Sarcolab pilot study into skeletal muscle's adaptation to long-term spaceflight

Abstract

Spaceflight causes muscle wasting. The Sarcolab pilot study investigated two astronauts with regards to plantar flexor muscle size, architecture, and function, and to the underlying molecular adaptations in order to further the understanding of muscular responses to spaceflight and exercise countermeasures. Two crew members (A and B) spent 6 months in space. Crew member A trained less vigorously than B. Postflight, A showed substantial decrements in plantar flexor volume, muscle architecture, in strength and in fiber contractility, which was strongly mitigated in B. The difference between these crew members closely reflected FAK-Y397 abundance, a molecular marker of muscle's loading history. Moreover, crew member A showed downregulation of contractile proteins and enzymes of anaerobic metabolism, as well as of systemic markers of energy and protein metabolism. However, both crew members exhibited decrements in muscular aerobic metabolism and phosphate high energy transfer. We conclude that countermeasures can be effective, particularly when resistive forces are of sufficient magnitude. However, to fully prevent space-related muscular deterioration, intersubject variability must be understood, and intensive exercise countermeasures programs seem mandatory. Finally, proteomic and metabolomic analyses suggest that exercise benefits in space may go beyond mere maintenance of muscle mass, but rather extend to the level of organismic metabolism.

Fig. 1

Onboard exercise. Survey of the load and distance per treadmill session, and the load and number of heel raise exercise with aRED for crew members A and B during their sojourn on the ISS. Data are means for each week on board ISS, interpolated by a spline function

Fig. 2

Effects of spaceflight upon muscle function. Data are given in percent changes from baseline, for crew members A and B

Fig. 3

Proteomic analysis in human skeletal muscle. Histograms of differential protein expression in soleus muscle between baseline vs. PF-1 (colored bars) and baseline vs. PF-2 (striped bars) in crew member A (green bars) and B (red bars), as detected by 2D DIGE analysis. Proteins significantly altered (paired one-way ANOVA and Tukey, α = 0.01) are indicated by their gene name and expressed as a percent of spot volume variation. a Contractile proteins; b Metabolism

Fig. 4

Metabolomic analysis. Panels a, b show amino acid and energetic metabolites, respectively, in box plot analysis and in arbitrary units concentrations (C.A.U.) of the most significant metabolites. Astronauts A and B are represented by red and green colors, respectively. Circle, square, and triangle represent baseline, PF-1 and PF-2, respectively. Gray circles represent the control cohort (79 volunteers). Significant (P < 0.01) and barely significant (P < 0.05) P values are also reported