SKELETAL-MUSCLE MYOCYTES UNDERGO PROTEIN LOSS AND REACTIVE OXYGEN-MEDIATED NF-KAPPA-B ACTIVATION IN RESPONSE TO TUMOR-NECROSIS-FACTOR-ALPHA

Skeletal muscle atrophy and weakness are thought to be stimulated by t umor necrosis factor a (TNF-alpha) in a variety of chronic diseases. H owever, little is known about the direct effects of TNF-alpha on diffe rentiated skeletal muscle cells or the signaling mechanisms involved, We have tested the effects of TNF-alpha on the mouse-derived C2C12 mus cle cell line and on primary cultures from rat skeletal muscle. TNF-al pha treatment of differentiated myotubes stimulated time- and concentr ation-dependent reductions in total protein content and loss of adult myosin heavy chain (MHCf) content; these changes were evident at low T NF-alpha concentrations (1-3 ng/ml) that did not alter muscle DNA cont ent and were not associated with a decrease in MHCf synthesis. TNF-alp ha activated binding of nuclear factor KB (NF-kappa B) to its targeted DNA sequence and stimulated degradation of I-kappa B alpha, an NF-kap pa B inhibitory protein. TNF-alpha stimulated total ubiquitin conjugat ion whereas a 26S proteasome inhibitor (MG132 10-40 mu M) blocked TNF- alpha activation of NF-kappa B, Catalase 1 kU/ml inhibited NF-kappa B activation by TNF-alpha; exogenous hydrogen peroxide 200 mu M activate d NF-kappa B and stimulated I-kappa B alpha degradation. These data de monstrate that TNF-alpha directly induces skeletal muscle protein loss , that NF-kappa B is rapidly activated by TNF-alpha in differentiated skeletal muscle cells, and that TNF-alpha/NF-kappa B signaling in skel etal muscle is regulated by endogenous reactive oxygen species.-Li, Y. -P., Schwartz, R. J., Waddell, I. D., Holloway, B. R., Reid, M. B. Ske letal muscle myocytes undergo protein loss and reactive oxygen-mediate d NF-kappa B activation in response to tumor necrosis factor alpha.