Cellular mechanism of immobilization-induced muscle atrophy: A mini review

Therapeutic Potential of Hydrogen-Rich Water on Muscle Atrophy Caused by Immobilization in a Mouse Model

Skeletal muscle atrophy is associated with poor quality of life and disability. Thus, finding a new strategy for the prevention and treatment of skeletal muscle atrophy is very crucial. This study aimed to investigate the therapeutic potential of hydrogen-rich water (HRW) on muscle atrophy in a unilateral hind limb immobilization model. Thirty-six male Balb/C mice were divided into control (without immobilization), atrophy, and atrophy + hydrogen-rich water (HRW). Unilateral hind limb immobilization was induced using a splint for 7 days (atrophy) and removed for 10 days (recovery). At the end of each phase, gastrocnemius and soleus muscle weight, limb grip strength, skeletal muscle histopathology, muscle fiber size, cross-section area (CSA), serum troponin I and skeletal muscle IL-6, TNF-α and Malondialdehyde (MDA), and mRNA expression of NF-κB, BAX and Beclin-1 were evaluated. Muscle weight and limb grip strength in the H2-treated group were significantly improved during the atrophy phase, and this improvement continued during the recovery period. Treatment by HRW increased CSA and muscle fiber size and reduced muscle fibrosis, serum troponin I, IL-6, TNF-α and MDA which was more prominent in the atrophy phase. These data suggest that HRW could improve muscle atrophy in an immobilized condition and could be considered a new strategy during rehabilitation.

Atenolol Ameliorates Skeletal Muscle Atrophy and Oxidative Stress Induced by Cast Immobilization in Rats

(1) Background: Skeletal muscle atrophy is a common and debilitating condition associated with disease, bed rest, and inactivity. We aimed to investigate the effect of atenolol (ATN) on cast immobilization (IM)-induced skeletal muscle loss. (2) Methods: Eighteen male albino Wistar rats were divided into three groups: a control group, an IM group (14 days), and an IM+ATN group (10 mg/kg, orally for 14 days). After the last dose of atenolol, forced swimming test, rotarod test, and footprint analysis were performed, and skeletal muscle loss was determined. Animals were then sacrificed. Serum and gastrocnemius (GN) muscles were then collected, serum creatinine, GN muscle antioxidant, and oxidative stress levels were determined, and histopathology and ¹H NMR profiling of serum metabolites were performed. (3) Results: Atenolol significantly prevented immobilization-induced changes in creatinine, antioxidant, and oxidative stress levels. Furthermore, GN muscle histology results showed that atenolol significantly increased cross-sectional muscle area and Feret's diameter. Metabolomics profiling showed that glutamine-to-glucose ratio and pyruvate, succinate, valine, citrate, leucine, isoleucine, phenylalanine, acetone, serine, and 3-hydroxybutyrate levels were significantly higher, that alanine and proline levels were significantly lower in the IM group than in the control group, and that atenolol administration suppressed these metabolite changes. (4) Conclusions: Atenolol reduced immobilization-induced skeletal muscle wasting and might protect against the deleterious effects of prolonged bed rest.

A deep analysis of the proteomic and phosphoproteomic alterations that occur in skeletal muscle after the onset of immobilization

KEY POINTS

A decrease in protein synthesis plays a major role in the loss of muscle mass that occurs in response to immobilization. In mice, immobilization leads to a rapid (within 6 h) and progressive decrease in the rate of protein synthesis and this effect is mediated by a decrease in translational efficiency. Deep proteomic and phosphoproteomic analyses of mouse skeletal muscles revealed that the rapid immobilization-induced decrease in protein synthesis cannot be explained by changes in the abundance or phosphorylation state of proteins that have been implicated in the regulation of translation.

ABSTRACT

The disuse of skeletal muscle, such as that which occurs during immobilization, can lead to the rapid loss of muscle mass, and a decrease in the rate of protein synthesis plays a major role in this process. Indeed, current dogma contends that the decrease in protein synthesis is mediated by changes in the activity of protein kinases (e.g. mTOR); however, the validity of this model has not been established. Therefore, to address this, we first subjected mice to 6, 24 or 72 h of unilateral immobilization and then used the SUnSET technique to measure changes in the relative rate of protein synthesis. The result of our initial experiments revealed that immobilization leads to a rapid (within 6 h) and progressive decrease in the rate of protein synthesis and that this effect is mediated by a decrease in translational efficiency. We then performed a deep mass spectrometry-based analysis to determine whether this effect could be explained by changes in the expression and/or phosphorylation state of proteins that regulate translation. From this analysis, we were able to quantify 4320 proteins and 15,020 unique phosphorylation sites, and surprisingly, the outcomes revealed that the rapid immobilization-induced decrease in protein synthesis could not be explained by changes in either the abundance, or phosphorylation state, of proteins. The results of our work not only challenge the current dogma in the field, but also provide an expansive resource of information for future studies that are aimed at defining how disuse leads to loss of muscle mass.