Clerodendrum japonicum Extract Suppresses the Pathogenicity of Rheumatoid Arthritis Fibroblast-Like Synoviocytes by Inhibiting METTL3-Mediated ICAM2 mRNA Methylation.

Clerodendrum japonicum (Thunb.) Sweet (Clerodendrum japonicum) is a traditional medicinal plant with reported anti-inflammatory use, but its anti-rheumatoid arthritis (RA) activity and molecular basis remain insufficiently characterized. Activated fibroblast-like synoviocytes (FLSs) contribute to persistent inflammation and joint destruction in rheumatoid arthritis (RA). This study investigated whether extracts of Clerodendrum japonicum attenuate pathogenic RA-FLS phenotypes and examined the possible involvement of METTL3-dependent N6-methyladenosine (m6A) regulation of ICAM2 mRNA. Tumor necrosis factor-α-stimulated human RA-FLSs (MH7A cell line) were used as an in vitro model to evaluate the anti-RA effects of Clerodendrum japonicum extracts. Cell proliferation, apoptosis, migration, invasion, and inflammatory cytokine secretion were evaluated. The underlying mechanisms were further investigated using real-time quantitative polymerase chain reaction, Western blot, and RNA immunoprecipitation. In addition, a collagen-induced arthritis (CIA) mouse model was employed to validate the anti-RA effects of the extracts in vivo. Drug-containing serum derived from Clerodendrum japonicum extracts attenuated TNF-α-induced proliferation, migration, invasion, and pro-inflammatory cytokine release in MH7A cells while increasing apoptosis. The ethyl acetate fraction (CJEA) produced the most pronounced effects among the tested fractions. CJEA-containing serum reduced global m6A abundance and METTL3 expression. METTL3 overexpression partially reversed the cellular effects associated with CJEA-containing serum. METTL3 knockdown reduced m6A enrichment and stability of ICAM2 mRNA, whereas METTL3 or ICAM2 overexpression partially restored ICAM2 expression and pathogenic RA-FLS phenotypes. Oral CJEA also reduced clinical and histological arthritis severity in CIA mice and was associated with lower synovial METTL3 and ICAM2 expression. Our findings support the involvement of METTL3-dependent m6A regulation of ICAM2 mRNA in the response of RA-FLSs to CJEA-containing serum. CJEA may attenuate pathogenic RA-FLS behavior and experimental arthritis at least partly through modulation of this pathway. Because the active constituent(s), direct molecular target, pharmacokinetics, and comprehensive safety profile remain undefined, further chemical and pharmacological validation is required.