ANA-12 Targets and Inhibits BDNF/TrkB Signaling to Alleviate Pain Behaviors in Rheumatoid Arthritis Mice.

Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory disease. Sensitization of central pain pathways by pro-inflammatory mediators has been implicated in RA pain. Locus coeruleus (LC) functions in pain pathways. Brain-derived neurotrophic factor (BDNF) participates in the modulation of nociception and pain. A mouse model of RA immunized with collagen-induced arthritis (CIA) was used for investigating the mechanisms of pain relief by administration of the tropomyosin receptor kinase B (TrkB) receptor antagonist ANA-12. We measured the pain behaviors and locomotor activity and found increased pain sensitivity and locomotor deficit in RA mice; ANA-12 treatment reduced pain behaviors and promoted locomotor function recovery. The glial activation and increased activities of BDNF/TrkB and MAPK signal pathways were found in LC of RA mice. The components of NLRP3 inflammasome were all increased and consequently enhanced the production of pro-inflammatory cytokine interleukin (IL)-1β. Upon ANA-12 treatment, glial cell activation was reduced, BDNF/TrkB and MAPK pathways were suppressed, and the expression levels of the above-mentioned proteins were reduced. Finally, U251 cells were conducted to further confirm the regulatory mechanisms of ANA-12 on inflammation. The results showed the colocalization of BDNF/NLRP3/IL-1β and GFAP. ANA-12 treatment decreased the protein levels of BDNF, TrkB, MAPK, NLRP3, and caspase-1 in IL-1β-induced cells. Besides, ANA-12 treatment decreased NLRC4 and AIM2 inflammasomes both in RA mice and IL-1β-induced cells. These results suggested that ANA-12 alleviates hyperalgesia in RA mice by inhibiting BDNF/TrkB signaling in LC, thereby reducing glial cell activation and inflammatory cytokine release.