Satellite cell proliferation in response to a chronic laboratory-controlled uphill vs. downhill interval training intervention

[摘要] Despite a growing interest into the mechanisms of the repeated bout effect, little is known about theconsequences of chronic eccentrically biased training and the possible advantageous such training may offerto athletes as well as patients with muscle-debilitating disease. This study investigated the role of satellitecells in the muscle adaptation in response to either downhill or uphill high intensity training (HIT). Welltrainedendurance runners were divided into two training groups matched for training volume and 10 kmrunning times (n = 6, uphill training, UP; n = 6, downhill training, DH) and subjects in both groupscompleted 10 HIT sessions over a period of 4 weeks. Running performance was tested before and after thetraining intervention by a 10 km road race and peak treadmill speed (PTS) in horizontal and inclined (+5%)laboratory incremental tests to exhaustion. Skeletal muscle biopsies were sampled at baseline, after 2 HITsessions, and after 4 weeks of HIT. Muscle was analysed immunohistochemically for satellite cell frequencyas identified by CD56 and M-cadherin (Mcad) expression. Myogenin protein contents of muscle homogenateswere determined by western blotting. Myosin heavy chain (MyHC) isoform proportions and mean fibre crosssectionalarea was measured. During the HIT intervention, UP exercised at a higher percentage of their HRmaxthan DH (mean ± SD, 97 ± 1 vs. 92 ± 3 %HRmax, p < 0.005), but at a similar rate of perceived exertion (RPE).DH completed more intervals per session and covered greater distance per session than their UPcounterparts. Both training groups increased their training intensity but decreased their training volumeduring the 4 weeks of HIT. The combined group of 12 athletes improved their PTSgradient (mean ± SD, 16.7 ±0.8 vs. 17.3 ± 1.0 km/h, p < 0.05). No significant differences between groups were found for PTS, VO2max or10 km performance. Satellite cell frequency in this cohort of trained runners (48.9 ± 10.3 km/week) atbaseline was similar to healthy young males (CD56+ cells/fibre, 0.19 ± 0.10). Satellite cell frequencyincreased significantly in DH after 4 weeks (Mcad, 123%; CD56, 138%) and non-significantly in UP (Mcad,45%, CD56, 39%). No significant differences were found after two training sessions or at any time betweengroups. Mcad and CD56 expression correlated well (r = 0.95, p < 0.0001). Muscle myogenin contentincreased for both groups (UP: 56%; DH: 60%) after 4 weeks. No notable changes were seen after two trainingsessions. However, myogenin levels 2 days after session 1 correlated well (r= 0.99, p<0.005) with muscle painexperienced on the same day, as measured by the visual analogue scale. No changes were seen in the MyHCproportions or the fibre cross-sectional area after the training intervention. It was concluded that the trainingintervention was too short to induce changes in MyHC distribution or fibre area. Is seems likely that satellitecell proliferation was initiated as an early response to DOMS, but the response was maintained for 4 weeks.However, due to the lack of change in fibre morphology and myonuclear number, the role of satellite cellproliferation in fibre type transformation or muscle hypertrophy could not be established. Similarly, variouspossible roles for increased myogenin protein are offered, but since the origin of myogenin expression(satellite cells vs. myonuclei) was not determined, no definite conclusion regarding the precise function canbe made. In conclusion, this study is the first to definitively indicate satellite cell proliferation in well-trainedendurance runners in response to a change in training, including specifically downhill HIT. This responsewas early and sustained. This study asks several questions about the role of satellite cells during muscleadaptation to repetitive downhill training, and lays a foundation for further research into this unexploredfield.

[发布机构] Stellenbosch University