Acute and Chronic Effects of High Frequency Electric Pulse Stimulation on the Akt/mTOR Pathway in Human Primary Myotubes.

Louise Deldicque,Geoffrey Warnier,Hermann Zbinden-Foncea,Mauricio Castro-Sepulveda,Mayalen Valero-Breton

doi:10.3389/fbioe.2020.565679

Abstract

Electrical pulse stimulation (EPS) has been suggested to be a useful method to investigate the mechanisms underlying the adaptations of human skeletal muscle to both endurance and resistance exercise. Although different myotube stimulation protocols mimicking acute and chronic endurance exercise have been developed, no convincing protocol mimicking resistance exercise exists. Adaptations to resistance exercise mainly ensue via the Akt/mTOR pathway. Therefore, the aim of this study was to develop a high frequency EPS protocol mimicking resistance exercise both acutely (100 Hz, 15 V, 0.4 ms with 4 s rest between each contraction for 30 min) and chronically (acute EPS protocol repeated on three consecutive days) on human myotubes. Compared to control conditions, the acute EPS protocol increased the phosphorylation of AktSer473 at 0 h (+91%, p = 0.02) and 3 h (+95%, p = 0.01), and mTORSer2448 at 0 h (+93%, p = 0.03), 1 h (+129%, p = 0.01), and 3 h (+104%, p = 0.0250) post-stimulation. The phosphorylation of ERK1/2Thr202/Tyr204 was increased at 0 h (+69%, p = 0.02) and 3 h (+117%, p = 0.003) post-stimulation compared to control conditions. In addition, both S6K1Thr389 (+157%, p = 0.009) and S6Ser240/244 (+153%, p = 0.003) phosphorylation increased 1 h after EPS compared to control conditions. Chronic EPS protocol increased the phosphorylation of S6K1Thr389 1 h (+105%, p = 0.03) and 3 h (+126%, p = 0.02) and the phosphorylation of S6Ser240/244 1 h (+32%, p = 0.02) after the end of the last stimulation. In conclusion, the present work shows that human muscle cells subjected to EPS can be used as an in vitro model of acute and chronic resistance exercise.

Highlights

Electrical pulse stimulation (EPS) of muscle cells is an in vitro exercise model that mimics muscle adaptations in vivo (Manabe et al, 2012; Carter and Solomon, 2019)
The phosphorylation of Akt was increased at 0 h (+91%, p = 0.0283) and 3 h after stimulation (+95%, p = 0.0103) in EPS compared to control conditions, but not at 1 h (Figure 1A)
The phosphorylation of mammalian target of rapamycin (mTOR) increased at 0 h (+93%, p = 0.0364), 1 h (+129%, p = 0.0071), and 3 h (+104%, p = 0.0250) after EPS compared to control conditions (Figure 1B)

Summary

Introduction

Electrical pulse stimulation (EPS) of muscle cells is an in vitro exercise model that mimics muscle adaptations in vivo (Manabe et al, 2012; Carter and Solomon, 2019). EPS has been suggested to be a useful method to investigate the mechanisms underlying acute and chronic adaptations of human skeletal muscle to both endurance (Lambernd et al, 2012) and resistance exercise (Görgens et al, 2015; Tarum et al, 2017). Several studies have shown low frequency EPS (0.2–2 Hz) to act as an endurance exercise mimetic (Lambernd et al, 2012; Nikolicet al., 2012; Brown et al, 2015). Medium frequency EPS (1–30 Hz) has been suggested to act as a resistance exercise mimetic in human muscle cells and C2C12 cells (Scheler et al, 2013; Tarum et al, 2017). As stimulation at either high or low frequencies appear to activate different signaling pathways (Nikolicet al., 2012), it is crucial to carefully investigate the adaptations to high frequency stimulation (100 Hz)

Objectives

Methods

Results

Conclusion