The Effect Of TAZ On Functional Recovery Of Spinal Cord Injury By Regulating Microglial Migration

Background: Following spinal cord injury(SCI),microglia gradually migrate to the edge of the lesion,interweaving around the border of the lesion to form the microglial scar,which performs inflammatory limiting and neuroprotective functions.Recent reports showed that Yes-associated protein(YAP)was expressed in astrocytes and promoted the formation of astroglial scar,while YAP was not expressed in microglia after SCI.YAP and its paralogue transcriptional coactivator with PDZ-binding motif(TAZ)are transcriptional coactivators,which have a similar functional role as both are negatively regulated by the Hippo signalling pathway.However,the expression and function of TAZ after SCI are unclear.Our research group previously found that Fascin-1 was highly expressed in microglia and promoted migration of microglia after SCI,and that,there was a close regulatory relationship between Fascin-1 and YAP/TAZ.In this study,we aimed to explore the expression and function of TAZ in microglia,the association between Fascin-1 and TAZ in microglia and the effect of this association on microglial migration after SCI.Methods: After SCI model of C57BL/6J mice was established by clamp method,the expression and localization of TAZ in vivo were evaluated by Western blot and tissue immunofluorescence staining before and after SCI.After BV-2 microglia were treated with myelin and polarization,the expression and localization of TAZ in vitro were studied by Western blot and immunofluorescence staining.An intraperitoneal injection of XMU-MP-1(the Hippo kinase MST1/2 inhibitor)activated TAZ and assessed the changes in microglial scar by tissue immunofluorescence,followed by BMS scoring and footprint analysis to assess functional recovery after SCI in mice.After knockdown and overexpression of TAZ in vitro,Western blot,cell scratch assay,and Transwell assay were used to evaluate the effect of TAZ on microglial migration.Finally,knockdown and overexpression of Fascin-1,a combination of molecular and histological methods was used to evaluate the association between Fascin-1 and TAZ,and the effects of mutual regulation of Fascin-1 and TAZ on the migration of microglia.Results: This study demonstrated that TAZ was significantly upregulated and mainly expressed in microglia after SCI,and accumulated in the nuclei of microglia in the spinal cord at 14 days post-SCI.Moreover,TAZ was upregulated and accumulated in the nucleus of M2-L polarized or myelin-treated microglia.Additionally,XMU-MP-1(an inhibitor of the Hippo kinase MST1/2 that actives TAZ)promoted the aggregation of microglia around the lesion core,resulting in the formation of microglial scar and the functional recovery of mice after SCI.Our findings also indicated that TAZ promoted microglial migration in vitro.Mechanistically,Fascin-1 interacted with TAZ,which upregulated TAZ expression and induced TAZ nuclear accumulation in microglia to promote microglial migration.Conclusion: Taken together,our study revealed that TAZ was upregulated and activated in microglia after SCI and mediated microglial migration to the edge of the lesion core,promoting the formation of microglial scars and neurological recovery after SCI.Moreover,TAZ was downstream of Fascin-1,which positively regulated microglial migration after SCI.