Myotendinous junction: a microenvironment favorable for short-term adaptations to resistance training following gastrocnemius muscle atrophy

Figures

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  FIGURE 1. Design of the experimental protocols of the groups in the periods of joint immobilization (10 days), and resistance training (7 and 14 days). Created with Biorender®.

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  FIGURE 2. Histological analysis of the groups using the HE technique revealed the presence of muscle fibers (f) and peripheral nuclei (arrows). In the I group, a centrally located nucleus (arrowhead) was observed. Bars: 25 µm. Means and standard deviations of gastrocnemius muscle mass (g) and relative muscle mass (%). *p < 0.05; **p < 0.01; ***p < 0.0005; ****p < 0.0001.

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  FIGURE 3. Ultrastructural analysis of the belly muscle and myotendinous junction (MTJ) region by transmission electron microscopy. We observed in the muscle belly the sarcomeres in series (s) delimited by the z-lines (white arrowhead) and the presence of subsarcolemmal mitochondria (sm) and intermyofibrillar mitochondria (circle). In the myotendinous region, we presented the sarcoplasmic projections as invaginations (black arrowhead) and evaginations (black arrow) that compose the MTJ (*); in this region, the proximal (ps) and distal (ds) sarcomeres. In the ECM adjacent to the MTJ, we identified the presence of SR (sr), telocyte (t) with its telopods (white arrow), and pods (p). Besides that, we showed a muscle fiber in a regenerative process in a new muscle fiber in the myotendinous region (mf) and a myonuclei (m) in some experimental groups. Bars: 1 µm.

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  FIGURE 4. Morphometrics analysis of sarcoplasmic invaginations and evaginations of the experimental groups. Transmission electron micrograph of the MTJ, depicting sarcoplasmic invaginations and evaginations. The length and thickness of the sarcoplasmic invaginations are indicated by red and yellow lines, respectively, while the length and thickness of the sarcoplasmic evaginations are represented by blue and green lines, respectively. Bar: 1 µm. Means and standard deviations of the length of the sarcoplasmic invaginations. Means and standard deviations of the thickness of the sarcoplasmic invaginations. Means and standard deviations of the length of the sarcoplasmic evaginations of the. Means and standard deviations of the thickness of the sarcoplasmic evaginations of the experimental groups. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.

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  FIGURE 5. Morphometry of the sarcomere length of the muscle belly and myotendinous region. Bars: 1 µm. Means ± standard deviations of the sarcomere length of the belly (red), proximal sarcomere (purple), and distal sarcomere (green). *p < 0.05; **p < 0.001; ***p < 0.0001.

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  FIGURE 6. Analysis of the myotendinous region by fluorescence microscopy of the myotendinous junction (MTJ) highlighting muscle (m) and tendon (t) tissue, with the identification of satellite cells (PAX7+DAPI) and telocytes (CD34+DAPI) across the experimental groups. Bars: 20 µm.

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  FIGURE 7. Morphometric analysis of collagen XXII (Col22a1) of the MTJ. Immunofluorescence and binarized image of collagen XXII as an example for morphometric analysis. Bar: 10 µm. Means ± standard deviations of the collagen XXII area of the MTJ (µm2/muscle fiber). Means ± standard deviations of the collagen XXII perimeter of the MTJ (µm/muscle fiber). *p < 0.05; ***p < 0.001.