An in vitro human skeletal muscle model: coculture of myotubes,neuron-like cells, and the capillary network

Aged skeletal muscle is markedly affected by fatty muscle infiltration, and strategies to reduce the occurrence of intramuscular adipocytes are urgently needed. Here, we show that fibroblast growth factor-2 (FGF-2) not only stimulates muscle growth but also promotes intramuscular adipogenesis. Using multiple screening assays upstream and downstream of microRNA (miR)-29a signaling, we located the secreted protein and adipogenic inhibitor SPARC to an FGF-2 signaling pathway that is conserved between skeletal muscle cells from mice and humans and that is activated in skeletal muscle of aged mice and humans. FGF-2 induces the miR-29a/SPARC axis through transcriptional activation of FRA-1, which binds and activates an evolutionary conserved AP-1 site element proximal in the miR-29a promoter. Genetic deletions in muscle cells and adeno-associated virus–mediated overexpression of FGF-2 or SPARC in mouse skeletal muscle revealed that this axis regulates differentiation of fibro/adipogenic progenitors in vitro and intramuscular adipose tissue (IMAT) formation in vivo. Skeletal muscle from human donors aged >75 y versus <55 y showed activation of FGF-2–dependent signaling and increased IMAT. Thus, our data highlights a disparate role of FGF-2 in adult skeletal muscle and reveals a pathway to combat fat accumulation in aged human skeletal muscle.

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Microdialysis of skeletal muscle at rest

Proceedings of The Nutrition Society ◽

10.1017/s0029665199001226 ◽

1999 ◽

Vol 58 (4) ◽

pp. 919-923 ◽

Cited By ~ 28

Author(s):

Jan Henriksson

Keyword(s):

Skeletal Muscle ◽

Blood Flow ◽

Human Skeletal Muscle ◽

Human Metabolism ◽

High Expectations ◽

Perfusate Flow ◽

Muscle Research ◽

Interstitial Glucose

Techniques in human skeletal muscle research are by necessity predominantly 'descriptive'.Microdialysis has raised high expectations that it could meet the demand for a method that allows 'mechanistic' investigations to be performed in human skeletal muscle. In the present review, some views are given on how well the initial expectations on the use of the microdialysis technique in skeletal muscle have been fulfilled, and the areas in which additional work is needed in order to validate microdialysis as an important metabolic technique in this tissue. The microdialysis catheter has been equated to an artificial blood vessel, which is introduced into the tissue. By means of this 'vessel' the concentrations of compounds in the interstitial space can be monitored. The concentration of substances in the collected samples is dependent on the rate of perfusate flow. When perfusate flow is slow enough to allow complete equilibration between interstitial and perfusate fluids, the concentration in the perfusate is maximal and identical to the interstitial concentration. Microdialysis data may be influenced by changes in blood flow, especially in instances where the tissue diffusivity limits the recovery in vivo, i.e. when recovery in vitro is 100 %, whereas the recovery in vivo is less than 100 %. Microdialysis data indicate that a significant arterial-interstitial glucose concentration gradient exists in skeletal muscle but not in adipose tissue at rest. While the concentrations of glucose and lactate in the dialysate from skeletal muscle are close to the expected values, the glycerol values obtained for muscle are still puzzling. Ethanol added to the perfusate will be cleared by the tissue at a rate that is determined by the nutritive blood flow (the microdialysis ethanol technique). It is concluded that microdialysis of skeletal muscle has become an important technique for mechanistic studies in human metabolism and nutrition.

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A multiplexed in vitro assay system for evaluating human skeletal muscle functionality in response to drug treatment

Biotechnology and Bioengineering ◽

10.1002/bit.27231 ◽

2019 ◽

Vol 117 (3) ◽

pp. 736-747

Author(s):

Sarah A. Najjar ◽

Alexander S.T. Smith ◽

Christopher J. Long ◽

Christopher W. McAleer ◽

Yunqing Cai ◽

...

Keyword(s):

Skeletal Muscle ◽

Drug Treatment ◽

Human Skeletal Muscle ◽

In Vitro Assay ◽

Assay System ◽

Vitro Assay

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Oxygen electrode studies with human skeletal muscle mitochondria in vitro

Journal of the Neurological Sciences ◽

10.1016/0022-510x(85)90143-1 ◽

1985 ◽

Vol 69 (3) ◽

pp. 319-333 ◽

Cited By ~ 41

Author(s):

E. Byrne ◽

I. Trounce

Keyword(s):

Skeletal Muscle ◽

Human Skeletal Muscle ◽

Oxygen Electrode ◽

Muscle Mitochondria ◽

Skeletal Muscle Mitochondria

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Carbohydrate metabolism in human skeletal muscle during exercise is not regulated by G-1,6-P2

Journal of Applied Physiology ◽

10.1152/jappl.1988.65.1.487 ◽

1988 ◽

Vol 65 (1) ◽

pp. 487-489 ◽

Cited By ~ 9

Author(s):

A. Katz ◽

K. Sahlin ◽

J. Henriksson

Keyword(s):

Skeletal Muscle ◽

Human Skeletal Muscle ◽

Work Load ◽

Short Term ◽

Catalytic Function ◽

Muscle Ph ◽

Induced Changes ◽

Femoris Muscle

Glucose 1,6-bisphosphate (G-1,6-P2) is a potent activator of phosphofructokinase (PFK) and an inhibitor of hexokinase in vitro. It has been suggested that increases in G-1,6-P2 are a main means by which PFK can achieve significant catalytic function in vivo despite falling pH and that increases in G-1,6-P2 will inhibit hexokinase in vivo. The purpose of the present study was to determine whether contraction-induced changes in flux through PFK and hexokinase are associated with changes in G-1,6-P2 in skeletal muscle. Ten men performed bicycle exercise for 10 min at 40 and 75% of maximal O2 uptake (VO2max) and to fatigue [4.8 +/- 0.6 (SE) min] at 100% VO2max. Biopsies were obtained from the quadriceps femoris muscle at rest and after each work load and analyzed for G-1,6-P2. G-1,6-P2 averaged 111 +/- 13 mumol/kg dry wt at rest and 121 +/- 16, 123 +/- 15, and 123 +/- 11 mumol/kg dry wt after the low-, moderate-, and high-intensity exercise bouts, respectively (P less than 0.05 for all means vs. rest). Flux through PFK was estimated to increase exponentially as the exercise intensity increased and muscle pH decreased at the higher work loads, whereas flux through hexokinase was estimated to increase during exercise at 40 and 75% VO2max but decrease sharply at 100% VO2max. These data demonstrate that flux through neither PFK nor hexokinase is mediated by changes in G-1,6-P2 in human skeletal muscle during short-term dynamic exercise.

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Chlorella vulgaris Modulates Genes and Muscle-Specific microRNAs Expression to Promote Myoblast Differentiation in Culture

Evidence-based Complementary and Alternative Medicine ◽

10.1155/2019/8394648 ◽

2019 ◽

Vol 2019 ◽

pp. 1-16 ◽

Cited By ~ 3

Author(s):

Nurhazirah Zainul Azlan ◽

Yasmin Anum Mohd Yusof ◽

Ekram Alias ◽

Suzana Makpol

Keyword(s):

Skeletal Muscle ◽

Chlorella Vulgaris ◽

Muscle Regeneration ◽

Human Skeletal Muscle ◽

The Elderly ◽

Myoblast Differentiation ◽

Gradual Decline ◽

Proliferation And Differentiation ◽

And Function

Background. Loss of skeletal muscle mass, strength, and function due to gradual decline in the regeneration of skeletal muscle fibers was observed with advancing age. This condition is known as sarcopenia. Myogenic regulatory factors (MRFs) are essential in muscle regeneration as its activation leads to the differentiation of myoblasts to myofibers. Chlorella vulgaris is a coccoid green eukaryotic microalga that contains highly nutritious substances and has been reported for its pharmaceutical effects. The aim of this study was to determine the effect of C. vulgaris on the regulation of MRFs and myomiRs expression in young and senescent myoblasts during differentiation in vitro. Methods. Human skeletal muscle myoblast (HSMM) cells were cultured and serial passaging was carried out to obtain young and senescent cells. The cells were then treated with C. vulgaris followed by differentiation induction. The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, PTEN, and MYH2 genes and miR-133b, miR-206, and miR-486 was determined in untreated and C. vulgaris-treated myoblasts on Days 0, 1, 3, 5, and 7 of differentiation. Results. The expression of Pax7, MyoD1, Myf5, MEF2C, IGF1R, MYOG, TNNT1, and PTEN in control senescent myoblasts was significantly decreased on Day 0 of differentiation (p<0.05). Treatment with C. vulgaris upregulated Pax7, Myf5, MEF2C, IGF1R, MYOG, and PTEN in senescent myoblasts (p<0.05) and upregulated Pax7 and MYOG in young myoblasts (p<0.05). The expression of MyoD1 and Myf5 in young myoblasts however was significantly decreased on Day 0 of differentiation (p<0.05). During differentiation, the expression of these genes was increased with C. vulgaris treatment. Further analysis on myomiRs expression showed that miR-133b, miR-206, and miR-486 were significantly downregulated in senescent myoblasts on Day 0 of differentiation which was upregulated by C. vulgaris treatment (p<0.05). During differentiation, the expression of miR-133b and miR-206 was significantly increased with C. vulgaris treatment in both young and senescent myoblasts (p<0.05). However, no significant change was observed on the expression of miR-486 with C. vulgaris treatment. Conclusions. C. vulgaris demonstrated the modulatory effects on the expression of MRFs and myomiRs during proliferation and differentiation of myoblasts in culture. These findings may indicate the beneficial effect of C. vulgaris in muscle regeneration during ageing thus may prevent sarcopenia in the elderly.

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