Role of spinal and peripheral HMGB1 in arthritis-induced pain

Chronic pain is one of the most debilitating and repeatedly reported symptoms by rheumatoid arthritis (RA) patients. Despite good disease control achieved with disease modifying antirheumatic drugs (DMARDs), joint pain remains a major problem for a subgroup of patients. Therefore, it appears episodes of joint inflammation can have long-term effects on the peripheral sensory nervous system. Additionally, changes in the central nervous system may contribute to chronification of RA pain. High mobility group box-1 protein (HMGB1) is an important molecule in the pathogenesis of RA, but the role of HMGB1 in RA associated pain has not been studied. Thus, the involvement of spinal and peripheral HMGB1 in rheumatoid arthritis-induced pain is the focus of this thesis. In Paper I, we characterized the collagen antibody-induced arthritis (CAIA) model from a pain perspective. As expected, injection of collagen type II antibodies induces transient joint inflammation and pain-like behavior. Surprisingly, pain-like behavior did not normalize when the inflammation resolved. We found that transient antibody-induced joint inflammation led to long-lasting mechanical hypersensitivity that outlasted the inflammation. Buprenorphine and gabapentin attenuated pain like behavior in both the inflammatory and late “postinflammatory” phase of the model, whereas diclofenac was antinociceptive only during the inflammatory phase. This indicates that there is a temporal shift in the mechanisms that maintain arthritis-induced nociception. The CAIA model can thus be used to explore mechanisms of persistent pain induced by inflammation in the articular joint. In Paper II and III, we investigated the spinal role of HMGB1 in arthritis-induced pain and sex-dependent microglial involvement in disulfide HMGB1 mediated nociception. Peripheral joint inflammation in the CAIA model increases expression and extranuclear levels of HMGB1 in the lumbar spinal cord. Blocking the endogenous action of HMGB1 with HMGB1 inhibitors attenuated CAIA-induced mechanical hypersensitivity in both male and female mice. A pronociceptive effect dependent on the redox state of HMGB1 was also revealed. The disulfide, but not the all-thiol or oxidized form, of HMGB1 induced nociception in male and female mice after intrathecal delivery. This effect was regulated via toll-like receptor 4 (TLR4) and associated with cytokine and chemokine production and elevated expression of factors related to increased glial cell reactivity. Intrathecal delivery of minocycline attenuated the disulfide HMGB1 induced hypersensitivity in male but not in female mice. Global protein analysis of lumbar spinal cords from male and female mice injected intrathecally with HMGB1 and vehicle or minocycline showed that 36 proteins were differentially expressed between male and female injected with HMGB1 and that 44 proteins in males and 8 in females were altered in mice receiving HMGB1 and minocycline. Interestingly, up-regulation of antinociceptive and anti-inflammatory molecules was found in male but not in female mice after intrathecal injection of HMGB1 and minocycline. This work points to a prominent and redox-dependent role of HMGB1 in spinal pain signal transmission. In Paper IV, we demonstrated that a repetitive systemic injection of a HMGB1 neutralizing antibody attenuates CAIA-induced nociception in male but not in female mice. Intraarticular injection of disulfide but not all-thiol HMGB1 induced mechanical hypersensitivity in both male and female mice, but with a more pronounced induction of cytokine and chemokine mRNA expression in male compared to female mice. Moreover, nociception induced by disulfide HMGB1 is mediated by TLR4 expressed on nociceptors and myeloid cells in male and female mice, with a stronger contribution of TLR4 on myeloid cells in male mice. In summary, we have described novel redox state and sex-dependent roles of HMGB1 in nociception at spinal and peripheral sites in a model of arthritis-induced pain. These results also reveal sex-dependent analgesic pharmacology and highlight the importance of taking sex into account in preclinical pain research. While further studies are warranted in order to further advance our knowledge on the role of HMGB1 in pain pathology, the work in this thesis highlights HMGB1 as an intriguing new target for pain relief. LIST OF SCIENTIFIC PAPERS I Bas DB, Su J, Sandor K, Agalave NM, Lundberg J, Codeluppi S, Baharpoor A, Nandakumar KS, Holmdahl R, Svensson CI. Collagen antibody-induced arthritis evokes persistent pain with spinal glial involvement and transient prostaglandin dependency Arthritis Rheum. 2012 Dec;64(12):3886-96. doi: 10.1002/art.37686. II Agalave NM, Larsson M, Abdelmoaty S, Su J, Baharpoor A, Lundbäck P, Palmblad K, Andersson U, Harris H, Svensson CI. Spinal HMGB1 induces TLR4-mediated long-lasting hypersensitivity and glial activation and regulates pain-like behavior in experimental arthritis Pain. 2014 Sep;155(9):1802-13. doi: 10.1016/j.pain. 2014.06. 007. Epub 2014 Jun 20. III Agalave NM, Bersellini Farinotti A, Khoonsari PE, Krishnan S, Palada V, Umbria CM, Sandor K, Andersson U, Harris H, Kultima K, Svensson CI. Sex-dependent role of microglia in disulphide HMGB1-mediated mechanical hypersensitivity