Treatment with EUK-134 Enhance Anabolic Akt/mTOR/p70S6kinase Pathways, Protecting Against Muscle Atrophy in the Rat Soleus in a 7 Day Hindlimb Unloading

Muscle atrophy occurs with mechanical unloading, disease and aging. Mechanical unloading occurs with bedrest, microgravity, and casting/immobilization, all of which elicit the unloading-induced phenotype: (a) reduction of muscle fiber cross-section area (CSA) and (b) a shift from slow-twitch to fast-twitch muscle fibers. Unloading-induces muscle fiber atrophy appears to be a consequence of both decrease in contractile protein synthesis combined with increased protein catabolism. Oxidative stress has been cited as potential contributing factor to the unloading phenotype, although the mechanisms remain unresolved and controversial. We recently reported that a superoxide dismutase/catalase mimetic (EUK-134) reduced muscle atrophy, fiber-type shift, and pro-catabolic signaling. The purpose of this study was to test the hypothesis that EUK-134 would attenuate loss in a canonical, pro-anabolic signaling pathway involving phosphorylation of Akt, mTOR, and p70S6K and would ameliorate muscle fiber atrophy after seven-days hindlimb unloading. Male Fisher-344 rats were divided into three groups: ambulatory control group (CON, N=11), 7 days of hindlimb unloading plus saline injections (HU, n=11), or 7 days of hindlimb unloading plus 3 mg/kg/day EUK-134 (HU-EUK, n=9). The soleus muscles from both hindlimbs were dissected for histochemistry and immunoflorescence analyses. The soleus muscle of the HU group exhibited a decrease in CSA compared to the CON group, while soleus muscle fiber CSA from HU-EUK group was greater than the HU group, but lower than CON. Furthermore, the HU group displayed a partial shift from slow-twitch to fast-twitch, an effect attenuated by EUK-134. The ratio of phosphorylated Akt to total Akt was significant lower in the HU group compared to the CON group. However, the p-Akt/Akt was significantly higher in the HU-EUK group vs. HU group, but lower than the CON. The ratio of phosphorylated m-TOR to total m-TOR from the HU group was not different than controls. However, the ratio of p-mTOR/mTOR was a significantly higher in the EUK group compared to the CON group. Moreover, the HU group displayed a decrease in phosphorylation of p70S6Kinase, while but treatment with EUK-134 enhanced phosphorylation of p70S6Kinase. Therefore, our data are consistent with the hypothesis that EUK-134 protects anabolic signaling in the unloaded rat soleus

ROS-Mediated Localization of Caveolin-3 in the Sarcolemma During Short-term Mechanical Unloading

The dystroglycan complex (DGC) is a latticework of cell membrane proteins that provide a mechanical link to the cytoskeleton and initiate cell signaling that provides integrity, regulates protein turnover, stimulates growth, etc. Caveolin-3 has been identified as a muscle-specific isoform of the caveolin family of proteins, and in skeletal muscle, caveolin-3 is localized in caveolae within the sarcolemma. Evidence from Duchenne and Limb-Girdle Muscular Dystrophies suggests the involvement of caveolin-3 and reactive oxygen species (ROS) in the disruption of the DGC and thus myopathy. We examined ROS as upstream activators of caveolin-3 sarcolemmal localization in skeletal muscle during disuse atrophy. EUK-134, a catalytic mimetic of superoxide dismutase (SOD) and catalase that degrades superoxide and hydrogen peroxide, was administered to hindlimb unloaded, fully mature rats, 24 hours prior to and during 54 hours of mechanical unloading. We observed that disuse-induced ROS production, using 4-hydroxynonenal as a marker, was accompanied by elevated localization of caveolin-3 in the sarcolemma and fiber atrophy in the unloaded group. In contrast, the unloaded+EUK-134 treatment group resulted in less caveolin-3 localization at the sarcolemma, attenuation of oxidative stress, and mitigation of muscle fiber atrophy. These results suggest that the increased sarcolemmal localization of caveolin-3 following mechanical unloading is redox dependent. Our findings imply that ROS play an important role in the early signaling events of mechanical unloading that elicit muscle atrophy. Our data also offer the prospect that targeted antioxidants such as the EUK family of drugs could have therapeutic potential during inactivity or other forms of myopathy

Twenty-One Days of Lunar Environment Alters Muscle Fiber Areas in Mouse Gastrocnemius

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Epithelial cancers in the post-genomic era: should we reconsider our lifestyle?

The age-related epithelial cancers of the breast, colorectum and prostate are the most prevalent and are increasing in our aging populations. Epithelial cells turnover rapidly and mutations naturally accumulate throughout life. Most epithelial cancers arise from this normal mutation rate. All elderly individuals will harbour many cells with the requisite mutations and most will develop occult neoplastic lesions. Although essential for initiation, these mutations are not sufficient for the progression of cancer to a life-threatening disease. This progression appears to be dependent on context: the tissue ecosystem within individuals and lifestyle exposures across populations of individuals. Together, this implies that the seeds may be plentiful but they only germinate in the right soil. The incidence of these cancers is much lower in Eastern countries but is increasing with Westernisation and increases more acutely in migrants to the West. A Western lifestyle is strongly associated with perturbed metabolism, as evidenced by the epidemics of obesity and diabetes: this may also provide the setting enabling the progression of epithelial cancers. Epidemiology has indicated that metabolic biomarkers are prospectively associated with cancer incidence and prognosis. Furthermore, within cancer research, there has been a rediscovery that a switch in cell metabolism is critical for cancer progression but this is set within the metabolic status of the host. The seed may only germinate if the soil is fertile. This perspective brings together the different avenues of investigation implicating the role that metabolism may play within the context of post-genomic concepts of cancer