HtrA2 is required for inflammatory responses in BMDMs via controlling TRAF2 stability in collagen-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by the destruction of cartilage and bone. The present study aims to investigate the role of HtrA serine peptidase 2 (HtrA2) in the collagen-induced arthritis. The expressions of HtrA2 were determined in the database BioGPS and bone marrow-derived macrophages (BMDMs). The populations of myeloid and lymphoid cells were determined in wild type and HtrA2 knockout (HtrA2^MKO) mice using flow cytometry. In addition, the expressions of pro-inflammatory cytokines (Il6, Tnf, and Il1β) were determined in the activated BMDMs from wild type (WT) and HtrA2^MKO mice. STRING database was used to predict the interactive proteins of HtrA2 and Co-Immunoprecipitation was used to confirm these interactions. A collagen-induced arthritis model was established to investigate the effects of HtrA2 on the arthritis symptoms. It was found that HtrA2 reduction was associated with the activation of myeloid cells. Interestingly, HtrA2 deficiency did not affect the development of myeloid and lymphoid cells. Further studies demonstrated that HtrA2 deficiency suppressed the production of pro-inflammatory cytokines in BMDMs induced by lipopolysaccharide or CpG. Co-Immunoprecipitation results demonstrated that HtrA2 enhanced the stability of TNF receptor-associated factor 2 (TRAF2). HtrA2 participated in the activation of the inflammatory response in a collagen-induced arthritis model. In summary, HtrA2 modulates inflammatory responses in BMDMs by controlling TRAF2 stability in a collagen-induced arthritis mouse model.