We then applied different concentrations of Metrnl recombinant protein (0 ng/mL, 50 ng/mL, 100 ng/mL, 200 ng/mL, and 300 ng/mL) to LPS-induced RA-FLS cells to investigate the direct effects of Metrnl stimulation on PPARγ expression. This evidence concerns the gene PPARG and rheumatoid arthritis.