Effect of Nox2 inhibition Unloading‐induced Changes in Morphology and nNOSμ Translocation in the Rat Soleus

Abstract

Removal of mechanical loading (spaceflight, bedrest, casting) causes rapid atrophy of affected skeletal muscles. Recently, we identified that translocation of the mu‐splice variant of neuronal nitric oxide synthase (nNOSμ) and downstream activation of FoxO3a were redox‐sensitive phenomena. Prospective sources or reactive oxygen species (ROS) include mitochondria and NADPH oxidase‐2 (Nox2). We tested the causal role of Nox2 in unloading induced atrophy using a peptidyl inhibitor (gp91ds‐tat) with the following groups: ambulatory controls (CON), hindlimb unloaded for 7 days with scrambled sequence (HUScr), and unloading for 7 days + 5 mg/kg/day gp91dsTAT (HUG). Nox2 inhibition provided significant against HU‐induced reduction of plantarflexor muscle mass and soleus muscle fiber cross‐sectional area (CSA), measured using ImageJ and SMASH programs. There was a trend towards protection against a partial shift in fiber‐type shift from slow to fast twitch. Loss of sarcolemmal nNOSμ activity with HU, visualized using NADPH diaphorase and confirmed with immunofluorescence were also mitigated by gp91dsTAT. Gp91dsTAT also attenuated membrane localization of the Nox2 subunit p67phox. We conclude that Nox2 inhibition protects against muscle fiber atrophy and translocation of nNOSμ.Support or Funding InformationSupported by NASA (NNX13AE45G), NSBRI, NIH (AR054084), ACSM, Huffines Institute.