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

Abstract Objective Rheumatoid arthritis (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 emphasised the mechanistic role of one of the major altered proteins, Inter-alpha-trypsin-inhibitor heavy chain 4 (ITIH4), in RA pathogenesis. Methods Expression level of ITIH4 was validated in RA patients' plasma and peripheral blood mononuclear cells (PBMCs) using enzyme-linked immunosorbent assay (ELISA) and western blotting (WB). The interaction of ITIH4 with the C-X-C chemokine receptor type 4 (CXCR4) complex was analysed by Molecular Dynamics (MD) simulation. In vitro studies targeting ITIH4 with siRNA were conducted to confirm its interaction with CXCR4 and its mediated downstream signaling molecules in apoptosis and inflammation in rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS). An in vivo study was conducted to validate the in vitro findings using a collagen-induced arthritis (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 PI3K/Akt signaling 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 signaling. Targeting ITIH4 could represent a promising therapeutic strategy for RA management.