Effects Of Electrical Pulse Stimulation On Mitochondrial Dynamics In Myotubes From Lean And Severely Obese Humans

Abstract

Exercise/contractile activity improves skeletal muscle mitochondrial dynamics and insulin sensitivity. However, the adaptations in mitochondrial dynamics in response to exercise/contractile activity between lean and severely obese humans have not been directly compared. Electrical pulse stimulation (EPS) has been used in human skeletal muscle cells (HSkMCs) as an in vitro exercise model and can produce physiological adaptations similar to exercise/exercise training. PURPOSE: The purpose of the study was to compare the effects of EPS on mitochondrial network structure and expression of regulatory proteins in mitochondrial dynamics processes in cultured myotubes derived from lean and severely obese humans. METHODS: HSkMCs isolated from muscle biopsies from lean (n=8, BMI = 23.8 ± 1.1 kg/m2) and severely obese humans (n=8, BMI = 45.5 ± 1.5 kg/m2) were differentiated to mature myotubes and electrically stimulated for 24 hours by applying an electrical pulse at 11.5V, 1Hz and 2ms. Four-hours after EPS, mitochondrial network structure was determined in live cells via confocal microscopy and protein markers of mitochondrial dynamics were measured by immunoblotting. RESULTS: Mitochondrial content was significantly lower in myotubes from severely obese humans when compared to the leans (Total MitoTracker Intensity: 376.0 ± 36.1 vs. 224.8 ± 15.1, P<0.05) and EPS had no effect on mitochondrial content. Myotubes from severely obese humans also exhibited more fragmented mitochondrial networks when compared to the leans (Number of Non-Networked Individual Mitochondria: 2.6 ± 0.4 vs. 1.9 ± 0.2, P<0.05). Interestingly, EPS improves mitochondrial network structure by enhancing mitochondrial network size in both groups (Mitochondrial Network Size: 7.2 ± 0.3 vs. 8.7 ± 0.6, P<0.05). Consistently, mitochondrial fission protein Drp1 ser616 phosphorylation was significantly reduced following EPS in both groups (1.09 ± 0.07 vs. 0.95 ± 0.06, P<0.05). No differences of mitochondrial fusion proteins were found between any groups. CONCLUSIONS: Our data reveal that EPS induces similar intrinsic adaptations in mitochondrial dynamics in cultured myotubes derived from lean and severely obese humans.