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TRAF6 (TNF receptor-associated factor 6), a member of tumor necrosis factor receptor-associated factors family was identified as a molecule that binds to the cytoplasmic domain of CD40. TRAF6 functions as an adaptor, positively regulating the NF-κB, JNK pathway. Additionally, some studies have reported that TRAF6 is required for apoptosis within the developing CNS and regulates cell fate decisions by inducing caspase 8-dependent apoptosis. However, its distribution and function in the central nervous system (CNS) lesion are not well understood. In this study, we performed an acute traumatic brain injury model in adult rats. And we mainly examined protein expression and cellular localization of TRAF6 during rat traumatic brain injury (TBI). Western blot analysis showed TRAF6 level significantly improved at 7 days after injury, and then declined during the following days. The protein expression of TRAF6 was further analysed by immunohistochemistry. In comparison to contralateral cerebral cortex, we observed a highly significant accumulation of TRAF6 at the ipsilateral brain. Immunofluorescence double-labeling showed that TRAF6 was co-expressed with NeuN and GFAP. Besides, co-localization of TRAF6/active caspase 3 and TRAF6/proliferating cell nuclear antigen (PCNA) were detected in NeuN and GFAP, respectively. We also examined the expression profiles of proliferating cell nuclear antigen (PCNA) and active caspase 3 whose changes were correlated with the expression profiles of TRAF6. In conclusion, this is the first description of TRAF6 expression in traumatic brains. Our data suggested that TRAF6 might play important roles in CNS pathophysiology after TBI.

The proliferation and migration of vascular smooth muscle cells (VSMC) is extensively involved in pathogenesis of neointimal hyperplasia. All- trans -retinoic acid (ATRA) is a natural metabolite of vitamin A. Here, we investigated the involvement of AMP-activated protein kinase (AMPK) in the anti-neointimal hyperplasia effects of ATRA. We found that treatment with ATRA significantly reduced neointimal hyperplasia in the left common carotid artery ligation mouse model. ATRA reduced the proliferation and migration of VSMC, A7r5 and HASMC cell lines. Our results also demonstrated that ATRA altered the expression of proliferation-related proteins, including CyclinD1, CyclinD3, CyclinA2, CDK2, CDK4, and CDK6 in VSMC. ATRA dose-dependently enhanced the phosphorylation level of AMPKα (Thr172) in the left common carotid artery of experimental mice. Also, the phosphorylation level of AMPKα in A7r5 and HASMC was significantly increased. In addition, ATRA dose-dependently reduced the phosphorylation levels of mTOR and mTOR target proteins p70 S6 kinase (p70S6K) and 4E-binding protein 1 (4EBP1) in A7r5 and HASMC. Notably, the inhibition of AMPKα by AMPK inhibitor (compound C) negated the protective effect of ATRA on VSMC proliferation in A7r5. Also, knockdown of AMPKα by siRNA partly abolished the anti-proliferative and anti-migratory effects of ATRA in HASMC. Molecular docking analysis showed that ATRA could dock to the agonist binding site of AMPK, and the binding energy between AMPK and ATRA was -7.91 kcal/mol. Molecular dynamics simulations showed that the binding of AMPK-ATRA was stable. These data demonstrated that ATRA might inhibit neointimal hyperplasia and suppress VSMC proliferation and migration by direct activation of AMPK and inhibition of mTOR signaling.