Impact of physical activity on physical function, mitochondrial energetics, ROS production, and Ca2+ handling across the adult lifespan in men

Abstract

Aging-related muscle atrophy and weakness contribute to loss of mobility, falls, and disability. Mitochondrial dysfunction is widely considered a key contributing mechanism to muscle aging. However, mounting evidence positions physical activity as a confounding factor, making unclear whether muscle mitochondria accumulate bona fide defects with aging. To disentangle aging from physical activity-related mitochondrial adaptations, we functionally profiled skeletal muscle mitochondria in 51 inactive and 88 active men aged 20-93. Physical activity status confers partial protection against age-related decline in physical performance. Mitochondrial respiration remains unaltered in active participants, indicating that aging per se does not alter mitochondrial respiratory capacity. Mitochondrial reactive oxygen species (ROS) production is unaffected by aging and higher in active participants. In contrast, mitochondrial calcium retention capacity decreases with aging regardless of physical activity and correlates with muscle mass, performance, and the stress-responsive metabokine/mitokine growth differentiation factor 15 (GDF15). Targeting mitochondrial calcium handling may hold promise for treating aging-related muscle impairments.

Keywords: calcium retention capacity; functional capacities; intermuscular fat accumulation; mitochondria; mitochondrial permeability transition pore; muscle atrophy and weakness; physical performance; reactive oxygen species; sarcopenia; skeletal muscle aging.

Graphical abstract

Figure 1

The impact of aging and physical activity status on physical function Quantification of the performance at the (A and B) 6 min walk test, (C and D) step test, (E and F) sit-to-stand test (number of repetitions performed in 30 s), and (G and H) timed up and go test in inactive and active participants. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Data in bar graphs are presented as mean ± SEM. Tukey post hoc tests were performed to test differences between age groups. Differences between inactive and active participants within each age group were assessed using multiple bilateral t tests with false discovery rate (FDR) correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. Icons in (A), (C), (E), and (G) were created with BioRender.com. See also Figures S1, S5, S9, and S10.

Figure 2

The impact of aging and physical activity status on muscle strength, power, and composition (A and B) Quantification of the maximal isometric knee extension strength relative to body mass in inactive and active participants. (C and D) Quantification of the maximal lower limb power relative to body mass in inactive and active participants. (E) Representative pQCT images of the thigh of young and old inactive and active participants (scale bar: 1 cm). (F–I) Quantification of the (F and G) muscle cross-sectional area and (H and I) intermuscular fat area in inactive and active participants. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Data in bar graphs are presented as mean ± SEM. Tukey post hoc tests were performed to test differences between age groups. Differences between inactive and inactive participants within each age group were assessed using multiple bilateral t tests with false discovery rate (FDR) correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. See also Figures S1, S2, S5, S9, and S10.

Figure 3

The impacts of aging and physical activity status on muscle fiber type, size, and proportion (A) Representative triple MHCs (MHC type I: blue; MHC type IIa: red; MHC type IIx: green) and laminin (green) immunolabeling performed on muscle cross-sections (scale bar: 200 μm). (B) Quantifications of the overall myofiber cross-sectional area in inactive and active participants. (C–H) Quantification of the proportion of type I (C and D), IIa (E and F), and IIa/IIx (G and H) myofibers in inactive and active participants. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Data in bar graphs are presented as mean ± SEM. Tukey post hoc tests were performed to test differences between age groups. Differences between inactive and active participants within each age group were assessed using multiple bilateral t tests with false discovery rate (FDR) correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. See also Figure S3.

Figure 4

The impact of aging and physical activity status on skeletal muscle mitochondrial respiration and citrate synthase activity (A) Schematic representation of the experimental design used to assess mitochondrial respiration in permeabilized myofibers. (B and C) State III (ADP-stimulated) respiration rate driven by complex I and II substrates (glutamate + malate + succinate) in inactive and active participants. (D and E) State III (ADP-stimulated) respiration rates driven by lipid substrates (palmitoyl-L-carnitine + malate) in inactive and active participants. (F and G) Citrate synthase activity in inactive and active participants. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Data in bar graphs are presented as mean ± SEM. Tukey post hoc tests were performed to test differences between age groups. Differences between inactive and active participants within each age group were assessed using multiple bilateral t tests with FDR correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. (A) was created with BioRender.com. See also Figures S4, S5, S7, and S13.

Figure 5

The impact of aging and physical activity status on skeletal muscle mitochondrial H₂O₂ emission (A) Schematic representation of the experimental design used to assess mitochondrial H₂O₂ emission in permeabilized myofibers. (B and C) State III H₂O₂ emission rates driven by complex I and II substrates (glutamate + malate + succinate) in inactive and active participants. (D and E) Maximal H₂O₂ emission rates induced by the addition of antimycin A (AA) and oligomycin (O) in the presence of complex I and II substrates in inactive and active participants. (F and G) State III H₂O₂ emission rates driven by lipid substrates (palmitoyl-L-carnitine + malate) in inactive and active participants. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Data in bar graphs are presented as mean ± SEM. Tukey post hoc tests were performed to test differences between age groups. Differences between inactive and active participants within each age group were assessed using multiple bilateral t tests with FDR correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. AA, antimycin A; O, oligomycin. (A) was created with BioRender.com. See also Figures S6–S10 and S13.

Figure 6

The impact of aging and physical activity status on skeletal muscle mitochondrial calcium handling (A) Schematic representation of the experimental design used to assess mitochondrial calcium retention capacity (mCRC), calcium uptake rate, and time to mitochondrial permeability transition pore opening (T mPTP O) in permeabilized phantom myofibers. (B–D) Quantification of the time to mitochondrial permeability transition pore opening (B) and mCRC (C and D) in inactive and active participants. (E–I) Relationship between mCRC and (E) thigh lean mass, (F) maximal isometric knee extension strength, (G) distance at the 6 min walk test, (H) performance at the step test, and (I) plasma GDF15 levels (log-transformed) in our entire cohort (all) and for inactive and active participants separately. Three linear regressions are displayed in each graph to represent all, inactive, and active participants only. (J) Schematic representation of the potential consequences of mPTP opening in muscle cells. For group analyses, results of the two-way ANOVA are displayed above each bar graph. Tukey post hoc tests were performed to test differences between age groups. Data in bar graphs are presented as mean ± SEM. Differences between inactive and active participants within each age group were assessed using multiple bilateral t tests with false discovery rate (FDR) correction. Groups that do not share the same letter are significantly different. Linear regressions were performed to assess associations between age and variables of interest in the entire cohort (all) and for inactive and active participants separately. Pearson correlation coefficients (r) and p values are displayed above each scatterplot. For two-way ANOVA, post hoc testing, and regression analyses, p < 0.05 was considered statistically significant. For FDR analyses, q < 0.05 was considered statistically significant. ∗, q < 0.05. (A) and (J) were created with BioRender.com. See also Figures S11–S13.