Spinal injection of disulfide extracellular high mobility group box-1 protein (HMGB1) induces mechanical hypersensitivity and spinal glial activation, and inhibition of spinal HMGB1 resolves mechanical hypersensitivity induced by collagen antibody-induced arthritis.
Extracellular high mobility group box-1 protein (HMGB1) plays important roles in the pathogenesis of nerve injury- and cancer-induced pain. However, the involvement of spinal HMGB1 in arthritis-induced pain has not been examined previously and is the focus of this study. Immunohistochemistry showed that HMGB1 is expressed in neurons and glial cells in the spinal cord. Subsequent to induction of collagen antibody-induced arthritis (CAIA), Hmgb1 mRNA and extranuclear protein levels were significantly increased in the lumbar spinal cord. Intrathecal (i.t.) injection of a neutralizing anti-HMGB1 monoclonal antibody or recombinant HMGB1 box A peptide (Abox), which each prevent extracellular HMGB1 activities, reversed CAIA-induced mechanical hypersensitivity. This occurred during ongoing joint inflammation as well as during the postinflammatory phase, indicating that spinal HMGB1 has an important function in nociception persisting beyond episodes of joint inflammation. Importantly, only HMGB1 in its partially oxidized isoform (disulfide HMGB1), which activates toll-like receptor 4 (TLR4), but not in its fully reduced or fully oxidized isoforms, evoked mechanical hypersensitivity upon i.t. injection. Interestingly, although both male and female mice developed mechanical hypersensitivity in response to i.t. HMGB1, female mice recovered faster. Furthermore, the pro-nociceptive effect of i.t. injection of HMGB1 persisted in Tlr2- and Rage-, but was absent in Tlr4-deficient mice. The same pattern was observed for HMGB1-induced spinal microglia and astrocyte activation and cytokine induction. These results demonstrate that spinal HMGB1 contributes to nociceptive signal transmission via activation of TLR4 and point to disulfide HMGB1 inhibition as a potential therapeutic strategy in treatment of chronic inflammatory pain.
aDepartment of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
bDepartment of Neuroscience, Karolinska Institutet, Stockholm, Sweden
cDepartment of Medicine, Karolinska Institutet, Stockholm, Sweden
dWomen’s and Children’s Health, Karolinska Institutet, Stockholm, Sweden
*Corresponding author. Address: Karolinska Institutet, Von Eulers väg 8, 171 77 Stockholm, Sweden. Tel.: +46 8 524 87948; fax: +46 8 310622.
1Current address: Department of Clinical and Experimental Medicine, Division of Cell Biology, Linköping University, Linköping, Sweden.
Submitted April 12, 2014; revised June 11, 2014; accepted June 13, 2014.
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