Fig. 2: CR promotes a fast-to-slow muscle fiber phenotype shift.
From: Distinct and additive effects of calorie restriction and rapamycin in aging skeletal muscle
A Muscle mass for quadriceps (QUAD), gastrocnemius (GAS), tibialis anterior (TA), plantaris (PLA), extensor digitorum longus (EDL), soleus (SOL), and triceps brachii (TRI) was averaged across both limbs, normalized to body mass and then to 10-month-old control mice. B Scatterplots and linear regressions of the relationship between body and muscle mass of the fast twitch TA, TRI, GAS, QUAD and EDL muscles and the slow twitch SOL muscle. Isolated muscle function parameters, including C force-frequency curve (left) and fatigue response to multiple stimulations (right), D peak force normalized to body mass, E peak force normalized to cross sectional area (specific force), and F mean twitch responses including time-to-peak tension (TPT), half-relaxation time (1/2-RT) and peak twitch (Pt) for SOL (top panel) and EDL muscle (bottom panel). G Proportional total fiber-type-specific cross-sectional area analyzed on whole cross-sections of (left to right) SOL (n = 6), EDL (n = 7, 9 and 8), TA (n = 11, 13 and 7) and TRI (n = 5, 9 and 9) for 10mCON, 30mCON and 30mCR, stained with antibodies against type I (blue), type IIA (yellow), and type IIB (green) fibers as well as laminin (red), while fibers without staining were classified as IIX. H Representative magnifications of images from whole-muscle cross sections for SOL, EDL, TA and TRI, quantified in 2G and Supplementary Fig. 2. Group numbers for 10mCON are n = 17 (A, B), 10 (C–F: EDL) and 8 for fatigue, 11 (C–E: SOL) or 9 for fatigue, for 30mCON n = 20 (A, B), 19 (C–F: EDL), 15 (C, D, F: SOL) and 14 (E: SOL), and for 30mCR n = 20 (A, B), 18 (C–E: EDL) or 16 for fatigue, 15 (C–E: SOL) or 13 for fatigue, 12 (F: SOL) and 15 (F: EDL). Data are presented as mean ± SEM. One-way (A and D–F) or two-way repeated- measure (C, G) ANOVAs with Fisher’s LSD or Tukey’s post hoc tests, respectively, were used to compare between data. *, **, and *** denote a significant difference between groups of P < 0.05, P < 0.01, and P < 0.001, respectively. Colored asterisks refer to the group of comparison.
