Brendon J. Gurd

Prior heavy exercise elevates pyruvate dehydrogenase activity and speeds O2 uptake kinetics during subsequent moderate‐intensity exercise in healthy young adults

The adaptation of pulmonary oxygen uptake during the transition to moderate‐intensity exercise (Mod) is faster following a prior bout of heavy‐intensity exercise. In the present study we examined the activation of pyruvate dehydrogenase (PDHa) during Mod both with and without prior heavy‐intensity exercise. Subjects (n= 9) performed a Mod1–heavy‐intensity–Mod2 exercise protocol preceded by 20 W baseline. Breath‐by‐breath kinetics and near‐infrared spectroscopy‐derived muscle oxygenation were measured continuously, and muscle biopsy samples were taken at specific times during the transition to Mod. In Mod1, PDHa increased from baseline (1.08 ± 0.2 mmol min−1 (kg wet wt)−1) to 30 s (2.05 ± 0.2 mmol min−1 (kg wet wt)−1), with no additional change at 6 min exercise (2.07 ± 0.3 mmol min−1 (kg wet wt)−1). In Mod2, PDHa was already elevated at baseline (1.88 ± 0.3 mmol min−1 (kg wet wt)−1) and was greater than in Mod1, and did not change at 30 s (1.96 ± 0.2 mmol min−1 (kg wet wt)−1) but increased at 6 min exercise (2.70 ± 0.3 mmol min−1 (kg wet wt)−1). The time constant of was lower in Mod2 (19 ± 2 s) than Mod1 (24 ± 3 s). Phosphocreatine (PCr) breakdown from baseline to 30 s was greater (P < 0.05) in Mod1 (13.6 ± 6.7 mmol (kg dry wt)−1) than Mod2 (6.5 ± 6.2 mmol (kg dry wt)−1) but total PCr breakdown was similar between conditions (Mod1, 14.8 ± 7.4 mmol (kg dry wt)−1; Mod2, 20.1 ± 8.0 mmol (kg dry wt)−1). Both oxyhaemoglobin and total haemoglobin were elevated prior to and throughout Mod2 compared with Mod1. In conclusion, the greater PDHa at baseline prior to Mod2 compared with Mod1 may have contributed in part to the faster kinetics in Mod2. That oxyhaemoglobin and total haemoglobin were elevated prior to Mod2 suggests that greater muscle perfusion may also have contributed to the observed faster kinetics. These findings are consistent with metabolic inertia, via delayed activation of PDH, in part limiting the adaptation of pulmonary and muscle O2 consumption during the normal transition to exercise.

Deacetylation of PGC-1α by SIRT1: importance for skeletal muscle function and exercise-induced mitochondrial biogenesis

Activation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α)-mediated transcription is important for both the determination of mitochondrial content and the induction of mitochondrial biogenesis in skeletal muscle. SIRT1 (silent mating type information regulator 2 homolog 1) deactetylation is proposed as a potential activator of PGC-1α transcriptional activity. The current review examines the importance of SIRT1 deacetylation of PGC-1α in skeletal muscle. Models of SIRT1 overexpression and pharmacological activation are examined, but changes in SIRT1 expression and deacetylase activity following acute and chronic contractile activity will be emphasized. In addition, potential mechanisms of SIRT1 activation in skeletal muscle will be examined. The importance of the PGC-1α acetyltransferase GCN5 will also be briefly discussed. The current evidence supports the contribution of SIRT1 deacetylation of PGC-1α to exercise-induced mitochondrial biogenesis. Further research examining exercise-mediated activation of SIRT1 and the role of GCN5 in regulating PGC-1α transcriptional activity in skeletal muscle is required.

Nuclear SIRT1 activity, but not protein content, regulates mitochondrial biogenesis in rat and human skeletal muscle

Silent mating type information regulator 2 homolog 1 (SIRT1)-mediated peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) deacetylation is potentially key for activating mitochondrial biogenesis. Yet, at the whole muscle level, SIRT1 is not associated with mitochondrial biogenesis (Gurd, BJ, Yoshida Y, Lally J, Holloway GP, Bonen A. J Physiol 587: 1817-1828, 2009). Therefore, we examined nuclear SIRT1 protein and activity in muscle with varied mitochondrial content and in response to acute exercise. We also measured these parameters after stimulating mitochondrial biogenesis with chronic muscle contraction and 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) administration in rodents and exercise training in humans. In skeletal and heart muscles, nuclear SIRT1 protein was negatively correlated with indices of mitochondrial density (citrate synthase activity, CS; cytochrome oxidase IV, COX IV), but SIRT1 activity was positively correlated with these parameters (r > 0.98). Acute exercise did not alter nuclear SIRT1 protein but did induce a time-dependent increase in nuclear SIRT1 activity. This increase in SIRT1 activity was temporally related to increases in mRNA expression of genes activated by PGC-1α. Both chronic muscle stimulation and AICAR increased mitochondrial biogenesis and muscle PGC-1α, but not nuclear PGC-1α. Concomitantly, muscle and nuclear SIRT1 protein contents were reduced, but nuclear SIRT1 activity was increased. In human muscle, training-induced mitochondrial biogenesis did not alter muscle or nuclear SIRT1 protein content, but it did increase muscle and nuclear PGC-1α and SIRT1 activity. Thus, nuclear SIRT1 activity, but not muscle or nuclear SIRT1 protein content, is associated with contraction-stimulated mitochondrial biogenesis in rat and human muscle, possibly via AMPK activation.

High-intensity interval training increases SIRT1 activity in human skeletal muscle.

The effects of training on silent mating-type information regulator 2 homolog 1 (SIRT1) activity and protein in relationship to peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) and mitochondrial content were determined in human skeletal muscle. Six weeks of high-intensity interval training ( approximately 1 h of 10 x 4 min intervals at 90% peak oxygen consumption separated by 2 min rest, 3 days per week) increased maximal activities of mitochondrial enzymes in skeletal muscle by 28% to 36% (citrate synthase, beta-hydroxyacyl-coenzyme A dehydrogenase, and cytochrome c oxidase subunit IV) and PGC-1alpha protein (16%) when measured 4 days after training. Interestingly, total muscle SIRT1 activity (31%) and activity per SIRT1 protein (58%) increased despite decreased SIRT1 protein (20%). The present data demonstrate that exercise-induced mitochondrial biogenesis is accompanied by elevated SIRT1 activity in human skeletal muscle.

Compensatory increases in nuclear PGC1α protein are primarily associated with subsarcolemmal mitochondrial adaptations in ZDF rats

OBJECTIVE We examined in insulin-resistant muscle if, in contrast to long-standing dogma, mitochondrial fatty acid oxidation is increased and whether this is attributed to an increased nuclear content of peroxisome proliferator–activated receptor (PPAR) γ coactivator (PGC) 1α and the adaptations of specific mitochondrial subpopulations. RESEARCH DESIGN AND METHODS Skeletal muscles from male control and Zucker diabetic fatty (ZDF) rats were used to determine 1) intramuscular lipid distribution, 2) subsarcolemmal and intermyofibrillar mitochondrial morphology, 3) rates of palmitate oxidation in subsarcolemmal and intermyofibrillar mitochondria, and 4) the subcellular localization of PGC1α. Electotransfection of PGC1α cDNA into lean animals tested the notion that increased nuclear PGC1α preferentially targeted subsarcolemmal mitochondria. RESULTS Transmission electron microscope analysis revealed that in ZDF animals the number (+50%), width (+69%), and density (+57%) of subsarcolemmal mitochondria were increased (P < 0.05). In contrast, intermyofibrillar mitochondria remained largely unchanged. Rates of palmitate oxidation were ∼40% higher (P < 0.05) in ZDF subsarcolemmal and intermyofibrillar mitochondria, potentially as a result of the increased PPAR-targeted proteins, carnitine palmitoyltransferase-I, and fatty acid translocase (FAT)/CD36. PGC1α mRNA and total protein were not altered in ZDF animals; however, a greater (∼70%; P < 0.05) amount of PGC1α was located in nuclei. Overexpression of PGC1α only increased subsarcolemmal mitochondrial oxidation rates. CONCLUSIONS In ZDF animals, intramuscular lipids accumulate in the intermyofibrillar region (increased size and number), and this is primarily associated with increased oxidative capacity in subsarcolemmal mitochondria (number, size, density, and oxidation rates). These changes may result from an increased nuclear content of PGC1α, as under basal conditions, overexpression of PGC1α appears to target subsarcolemmal mitochondria.

Dissociation of increases in PGC-1α and its regulators from exercise intensity and muscle activation following acute exercise.

Muscle activation as well as changes in peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) following high-intensity interval exercise (HIIE) were examined in young healthy men (n  = 8; age, 21.9±2.2 yrs; VO2peak, 53.1±6.4 ml/min/kg; peak work rate, 317±23.5 watts). On each of 3 visits HIIE was performed on a cycle ergometer at a target intensity of 73, 100, or 133% of peak work rate. Muscle biopsies were taken at rest and three hours after each exercise condition. Total work was not different between conditions (∼730 kJ) while average power output (73%, 237±21; 100%, 323±26; 133%, 384±35 watts) and EMG derived muscle activation (73%, 1262±605; 100%, 2089±737; 133%, 3029±1206 total integrated EMG per interval) increased in an intensity dependent fashion. PGC-1α mRNA was elevated after all three conditions (p<0.05), with a greater increase observed following the 100% condition (∼9 fold, p<0.05) compared to both the 73 and 133% conditions (∼4 fold). When expressed relative to muscle activation, the increase in PGC-1α mRNA for the 133% condition was less than that for the 73 and 100% conditions (p<0.05). SIRT1 mRNA was also elevated after all three conditions (∼1.4 fold, p<0.05), with no difference between conditions. These findings suggest that intensity-dependent increases in PGC-1α mRNA following submaximal exercise are largely due to increases in muscle recruitment. As well, the blunted response of PGC-1α mRNA expression following supramaximal exercise may indicate that signalling mediated activation of PGC-1α may also be blunted. We also indentify that increases in PDK4, SIRT1, and RIP140 mRNA following acute exercise are dissociated from exercise intensity and muscle activation, while increases in EGR1 are augmented with supramaximal HIIE (p<0.05).

Fibre-Specific Responses to Endurance and Low Volume High Intensity Interval Training: Striking Similarities in Acute and Chronic Adaptation

The current study involved the completion of two distinct experiments. Experiment 1 compared fibre specific and whole muscle responses to acute bouts of either low-volume high-intensity interval training (LV-HIT) or moderate-intensity continuous endurance exercise (END) in a randomized crossover design. Experiment 2 examined the impact of a six-week training intervention (END or LV-HIT; 4 days/week), on whole body and skeletal muscle fibre specific markers of aerobic and anaerobic capacity. Six recreationally active men (Age: 20.7±3.8 yrs; VO2peak: 51.9±5.1 mL/kg/min) reported to the lab on two separate occasions for experiment 1. Following a muscle biopsy taken in a fasted state, participants completed an acute bout of each exercise protocol (LV-HIT: 8, 20-second intervals at ∼170% of VO2peak separated by 10 seconds of rest; END: 30 minutes at ∼65% of VO2peak), immediately followed by a muscle biopsy. Glycogen content of type I and IIA fibres was significantly (p<0.05) reduced, while p-ACC was significantly increased (p<0.05) following both protocols. Nineteen recreationally active males (n = 16) and females (n = 3) were VO2peak-matched and assigned to either the LV-HIT (n = 10; 21±2 yrs) or END (n = 9; 20.7±3.8 yrs) group for experiment 2. After 6 weeks, both training protocols induced comparable increases in aerobic capacity (END: Pre: 48.3±6.0, Mid: 51.8±6.0, Post: 55.0±6.3 mL/kg/min LV-HIT: Pre: 47.9±8.1, Mid: 50.4±7.4, Post: 54.7±7.6 mL/kg/min), fibre-type specific oxidative and glycolytic capacity, glycogen and IMTG stores, and whole-muscle capillary density. Interestingly, only LV-HIT induced greater improvements in anaerobic performance and estimated whole-muscle glycolytic capacity. These results suggest that 30 minutes of END exercise at ∼65% VO2peak or 4 minutes of LV-HIT at ∼170% VO2peak induce comparable changes in the intra-myocellular environment (glycogen content and signaling activation); correspondingly, training-induced adaptations resulting for these protocols, and other HIT and END protocols are strikingly similar.

In mammalian muscle, SIRT3 is present in mitochondria and not in the nucleus; and SIRT3 is upregulated by chronic muscle contraction in an adenosine monophosphate-activated protein kinase–independent manner

In selected cell lines, it appears (a) that metabolic stressors induce the translocation of SIRT3 from the nucleus to mitochondria and (b) that SIRT3 may contribute to the regulation of mitochondrial biogenesis and/or fatty acid utilization. We have examined in mammalian muscle (1) the association between SIRT3 protein content and muscle oxidative capacity and mitochondrial fatty acid oxidation, (2) the subcellular location of SIRT3, (3) whether exercise induces the translocation of SIRT3 from the nucleus to the mitochondria, and (4) the response of SIRT3 protein to stressors known to induce mitochondrial biogenesis (chronic muscle stimulation and 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside administration). SIRT3 protein displayed hierarchical expression based on oxidative potential of muscle tissues (heart >> red >> white). In contrast to studies in some cell lines, metabolic stress (exercise) did not induce the translocation of SIRT3 from the nucleus to mitochondria, as SIRT3 was only present in subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria, not in the nucleus. Chronic stimulation increased muscle mitochondrial content and SIRT3 protein in SS (+33%) and IMF (+27%) mitochondria (P < .05). In contrast, chronic 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside administration, while inducing mitochondrial biogenesis, did not alter SS or IMF mitochondrial SIRT3 protein content. These studies have shown that, in muscle, SIRT3 (a) scales with muscle oxidative capacity and with enzymes regulating fatty acid oxidation, (b) in resting muscle is localized to SS and IMF mitochondria and not nuclei, (c) in contracting muscle is not acutely translocated to mitochondria, and (d) is upregulated with chronic stimulation in an adenosine monophosphate-activated protein kinase-independent manner.

Resveratrol supplementation does not augment performance adaptations or fibre-type-specific responses to high-intensity interval training in humans

The present study examined the effect of concurrent exercise training and daily resveratrol (RSV) supplementation (150 mg) on training-induced adaptations following low-dose high-intensity interval training (HIIT). Sixteen recreationally active (∼22 years, ∼51 mL·kg(-1)·min(-1)) men were randomly assigned in a double-blind fashion to either the RSV or placebo group with both groups performing 4 weeks of HIIT 3 days per week. Before and after training, participants had a resting muscle biopsy taken, completed a peak oxygen uptake test, a Wingate test, and a submaximal exercise test. A main effect of training (p < 0.05) and interaction effect (p < 0.05) on peak aerobic power was observed; post hoc pairwise comparisons revealed that a significant (p < 0.05) increase occurred in the placebo group only. Main effects of training (p < 0.05) were observed for both peak oxygen uptake (placebo - pretraining: 51.3 ± 1.8, post-training: 54.5 ± 1.5 mL·kg(-1)·min(-1), effect size (ES) = 0.93; RSV - pretraining: 49.6 ± 2.2, post-training: 52.3 ± 2.5 mL·kg(-1)·min(-1), ES = 0.50) and Wingate peak power (placebo: pretraining: 747 ± 39, post-training: 809 ± 31 W, ES = 0.84; RSV - pretraining: 679 ± 39, post-training: 691 ± 43 W, ES = 0.12). Fibre-type distribution was unchanged, while a main effect of training (p < 0.05) was observed for succinate dehydrogenase activity and glycogen content, but not α-glycerophosphate dehydrogenase activity or intramuscular lipids in type I and IIA fibres. The fold change in PGC-1α, SIRT1, and SOD2 gene expression following training was significantly (p < 0.05) lower in the RSV group than placebo. These results suggest that concurrent exercise training and RSV supplementation may alter the normal training response induced by low-volume HIIT.

Reducing the Intensity and Volume of Interval Training Diminishes Cardiovascular Adaptation but Not Mitochondrial Biogenesis in Overweight/Obese Men

Objective The purpose of this research was to determine if the adaptations to high intensity interval training (HIT) are mitigated when both intensity and training volume (i.e. exercise energy expenditure) are reduced. Methods 19 overweight/obese, sedentary males (Age: 22.7±3.9 yrs, Body Mass Index: 31.4±2.6 kg/m2, Waist Circumference: 106.5±6.6 cm) performed 9 sessions of interval training using a 1-min on, 1-min off protocol on a cycle ergometer over three weeks at either 70% (LO) or 100% (HI) peak work rate. Results Cytochrome oxidase I protein content, cytochrome oxidase IV protein content, and citrate synthase maximal activity all demonstrated similar increases between groups with a significant effect of training for each. β-hydroxyacyl-CoA dehydrogenase maximal activity tended to increase with training but did not reach statistical significance (p = 0.07). Peroxisome proliferator-activated receptor gamma coactivator-1α and silent mating type information regulator 2 homolog 1 protein contents also increased significantly (p = 0.047), while AMP-activated protein kinase protein content decreased following the intervention (p = 0.019). VO2peak increased by 11.0±7.4% and 27.7±4.4% in the LO and HI groups respectively with significant effects of both training (p<0.001) and interaction (p = 0.027). Exercise performance improved by 8.6±7.6% in the LO group and 14.1±4.3% in the HI group with a significant effect of training and a significant difference in the improvement between groups. There were no differences in perceived enjoyment or self-efficacy between groups despite significantly lower affect scores during training in the HI group. Conclusions While improvements in aerobic capacity and exercise performance were different between groups, changes in oxidative capacity were similar despite reductions in both training intensity and volume.