William J. Smiles

Acute Endurance Exercise Induces Nuclear p53 Abundance in Human Skeletal Muscle

Purpose: The tumor suppressor protein p53 may have regulatory roles in exercise response-adaptation processes such as mitochondrial biogenesis and autophagy, although its cellular location largely governs its biological role. We investigated the subcellular localization of p53 and selected signaling targets in human skeletal muscle following a single bout of endurance exercise. Methods: Sixteen, untrained individuals were pair-matched for aerobic capacity (VO2peak) and allocated to either an exercise (EX, n = 8) or control (CON, n = 8) group. After a resting muscle biopsy, EX performed 60 min continuous cycling at ~70% of VO2peak during which time CON subjects rested. A further biopsy was obtained from both groups 3 h post-exercise (EX) or 4 h after the first biopsy (CON). Results: Nuclear p53 increased after 3 h recovery with EX only (~48%, p < 0.05) but was unchanged in the mitochondrial or cytoplasmic fractions in either group. Autophagy protein 5 (Atg-5) decreased in the mitochondrial protein fraction 3 h post-EX (~69%, P < 0.05) but remained unchanged in CON. There was an increase in cytoplasmic levels of the mitophagy marker PINK1 following 3 h of rest in CON only (~23%, P < 0.05). There were no changes in mitochondrial, nuclear, or cytoplasmic levels of PGC-1α post-exercise in either group. Conclusions: The selective increase in nuclear p53 abundance following endurance exercise suggests a potential pro-autophagy response to remove damaged proteins and organelles prior to initiating mitochondrial biogenesis and remodeling responses in untrained individuals.

Effects of skeletal muscle energy availability on protein turnover responses to exercise

ABSTRACT Skeletal muscle adaptation to exercise training is a consequence of repeated contraction-induced increases in gene expression that lead to the accumulation of functional proteins whose role is to blunt the homeostatic perturbations generated by escalations in energetic demand and substrate turnover. The development of a specific ‘exercise phenotype’ is the result of new, augmented steady-state mRNA and protein levels that stem from the training stimulus (i.e. endurance or resistance based). Maintaining appropriate skeletal muscle integrity to meet the demands of training (i.e. increases in myofibrillar and/or mitochondrial protein) is regulated by cyclic phases of synthesis and breakdown, the rate and turnover largely determined by the proteins half-life. Cross-talk among several intracellular systems regulating protein synthesis, breakdown and folding is required to ensure protein equilibrium is maintained. These pathways include both proteasomal and lysosomal degradation systems (ubiquitin-mediated and autophagy, respectively) and the protein translational and folding machinery. The activities of these cellular pathways are bioenergetically expensive and are modified by intracellular energy availability (i.e. macronutrient intake) and the ‘training impulse’ (i.e. summation of the volume, intensity and frequency). As such, exercise–nutrient interactions can modulate signal transduction cascades that converge on these protein regulatory systems, especially in the early post-exercise recovery period. This review focuses on the regulation of muscle protein synthetic response-adaptation processes to divergent exercise stimuli and how intracellular energy availability interacts with contractile activity to impact on muscle remodelling. Summary: Skeletal muscle adaptation to exercise training serves to blunt the homeostatic intracellular perturbations caused by accelerated energetic demands, and these responses are influenced by exogenous and endogenous energy availability.

Modulation of autophagy signaling with resistance exercise and protein ingestion following short-term energy deficit

Autophagy contributes to remodeling of skeletal muscle and is sensitive to contractile activity and prevailing energy availability. We investigated changes in targeted genes and proteins with roles in autophagy following 5 days of energy balance (EB), energy deficit (ED), and resistance exercise (REX) after ED. Muscle biopsies from 15 subjects (8 males, 7 females) were taken at rest following 5 days of EB [45 kcal·kg fat free mass (FFM)(-1)·day(-1)] and 5 days of ED (30 kcal·kg FFM(-1)·day(-1)). After ED, subjects completed a bout of REX and consumed either placebo (PLA) or 30 g whey protein (PRO) immediately postexercise. Muscle biopsies were obtained at 1 and 4 h into recovery in each trial. Resting protein levels of autophagy-related gene protein 5 (Atg5) decreased after ED compared with EB (∼23%, P < 0.001) and remained below EB from 1 to 4 h postexercise in PLA (∼17%) and at 1 h in PRO (∼18%, P < 0.05). In addition, conjugated Atg5 (cAtg12) decreased below EB in PLA at 4 h (∼20, P < 0.05); however, its values were increased above this time point in PRO at 4 h alongside increases in FOXO1 above EB (∼22-26%, P < 0.05). Notably, these changes were subsequent to increases in unc-51-like kinase 1(Ser757) phosphorylation (∼60%) 1 h postexercise in PRO. No significant changes in gene expression of selected autophagy markers were found, but EGR-1 increased above ED and EB in PLA (∼417-864%) and PRO (∼1,417-2,731%) trials 1 h postexercise (P < 0.001). Postexercise protein availability, compared with placebo, can selectively promote autophagic responses to REX in ED.

Dynamic proteome profiling of individual proteins in human skeletal muscle after a high-fat diet and resistance exercise

It is generally accepted that muscle adaptation to resistance exercise (REX) training is underpinned by contraction‐induced, increased rates of protein synthesis and dietary protein availability. By using dynamic proteome profiling (DPP), we investigated the contribution of both synthesis and breakdown to changes in abundance on a protein‐by‐protein basis in human skeletal muscle. Age‐matched, overweight males consumed 9 d of a high‐fat, low‐carbohydrate diet during which time they either undertook 3 sessions of REX or performed no exercise. Precursor enrichment and the rate of incorporation of deuterium oxide into newly synthesized muscle proteins were determined by mass spectrometry. Ninety proteins were included in the DPP, with 28 proteins exhibiting significant responses to REX. The most common pattern of response was an increase in turnover, followed by an increase in abundance with no detectable increase in protein synthesis. Here, we provide novel evidence that demonstrates that the contribution of synthesis and breakdown to changes in protein abundance induced by REX differ on a protein‐by‐protein basis. We also highlight the importance of the degradation of individual muscle proteins after exercise in human skeletal muscle.—Camera, D. M., Burniston, J. G., Pogson, M. A., Smiles, W. J., Hawley, J. A. Dynamic proteome profiling of individual proteins in human skeletal muscle after a high‐fat diet and resistance exercise. FASEB J. 31, 5478–5494 (2017). www.fasebj.org

The relationship between exercise, nutrition and type 2 diabetes

Type 2 diabetes mellitus and its precursor, insulin resistance, are metabolic disease states characterized by impaired regulation in the delivery, transport, and/or storage of energy substrates (primarily carbohydrate- and fat-based fuels). A hallmark feature of patients with type 2 diabetes is prolonged periods of hyperglycemia due to a decreased responsiveness of metabolically active peripheral tissues to the actions of insulin (i.e., metabolic inflexibility). Accordingly, efforts to modify skeletal muscle substrate handling in type 2 diabetes patients so that the capacity for fat oxidation and metabolic flexibility is improved should be a primary goal for the treatment of these disorders. Two potent interventions for improving whole-body glucose homeostasis are exercise and diet. A single bout of either resistance or endurance exercise reduces the prevalence and duration of hyperglycemic excursions in patients with type 2 diabetes, an effect lasting well into the next day. With regard to diet, the carbohydrate content of a meal and the glycemic index (GI) of the carbohydrate consumed are both major determinants of the postprandial glycemic response. Diets containing high-GI carbohydrates have been shown to be independent risk factors for type 2 diabetes onset, while in obese insulin-resistant individuals, low-GI diets are effective for inducing both weight loss and improving insulin action and glucose tolerance. The implementation of physical activity and dietary modifications are effective low-cost treatment options for controlling hyperglycemic episodes in patients with type 2 diabetes.

Autophagy, Exercise, and Lifestyle Modification

Regular exercise is an established stimulus to promote multiple health benefits and subsequently improve well-being and physical performance. In order to mediate these responses, exercise must induce widespread perturbations to cellular homeostasis so as to meet muscle energy and oxygen demands. Autophagy has recently been implicated in the adaptation responses to resistance and endurance exercise through the degradation of macromolecules and subcellular organelles, particularly the mitochondria, and release of amino acids which can be used for metabolic processes such as muscle protein synthesis. This chapter will focus on the molecular mechanisms mediating autophagic signaling responses in skeletal muscle following resistance and endurance exercise, and the adaptation processes these responses regulate with altered nutrient availability and energetic demands.