Energy Metabolism Disorder as a Contributing Factor of Rheumatoid Arthritis: A Comparative Proteomic and Metabolomic Study.

OBJECTIVES: To explore the pathogenesis of rheumatoid arthritis (RA), the different metabolites were screened in synovial fluid by metabolomics. METHODS: Synovial fluid from 25 RA patients and 10 normal subjects were analyzed by GC/TOF MS analysis so as to give a broad overview of synovial fluid metabolites. The metabolic profiles of RA patients and normal subjects were compared using multivariate statistical analysis. Different proteins were verified by qPCR and western blot. Different metabolites were verified by colorimetric assay kit in 25 inactive RA patients, 25 active RA patients and 20 normal subjects. The influence of hypoxia-inducible factor (HIF)-1α pathway on catabolism was detected by HIF-1α knockdown. RESULTS: A subset of 58 metabolites was identified, in which the concentrations of 7 metabolites related to energy metabolism were significantly different as shown by importance in the projection (VIP) (VIP ≥ 1) and Student's t-test (p<0.05). In the 7 metabolites, the concentration of glucose was decreased, and the concentration of lactic acid was increased in the synovial fluid of RA patients than normal subjects verified by colorimetric assay Kit. Receiver operator characteristic (ROC) analysis shows that the concentration of glucose and lactic acid in synovial fluid could be used as dependable biomarkers for the diagnosis of active RA, provided an AUC of 0.906 and 0.922. Sensitivity and specificity, which were determined by cut-off points, reached 84% and 96% in sensitivity and 95% and 85% in specificity, respectively. The verification of different proteins identified in our previous proteomic study shows that the enzymes of anaerobic catabolism were up-regulated (PFKP and LDHA), and the enzymes of aerobic oxidation and fatty acid oxidation were down-regulated (CS, DLST, PGD, ACSL4, ACADVL and HADHA) in RA patients. The expression of HIF-1α and the enzymes of aerobic oxidation and fatty acid oxidation were decreased and the enzymes of anaerobic catabolism were increased in FLS cells after HIF-1α knockdown. CONCLUSION: It was found that enhanced anaerobic catabolism and reduced aerobic oxidation regulated by HIF pathway are newly recognized factors contributing to the progression of RA, and low glucose and high lactic acid concentration in synovial fluid may be the potential biomarker of RA.

10-Hydroxy-2-decenoic acid inhibiting the proliferation of fibroblast-like synoviocytes by PI3K-AKT pathway.

To reveal the mechanism of 10H2DA inhibiting the proliferation of fibroblast-like synoviocytes (FLSs) of RA patients. Cell proliferation, HDAC activity and histone acetylation level of FLS cells treated with 10H2DA were detected by MTT assay, Colorimetric HDAC Activity Assay and Western-blot. Different genes in FLS cells from RA patients were primary cultured and treated with 10H2DA. They were then screened by Human Transcriptome 1.0 ST microarrays and verified by real-time PCR. The results showed dose-dependent and time-dependent decreases in cell viability and HDAC activity in FLSs treated with 10H2DA, and time-dependent induction in the acetylation of H3 and H4 at the same time. 697 different genes were identified by HTA 1.0. The expressions of 7 target genes of the PI3K-AKT pathway were decreased and 4 target genes of cytokine-cytokine receptor interaction were increased verified by real-time PCR. These results imply that 10H2DA is a potential HDACI which inhibits the proliferation of FLS cells by PI3K-AKT pathway.