Relationships Among Skeletal Muscle Satellite Cells, Capillarization, And Vo2peak In Older Adults

Abstract

PURPOSE: A reduction in satellite cells has been reported to contribute to muscle loss with aging. Exercise presents a powerful strategy to stimulate satellite cells, however, to what extent various forms of exercise stimulate skeletal muscle satellite cells in older adults is less understood. The purposes of this study were to 1) examine relationships of satellite cell density, capillary density, and VO2peak in older adults, and 2) identify changes in satellite cell density following two different intensities of aerobic exercise. METHODS: In a counter-balanced, cross-over design, six older adults (4M, 2F; 67±2yr; BMI: 26.6±2.0 kg·m-2) completed an acute bout of high-intensity interval (HIIE; ten, 1-min intervals, 85-95% heart rate max, 1-min rest between intervals) and moderate intensity continuous cycling (MOD; 30-min, 60-65% VO2peak), separated by ~1 week. Muscle biopsies (vastus lateralis) were obtained before exercise and 24h after each exercise bout. Immunofluorescence was used to identify myosin heavy chain (MHC), satellite cells, and capillaries. RESULTS: A significant relationship between capillary density and satellite cell density (P=0.018; R2=0.789) was observed. Significant correlations were also found between satellite cell density and VO2peak (P<0.001; R2=0.99), capillary density and VO2peak (P=0.019; R2=0.785), satellite cells/MHC I fiber and VO2peak (P=0.026; R2=0.750), and satellite cells/MHC II fiber and VO2peak (P=0.002; R2=0.93) at baseline. Total satellite cells/fiber and fiber type-specific satellite cells/fiber were unchanged in response to acute MOD or HIIE (P>0.05) and no differences were observed between exercise trials (P>0.05). CONCLUSIONS: These data reveal positive relationships between capillaries and satellite cell density in skeletal muscle of older adults. Further, while no changes in satellite cell density were observed 24h following acute MOD or HIIE, our preliminary findings suggest an association between satellite cell density and VO2peak in older adults. Thus, future research is needed to examine whether these exercise strategies differentially impact changes in proliferation or differentiation of satellite cells in older adults, and to what extent capillary density may be related to chronic adaptations in satellite cell density and VO2peak.