Background/Purpose: HMGB1 has received attention for its emerging roles in the extracellular environment acting as damage associated molecular pattern molecule. The redox state of HMGB1 is key in determining which receptors HMGB1 activates and partially reduced HMGB1 (disulfide HMGB1) functions as a cytokine-inducing TLR4 ligand. Accumulating data indicate that HMGB1 plays important roles in the pathogenesis of inflammatory and autoimmune diseases. Blocking the action of HMGB1 with neutralizing antibodies ameliorates experimental arthritis in both mice and rats. Peripheral HMGB1 has also been linked to induction of pain-like behavior in experimental models of neuropathic and low back pain. However, the role of peripheral HMGB1 in pain hypersensitivity subsequent to development of arthritis has not been investigated. Thus the aim of the current study was to investigate if peripheral HMGB1 regulate arthritis-induced pain-like behavior.

Methods: BALB/c and C57BL/6 male and female mice (12-18 weeks) were used for this study. Collagen antibody-induced arthritis (CAIA) was induced by i.v. injection of anti-collagen antibody cocktail (1.5 mg/mice) followed by i.p. injection of LPS (25 ug). Disulfide HMGB1 (1 μg) was injected intraarticularly to the ankle joint. Mechanical hypersensitivity was assessed by von Frey filaments and the degree of joint inflammation by visual inspection and joint histology (H&E). The HMGB1 neutralizing antibody 2G7 (4 mg/kg) and the recombinant Abox protein (12 mg/kg) (blocks extracellular HMGB1 activities, although the exact mechanisms of action are unknown) were injected once/day for 6 consecutive days in both the inflammatory and late phase. Primary neuronal cultures were prepared from dorsal root ganglia and calcium flux subsequent to HMGB1 stimulation (100 nM) examined by calcium imaging. KCl (50 mM) was used as positive control to detect functional neurons.

Results: While CAIA mice developed transient joint inflammation with visual and histological arthritis scores, induction of mechanical hypersensitivity, which coincided with the inflammatory phase, did not resolve and remained pronounced throughout the study (“late phase” from day 38 to 51). Repeated systemic injection of 2G7 and Abox reversed CAIA-induced mechanical hypersensitivity in the inflammatory phase while in the late phase, Abox, but not 2G7, partially reversed the pain-like behavior. Intraarticular injection of dsHMGB1 in naïve mice induced mechanical hypersensitivity for at least 6h in both male and female mice. Stimulation of primary DRG neurons with dsHMGB1 did not evoke calcium flux in KCl responding neurons. 

Conclusion:

Our findings suggest that extracellular HMGB1 is an important factor in arthritis-induced pain during ongoing inflammation, but that it has a less pronounced role in mechanisms that maintain nociception subsequent to a period of joint inflammation. The TLR4 activating redox form of HMGB1 has nociceptive properties in the joint in naïve conditions, most likely via actions on immune cells as dsHMGB1 does not directly activate DRG neurons. Future studies are warranted to define the mechanisms by which peripheral HMGB1 contribute to arthritis-induced pain.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/peripheral-hmgb1-regulates-arthrtis-associated-pain-like-behaviour/