Hypoxia-Inducible Factor-1α–Induced Astrocytic D-Dopachrome Tautomerase Activates Microglial Inflammatory Response following Spinal Cord Injury

Spinal cord injury (SCI) often results in severe hypoxia and excessive activation of neuroinflammation, which aggravates neuropathology and neurologic dysfunction. D-dopachrome tautomerase (D-DT), the homolog of macrophage migration inhibitory factor, is a key proinflammatory mediator implicated in inflammatory diseases of multiple tissues. However, its relation with hypoxia and the potential impact on neuroinflammation following SCI remain elusive. Herein, the dynamic expression of D-DT, p65NF-κB, and the downstream proinflammatory cytokines tumor necrosis factor-α, IL-1β, and IL-6 at the lesion site was determined following SCI. D-DT inhibitor 4-(3-carboxyphenyl)-2,5pyridinedicarboxylic acid was applied to evaluate its effects on the inflammatory responses of the injured tissues. By using an in vitro cell model, the D-DT-mediated activation of microglia and the underlying regulatory mechanism were also investigated, showing that CD74/mitogen-activated protein kinase signaling was driven by D-DT to activate microglial inflammation. Analysis of rat D-DT promoter identified the binding element of hypoxia-inducible factor-1α. Hypoxia or dimethyloxallyl glycine stimulation of astrocytes was shown efficient in promoting the expression of hypoxia-inducible factor-1α and D-DT, whereas incubation of the microglia with the astrocytes' conditional medium increased the production of tumor necrosis factor-α, IL-1β, and IL-6. Pharmacologic treatment of the subjects with 4-(3-carboxyphenyl)-2,5pyridinedicarboxylic acid or LW6 following SCI remarkably promoted the recovery of rat locomotor function. The results have presented a novel neuropathologic function of D-DT, which might be beneficial for development of potential drug targeting neuroinflammation.