Correction: Carnitine supplementation to obese Zucker rats prevents obesity-induced type I to type II muscle fiber transition and favors an oxidative phenotype of skeletal muscle

Satellite cells (SC) are essential for skeletal muscle growth and repair. Because sarcopenia is associated with type II muscle fiber atrophy, we hypothesized that SC content is specifically reduced in the type II fibers in the elderly. A total of eight elderly (E; 76 ± 1 yr) and eight young (Y; 20 ± 1 yr) healthy males were selected. Muscle biopsies were collected from the vastus lateralis in both legs. ATPase staining and a pax7-antibody were used to determine fiber type-specific SC content (i.e., pax7-positive SC) on serial muscle cross sections. In contrast to the type I fibers, the proportion and mean cross-sectional area of the type II fibers were substantially reduced in E vs. Y. The number of SC per type I fiber was similar in E and Y. However, the number of SC per type II fiber was substantially lower in E vs. Y (0.044 ± 0.003 vs. 0.080 ± 0.007; P < 0.01). In addition, in the type II fibers, the number of SC relative to the total number of nuclei and the number of SC per fiber area were also significantly lower in E. This study is the first to show type II fiber atrophy in the elderly to be associated with a fiber type-specific decline in SC content. The latter is evident when SC content is expressed per fiber or per fiber area. The decline in SC content might be an important factor in the etiology of type II muscle fiber atrophy, which accompanies the loss of skeletal muscle with aging.

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Histochemical and Morphometric Evaluation of Skeletal Muscle of Cachectic Sheep

Veterinary Pathology ◽

10.1177/030098588101800301 ◽

1981 ◽

Vol 18 (3) ◽

pp. 279-298 ◽

Cited By ~ 12

Author(s):

T. J. Hulland

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Succinic Dehydrogenase ◽

Adult Life ◽

Biological Behavior ◽

Type I ◽

Fiber Types ◽

Type Ii ◽

Atrophy And Hypertrophy ◽

Type I Fibers

Skeletal muscle of sheep was examined histochemically in an attempt to define muscle fiber populations capable of distinctive biological behavior. ATPase at alkaline and acid pH, NADH-TR, and succinic dehydrogenase showed at least 12 fiber types, but only three often enough to be considered biologically important muscle fiber populations. The proportions of the three major types altered during early life, but not perceptibly during adult life. Proportions of Type I and Type II fibers were different, sometimes significantly, from breed to breed. Histochemical techniques and morphometric analyses of fiber cross-sectional area were used to study muscle fiber changes in moderate to marked cachectic atrophy. Progressive reduction of gross muscle volume was attended by complex interrelationships between the two major muscle fiber types, including alternate episodes of atrophy and hypertrophy, resulting in marked inequality of mean fiber size between the fiber types. The patterns appeared to be different but characteristic for each muscle. The usual pattern of cachectic atrophy shows atrophy resistance of Type I fibers, but here a Type II-dominant atrophy also was seen. It is concluded that the large muscle fibers often seen in advanced cachectic atrophy are those Type I fibers that are more labile in both atrophy and hypertrophy than most.

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Microbiopsy Sampling for Examining Age-Related Differences in Skeletal Muscle Fiber Morphology and Composition

Frontiers in Physiology ◽

10.3389/fphys.2021.756626 ◽

2022 ◽

Vol 12 ◽

Author(s):

Garrett M. Hester ◽

Trisha A. VanDusseldorp ◽

Phuong L. Ha ◽

Kaveh Kiani ◽

Alex A. Olmos ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Vastus Lateralis ◽

Peak Torque ◽

Type I ◽

Type Ii ◽

Fiber Morphology ◽

Specific Strength ◽

Age Related ◽

Whole Muscle

Introduction: The increasingly popular microbiopsy is an appealing alternative to the more invasive Bergström biopsy given the challenges associated with harvesting skeletal muscle in older populations. Parameters of muscle fiber morphology and composition derived from the microbiopsy have not been compared between young and older adults.Purpose: The purpose of this study was to examine muscle fiber morphology and composition in young (YM) and older (OM) males using the microbiopsy sampling technique. A secondary aim was to determine if specific strength is associated with serum levels of C-terminal agrin fragment [CAF; an indicator of neuromuscular junction (NMJ) degradation].Methods: Thirty healthy, YM (n = 15, age = 20.7 ± 2.2 years) and OM (n = 15, age = 71.6 ± 3.9 years) underwent ultrasound imaging to determine whole-muscle cross-sectional area (CSA) of the vastus lateralis and rectus femoris as well as isometric and isokinetic (60°⋅s–1 and 180°⋅s–1) peak torque testing of the knee extensors. Microbiopsy samples of the vastus lateralis were collected from 13 YM and 11 OM, and immunofluorescence was used to calculate CSA and proportion of type I and type II fibers.Results: Peak torque was lower in OM at all velocities (p ≤ 0.001; d = 1.39–1.86) but only lower at 180°⋅s–1 (p = 0.003; d = 1.23) when normalized to whole-muscle CSA. Whole-muscle CSA was smaller in OM (p = 0.001; d = 1.34), but atrophy was not present at the single fiber level (p > 0.05). Per individual, ∼900 fibers were analyzed, and type I fiber CSA was larger (p = 0.05; d = 0.94) in OM which resulted in a smaller type II/I fiber CSA ratio (p = 0.015; d = 0.95). CAF levels were not sensitive to age (p = 0.159; d = 0.53) nor associated with specific strength or whole-muscle CSA in OM.Conclusion: The microbiopsy appears to be a viable alternative to the Bergström biopsy for histological analyses of skeletal muscle in older adults. NMJ integrity was not influential for age-related differences in specific strength in our healthy, non-sarcopenic older sample.

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Evidence for Three Fast Myosin Heavy Chain Isoforms in Type II Skeletal Muscle Fibers in the Adult Llama (Lama glama)

Journal of Histochemistry & Cytochemistry ◽

10.1177/002215540104900811 ◽

2001 ◽

Vol 49 (8) ◽

pp. 1033-1044 ◽

Cited By ~ 54

Author(s):

Guillermo H. Graziotti ◽

Clara M. Ríos ◽

José-Luis L. Rivero

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Rank Order ◽

Muscle Fiber Types ◽

Type I ◽

Fiber Types ◽

Type Ii ◽

Lama Glama ◽

Fast Twitch ◽

Matpase Histochemistry

Skeletal muscle fiber types classified on the basis of their content of different myosin heavy chain (MHC) isoforms were analyzed in samples from hindlimb muscles of adult sedentary llamas ( Lama glama) by correlating immunohistochemistry with specific anti-MHC monoclonal antibodies, myofibrillar ATPase (mATPase) histochemistry, and quantitative histochemistry of fiber metabolic and size properties. The immunohistochemical technique allowed the separation of four pure (i.e., expressing a unique MHC isoform) muscle fiber types: one slow-twitch (Type I) and three fast-twitch (Type II) phenotypes. The same four major fiber types could be objectively discriminated with two serial sections stained for mATPase after acid (pH 4.5) and alkaline (pH 10.5) preincubations. The three fast-twitch fiber types were tentatively designated as IIA, IIX, and IIB on the basis of the homologies of their immunoreactivities, acid denaturation of their mATPase activity, size, and metabolic properties expressed at the cellular level with the corresponding isoforms of rat and horse muscles. Acid stability of their mATPase activity increased in the rank order IIA>IIX>IIB. The same was true for size and glycolytic capacity, whereas oxidative capacity decreased in the same rank order IIA>IIX>IIB. In addition to these four pure fibers (I, IIA, IIX, and IIB), four other fiber types with hybrid phenotypes containing two (I + IIA, IIAX, and IIXB) or three (IIAXB) MHCs were immunohistochemically delineated. These frequent phenotypes (40% of the semitendinosus muscle fiber composition) had overlapped mATPase staining intensities with their corresponding pure fiber types, so they could not be delineated by mATPase histochemistry. Expression of the three fast adult MHC isoforms was spatially regulated around islets of Type I fibers, with concentric circles of fibers expressing MHC-IIA, then MHC-IIX, and peripherally MHC-IIB. This study demonstrates that three adult fast Type II MHC isoproteins are expressed in skeletal muscle fibers of the llama. The general assumption that the very fast MHC-IIB isoform is expressed only in small mammals can be rejected. (J Histochem Cytochem 49:1033–1044, 2001)

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Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle fiber growth

Journal of Applied Physiology ◽

10.1152/japplphysiol.00261.2014 ◽

2014 ◽

Vol 117 (8) ◽

pp. 898-909 ◽

Cited By ~ 32

Author(s):

Jean Farup ◽

Stine Klejs Rahbek ◽

Simon Riis ◽

Mikkel Holm Vendelbo ◽

Frank de Paoli ◽

...

Keyword(s):

Skeletal Muscle ◽

Resistance Training ◽

Whey Protein ◽

Muscle Fiber ◽

Satellite Cells ◽

Fiber Type ◽

Protein Supplementation ◽

Type I ◽

Type Ii ◽

Type Ii Fibers

Skeletal muscle satellite cells (SCs) are involved in remodeling and hypertrophy processes of skeletal muscle. However, little knowledge exists on extrinsic factors that influence the content of SCs in skeletal muscle. In a comparative human study, we investigated the muscle fiber type-specific association between emergence of satellite cells (SCs), muscle growth, and remodeling in response to 12 wk unilateral resistance training performed as eccentric (Ecc) or concentric (Conc) resistance training ± whey protein (Whey, 19.5 g protein + 19.5 g glucose) or placebo (Placebo, 39 g glucose) supplementation. Muscle biopsies (vastus lateralis) were analyzed for fiber type-specific SCs, myonuclei, and fiber cross-sectional area (CSA). Following training, SCs increased with Conc in both type I and type II fibers ( P < 0.01) and exhibited a group difference from Ecc ( P < 0.05), which did not increase. Myonuclei content in type I fibers increased in all groups ( P < 0.01), while a specific accretion of myonuclei in type II fibers was observed in the Whey-Conc ( P < 0.01) and Placebo-Ecc ( P < 0.01) groups. Similarly, whereas type I fiber CSA increased independently of intervention ( P < 0.001), type II fiber CSA increased exclusively with Whey-Conc ( P < 0.01) and type II fiber hypertrophy correlated with whole muscle hypertrophy exclusively following Conc training ( P < 0.01). In conclusion, isolated concentric knee extensor resistance training appears to constitute a stronger driver of SC content than eccentric resistance training while type II fiber hypertrophy was accentuated when combining concentric resistance training with whey protein supplementation.

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Satellite cell and myonuclear accretion is related to training-induced skeletal muscle fiber hypertrophy in young males and females

Journal of Applied Physiology ◽

10.1152/japplphysiol.00424.2021 ◽

2021 ◽

Author(s):

Sidney Abou Sawan ◽

Nathan Hodson ◽

Paul Babits ◽

Julia M. Malowany ◽

Dinesh A. Kumbhare ◽

...

Keyword(s):

Skeletal Muscle ◽

Resistance Exercise ◽

Muscle Fiber ◽

Fiber Type ◽

Whole Body ◽

Type I ◽

Type Ii ◽

Young Males ◽

Males And Females ◽

Type Ii Fibers

Satellite cells (SC) play an integral role in the recovery from skeletal muscle damage and supporting muscle hypertrophy. Acute resistance exercise typically elevates type I and type II SC content 24-96 hours post-exercise in healthy young males, although comparable research in females is lacking. We aimed to elucidate whether sex-based differences exist in fiber type-specific SC content after resistance exercise in the untrained (UT) and trained (T) states. Ten young males (23.0 ± 4.0y) and females (23.0 ± 4.8y) completed an acute bout of resistance exercise before and after 8 weeks of whole-body resistance training. Muscle biopsies were taken from the vastus lateralis immediately prior to and 24 and 48-hours after each bout to determine SC and myonuclear content by immunohistochemistry. Males had greater SC associated with type II fibers (P ≤ 0.03). There was no effect of acute resistance exercise on SC content in either fiber type (P ≥ 0.58) for either sex, however, training increased SC in type II fibers (P < 0.01) irrespective of sex. The change in mean 0-48 h type II SC was positively correlated with muscle fiber hypertrophy in type II fibers (r = 0.47; P = 0.035). Furthermore, the change in myonuclei per fiber was positively correlated with type I and type II fiber hypertrophy (both r = 0.68; P < 0.01). Our results suggest that SC responses to acute and chronic resistance exercise are similar in males and females and that SC and myonuclear accretion is related to training-induced muscle fiber hypertrophy.

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