Exercise training increases skeletal muscle mitochondrial volume density by enlargement of existing mitochondria and not de novo biogenesis

Abstract

Mito increased with 55 ± 9% (P < 0.001), whereas the number of mitochondrial profiles per area of skeletal muscle remained unchanged following training. Citrate synthase activity (CS) increased (44 ± 12%, P < 0.001); however, there were no functional changes in oxidative phosphorylation capacity (OXPHOS, CI+II ) or cytochrome c oxidase (COX) activity. Correlations were found between Mito and CS (P = 0.01; r = 0.58), OXPHOS, CI+CIIP (P = 0.01; R = 0.58) and COX (P = 0.02; R = 0.52) before training; after training, a correlation was found between Mito and CS activity only (P = 0.04; R = 0.49). Intrinsic respiratory capacities decreased (P < 0.05) with training when respiration was normalized to Mito This was not the case when normalized to CS activity although the percentage change was comparable CONCLUSIONS: Mito was increased by inducing mitochondrial enlargement rather than de novo biogenesis. CS activity may be appropriate to track training-induced changes in Mito

Determinants of maximal whole‐body fat oxidation in elite cross‐country skiers: Role of skeletal muscle mitochondria

“…Moreover, Nielsen et al reported a difference in mitochondrial cristae density of 25% between endurance and untrained individuals, which could indicate that mitochondrial function is improved in this group. However, in recent studies in which we have determined Mito VD directly by means of electron microscopy (as in the present study) we have observed an unchanged or even decreased intrinsic mitochondrial function . In line with this, the augmented FAO p observed in the endurance athletes seemed to disappear when normalizing for Mito VD or CS‐activity (Figure BC), and the same was observed for CI p , OXPHOS p , and ETS respiration.…”

“…Indeed, a strong correlation was observed between Mito VD and MFO (Table , Figure BC), which may suggest that in this group of endurance athletes, expansion of Mito VD was rate‐limiting for MFO. Moreover, CS‐activity, which can be used as a marker of mitochondrial content also correlated strongly with MFO.…”

“…Mito VD was measured as described previously . Importantly, four 1 mm 3 pieces of each muscle biopsy were fixed in 2.5% glutaraldehyde in 0.1 mol/L cacodylate buffer at room temperature in a non‐oriented manner and processed according to standard electron‐microscopy protocols.…”

Google maps for tissues: Multiscale imaging of biological systems and disease

“…3 Unlike MR renography, the measurement of GFR by clearance techniques would require much longer sampling periods. 8 This approach revealed that exercise training increases skeletal muscle mitochondrial volume density by enlargement of existing mitochondria and not de novo biogenesis. Other highlights of DCE-MRI applications include monitoring of microcirculation to evaluate the role of exchange protein activated by cyclic adenosine monophosphate 1 in the response of transvascular fluid exchange to histamine in mice.…”

“…This is prohibitive for the study of very short-term effects such as olfactory CaSR activation and highlights the benefits and value of DCE-MRI based characterization. 8 Winje et al used microscopic imaging to address the question if cachexia-a severe wasting disorder including muscle atrophy-is a mere perturbation of the protein balance or if the condition also involves a degenerative loss of myonuclei within the fibre syncytia or loss of whole muscle fibres. 4 Parametric MRI enables in vivo temperature mapping that opens an entirely new imaging driven research field of thermal phenotyping.…”