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Electrical pulse stimulation: an in vitro exercise model for the induction of human skeletal muscle cell hypertrophy. A proof-of-concept study
Örebro University, School of Health Sciences.
Örebro University, School of Health Sciences.
School of Medicine, Royal Derby Hospital, University of Nottingham, Derby, UK.
Örebro University, School of Health Sciences.ORCID iD: 0000-0002-9831-0896
2017 (English)In: Experimental Physiology, ISSN 0958-0670, E-ISSN 1469-445X, Vol. 102, no 11, p. 1405-1413Article in journal (Refereed) Published
Abstract [en]

New Findings:

  • What is the central question of this study?

Is electrical pulse stimulation (EPS) an in vitro exercise model able to elicit the hypertrophy of human muscle cells?

  • What is the main finding and its importance?

The addition of a restitution period of 8h after EPS induces the enlargement of human muscle cells, a major physiological end-point to resistance exercise. This is supported by downregulationof myostatin, a negative regulator of muscle mass, and increased phosphorylated mTOR and 4E-BP1, key factors in the growth cascade. This proof-of-concept study provides a model of physiologically mediated muscle growth, which will be the basis for future studies aiming to depict molecular events governing the hypertrophy of human muscle cells.

Electrical pulse stimulation (EPS) of muscle cells has previouslybeenused as an in vitro exercise model. The present study aimedto establish an EPS protocol promoting the hypertrophy ofhuman muscle cells, which represents a major physiological end-point to resistance exercise in humans. We hypothesized that adding a resting period after EPS would be crucial for the occurrence of the morphological change. Myoblasts obtained from human muscle biopsies (n=5) were differentiated into multinucleated myotubes and exposed to 8h of EPS consisting of 2ms pulses at 12V, with a frequency of 1Hz. Myotube size was assessed using immunohistochemistry immediately, 4 and 8h after completed EPS. Gene expression and phosphorylation status of selected markers of hypertrophy were assessed using RT-PCR and Western blotting, respectively. Release of the myokine interleukin-6 in culture medium was measured using enzyme-linked immunosorbent assay. We demonstrated a significant increase (31 +/- 14%; P=0.03) in the size of myotubes when EPS was followed by an 8h resting period, but not immediately or 4h after completion of EPS. The response was supported by downregulation (P=0.04) of the gene expression of myostatin, a negative regulator of muscle mass, and an increase in phosphorylated mTOR (P=0.03) and 4E-BP1 (P=0.01), which are important factors in the cellular growth signalling cascade. The present work demonstrates that EPS is an in vitro exercise model promoting the hypertrophy of human muscle cells, recapitulating a major physiological end-point to resistance exercise in human skeletal muscle.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017. Vol. 102, no 11, p. 1405-1413
Keywords [en]
Cell growth, muscle contraction, myotube morphology
National Category
Physiology
Identifiers
URN: urn:nbn:se:oru:diva-61685DOI: 10.1113/EP086581ISI: 000414175100010PubMedID: 28861930Scopus ID: 2-s2.0-85032974682OAI: oai:DiVA.org:oru-61685DiVA, id: diva2:1156787
Available from: 2017-11-14 Created: 2017-11-14 Last updated: 2018-09-24Bibliographically approved
In thesis
1. Heat shock proteins in exercised human skeletal muscle
Open this publication in new window or tab >>Heat shock proteins in exercised human skeletal muscle
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Exercise is considered as an important stressor accompanied by concerted molecular and cellular changes leading to adaptations at the level of skeletal muscle size and function. An important protein family produced by cells in response to stressful conditions is the heat shock proteins (HSPs). It is suggested that the different HSPs play specific roles in acute and longterm responses to exercise-induced stress. The overall aim of this thesis was to explore the expression of four different HSPs (αB-crystallin, HSP27, HSP60 and HSP70) in human skeletal muscle exposed to exercise, with a special emphasis on the role played by HSP27 in the hypertrophy of human skeletal muscle.

One of the major findings was the fibre type-specific expression of HSPs in resting human skeletal muscle, including the preferential expression of HSP27 in fast type II muscle fibres. Another finding was the occurrence of training background-related differences in the expression of HSPs. Also, a cytoplasmic relocation of HSP27, occurring specifically in type II muscle fibres, was shown in response to a single bout of resistance exercise. Interestingly, there were no corresponding changes in response to an endurance exercise bout, suggesting that HSP27 may be specifically involved in the adaptations to resistance exercise. In order to test this hypothesis, an in-vitro exercise model based on the electrical pulse stimulation (EPS) of muscle cells was developed. The EPS protocol, including an 8 h restitution period, induced a significant hypertrophy of muscle cells together with molecular changes similar to those previously described in response to exercise in humans. The role of HSP27 in the hypertrophy of human muscle cells was examined through the downregulation of HSP27. Based on data from morphological and microarray analyses, findings indicate that HSP27 is not mandatory for the hypertrophy of human muscle cells. Overall, the present thesis clarified the expression of different HSPs in human skeletal muscle and provided an in-vitro-based approach for the elucidation of the exact role played by HSPs in the adaptations of human skeletal muscle to exercise.

Place, publisher, year, edition, pages
Örebro: Örebro University, 2018. p. 56
Series
Örebro Studies in Sport Sciences, ISSN 1654-7535 ; 28
Keywords
Endurance training, Resistance training, Muscle Fibre Type, Electrical Pulse Stimulation, Muscle Hypertrophy
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:oru:diva-68028 (URN)978-91-7529-260-1 (ISBN)
Public defence
2018-10-17, Örebro universitet, Gymnastik- och idrottshuset, Hörsal G, Fakultetsgatan 1, Örebro, 09:00 (English)
Opponent
Supervisors
Available from: 2018-07-23 Created: 2018-07-23 Last updated: 2018-09-25Bibliographically approved

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Tarum, JanelleFolkesson, MattiasKadi, Fawzi

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