The serine protease inhibitor SerpinA3N attenuates neuropathic pain by inhibiting T cell–derived leukocyte elastase

Inhibition of T cell–derived leukocyte elastase by neuronal SerpinA3N or the drug Sivelestat reduces neuropathic pain. Neuropathic pain is a major, intractable clinical problem and its pathophysiology is not well understood. Although recent gene expression profiling studies have enabled the identification of novel targets for pain therapy1,2,3,4, classical study designs provide unclear results owing to the differential expression of hundreds of genes across sham and nerve-injured groups, which can be difficult to validate, particularly with respect to the specificity of pain modulation5. To circumvent this, we used two outbred lines of rats6, which are genetically similar except for being genetically segregated as a result of selective breeding for differences in neuropathic pain hypersensitivity7. SerpinA3N, a serine protease inhibitor, was upregulated in the dorsal root ganglia (DRG) after nerve injury, which was further validated for its mouse homolog. Mice lacking SerpinA3N developed more neuropathic mechanical allodynia than wild-type (WT) mice, and exogenous delivery of SerpinA3N attenuated mechanical allodynia in WT mice. T lymphocytes infiltrate the DRG after nerve injury and release leukocyte elastase (LE), which was inhibited by SerpinA3N derived from DRG neurons. Genetic loss of LE or exogenous application of a LE inhibitor (Sivelastat) in WT mice attenuated neuropathic mechanical allodynia. Overall, we reveal a novel and clinically relevant role for a member of the serpin superfamily and a leukocyte elastase and crosstalk between neurons and T cells in the modulation of neuropathic pain.