inhibitor UO126. Aldosterone‐treated VSMC also showed increased LDL oxidation, (～2‐fold; P < 0.001), which was blocked by spironolactone. In conclusion, aldosterone increased 12‐ and 15‐LO expression in human VSMC, in association with increased 12‐ and 15‐HETE generation and enhanced LDL oxidation and may directly augment VSMC contractility, hypertrophy, and migration through 12‐HETE and promote LDL oxidation via the pro‐oxidative properties of these enzymes. J. Cell. Biochem. 108: 1203–1210, 2009. © 2009 Wiley‐Liss, Inc.     

Heart failure increases atrogin-1 and MuRF1 gene expression in skeletal muscle with fiber type-specific atrophy

Heart failure (HF) is characterized by a reduced tolerance to exercise due to early fatigue and dyspnea; this may be due in part to skeletal muscle myopathy with a shift from slow to fast fibers and loss of muscle mass. Muscle wasting does not occur similarly in all types of muscle fiber, thus we tested the hypothesis that HF induces skeletal muscle atrophy in a fiber type-specific manner altering the expression of atrogin-1 and MuRF1 in a fast muscle of rats with monocrotaline-induced heart failure. We studied extensor digitorum longus (EDL) muscle from both HF and control Wistar rats. Atrogin-1 and MuRF1 mRNA content were determined using Real-Time RT-qPCR while muscle fiber cross-sectional area (CSA) from sections stained histochemically for myofibrillar ATPase were used as an index of type-specific fiber atrophy. The measurement of gene expression by RT-qPCR revealed that EDL muscle mRNA expression of MuRF1 and atrogin-1 was significantly increased in the HF group. Muscle fiber type IIB CSA decreased in the HF group compared to the CT group; there was no significant difference in muscle fiber types I and IIA/D CSA between the HF and CT groups. In conclusion, we showed that HF induces fiber type IIB specific atrophy, up-regulating atrogin-1 and MuRF1 mRNA expression in EDL muscle of monocrotaline treated rats.     

Age-related changes in human skeletal muscle microstructure and architecture assessed by diffusion-tensor magnetic resonance imaging and their association with muscle strength

Diffusion-tensor magnetic resonance imaging (DT-MRI) offers objective measures of muscle characteristics, providing insights into age-related changes. We used DT-MRI to probe skeletal muscle microstructure and architecture in a large healthy-aging cohort, with the aim of characterizing age-related differences and comparing these to muscle strength. We recruited 94 participants (43 female; median age = 56, range = 22–89 years) and measured microstructure parameters—fractional anisotropy (FA) and mean diffusivity (MD)—in 12 thigh muscles, and architecture parameters—pennation angle, fascicle length, fiber curvature, and physiological cross-sectional area (PCSA)—in the rectus femoris (RF) and biceps femoris longus (BFL). Knee extension and flexion torques were also measured for comparison to architecture measures. FA and MD were associated with age (β = 0.33, p = 0.001, R² = 0.10; and β = −0.36, p < 0.001, R² = 0.12), and FA was negatively associated with Type I fiber proportions from the literature (β = −0.70, p = 0.024, and R² = 0.43). Pennation angle, fiber curvature, fascicle length, and PCSA were associated with age in the RF (β = −0.22, 0.26, −0.23, and −0.31, respectively; p < 0.05), while in the BFL only curvature and fascicle length were associated with age (β = 0.36, and −0.40, respectively; p < 0.001). In the RF, pennation angle and PCSA were associated with strength (β = 0.29, and 0.46, respectively; p < 0.01); in the BFL, only PCSA was associated with strength (β = 0.43; p < 0.001). Our results show skeletal muscle architectural changes with aging and intermuscular differences in the microstructure. DT-MRI may prove useful for elucidating muscle changes in the early stages of sarcopenia and monitoring interventions aimed at preventing age-associated microstructural changes in muscle that lead to functional impairment.