NR4A1 attenuates neuroinflammation after spinal cord injury by modulating microglial polarization via negatively regulating the VAV1 pathway.

Spinal cord injury (SCI) is a global health issue which can lead to severe neurological impairment. NR4A1 is rapidly induced in response to diverse stimuli and shows multiple important functions in the central nervous system (CNS). However, its functional contribution to spinal cord injury remains undefined. In this study, NR4A1 expression was significantly down-regulated in microglia of a mouse contusion SCI model, accompanied by increased expression of VAV1 and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). Treating with cytosporone B (CsnB) can decrease VAV1 expression, reduced inflammatory response, reduced injury area, and improved locomotor function of SCI mice. Further analysis indicated that Csn-B promoted microglial polarization from M1 to M2 phenotype, with decrease of TNF-α, IL-1β and IL-6expression. Conversely, administration of DIM-C-pPhOH (C-DIM8) produced completely opposite results. In vitro, an inflammatory model that mimics SCI in vivo was established by stimulating BV2 microglial cells with LPS (200 ng/ml, 24 h). Further mechanistic investigation revealed that NR4A1 over-expression active BV2 cells from M1 to M2 phenotype and suppressed TNF-α, IL-1β and IL-6 release. NR4A1 knockdown, in contrast, promoted BV2 from M2 to M1 phenotype and enhanced TNF-α, IL-1β and IL-6 release. Further studies identified that NR4A1 functions as a direct transcriptional repressor of VAV1. Knockdown/over-express VAV1 could reverse the effects of NR4A1 knockdown/over-express on LPS-stimulated BV2 cells, respectively. Collectively, this study demonstrates that NR4A1 alleviates SCI-induced neuroinflammation by modulating microglial polarization via negatively regulating the VAV1 signaling pathway. Targeting the NR4A1-VAV1 axis may be a promising therapeutic target for mitigating SCI progression.