| Summary: | <p>Abstract</p> <p>Background</p> <p>We hypothesized that gp91<sup>phox </sup>(NOX2), a subunit of NADPH oxidase, generates superoxide anion (O<sub>2</sub><sup>-</sup>) and has a major causative role in traumatic brain injury (TBI). To evaluate the functional role of gp91<sup>phox </sup>and reactive oxygen species (ROS) on TBI, we carried out controlled cortical impact in gp91<sup>phox </sup>knockout mice (gp91<sup>phox-/-</sup>). We also used a microglial cell line to determine the activated cell phenotype that contributes to gp91<sup>phox </sup>generation.</p> <p>Methods</p> <p>Unilateral TBI was induced in gp91<sup>phox-/- </sup>and wild-type (Wt) mice (C57/B6J) (25-30 g). The expression and roles of gp91<sup>phox </sup>after TBI were investigated using immunoblotting and staining techniques. Levels of O<sub>2</sub><sup>- </sup>and peroxynitrite were determined <it>in situ </it>in the mouse brain. The activated phenotype in microglia that expressed gp91<sup>phox </sup>was determined in a microglial cell line, BV-2, in the presence of IFNγ or IL-4.</p> <p>Results</p> <p>Gp91<sup>phox </sup>expression increased mainly in amoeboid-shaped microglial cells of the ipsilateral hemisphere of Wt mice after TBI. The contusion area, number of TUNEL-positive cells, and amount of O<sub>2</sub><sup>- </sup>and peroxynitrite metabolites produced were less in gp91<sup>phox-/- </sup>mice than in Wt. In the presence of IFNγ, BV-2 cells had increased inducible nitric oxide synthase and nitric oxide levels, consistent with a classical activated phenotype, and drastically increased expression of gp91<sup>phox</sup>.</p> <p>Conclusions</p> <p>Classical activated microglia promote ROS formation through gp91<sup>phox </sup>and have an important role in brain damage following TBI. Modulating gp91<sup>phox </sup>and gp91<sup>phox </sup>-derived ROS may provide a new therapeutic strategy in combating post-traumatic brain injury.</p>
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