Nrf1 is time-dependently expressed and distributed in the distinct cell types after trauma to skeletal muscles in rats

Our goal was to elucidate the dynamic expression and distribution of the nuclear factor erythroid-derived factor 2-related factor 1 (Nrf1) by immunohistochemistry, Western blotting, and real-time PCR during wound healing of contused skeletal muscle in rats. An animal model of skeletal muscle contusion was established in 40 Sprague-Dawley male healthy rats. Samples were taken at 6 h, 12 h, 1 day, 3 days, 5 days, 7 days, 10 days, and 14 days post-injury, respectively (5 rats in each posttraumatic interval). 5 rats were employed as control. A weak immunoreactivity of Nrf1 was observed in the sarcoplasm and nuclei of normal myofibers in control rats. Prominent immunostaining for Nrf1 was seen in a large number of polymorphonuclear cells, round-shaped mononuclear cells and spindle-shaped fibroblastic cells, and regenerated multinucleated myotubes in the injured tissue. Subsequently, neutrophils, macrophages and myofibroblasts were identified as expressing Nrf1 by double immunofluorescent procedures. By real-time PCR analysis, Nrf1 expression was up-regulated and peaked at inflammatory phase. The expression tendency was also confirmed by Western blot. In conclusion, Nrf1 is time-dependently expressed in certain cell types, such as neutrophils, macrophages, myofibroblasts and regenerated multinucleated myotubes, suggesting that Nrf1 may modulate oxidative stress response and regeneration after trauma to skeletal muscles.