Validation of the therapeutic potential of soluble CD93 lectin-like domain in arthritis and its inhibitory role in inflammatory osteolysis

TNF-α and receptor activators of nuclear factor-κB ligand (RANKL) are well-established as critical inducers of bone resorption, and their activity is amplified by inflammation. The ectodomains of CD93 can be shed and released as a soluble form at elevated levels observed during inflammatory osteolysis in rheumatoid arthritis (RA) patients. However, the functional role of soluble CD93 in modulating TNF-α- and RANKL- caused inflammatory osteolysis remains to be elucidated. We aimed to evaluate the functional role of soluble recombinant CD93 lectin-like domain (rCD93D1) in RA and further explore its underlying mechanisms. An experimental arthritis murine model was used to assess the effects of rCD93D1 in vivo. In vitro, the impacts of rCD93D1 on osteoclast formation, osteoclastogenic, and pro-inflammatory signaling cascades were investigated in RANKL incubated with TNF-α-primed murine macrophages. We revealed that the administration of rCD93D1 alleviates joint swelling and inflammatory bone loss in arthritis mice, while RANKL augmented osteoclast differentiation, multinucleated giant cell formation, and osteoclastogenic marker genes expression, resulting in co-adaptor TRAF6 activation requiring NF-κB translocation in TNF-α-primed cells, whereas rCD93D1 treatment effectively reversed these effects. Moreover, rCD93D1 suppressed the transcription factors of NFATc1 and c-Fos by abrogating MAPK phosphorylation by TNF-α and RANKL induction. Notably, rCD93D1 blockaded HMGB1 secretion and release during inflammatory osteolysis triggered by these stimuli. Our results demonstrate that rCD93D1 inhibits inflammatory osteolysis and osteoclast formation by reducing HMGB1 levels and downstream-signaling cascades elicited from TNF-α and RANKL. This evidence suggests that rCD93D1 holds promise as a therapeutic agent for preventing the progression of RA.