Up-regulation of Smurf1 after spinal cord injury in adult rats.

Smad ubiquitination regulatory factor 1 (Smurf1) is one of members of the Hect family of proteins, which also includes the ubiquitin E3-type ligases Nedd3 and E6-AP. As an E3 ligase, Smurf1 selectively interacts with receptor-regulated Smads to trigger their ubiquitination and degradation. Recently, a report indicates that Smurf1 can inhibit apoptosis by regulating p53 negatively, which depends on the effect of Smurf1 stabilizing the MDM2-MDMX complex. However, the roles of Smurf1 in central nervous system injury remain to be unknown. In our study, we finished acute spinal cord injury (SCI) in adult rats to research the protein expression and cellular localization of Smurf1 in spinal cord. Western blot analysis showed that Smurf1 was low expressed in normal spinal cord. It was increased at 6 h after SCI, peaked at 1 day, remained for 3 days, and then declined gradually during the following days. Immunohistochemistry further confirmed that Smurf1 immunoactivity was expressed at low levels in the gray matter and white matter in normal condition and increased after SCI. Double immunofluorescence staining showed that Smurf1 was co-expressed NeuN (neuronal marker), CNPase (oligodendroglial marker), and active caspase-3 at 1 day post-injury. Additionally, p53 and MDM2 levels were up-regulated after SCI consistently. All these findings suggest that Smurf1 might be involved in the pathophysiology of spinal cord after SCI.