Skeletal muscle healing by M1-like macrophages produced by transient expression of exogenous GM-CSF

Abstract Background After traumatic skeletal muscle injury, muscle healing is often incomplete and produces extensive fibrosis. The sequence of M1 and M2 macrophage accumulation and the duration of each subtype in the injured area may help to direct the relative extent of fibrogenesis and myogenesis during healing. We hypothesized that increasing the number of M1 macrophages early after traumatic muscle injury would produce more cellular and molecular substrates for myogenesis and fewer substrates for fibrosis, leading to better muscle healing. Methods To test this hypothesis, we transfected skeletal muscle with a plasmid vector to transiently express GM-CSF shortly after injury to drive the polarization of macrophages towards the M1 subset. C57BL/6 mouse tibialis anterior (TA) muscles were injured by contusion and electroporated with uP-mGM, which is a plasmid vector that transiently expresses GM-CSF. Myogenesis, angiogenesis, and fibrosis were evaluated by histology, immunohistochemistry, and RT-qPCR; subpopulations of macrophages by flow cytometry; and muscle functioning by the maximum running speed on the treadmill and the recovery of muscle mass. Results Muscle injury increased the number of local M1-like macrophages and decreased the number of M2-like macrophages on day 4, and uP-mGM treatment enhanced this variation. uP-mGM treatment decreased TGF-β1 protein expression on day 4, and the Sirius Red-positive area decreased from 35.93 ± 15.45% (no treatment) to 2.9% ± 6.5% (p < 0.01) on day 30. uP-mGM electroporation also increased Hgf, Hif1α, and Mtor gene expression; arteriole density; and muscle fiber number during regeneration. The improvement in the quality of the muscle tissue after treatment with uP-mGM affected the increase in the TA muscle mass and the maximum running speed on a treadmill. Conclusion Collectively, our data show that increasing the number of M1-like macrophages immediately after traumatic muscle injury promotes muscle recovery with less fibrosis, and this can be achieved by the transient expression of GM-CSF.

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Endocrine regulation of fetal skeletal muscle growth: impact on future metabolic health

Journal of Endocrinology ◽

10.1530/joe-13-0567 ◽

2014 ◽

Vol 221 (2) ◽

pp. R13-R29 ◽

Cited By ~ 55

Author(s):

Laura D Brown

Keyword(s):

Skeletal Muscle ◽

Muscle Mass ◽

Muscle Fiber ◽

Muscle Growth ◽

Metabolic Health ◽

Endocrine Regulation ◽

Intrauterine Environment ◽

Skeletal Muscle Growth ◽

Fiber Number ◽

Muscle Fiber Number

Establishing sufficient skeletal muscle mass is essential for lifelong metabolic health. The intrauterine environment is a major determinant of the muscle mass that is present during the life course of an individual, because muscle fiber number is set at the time of birth. Thus, a compromised intrauterine environment from maternal nutrient restriction or placental insufficiency that restricts muscle fiber number can have permanent effects on the amount of muscle an individual will live with. Reduced muscle mass due to fewer muscle fibers persists even after compensatory or ‘catch-up’ postnatal growth occurs. Furthermore, muscle hypertrophy can only partially compensate for this limitation in fiber number. Compelling associations link low birth weight and decreased muscle mass to future insulin resistance, which can drive the development of the metabolic syndrome and type 2 diabetes, and the risk of cardiovascular events later in life. There are gaps in knowledge about the origins of reduced muscle growth at the cellular level and how these patterns are set during fetal development. By understanding the nutrient and endocrine regulation of fetal skeletal muscle growth and development, we can direct research efforts toward improving muscle growth early in life to prevent the development of chronic metabolic diseases later in life.

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Muscle atrophy and hypoplasia with aging: impact of training and food restriction

Journal of Applied Physiology ◽

10.1152/jappl.1988.64.6.2428 ◽

1988 ◽

Vol 64 (6) ◽

pp. 2428-2432 ◽

Cited By ~ 47

Author(s):

C. K. Daw ◽

J. W. Starnes ◽

T. P. White

Keyword(s):

Skeletal Muscle ◽

Muscle Mass ◽

Muscle Atrophy ◽

Food Restriction ◽

Skeletal Muscle Atrophy ◽

Free Access ◽

Sedentary Control ◽

Fiber Number ◽

Edl Muscle ◽

The Masses

The purpose of this work is to study the influence of aging, training, and food restriction on skeletal muscle mass and fiber number. Male Fischer 344 rats (n = 49) at 3 mo postpartum were assigned to three groups: 1) sedentary control (confined to cage), 2) exercise trained (18 m/min, 8 degrees grade, 20 min/day, 5 days/wk), or 3) food restricted (alternate days of free access and no access to food). At 12 and 27 mo postpartum the soleus and extensor digitorum longus (EDL) muscles were excised, weighed, and fiber number was quantified after HNO3 digestion. At 27 mo the masses of soleus and EDL muscles of sedentary control rats were 83 and 70%, respectively, of 12-mo values (138 +/- 5 and 151 +/- 4 mg). At 27 mo, soleus muscle mass of trained rats was 113% of sedentary control values, whereas EDL muscle mass was unaffected by training. At 27 mo, food restriction had no effect on the mass of both muscles compared with 27-mo sedentary control values. Fiber number was not affected by training or food restriction in both muscles. Fiber number for soleus and EDL muscles of combined groups declined with age by 5.6 and 4.2%, respectively. With aging, the small loss of muscle fibers can account at most for approximately 25% of the observed skeletal muscle atrophy.

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Estimation of skeletal muscle fiber number by mean fiber dry weight

Journal of Applied Physiology ◽

10.1152/jappl.1984.56.1.244 ◽

1984 ◽

Vol 56 (1) ◽

pp. 244-247

Author(s):

B. F. Timson ◽

G. A. Dudenhoeffer

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Biceps Brachii ◽

Estimation Method ◽

Dry Weight ◽

Skeletal Muscle Fiber ◽

Anterior Latissimus Dorsi ◽

Fiber Number ◽

Nitric Acid Digestion ◽

Muscle Fiber Number

The purpose of this study was to determine whether skeletal muscle fiber number could be accurately estimated by the determination of mean fiber dry weight (MFD) and total muscle dry weight. The muscles studied were the soleus, plantaris, gastrocnemius, extensor digitorum longus, tibialis anterior, and biceps brachii of the rat, the anterior latissimus dorsi of the chicken, and the flexor carpi radialis of the cat. Bundles of fibers were carefully separated from the muscle following nitric acid digestion (ND) and placed in groups of similar length. MFD determined from 400 to 800 fibers from each group was used to estimate the number of fibers in the remainder of the group. Estimated fiber number was compared with the fiber number determined in the muscle from the contralateral limb by the ND method. No difference in fiber number was observed between the ND method and the MFD estimation method for any of the muscles used in the study. The results indicate that the MFD estimation method is an accurate and relatively rapid method of fiber number determination in skeletal muscle.

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The Effect of Severe Dietary Protein Restriction on Skeletal Muscle Fiber Number, Area and Composition in Weanling Rats

Journal of Animal Science ◽

10.2527/jas1985.612416x ◽

1985 ◽

Vol 61 (2) ◽

pp. 416-422 ◽

Cited By ~ 2

Author(s):

B. F. Timson ◽

G. A. Dudenhoeffer

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Dietary Protein ◽

Protein Restriction ◽

Skeletal Muscle Fiber ◽

Dietary Protein Restriction ◽

Weanling Rats ◽

Fiber Number ◽

Muscle Fiber Number

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Role of exercise in inducing increases in skeletal muscle fiber number

Journal of Applied Physiology ◽

10.1152/jappl.1980.48.3.421 ◽

1980 ◽

Vol 48 (3) ◽

pp. 421-426 ◽

Cited By ~ 51

Author(s):

W. J. Gonyea

Keyword(s):

Skeletal Muscle ◽

Muscle Fiber ◽

Skeletal Muscle Fiber ◽

Fiber Number ◽

Muscle Fiber Number

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Aging and its effects on inflammation in skeletal muscle at rest and following exercise-induced muscle injury

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00467.2009 ◽

2010 ◽

Vol 298 (6) ◽

pp. R1485-R1495 ◽

Cited By ~ 92

Author(s):

Jonathan Peake ◽

Paul Della Gatta ◽

David Cameron-Smith

Keyword(s):

Gene Expression ◽

Skeletal Muscle ◽

Young People ◽

Elderly People ◽

Muscle Mass ◽

Muscle Injury ◽

Elderly Population ◽

Indirect Evidence ◽

The Elderly ◽

Exercise Induced

The world's elderly population is expanding rapidly, and we are now faced with the significant challenge of maintaining or improving physical activity, independence, and quality of life in the elderly. Counteracting the progressive loss of muscle mass that occurs in the elderly, known as sarcopenia, represents a major hurdle in achieving these goals. Indirect evidence for a role of inflammation in sarcopenia is that markers of systemic inflammation correlate with the loss of muscle mass and strength in the elderly. More direct evidence is that compared with skeletal muscle of young people, the number of macrophages is lower, the gene expression of several cytokines is higher, and stress signaling proteins are activated in skeletal muscle of elderly people at rest. Sarcopenia may also result from inadequate repair and chronic maladaptation following muscle injury in the elderly. Macrophage infiltration and the gene expression of certain cytokines are reduced in skeletal muscle of elderly people compared with young people following exercise-induced muscle injury. Further research is required to identify the cause(s) of inflammation in skeletal muscle of elderly people. Additional work is also needed to expand our understanding of the cells, proteins, and transcription factors that regulate inflammation in the skeletal muscle of elderly people at rest and after exercise. This knowledge is critical for devising strategies to restrict sarcopenia, and improve the health of today's elderly population.

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Mechanical overload and skeletal muscle fiber hyperplasia: a meta-analysis

Journal of Applied Physiology ◽

10.1152/jappl.1996.81.4.1584 ◽

1996 ◽

Vol 81 (4) ◽

pp. 1584-1588 ◽

Cited By ~ 46

Author(s):

George Kelley

Keyword(s):

Skeletal Muscle ◽

Confidence Interval ◽

Muscle Fiber ◽

Meta Analysis ◽

Compensatory Hypertrophy ◽

Skeletal Muscle Fiber ◽

Fiber Number ◽

Nitric Acid Digestion ◽

Mechanical Overload ◽

Muscle Fiber Number

Kelley, George. Mechanical overload and skeletal muscle fiber hyperplasia: a meta-analysis. J. Appl. Physiol. 81(4): 1584–1588, 1996.—With use of the meta-analytic approach, the purpose of this study was to examine the effects of mechanical overload on skeletal muscle fiber number in animals. A total of 17 studies yielding 37 data points and 360 subjects met the initial inclusion criteria: 1) “basic” research studies published in journals, 2) animals (no humans) as subjects, 3) control group included, 4) some type of mechanical overload (stretch, exercise, or compensatory hypertrophy) used to induce changes in muscle fiber number, and 5) sufficient data to accurately calculate percent changes in muscle fiber number. Across all designs and categories, statistically significant increases were found for muscle fiber number [15.00 ± 19.60% (SD), 95% confidence interval = 8.65–21.53], muscle fiber area (31.60 ± 44.30%, 95% confidence interval = 16.83–46.37), and muscle mass (90.50 ± 86.50%, 95% confidence interval = 61.59–119.34). When partitioned according to the fiber-counting technique, larger increases in muscle fiber number were found by using the histological vs. nitric acid digestion method (histological = 20.70%, nitric acid digestion = 11.10%; P = 0.14). Increases in fiber number partitioned according to species were greatest among those groups that used an avian vs. mammalian model (avian = 20.95%, mammalian = 7.97%; P = 0.07). Stretch overload yielded larger increases in muscle fiber number than did exercise and compensatory hypertrophy (stretch = 20.95%, exercise = 11.59%, compensatory hypertrophy = 5.44%; P = 0.06). No significant differences between changes in fiber number were found when data were partitioned according to type of control (intra-animal = 15.20%, between animal = 13.90%; P = 0.82) or fiber arrangement of muscle (parallel = 15.80%, pennate = 11.60%; P = 0.61). The results of this study suggest that in several animal species certain forms of mechanical overload increase muscle fiber number.

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Impact of different temperature stimuli on the expression of myosin heavy chain isoforms during recovery from bupivacaine-induced muscle injury in rats

Journal of Applied Physiology ◽

10.1152/japplphysiol.00930.2018 ◽

2019 ◽

Vol 127 (1) ◽

pp. 178-189

Author(s):

Tsubasa Shibaguchi ◽

Mizuki Hoshi ◽

Toshinori Yoshihara ◽

Hisashi Naito ◽

Katsumasa Goto ◽

...

Keyword(s):

Skeletal Muscle ◽

Heat Stress ◽

Myosin Heavy Chain ◽

Muscle Mass ◽

Heavy Chain ◽

Muscle Injury ◽

Heat Exposure ◽

Control Level ◽

Male Wistar Rats ◽

The Impact

Limited information exists regarding the impact of different temperature stimuli on myosin heavy chain (MyHC) expression in skeletal muscle during recovery from injury. Therefore, this experiment investigated the impact of both cold and heat exposure on the MyHC isoform profile in the rat soleus during recovery from injury. Male Wistar rats were randomly divided into control, bupivacaine-injected (BPVC), BPVC with icing, and BPVC with heat stress groups. Muscle injury was induced by intramuscular injection of bupivacaine into soleus muscles of male Wistar rats. Icing treatment (0°C for 20 min) was performed immediately after the injury. Intermittent heat stress (42°C for 30 min on alternating days) was carried out during 2–14 days after bupivacaine injection. In response to injury, a transient increase in developmental, IId/x, and IIb MyHC isoforms, as well as various types of hybrid fibers, followed by the recovery of the MyHC profile toward the control level, was noted in the regeneration of the soleus. The restoration of the MyHC profile in the regenerating muscle at whole-muscle and individual myofiber levels was partially delayed by icing but facilitated by heat stress. In addition, the application of repeated heat stress promoted the recovery of soleus muscle mass toward the control level following injury. We conclude that compared with acute and immediate cold (icing) treatment, chronic and repeated heat stress may be a more appropriate treatment for the enhancement of both normalization of the MyHC profile and restoration of muscle mass following injury. NEW & NOTEWORTHY Cold exposure (icing), but not heat exposure, has been well accepted as a first-aid treatment for accidental and/or sports-related injuries. However, recent evidence suggests the negative impact of icing treatment on skeletal muscle regeneration following injury. Here, we demonstrated that acute/immediate icing treatment delayed the restoration of the myosin heavy chain (MyHC) profile, but intermittent hyperthermia, repeated for several days, facilitated the recovery of both muscle mass and the MyHC profile in the regeneration of skeletal muscle following injury.

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