The role of ITIH4 in regulating the PI3K/Akt signalling in rheumatoid arthritis

Abstract Objective RA is a chronic inflammatory disease characterized by synovial membrane hyperplasia and joint degeneration. Aberrant protein expression has shed light on their association with disease pathogenesis. This study emphasized the mechanistic role of one of the major altered proteins, Inter-alpha-trypsin-inhibitor heavy chain 4 (ITIH4), in RA pathogenesis. Methods The expression level of ITIH4 was validated in RA patients’ plasma and peripheral blood mononuclear cells (PBMCs) using ELISA and western blotting. The interaction of ITIH4 with the C-X-C chemokine receptor type 4 (CXCR4) complex was analysed by molecular dynamics simulation. In vitro studies targeting ITIH4 with siRNA were conducted to confirm its interaction with CXCR4 and its mediated downstream signalling molecules in apoptosis and inflammation in RA fibroblast-like synoviocytes (RA-FLS). An in vivo study was conducted to validate the in vitro findings using a CIA rat model. Results Increased levels of ITIH4 were observed in RA patients’ plasma and PBMCs. In vitro studies show that, ITIH4 was positively interacted with CXCR4, leading to increased apoptosis and reduced pro-inflammatory cytokine production by regulating Phosphoinositide 3-kinase (PI3K)/Akt signalling after ITIH4 knockdown in RA-FLS. ITIH4 knockdown also significantly led to inhibit the progression of arthritis-like symptoms in the CIA rat model, shown by decreased arthritis index, cellular infiltration, cytokines production and pannus formation. Conclusion The study suggests that the ITIH4–CXCR4 interaction is linked to apoptosis and inflammation in RA through PI3K/Akt signalling. Targeting ITIH4 could represent a promising therapeutic strategy for RA management.