Enhanced Protein Translation Underlies Improved Metabolic and Physical Adaptations to Different Exercise Training Modes in Young and Old Humans

Abstract

The molecular transducers of benefits from different exercise modalities remain incompletely defined. Here we report that 12 weeks of high-intensity aerobic interval (HIIT), resistance (RT), and combined exercise training enhanced insulin sensitivity and lean mass, but only HIIT and combined training improved aerobic capacity and skeletal muscle mitochondrial respiration. HIIT revealed a more robust increase in gene transcripts than other exercise modalities, particularly in older adults, although little overlap with corresponding individual protein abundance was noted. HIIT reversed many age-related differences in the proteome, particularly of mitochondrial proteins in concert with increased mitochondrial protein synthesis. Both RT and HIIT enhanced proteins involved in translational machinery irrespective of age. Only small changes of methylation of DNA promoter regions were observed. We provide evidence for predominant exercise regulation at the translational level, enhancing translational capacity and proteome abundance to explain phenotypic gains in muscle mitochondrial function and hypertrophy in all ages.

Keywords: aging; exercise; human; insulin clamp; interval; methylation; proteome; skeletal muscle; tracer; transcriptome.

Conflict of interest statement

Conflicts of Interest: The authors declare no conflicts of interest.

Copyright © 2017 Elsevier Inc. All rights reserved.

Figures

Figure 1. Study Recruitment

Study recruitment flow chart and final group sizes for high-intensity aerobic interval training (HIIT), resistance training (RT), or combined training (CT) that included a 12 week sedentary control period (SED). Five young adults dropped out of study due to time constraints (2), health unrelated to study (2), and IV failure (1). Three older adults dropped out due to health unrelated to study (1), did not want to perform follow up testing (1), and completed sedentary-only portion (1).

Figure 2. Baseline and Training Differences in Aerobic Fitness, Skeletal Muscle Mass, and Insulin Sensitivity

(A) Peak aerobic capacity per kg body weight (VO2 peak) was measured by indirect calorimetry during a graded exercise test and was lower in older adults at baseline. (B) Exercise training improved the aerobic phenotype with pronounced gains following 12 weeks of aerobic training using high-intensity interval training (HIIT) compared to resistance training (RT) or combined training (CT) with sedentary (SED) control period. (C) Fat-free mass (FFM) was measured by dual-energy X-ray absorptiometry and was similar between age groups at baseline. (D) FFM increased in all training groups, particularly in young RT. (E) Maximal leg strength, as 1 repetition maximum (1RM) leg press, was lower in older adults at baseline. (F) 1RM increased in all training groups, with greatest gains following RT and CT. (G) Insulin sensitivity was measured by a hyper-insulinemic-euglycemic clamp. The glucose rate of disappearance (Rd) during hyperinsulinemia was similar between age groups at baseline. (H) Glucose Rd increased across training group with non-significant changes following CT in older. Changes during SED were analyzed separately and included in graphs for comparison. Data from baseline comparisons are displayed as mean ± SD with p values for unpaired t test. Changes with training are presented as least square adjusted mean with Tukey honest significant difference (HSD) 95% confidence intervals with the horizontal dotted line set at zero (no change from baseline). Within a training group, a difference between young and old is displayed as exact p value. Statistical significance from baseline is indicated as *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001. Exact p values are reported in Table S8.

Figure 3. Baseline and Training Differences in Skeletal Muscle Mitochondria Respiration and Protein Synthesis Rates

(A) Mitochondrial respiration was measured using high-resolution respirometry and was lower per tissue content in older adults at baseline. (B) Mitochondrial respiration per tissue increased with HIIT and CT groups, although less so in older CT. (C) Mitochondrial respiration per mitochondrial protein content was lower at baseline in older people. (D) Mitochondrial respiration per mitochondrial protein content did not change with training. (E) The fractional synthesis rate of mitochondrial proteins (Mito FSR) was measured as the incorporation of [13C6ring]-phenylalanine into mitochondrial proteins isolated from serial muscle biopsies. Mito FSR was similar between age groups at baseline. (F) Mito FSR increased with HIIT in both age groups and then with RT and CT in the older group. Changes during sedentary (SED) control period were analyzed separately and included in graphs for comparison. Data from baseline comparisons are displayed as mean ± SD with p values for unpaired t test. Changes with training are presented as least square adjusted mean with Tukey HSD 95% confidence intervals with the horizontal dotted line set at zero (no change from baseline). Within a training group, a difference between young and old is displayed as exact p value. Statistical significance from baseline is indicated as *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001. Exact p values are reported in Table S8.

Figure 4. Muscle Gene Expression Changes with Exercise Training

(A–F) Genes that were differentially expressed following high-intensity interval training (HIIT) in the young (A) or older (B), resistance training in the young (C) or older (D), and combined training in the young (E) or older (F) using an adjusted p value of ≤0.05 and an absolute fold change of ≥0.5 were annotated according to their mitochondrial specificity (using MitoCarta) and molecular function (using KEGG). Mito stands for mitochondrial. (G and H) Overlap of genes upregulated with different modes of exercise training in younger (G) and older (H) participants. (I) Overlap of genes that were upregulated with HIIT in older adults and any type of exercise training in younger adults. (J) Gene set enrichment analysis of baseline gene expression differences between young and old participants against genes that were upregulated with HIIT in older participants. Genes that increased expression with age were more likely to increase their expression with HIIT in older participants. (K) A “universal exercise training response gene set” was derived by looking for genes that increased with exercise with an adjusted p value of ≤0.05 and an absolute fold change of ≥0.3 in all groups. Gene Ontology (GO) process annotations enriched for this universal exercise training response gene set was derived using MetaCore software configured with an adjusted p value threshold of ≤0.05. (L) Ingenuity Pathway Analysis (QIAGEN) was used to detect up stream regulators of the “universal exercise training response gene set.”

Figure 5. Muscle Protein Abundance with Age and Changes with Exercise Training

(A–E) Baseline differences in muscle protein abundance between young and older adults revealed decreased expression of 33 mitochondrial proteins (A). MaxQuant software configured to process label-free data was used to detect differentially expressed proteins with an adjusted p value of ≤0.05 and an absolute fold change of ≥0.5 following resistance training in the young (B) or older (C) or high-intensity interval training (HIIT) in the young (D) or older (E). MitoCarta database was used to highlight mitochondrial proteins. Fold change in skeletal muscle protein expression following 12 weeks of resistance (RT) or high-intensity aerobic interval training (HIIT) in young and older adults (B–E). Mitochondrial protein abundance increased in both RT and HIIT modalities with pronounced gains following HIIT in older adults. (F and G) Overlap of proteins that increased abundance with RT and HIIT in younger (F) and older (G) subjects, respectively.

Figure 6. Downregulation of mRNA while Protein Abundance Increased for Mitochondrial and Ribosomal Protein with HIIT in Older Adults

(A) Gene set enrichment analysis of transcripts reveal downregulation ofmRNA for translational and protein catabolism pathways between pre-HIIT and post-HIIT in older cohort (adjusted p value