Time-Course of Muscle Mass Loss, Damage, and Proteolysis in Gastrocnemius following Unloading and Reloading: Implications in Chronic Diseases

Abstract

BackgroundDisuse muscle atrophy is a major comorbidity in patients with chronic diseases including cancer. We sought to explore the kinetics of molecular mechanisms shown to be involved in muscle mass loss throughout time in a mouse model of disuse muscle atrophy and recovery following immobilization.MethodsBody and muscle weights, grip strength, muscle phenotype (fiber type composition and morphometry and muscle structural alterations), proteolysis, contractile proteins, systemic troponin I, and mitochondrial content were assessed in gastrocnemius of mice exposed to periods (1, 2, 3, 7, 15 and 30 days) of non-invasive hindlimb immobilization (plastic splint, I cohorts) and in those exposed to reloading for different time-points (1, 3, 7, 15, and 30 days, R cohorts) following a seven-day period of immobilization. Groups of control animals were also used.ResultsCompared to non-exposed controls, muscle weight, limb strength, slow- and fast-twitch cross-sectional areas, mtDNA/nDNA, and myosin content were decreased in mice of I cohorts, whereas tyrosine release, ubiquitin-proteasome activity, muscle injury and systemic troponin I levels were increased. Gastrocnemius reloading following splint removal improved muscle mass loss, strength, fiber atrophy, injury, myosin content, and mtDNA/nDNA, while reducing ubiquitin-proteasome activity and proteolysis.ConclusionsA consistent program of molecular and cellular events leading to reduced gastrocnemius muscle mass and mitochondrial content and reduced strength, enhanced proteolysis, and injury, was seen in this non-invasive mouse model of disuse muscle atrophy. Unloading of the muscle following removal of the splint significantly improved the alterations seen during unloading, characterized by a specific kinetic profile of molecular events involved in muscle regeneration. These findings have implications in patients with chronic diseases including cancer in whom physical activity may be severely compromised.

Muscle unloading: A comparison between spaceflight and ground‐based models

“…Regarding the mechanism underlying the loss of specific force, it is shown that the reduction in myosin protein content accompanies the loss of specific force during muscle unloading (Figure ) . It is consistent with the finding that the extent of atrophy directly corelated with myosin concentration and reduction in specific force .…”

Muscle regeneration potential and satellite cell activation profile during recovery following hindlimb immobilization in mice

“…The rationale to use such methodologies was to identify a pure population of muscle progenitors as demonstrated in previous studies (Yin, Rice, & Rudnicki, ). In fact, one of the main goals in the study was to characterize the gene expression profile of the isolated progenitor cells during recovery following a period of hindlimb muscle disuse for 7 days, which was defined as a key time‐point to analyze early and late events as previously shown in this experimental model (Chacon‐Cabrera et al, ; Chacon‐Cabrera, Gea, et al, ). Furthermore, the use of methodologies such as histological procedures enabled us to define the localization and numbers of active and proliferating satellite cells in the study muscles.…”

“…Mice were exposed to unilateral hindlimb immobilization as previously described to reproduce a model of disuse muscle atrophy (Chacon‐Cabrera et al, ; Chacon‐Cabrera, Gea, et al, ). Briefly, the left hindlimb was shaved with clippers and was enveloped using surgical tape.…”

“…In all the study animals, food intake was measured daily, and food and water were supplied ad libitum for the entire duration of the immobilization or recovery periods. In all mice, body weight and limb strength were determined on day 0, and right at the end of the immobilization or recovery time‐points (day 7, as described above) using a scale and a grip strength meter (Bioseb, Vitrolles, France), respectively, as previously reported (Barreiro & Gea, ; Chacon‐Cabrera et al, , , ; Chacon‐Cabrera, Gea, et al, ; Chacon‐Cabrera, Mateu‐Jimenez, et al, ). In the two groups of animals, total body weight and limb strength gain variables were calculated as the percentage of the measurements performed at the end of the study period (7‐day I or 7‐day R) with respect to the same measurements obtained at baseline (day 0 or on day 7 following the immobilization protocol) in the 7‐day I and 7‐day R study groups, respectively.…”

“…Interestingly, reloading of the muscle after splint removal induced a rise of the histone deacetylase sirtuin‐1 along with a decrease in acetylation levels of the transcription factors FoxO 1 and 3, thus enabling the muscle fibers to regenerate in the mice (Chacon‐Cabrera, Gea, et al, ). We concluded that the kinetics of the biological events leading to skeletal muscle mass loss and recovery were tightly regulated in the gastrocnemius of mice exposed to different time‐points of muscle unloading and reloading (Chacon‐Cabrera et al, ; Chacon‐Cabrera, Gea, et al, ). Whether the potential of muscle regeneration was altered in response to disuse remained unexplored in the former investigations.…”