HMGB1-Induced Neurite Outgrowth in the Dorsal Root Ganglion Neurons and Regeneration Priming after their Axonal Injury by Sciatic Nerve Crush.

High mobility group box 1 (HMGB1), a nuclear protein, once released extracellularly, exists in two different active forms, i.e., all-thiol (at)- and disulfide (ds)-HMGB1. Given that HMGB1 promotes neuritogenesis, we examined whether at/ds-HMGB1 would promote neuritogenesis in dorsal root ganglion (DRG) neurons, and participate in regeneration priming of DRG neurons by sciatic nerve crush (SNC). In cultured mouse DRG neurons, at-HMGB1, but not ds-HMGB1, accelerated neuritogenesis, an effect blocked by an antagonist of receptor for advanced glycation end-product (RAGE). A combination of thrombin and thrombomodulin alfa (TMα) capable of sequestering HMGB1 with its D1 domain and promoting HMGB1 degradation by thrombin tethered to its D2 domain synergistically suppressed the at-HMGB1-induced neuritogenesis, an effect abolished by angiopoietin-1 capable of inhibiting the binding of thrombin to TMα. The DRG neurons from the mice subjected to SNC exhibited accelerated neuritogenesis, even in the presence of an anti-HMGB1-neutralizing antibody (HMGB1-Ab). However, the neurite regeneration priming of DRG neurons by SNC in mice was prevented by daily treatment with HMGB1-Ab, minocycline, a macrophage/microglia inhibitor, ethyl pyruvate capable of inhibiting HMGB1 release from macrophages, and azeliragon, a RAGE antagonist. SNC caused macrophage accumulation in the sciatic nerves, but not DRG. Our data suggest that extracellular at-HMGB1 causes RAGE-dependent acceleration of neuritogenesis in cultured DRG neurons, which is suppressed synergistically by thrombin and TMα. Nonetheless, neurite regeneration priming of DRG neurons by SNC is considered to involve HMGB1 derived from macrophages recruited to the damaged axon, but is not mediated by HMGB1 released from cultured DRG cells.