Endurance-Type Exercise Increases Bulk and Individual Mitochondrial Protein Synthesis Rates in Rats

Abstract

Physical activity increases muscle protein synthesis rates. However, the impact of exercise on the coordinated up- and/or downregulation of individual protein synthesis rates in skeletal muscle tissue remains unclear. The authors assessed the impact of exercise on mixed muscle, myofibrillar, and mitochondrial protein synthesis rates as well as individual protein synthesis rates in vivo in rats. Adult Lewis rats either remained sedentary (n = 3) or had access to a running wheel (n = 3) for the last 2 weeks of a 3-week experimental period. Deuterated water was injected and subsequently administered in drinking water over the experimental period. Blood and soleus muscle were collected and used to assess bulk mixed muscle, myofibrillar, and mitochondrial protein synthesis rates using gas chromatography–mass spectrometry and individual muscle protein synthesis rates using liquid chromatography–mass spectrometry (i.e., dynamic proteomic profiling). Wheel running resulted in greater myofibrillar (3.94 ± 0.26 vs. 3.03 ± 0.15%/day; p < .01) and mitochondrial (4.64 ± 0.24 vs. 3.97 ± 0.26%/day; p < .05), but not mixed muscle (2.64 ± 0.96 vs. 2.38 ± 0.62%/day; p = .71) protein synthesis rates, when compared with the sedentary condition. Exercise impacted the synthesis rates of 80 proteins, with the difference from the sedentary condition ranging between −64% and +420%. Significantly greater synthesis rates were detected for F1-ATP synthase, ATP synthase subunit alpha, hemoglobin, myosin light chain-6, and synaptopodin-2 (p < .05). The skeletal muscle protein adaptive response to endurance-type exercise involves upregulation of mitochondrial protein synthesis rates, but it is highly coordinated as reflected by the up- and downregulation of various individual proteins across different bulk subcellular protein fractions.

Fractional Synthesis Rates of Individual Proteins in Rat Soleus and Plantaris Muscles

“…For example, we report serotransferrin (TRFE) turnover of 5.11%/day whereas Holwerda et al report a >6-fold lesser rate (0.77%/day). Conversely, turnover of haemoglobin subunit beta 2 (HBB2) was 1.25%/day ± 0.14%/day in the current work and 4.74%/day ± 0.7%/day in [20]. FSR data exhibits greater biological variability than protein abundance data [19] but these inter-study differences may also relate to differences in rat strain or the analytical method used to calculate FSR.…”

“…We report that individual proteins exhibit a broad range of turnover rates within skeletal muscle, but our analysis primarily focuses on proteins that are common to both soleus and plantaris muscle. To date, at least 17 papers (Table 2) have reported protein-specific FSR data in various muscles of humans [16,19,27,28], rodents [13,18,20,23,24,[29][30][31][32][33][34][35] and chickens [17] in vivo. The earliest works (e.g., [16,23,30]) used biochemical techniques to isolate abundant individual proteins.…”

“…Herein, we report FSR data in %/day units that can be compared between animals and across studies. Similarly, Holwerda et al [20] report FSR data in rat soleus, including 24 proteins that were also included in the current dataset. The factional turnover rate was remarkably similar for the majority of proteins ( Figure 6), and the mean difference in FSR between the two studies was 0.15%/day.…”

“…FSR data exhibits greater biological variability than protein abundance data [19] but these inter-study differences may also relate to differences in rat strain or the analytical method used to calculate FSR. Holwerda et al [20], employed a non-linear calculation consistent with the two-point model (Figure 3) that uses data collected at the start and end of the labelling period only. The calculation of synthesis from two data points assumes all proteins adhere to the expected exponential rise-to-plateau kinetics of deuterium incorporation.…”

“…Infusion of stable isotope-labelled amino acids constrains studies to a relatively short duration (e.g., min-h timescales), whereas the turnover of abundant tissue proteins in vivo occurs over a period of days. Longer-term labelling studies have been conducted in animals fed a diet enriched with a stable-isotope-labelled amino acid [13,17], whereas we have focused on the application of deuterium oxide (D 2 O or 2 H 2 O) or "heavy water" [14,[18][19][20][21]. D 2 O can be administered via the drinking water in free-living animals and the majority of amino acids are labelled intracellularly via transamination reactions [22].…”