KLF4 drives aggressive RA-FLS phenotypes via HTR2A-mediated AKT/mTOR activation

Background Rheumatoid arthritis (RA) represents a chronic autoimmune disorder that primarily impacts the joints through inflammatory processes. Despite therapeutic advances, a subset of patients remains difficult-to-treat, necessitating the identification of novel molecular targets. This study aims to elucidate the regulatory network involving the transcription factor Kruppel-like factor 4 (KLF4) and the serotonin receptor 2A (HTR2A) in RA fibroblast-like synoviocytes (RA-FLSs). Methods Normal and RA fibroblast-like synoviocytes were isolated from the synvial tissue specimens from healthy donors and RA patients, respectively. Western blot and reverse-transcription quantitative polymerase chain reaction were applied to quantify proteins or genes. Cell counting kit-8 and EdU assays were utilized to assess cell proliferation. Cell apoptosis, migration, and invasion were evaluated by flow cytometry, migration, and invasion assays accordingly. Angiogenic ability was assessed by tube formation assay. ELISA assay was used to evaluate the levels of inflammatory factors including TNF-α, IL-1β, and IL-6. The JASPAR website, chromatin immunoprecipitation, and dual-luciferase reporter assays were used to predict and testify the interaction between HTR2A and KLF4. Results HTR2A and KLF4 were significantly upregulated in both clinical synovial tissues and isolated RA-FLSs. Knockdown of HTR2A markedly inhibited cell proliferation, migration, invasion, and angiogenesis, while promoting apoptosis and reducing inflammatory cytokine release. Mechanistically, KLF4 was identified as a transcriptional activator that directly binds to the HTR2A promoter to enhance its expression. Silencing KLF4 exerted suppressive effects on RA-FLS aggression similar to HTR2A knockdown, and these effects were reversed by HTR2A overexpression. KLF4 upregulation activated HTR2A-mediated AKT/mTOR axis in RA fibroblast-like synoviocytes. Conclusion KLF4 functions as an upstream regulator that promotes the aggressive behaviors and inflammatory secretion of RA-FLSs, as well as angiogenesis, by transcriptionally activating HTR2A. This study establishes the KLF4/HTR2A/AKT/mTOR axis as a potential therapeutic target for refractory RA.