Elevated fatty acid β-oxidation by leptin contributes to the proinflammatory characteristics of fibroblast-like synoviocytes from RA patients via LKB1-AMPK pathway

Fibroblast-like synoviocytes (FLS) maintain chronic inflammation leading to joint destruction in rheumatoid arthritis (RA). Fatty acid β-oxidation (FAO) regulates cell function. Here, we aimed to investigate the effect of FAO enhanced by leptin on the characteristics of RA-FLS and elucidate the potential metabolic mechanism. Key enzymes involved in lipid metabolism were detected with qPCR in HSF, MH7A cell line and isolated RA-FLS treated with RA or healthy control (HC) serum. In some experiments, FAO inhibitor, etomoxir (ETO) or anti-leptin antibody were added into serum-treated RA-FLS. In other experiments, RA-FLS were stimulated with leptin together with ETO or AMP-activated protein kinase (AMPK) inhibitor compound C (CC) or silencing liver kinase B1 (LKB1). Cell proliferation, proinflammatory factor production, pro-angiogenesis, chemoattractive potential, FAO-related key enzymes, AMPK and LKB1 in FLS were analyzed. FAO-related key enzymes were evaluated in serum-treated RA-FLS with or without anti-leptin antibody. Related functions of leptin-stimulated RA-FLS were examined in the presence or absence of ETO. AMP-activated protein kinase (AMPK) and liver kinase B1 (LKB1) in leptin-stimulated RA-FLS were tested with western blot. Activation of AMPK in leptin-stimulated RA-FLS was detected after silencing LKB1. We found that MH7A cell line and RA serum-treated FLS exhibited upregulated FAO, and ETO could inhibit the proinflammatory phenotypes of RA-FLS. The addition of anti-leptin antibody suppressed the elevation of FAO mediated by RA serum. More importantly, leptin promoted the proinflammatory characteristics of RA-FLS, which was reversed by ETO. Leptin activated AMPK by upregulating LKB1. CC impaired leptin-induced CPT-1A expression in RA-FLS. Our study uncovers that elevated FAO mediated by leptin drives abnormal function of RA-FLS and suggests leptin or FAO inhibition may serve as a promising therapeutic strategy for RA.