Low-frequency Electrical Stimulation Alleviates Immobilization-evoked Disuse Muscle Atrophy via Repressing Autophagy in Skeletal Muscle of Rabbits

Objective: The present study was to investigate the effect of low-frequency electrical stimulation on disuse muscle atrophy and its mechanism in a rabbit model of extending knee joint contracture.Methods: This study designed two experiments. In the time-point experiment, 24 rabbits were randomly divided into Control 1(Ctrl1), immobilization for 2 weeks (I-2), I-4, and I-6 groups. In the intervention experiment, 24 rabbits were also randomly divided into Control 2 (Ctrl2), electrical stimulation (ES), natural recovery (NR) and electrical stimulation treatment (EST) groups. All intervention effects were assessed by evaluating the knee joint range of motion (ROM), cross-sectional area (CSA) of muscle and the expression of autophagy-related proteins.Results: Time-point experiment showed that immobilization reduced knee ROM, muscle CSA, and activated autophagy in skeletal muscle. Levels of four autophagic proteins including p-mTOR, Atg7, p62 and LC3B-II, were significantly elevated in the skeletal muscle of I-4 group. The intervention experiment further presented that LFES significantly improved the immobilization-induced ROM and CSA reduction. Additionally, LFES significantly reversed autophagy activation of skeletal muscle caused by immobilization.Conclusions: Low-frequency electrical stimulation alleviates immobilization-evoked disuse muscle atrophy maybe via inhibiting autophagy in skeletal muscle of rabbits.

TNFa is Involved in the Development of Disuse Muscle Atrophy Through the Acid Sphingomyelinase/ Ceramide Up-Regulation and Pro-Oxidant Signaling

Background: There is paucity of data indicating the role of cytokines including TNFa in the development of disuse muscle atrophy, despite the growing interest to this problem emerging in the recent years. The aim of the present study was to test the hypothesis that TNFa/ TNFR1 may be involved in the development of disuse muscle atrophy caused by unloading through aSMase/ ceramide/ ROS mechanism. Methods: The experiments were performed on male Wistar rats (180 – 230g) subjected to 4 or 14 days of hindlimb suspension (HS) and treated with clomipramine (HS+Clom) or vehicle. The following parameters were studied: TNFR1, aSMase, nSMase and Nox2 proteins and ceramide in detergent-resistant membrane (DRM) fraction isolated from soleus muscle homogenates, pro-oxidant/anti-oxidant and pro-apoptotic/anti-apoptotic activities, immune fluorescence intensity and distribution of ceramide, Nox2, Nox4 and caveolin-3 on longitudinal and transverse muscle sections. The relative muscle mass, cross-sectional area (CSA) and Feret’s diameter (FD) of muscle fibers were used to confirm muscle atrophy. Statistical analysis was performed using one-way ANOVA followed by the Bonferroni post hoc test, or Cruskall-Wallis and Mann-Whitney U test. Results: Disuse caused an increase in membrane TNFR1, aSMase, ceramide abundance in DRM, up-regulation of pro-oxidant and pro-apoptotic capacities (increased Nox2, Nox4, TBA-active products, Bax/Bcl-2 ratio, elevated activity of caspase-3/7 and -6). The most of alterations were maximal on the 4 th day of unloading. The inhibitor of aSMase clomipramine attenuated ceramide accumulation, decreased pro-oxidant and pro-apoptotic activities and diminished muscle atrophy induced by unloading. It has been shown that in suspended for 14 days rats the loss in relative muscle mass, CSA and FD averaged -35%, -65% and -49%, respectively, whereas in clomipramine treated rats it was -25%, -45% and -25%, in comparison with the control values. Clomipramine also mitigated the inhibition of the mTORC1/p70S6 kinase inhibition caused by 14-day HS. Conclusions: The obtained results indicate the involvement of aSMase/ ceramide pathway in the development of disuse muscle atrophy. This effect may be triggered by TNFR1 and realized through enhanced prooxidant NADPH oxidase activity and pro-apoptotic signaling.

Flavonoids: nutraceutical potential for counteracting muscle atrophy

Skeletal muscle plays a vital role in the conversion of chemical energy into physical force. Muscle atrophy, characterized by a reduction in muscle mass, is a symptom of chronic disease (cachexia), aging (sarcopenia), and muscle disuse (inactivity). To date, several trials have been conducted to prevent and inhibit muscle atrophy development; however, few interventions are currently available for muscle atrophy. Recently, food ingredients, plant extracts, and phytochemicals have received attention as treatment sources to prevent muscle wasting. Flavonoids are bioactive polyphenol compounds found in foods and plants. They possess diverse biological activities, including anti-obesity, anti-diabetes, anti-cancer, anti-oxidation, and anti-inflammation. The effects of flavonoids on muscle atrophy have been investigated by monitoring molecular mechanisms involved in protein turnover, mitochondrial activity, and myogenesis. This review summarizes the reported effects of flavonoids on sarcopenia, cachexia, and disuse muscle atrophy, thus, providing an insight into the understanding of the associated molecular mechanisms.

Satellite Cells and Markers of Muscle Regeneration during Unloading and Reloading: Effects of Treatment with Resveratrol and Curcumin

We hypothesized that treatment with pharmacological agents known to increase sirtuin-1 activity (resveratrol and curcumin) may enhance muscle regeneration. In limb muscles of mice (C57BL/6J, 10 weeks) exposed to reloading for seven days following a seven-day period of hindlimb immobilization with/without curcumin or resveratrol treatment, progenitor muscle cell numbers (FACS), satellite cell subtypes (histology), early and late muscle regeneration markers, phenotype and morphometry, sirtuin-1 activity and content, and muscle function were assessed. Treatment with either resveratrol or curcumin in immobilized muscles elicited a significant improvement in numbers of progenitor, activated, quiescent, and total counts of muscle satellite cells, compared to non-treated animals. Treatment with either resveratrol or curcumin in reloaded muscles compared to non-treated mice induced a significant improvement in the CSA of both hybrid (curcumin) and fast-twitch fibers (resveratrol), sirtuin-1 activity (curcumin), sirtuin-1 content (resveratrol), and counts of progenitor muscle cells (resveratrol). Treatment with the pharmacological agents resveratrol and curcumin enhanced the numbers of satellite cells (muscle progenitor, quiescent, activated, and total satellite cells) in the unloaded limb muscles but not in the reloaded muscles. These findings have potential clinical implications as treatment with these phenolic compounds would predominantly be indicated during disuse muscle atrophy to enhance the muscle regeneration process.