Elsevier

Metabolism

Volume 54, Issue 8, August 2005, Pages 1048-1055
Metabolism

Substrate availability and transcriptional regulation of metabolic genes in human skeletal muscle during recovery from exercise

https://doi.org/10.1016/j.metabol.2005.03.008Get rights and content

Abstract

In skeletal muscle of humans, transcription of several metabolic genes is transiently induced during recovery from exercise when no food is consumed. To determine the potential influence of substrate availability on the transcriptional regulation of metabolic genes during recovery from exercise, 9 male subjects (aged 22-27) completed 75 minutes of cycling exercise at 75% V˙o2max on 2 occasions, consuming either a high-carbohydrate (HC) or low-carbohydrate (LC) diet during the subsequent 24 hours of recovery. Nuclei were isolated and tissue frozen from vastus lateralis muscle biopsies obtained before exercise and 2, 5, 8, and 24 hours after exercise. Muscle glycogen was restored to near resting levels within 5 hours in the HC trial, but remained depressed through 24 hours in the LC trial. During the 2- to 8-hour recovery period, leg glucose uptake was 5- to 15-fold higher with HC ingestion, whereas arterial plasma free fatty acid levels were ∼3- to 7-fold higher with LC ingestion. Exercise increased (P < .05) transcription and/or mRNA content of the pyruvate dehydrogenase kinase 4, uncoupling protein 3, lipoprotein lipase, carnitine palmitoyltransferase I, hexokinase II, peroxisome proliferator activated receptor γ coactivator-1α, and peroxisome proliferator activated receptor α. Providing HC during recovery reversed the activation of pyruvate dehydrogenase kinase 4, uncoupling protein 3, lipoprotein lipase, and carnitine palmitoyltransferase I within 5 to 8 hours after exercise, whereas providing LC during recovery elicited a sustained/enhanced increase in activation of these genes through 8 to 24 hours of recovery. These findings provide evidence that factors associated with substrate availability and/or cellular metabolic recovery (eg, muscle glycogen restoration) influence the transcriptional regulation of metabolic genes in skeletal muscle of humans during recovery from exercise.

Introduction

Exercise activates transcription and increases the mRNA content of several metabolic genes in human skeletal muscle [1], [2], [3], [4]. An interesting feature of this response is that both transcription and mRNA content may remain elevated or continue to increase during the initial hours of recovery, depending in part on the intensity and duration of the exercise bout [5], but then return to near baseline levels within 24 hours after exercise. The magnitude and timing of the response also varies among genes [2], [3], [5], reflecting differences in the regulatory sensitivity of each gene to exercise. Although not as well studied, exercise-induced increases in mRNA are generally followed by acute increases in the corresponding protein [1], [6], [7], [8], [9]. Taken together, these findings suggest that the recovery period after exercise represents the time frame during which the molecular responses to endurance exercise training occur in skeletal muscle [10].

The transient nature of the molecular response during recovery from exercise is similar to the timing of a number of other metabolic adjustments in skeletal muscle. These include an elevation in resting oxygen consumption [11], an initial enhanced glucose uptake independent of insulin [12], [13], a prolonged and marked increase in the sensitivity and responsiveness of glucose transport to insulin [12], [13], [14], and an increase in glycogen synthase activity [15], [16]. The initial elevation in postexercise glucose uptake and glycogen synthase activation, both in the absence and presence of insulin, is inversely related to muscle glycogen content [17], [18]. Whereas the noninsulin-dependent phase of glycogen resynthesis reverses within the first several hours after exercise [12], [19], the enhanced sensitivity of muscle to insulin persists until muscle glycogen stores are replenished [19], [20], [21]. These findings suggest that muscle glycogen content may play a significant role in regulating the activity of several intracellular signaling pathways [14], [17], [22], [23]. Muscle glycogen content also appears to influence the regulation of gene transcription, as we have previously found in humans that lowering muscle glycogen content before exercise enhances the exercise-induced transcriptional activation of exercise-responsive genes [24], [25]. Alternatively, other factors associated with dietary manipulation, including substrate availability and/or insulin/counterregulatory hormone levels, may contribute to the regulation of metabolic genes in skeletal muscle.

In the present study, we sought to further examine the potential association between metabolic state and the regulation of metabolic gene expression in skeletal muscle by investigating the effect of dietary intake during recovery from exercise. Specifically, we tested in humans the hypothesis that limiting metabolic recovery by restricting carbohydrate intake during the initial 24-hour period after exercise enhances and/or prolongs the activation of exercise-responsive metabolic genes in skeletal muscle as compared with when a high-carbohydrate (HC) diet is ingested. The regulation of gene expression was assessed at the level of both transcription (direct index of gene activation) and mRNA concentration. Several genes previously shown to be acutely activated in skeletal muscle by exercise and/or other metabolic challenges were selected for transcription/mRNA analysis. Particular attention was given to the pyruvate dehydrogenase kinase (PDK4) gene, the product of which has been suggested to play an important role in minimizing the oxidation of glucose in skeletal muscle under conditions in which glucose is needed for muscle glycogen resynthesis [26]. Other exercise-responsive genes examined included uncoupling protein 3 (UCP3), 3 glucose metabolism genes (GLUT4, hexokinase II [HKII], glycogen synthase [GS]), 3 lipid metabolism genes (lipoprotein lipase [LPL], carnitine palmitoyltransferase I [CPT I], fatty acid translocase [CD36]), and 3 transcriptional regulatory factors (peroxisome proliferator activated receptor gamma coactivator 1α [PGC-1α], peroxisome proliferator activated receptor α [PPARα], and forkhead homolog in rhabdomyosarcoma [FOXO1]).

Section snippets

Subjects

Nine healthy male subjects (age, 22-33 years; height, 178 ± 2 cm; weight, 73 ± 2 kg; V˙o2max, 4.2 ± 0.2 l/min [mean ± SE]) participated in the present study. The subjects were all physically active but had not participated in any regular physical training program during the 6 months before the study. The subjects were given both written and verbal information about the experimental protocol and procedures involved and informed about any discomfort that might be associated with the experiment

Blood variables

Providing carbohydrate-rich meals (HC trial) during recovery from exercise resulted in significantly (P < .05) higher plasma glucose and insulin concentrations as compared with when LC meals (LC trial) were provided, particularly in the first hour after each meal (Table 2). In the HC trial, glucose uptake across the leg increased (P < .05) from 2 to 7 hours of recovery relative to the initial postexercise blood sample (ie, 40 minutes after exercise), whereas glucose uptake decreased (P < .05)

Discussion

The major finding of the present study is that the type of diet consumed during recovery from exercise influences the postexercise regulation of metabolic gene expression in skeletal muscle. Specifically, LC feeding during recovery from exercise elicits a prolonged and/or secondary activation of select exercise-responsive metabolic genes (eg, PDK4, UCP3, LPL, CPT I, CD36, and FOXO1), whereas HC feeding elicits a reversal of the exercise-induced activation of these genes. The difference in

Acknowledgment

The authors wish to thank the subjects who participated in the study for their extraordinary effort. The technical assistance of Kristina Møller Kristensen, Carsten Nielsen, and Mari Person are gratefully acknowledged.

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    The study was supported by grants from the Danish National Research Foundation (504-14) and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (AR-45372), Bethesda, Md, USA. Additional support was obtained from the Ministry of Culture Committee on Sports Research, Denmark; the Danish Medical Research Council; the Danish Natural Science Research Council; and Team Denmark, Denmark. HP was in part supported by the Benzon Foundation, Denmark.

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