Fatiguing exercise reduces DNA binding activity of NF-κB in skeletal muscle nuclei

This study tested the hypothesis that skeletal muscle contraction activates nuclear factor-κB (NF-κB), a putative regulator of muscle protein breakdown. Muscle biopsies were obtained from the vastus lateralis of healthy humans before, immediately after, and 1 h after fatiguing resistance exercise of the lower limbs. Biopsies were analyzed for nuclear NF-κB DNA binding activity by using electrophoretic mobility shift assay. NF-κB activity, measured immediately after exercise, was less than preexercise activity; after 1-h recovery, activity returned to preexercise levels. In follow-up studies in adult mice, basal NF-κB activity varied among individual muscles. NF-κB activity in diaphragm fiber bundles was decreased after a 10-min bout of fatiguing tetanic contractions in. vitro. NF-κB activity in soleus was increased by 12 days of unloading by hindlimb suspension; this increase was reversed by 10 min of fatiguing exercise. These data provide no support for our original hypothesis. Instead, acute fatiguing exercise appears to decrease NF-κB activity in muscle under a variety of conditions.