S Pierno

Is oxidative stress a cause or consequence of disuse muscle atrophy in mice? A proteomic approach in hindlimb‐unloaded mice

Two‐dimensional proteomic maps of soleus (Sol), a slow oxidative muscle, and gastrocnemius (Gas), a fast glycolytic muscle of control mice (CTRL), of mice hindlimb unloaded for 14 days (HU mice) and of HU mice treated with trolox (HU‐TRO), a selective and potent antioxidant, were compared. The proteomic analysis identified a large number of differentially expressed proteins in a pool of ∼800 proteins in both muscles. The protein pattern of Sol and Gas adapted very differently to hindlimb unloading. The most interesting adaptations related to the cellular defense systems against oxidative stress and energy metabolism. In HU Sol, the antioxidant defense systems and heat shock proteins were downregulated, and protein oxidation index and lipid peroxidation were higher compared with CTRL Sol. In contrast, in HU Gas the antioxidant defense systems were upregulated, and protein oxidation index and lipid peroxidation were normal. Notably, both Sol and Gas muscles and their muscle fibres were atrophic. Antioxidant administration prevented the impairment of the antioxidant defense systems in Sol and further enhanced them in Gas. Accordingly, it restored normal levels of protein oxidation and lipid peroxidation in Sol. However, muscle and muscle fibre atrophy was not prevented either in Sol or in Gas. A general downsizing of all energy production systems in Sol and a shift towards glycolytic metabolism in Gas were observed. Trolox administration did not prevent metabolic adaptations in either Sol or Gas. The present findings suggest that oxidative stress is not a major determinant of muscle atrophy in HU mice.

Aging and chloride channel regulation in rat fast-twitch muscle fibres

By the use of pharmacological tools, we tested the hypothesis that age-related alterations in the regulatory pathways of chloride channels might contribute to the lowered chloride conductance (GCl) found in skeletal muscle of aged rats. The restingGCl of extensor digitorum longus (EDL) muscles from adult rats either young (3–4 months old) or aged (29 months old) was measured by means of computerized intracellular microelectrode recordings. In EDL muscle from 3 to 4-month-old rats, 4-β-phorbol 12,13-dibutyrate (4-β-PDB), a direct activator of protein kinase C (PKC), decreasedGCl in a concentration-dependent manner. The same effect was exerted by cholera toxin. The effects of both the phorbol ester and cholera toxin were inhibited by staurosporine, thus indicating that either direct or indirect (via G protein) activation of PKC accounts for the decrease ofGCl. An increase of cytosolic Ca2+ by the ionophore A23187 also significantly decreasedGCl by 25%. In EDL muscles from aged rats, 4-β-PDB was 20-fold more potent in blockingGCl than in muscles from younger controls, and the ionophore blockedGCl by 40%. On the other hand, cholera toxin was ineffective. Our findings support the hypothesis that in fast-twitch muscle the regulation of chloride channels by PKC and Ca2+ is a target of the aging process.

New 2-Aryloxy-3-phenyl-propanoic Acids As Peroxisome Proliferator-Activated Receptors alpha/gamma Dual Agonists with Improved Potency and Reduced Adverse Effects on Skeletal Muscle Function

The preparation of a new series of 2-aryloxy-3-phenyl-propanoic acids, resulting from the introduction of a linker into the diphenyl system of the previously reported PPARalpha/gamma dual agonist 1, allowed the identification of new ligands with improved potency on PPARalpha and unchanged activity on PPARgamma. For the most interesting stereoisomers S-2 and S-4, X-ray studies in PPARgamma and docking experiments in PPARalpha provided a molecular explanation for their different behavior as full and partial agonists of PPARalpha and PPARgamma, respectively. Due to the adverse effects provoked by hypolipidemic drugs on skeletal muscle function, we also investigated the blocking activity of S-2 and S-4 on skeletal muscle membrane chloride channel conductance and found that these ligands have a pharmacological profile more beneficial compared to fibrates currently used in therapy.

Expression of sarcolemmal ion channels in slow and fast-twitch muscles of rodents in simulated and actual microgravity

Abstracts presented at the 39th European Muscle Conference of the European Society for Muscle Researchs presented at the 39th European Muscle Conference of the European Society for Muscle Research Abano Terme, Padova, Italy, September 11–15th, 2010 European Society for Muscle Research 2011 Abstracts for the oral presentationss for the oral presentations Mechanism of muscle contraction Direct evidence for the cross-bridge lever arm mechanism in muscle contraction studied using the gas environmental chamber and site-directed antibodies H. Sugi, H. Minoda, T. Okabe, Y. Inayoshi, T. Miyakawa, M. Tanokura, E. Katayama Department of Physiology, Teikyo University, Tokyo, Japan; Department of Applied Physics, Tokyo Institute of Agriculture and Technology, Tokyo, Japan; Department of Life Sciences, University of Tokyo, Tokyo, Japan; Department of Electron Microscopy, University of Tokyo, Tokyo, Japan During muscle contraction, the cross-bridges in myosin filaments first attach to actin filaments in the form of MADPPi, undergo a conformational change (power stroke) associated with release of Pi and ADP to produce sliding between actin and myosin filaments, and then detach from actin filaments upon binding with next ATP. The detached cross-bridges undergo a reversed conformational change (recovery stroke) associated with reaction, MATP ? MADPPi. It is suggest that the cross-bridge strokes result from rotation of the crossbridge lever arm domain around the converter domain, while the catalytic domain remains rigid. To ascertain the validity of the lever arm mechanism in muscle contraction, we recorded ATP-induced movement at different regions within individual cross-bridges in living myosin filaments, using the gas environmental chamber, with which biological macromolecules can be kept in living state in an electron microscope. Three different regions of the cross-bridge were position-marked with site-directed antibodies; antibody 1 to the distal catalytic region, antibody 2 to the interface between the catalytic and converter domains, and antibody 3 to the boundary between the lever arm domain and myosin subfragment 2. We have found that the average amplitude of ATP-induced movement was 6.14 nm at both the distal catalytic domain and the catalytic-converter domain interface, and 3.77 nm at the lever arm domain-subfragment 2 boundary, providing the first direct evidence for the cross-bridge lever arm mechanism. Muscle force generation examined by laser temperature-jump and ramp shortening

Is oxidative stress a cause or consequence of disuse muscle atrophy in mice? A proteomic approach in hindlimb-unloaded mice: Experimental Physiology-Research Paper

Two‐dimensional proteomic maps of soleus (Sol), a slow oxidative muscle, and gastrocnemius (Gas), a fast glycolytic muscle of control mice (CTRL), of mice hindlimb unloaded for 14 days (HU mice) and of HU mice treated with trolox (HU‐TRO), a selective and potent antioxidant, were compared. The proteomic analysis identified a large number of differentially expressed proteins in a pool of ∼800 proteins in both muscles. The protein pattern of Sol and Gas adapted very differently to hindlimb unloading. The most interesting adaptations related to the cellular defense systems against oxidative stress and energy metabolism. In HU Sol, the antioxidant defense systems and heat shock proteins were downregulated, and protein oxidation index and lipid peroxidation were higher compared with CTRL Sol. In contrast, in HU Gas the antioxidant defense systems were upregulated, and protein oxidation index and lipid peroxidation were normal. Notably, both Sol and Gas muscles and their muscle fibres were atrophic. Antioxidant administration prevented the impairment of the antioxidant defense systems in Sol and further enhanced them in Gas. Accordingly, it restored normal levels of protein oxidation and lipid peroxidation in Sol. However, muscle and muscle fibre atrophy was not prevented either in Sol or in Gas. A general downsizing of all energy production systems in Sol and a shift towards glycolytic metabolism in Gas were observed. Trolox administration did not prevent metabolic adaptations in either Sol or Gas. The present findings suggest that oxidative stress is not a major determinant of muscle atrophy in HU mice.