SARM suppresses glioma progression in GL261 glioma cells and regulates microglial polarization.

Microglia is the major cellular component of glioma mass that promotes glioma growth, invasion, and chemoresistance by releasing inflammatory factors. Sterile alpha and HEAT/Armadillo motif (SARM), a member of the Toll-interleukin-1 receptor (TIR) domain-containing adaptor family, is primarily expressed in the central nervous system. However, the role of SARM in glioma is still undefined. In the present work, we examined the function of SARM in microglial polarization and glioma progression. Our results showed that forced the expression of SARM in GL261 glioma cells inhibited tumor growth, and reduced interleukin (IL)-6 secretion in conditioned media. Silencing of SARM in microglia cells inhibited IL-4-induced M2 polarization, enhanced lipopolysaccharide -induced M1 microglial polarization. Furthermore, overexpression of SARM increased the migration of microglia cells upon TGFß stimulation. These data suggested that SARM is involved in neuro-inflammation and microglia activation. In summary, this study provides novel insight into the mechanisms of microglial polarization.

ASK1 phosphorylation regulates astrocytic reactive gliosis in vitro and in vivo.

Apoptosis signal-regulating kinase 1 (ASK1) may play a pivotal role in reactive gliosis. To assess the role of ASK1 in trauma-induced reactive gliosis, we examined the phosphorylation of ASK1 and the expression of glial fibrillary acidic protein (GFAP) and vimentin after scratch injury in cultured astrocytes and spinal cord injury (SCI) in rats. Enhanced phosphorylation of ASK1 was detected during reactive gliosis both in vitro and in vivo, and P38 MAPK relayed the signal from phosphorylated ASK1 to the activation of astrocytes. Immunoprecipitation analyses suggested that 14-3-3 was dissociated from ASK1 during astrocyte activation. Finally, treatment with thioredoxin reduced ASK1 phosphorylation and reactive gliosis and promoted hindlimb locomotion recovery in SCI rats. These results indicated that ASK1 may play an important role in mechanical-injury-induced reactive gliosis.

Protease-activated receptor-2 regulates glial scar formation via JNK signaling.

The study aimed to determine the effects of protease-activated receptor-2 (PAR-2) on glial scar formation after spinal cord injury (SCI) in Sprague-Dawley (SD) rats and the underlying mechanisms. Rivlin and Tator's acute extradural clip compression injury (CCI) model of severe SCI was established in this study. Animals were divided into four groups: 1) sham group (laminectomy only); 2) model group, treated with normal saline; 3) PAR-2 inhibitor group; 4) PAR-2 activator group. Enhanced GFAP and vimentin expression were the markers of glial scar formation. To determine whether JNK was involved in the effects of PAR-2 on GFAP and vimentin expression, we administered anisomycin (a JNK activator) in the presence of PAR-2 inhibitor and SP600125 (a JNK inhibitor) in the presence of PAR-2 activator. At 1, 7, 14 and 28 day after SCI, Basso, Beattie, and Bresnahan (BBB) locomotor score test was used to assess the locomotor functional recovery; immunofluorescence and western blot analysis were used to assess the expression level of GFAP, vimentin and p-JNK. Double immunofluorescence staining with GFAP and tubulin beta was used to assess the glial scar formation and the remaining neurons. Results suggested that PAR-2 is involved in glial scar formation and reduces neurons residues which can cause a further worsening in the functional outcomes after SCI via JNK signaling. Therefore, it may be effective to target PAR-2 in the treatment of SCI.

[Effect of suppressing apoptosis signal regulating kinase 1 on GFAP and vimentin expression and hindlimb mobility in rats after spinal cord injury].

OBJECTIVE: To investigate the effect of suppressing apoptosis signal regulating kinase 1 (ASK1) on glial fibrillary acidic protein (GFAP) and vimentin expressions at the injury site and on hindlimb mobility in rats after spinal cord injury (SCI). METHODS: The rat models of SCI were established by extradural compression of the spinal cord using an aneurysm clip. The injured rats were treated with normal saline (model group), ASK1 specific inhibitor thioredoxin (Trx group), or ASK1 monoclonal antibody (Anti-ASK1 group), and the rats receiving a sham operation underwent laminectomy without SCI. The expression of GFAP and vimentin were detected by Western blotting and immunofluorescence assay at 1, 7, 14 and 28 days after SCI. The motion function of the hindlimbs of the injured rats was assessed with Basso Beattie Bresnahan (BBB) scores, and somatosensory-evoked potentials (SEP) and motor-evoked potentials (MEP) were determined to examine the electrophysiological changes. RESULTS: At 1 day after SCI, the expressions of GFAP and vimentin showed no significant differences among the groups; at 7, 14 and 28 days after SCI, GFAP and vimentin expressions significantly increased in Trx and Anti-ASK1 groups compared with those in the model group (P<0.01). The BBB scores showed no significant differences among the groups at 1, 7 and 14 days after SCI, while at 28 days, the BBB scores in Trx and Anti-ASK1 groups were significantly higher than those in the model group (P<0.01). At 28 days after SCI, the latent period of SEP and MEP decreased and the amplitude increased significantly in Trx and Anti-ASK1 groups compared with that in the model group (P<0.01). CONCLUSION: Blocking ASK1 can inhibit the expression of GFAP and vimentin in glial scars and improve the outcomes of hindlimb mobility in rats after SCI.