Insights into FcγR involvement in pain-like behavior induced by an RA-derived anti-modified protein autoantibody.

Joint pain is one of the most debilitating symptoms of rheumatoid arthritis (RA) and patients frequently rate improvements in pain management as their priority. RA is hallmarked by the presence of anti-modified protein autoantibodies (AMPA) against post-translationally modified citrullinated, carbamylated and acetylated proteins. It has been suggested that autoantibody-mediated processes represent distinct mechanisms contributing to pain in RA. In this study, we investigated the pronociceptive properties of monoclonal AMPA 1325:01B09 (B09 mAb) derived from the plasma cell of an RA patient. We found that B09 mAb induces pain-like behavior in mice that is not associated with any visual, histological or transcriptional signs of inflammation in the joints, and not alleviated by non-steroidal anti-inflammatory drugs (NSAIDs). Instead, we found that B09 mAb is retained in dorsal root ganglia (DRG) and alters the expression of several satellite glia cell (SGC), neuron and macrophage-related factors in DRGs. Using mice that lack activating FcγRs, we uncovered that FcγRs are critical for the development of B09-induced pain-like behavior, and partially drive the transcriptional changes in the DRGs. Finally, we observed that B09 mAb binds SGC in vitro and in combination with external stimuli like ATP enhances transcriptional changes and protein release of pronociceptive factors from SGCs. We propose that certain RA antibodies bind epitopes in the DRG, here on SGCs, form immune complexes and activate resident macrophages via FcγR cross-linking. Our work supports the growing notion that autoantibodies can alter nociceptor signaling via mechanisms that are at large independent of local inflammatory processes in the joint.

eEF2 improves dense connective tissue repair and healing outcome by regulating cellular death, autophagy, apoptosis, proliferation and migration.

Outcomes following human dense connective tissue (DCT) repair are often variable and suboptimal, resulting in compromised function and development of chronic painful degenerative diseases. Moreover, biomarkers and mechanisms that guide good clinical outcomes after DCT injuries are mostly unknown. Here, we characterize the proteomic landscape of DCT repair following human Achilles tendon rupture and its association with long-term patient-reported outcomes. Moreover, the potential regulatory mechanisms of relevant biomarkers were assessed partly by gene silencing experiments. A mass-spectrometry based proteomic approach quantified a large number (769) of proteins, including 51 differentially expressed proteins among 20 good versus 20 poor outcome patients. A novel biomarker, elongation factor-2 (eEF2) was identified as being strongly prognostic of the 1-year clinical outcome. Further bioinformatic and experimental investigation revealed that eEF2 positively regulated autophagy, cell proliferation and migration, as well as reduced cell death and apoptosis, leading to improved DCT repair and outcomes. Findings of eEF2 as novel prognostic biomarker could pave the way for new targeted treatments to improve healing outcomes after DCT injuries.Trial registration: NCT02318472 registered 17 December 2014 and NCT01317160 registered 17 March 2011, with URL http://clinicaltrials.gov/ct2/show/NCT02318472 and http://clinicaltrials.gov/ct2/show/study/NCT01317160 .

Antibody-induced pain-like behavior and bone erosion: links to subclinical inflammation, osteoclast activity, and acid-sensing ion channel 3-dependent sensitization.

ABSTRACT: Several bone conditions, eg, bone cancer, osteoporosis, and rheumatoid arthritis (RA), are associated with a risk of developing persistent pain. Increased osteoclast activity is often the hallmark of these bony pathologies and not only leads to bone remodeling but is also a source of pronociceptive factors that sensitize the bone-innervating nociceptors. Although historically bone loss in RA has been believed to be a consequence of inflammation, both bone erosion and pain can occur years before the symptom onset. Here, we have addressed the disconnection between inflammation, pain, and bone erosion by using a combination of 2 monoclonal antibodies isolated from B cells of patients with RA. We have found that mice injected with B02/B09 monoclonal antibodies (mAbs) developed a long-lasting mechanical hypersensitivity that was accompanied by bone erosion in the absence of joint edema or synovitis. Intriguingly, we have noted a lack of analgesic effect of naproxen and a moderate elevation of few inflammatory factors in the ankle joints suggesting that B02/B09-induced pain-like behavior does not depend on inflammatory processes. By contrast, we found that inhibiting osteoclast activity and acid-sensing ion channel 3 signaling prevented the development of B02/B09-mediated mechanical hypersensitivity. Moreover, we have identified secretory phospholipase A2 and lysophosphatidylcholine 16:0 as critical components of B02/B09-induced pain-like behavior and shown that treatment with a secretory phospholipase A2 inhibitor reversed B02/B09-induced mechanical hypersensitivity and bone erosion. Taken together, our study suggests a potential link between bone erosion and pain in a state of subclinical inflammation and offers a step forward in understanding the mechanisms of bone pain in diseases such as RA.

JAK inhibition increases bone mass in steady-state conditions and ameliorates pathological bone loss by stimulating osteoblast function.

Janus kinase (JAK)-mediated cytokine signaling has emerged as an important therapeutic target for the treatment of inflammatory diseases such as rheumatoid arthritis (RA). Accordingly, JAK inhibitors compose a new class of drugs, among which tofacitinib and baricitinib have been approved for the treatment of RA. Periarticular bone erosions contribute considerably to the pathogenesis of RA. However, although the immunomodulatory aspect of JAK inhibition (JAKi) is well defined, the current knowledge of how JAKi influences bone homeostasis is limited. Here, we assessed the effects of the JAK inhibitors tofacitinib and baricitinib on bone phenotype (i) in mice during steady-state conditions or in mice with bone loss induced by (ii) estrogen-deficiency (ovariectomy) or (iii) inflammation (arthritis) to evaluate whether effects of JAKi on bone metabolism require noninflammatory/inflammatory challenge. In all three models, JAKi increased bone mass, consistent with reducing the ratio of receptor activator of NF-κB ligand/osteoprotegerin in serum. In vitro, effects of tofacitinib and baricitinib on osteoclast and osteoblast differentiation were analyzed. JAKi significantly increased osteoblast function (P < 0.05) but showed no direct effects on osteoclasts. Additionally, mRNA sequencing and ingenuity pathway analyses were performed in osteoblasts exposed to JAKi and revealed robust up-regulation of markers for osteoblast function, such as osteocalcin and Wnt signaling. The anabolic effect of JAKi was illustrated by the stabilization of ß-catenin. In humans with RA, JAKi induced bone-anabolic effects as evidenced by repair of arthritic bone erosions. Results support that JAKi is a potent therapeutic tool for increasing osteoblast function and bone formation.