Changes in the Mechanical Properties of Fast and Slow Skeletal Muscle after 7 and 21 Days of Restricted Activity in Rats

Abstract

Disuse muscle atrophy is usually accompanied by changes in skeletal muscle structure, signaling, and contractile potential. Different models of muscle unloading can provide valuable information, but the protocols of experiments with complete immobilization are not physiologically representative of a sedentary lifestyle, which is highly prevalent among humans now. In the current study, we investigated the potential effects of restricted activity on the mechanical characteristics of rat postural (soleus) and locomotor (extensor digitorum longus, EDL) muscles. The restricted-activity rats were kept in small Plexiglas cages (17.0 × 9.6 × 13.0 cm) for 7 and 21 days. After this, soleus and EDL muscles were collected for ex vivo mechanical measurements and biochemical analysis. We demonstrated that while a 21-day movement restriction affected the weight of both muscles, in soleus muscle we observed a greater decrease. The maximum isometric force and passive tension in both muscles also significantly changed after 21 days of movement restriction, along with a decrease in the level of collagen 1 and 3 mRNA expression. Furthermore, the collagen content itself changed only in soleus after 7 and 21 days of movement restriction. With regard to cytoskeletal proteins, in our experiment we observed a significant decrease in telethonin in soleus, and a similar decrease in desmin and telethonin in EDL. We also observed a shift towards fast-type myosin heavy chain expression in soleus, but not in EDL. In summary, in this study we showed that movement restriction leads to profound specific changes in the mechanical properties of fast and slow skeletal muscles. Future studies may include evaluation of signaling mechanisms regulating the synthesis, degradation, and mRNA expression of the extracellular matrix and scaffold proteins of myofibers.

Spaceflight on the ISS changed the skeletal muscle proteome of two astronauts

“…As susceptibility to muscle atrophy has been shown to differ greatly among different subjects 32,46 and different muscles 25,26 , this might explain partially contrasting reports from different human cohorts of limited size and heterogeneous age. These data suggest that the decrease of muscle CSA caused by unloading can be accompanied by loss of mitochondria and oxidative capacity at Earth gravity, particularly at longer time points than ten days or in harsher unloading conditions, such as dry immersion 47 . However, data on short space flight in humans seem to indicate that the effects on mitochondrial downregulation may be much stronger and faster in the space environment 35 .…”

Tension load affects MYOZ2 expression and mediates paraspinal myofiber transformation in adolescent idiopathic scoliosis

“…It has been shown that mechanical tension load have an important effect on myo ber type transformation [20][21][22] . Fajardo et al overloaded the plantar exor muscles and unloaded the dorsal extensor muscles in mice and found that tension load could affect the transformation of myo ber types.…”

Effect of skeletal muscle immobilization in regional anisotropic viscohyperelastic properties change

“…However, to better identify the change in the mechanical behavior of the muscle, samples transversely cut could also be used (Simon and Zidi 2022), although this would be more difficult due to the small size of the immobilized muscle. In addition, muscle fibers could also be studied, as it has been shown that immobilization can lead to a transition from type I to type II fibers, specifically for slow MHC muscles (Booth and Kelso 1973b;Udaka et al 2008;Tyganov et al 2023) but not for fast MHC muscle (Tyganov et al 2023). A comparison with other immobilized skeletal muscles could confirm this.…”