Glucose-6-Phosphate Isomerase (G6PI) Mediates Hypoxia-Induced Angiogenesis in Rheumatoid Arthritis.

The higher level of Glucose-6-phosphate isomerase (G6PI) has been found in both synovial tissue and synovial fluid of rheumatoid arthritis (RA) patients, while the function of G6PI in RA remains unclear. Herein we found the enrichment of G6PI in microvascular endothelial cells of synovial tissue in RA patients, where a 3% O2 hypoxia environment has been identified. In order to determine the correlation between the high G6PI level and the low oxygen concentration in RA, a hypoxia condition (~3% O2) in vitro was applied to mimic the RA environment in vivo. Hypoxia promoted cellular proliferation of rheumatoid arthritis synovial fibroblasts (RASFs), and induced cell migration and angiogenic tube formation of human dermal microvascular endothelial cells (HDMECs), which were accompanied with the increased expression of G6PI and HIF-1α. Through application of G6PI loss-of-function assays, we confirmed the requirement of G6PI expression for those hypoxia-induced phenotype in RA. In addition, we demonstrated for the first time that G6PI plays key roles in regulating VEGF secretion from RASFs to regulate the hypoxia-induced angiogenesis in RA. Taken together, we demonstrated a novel pathway regulating hypoxia-induced angiogenesis in RA mediated by G6PI.

Decreased expression of alpha-enolase inhibits the proliferation of hypoxia-induced rheumatoid arthritis fibroblasts-like synoviocytes.

OBJECTIVES: To investigate the effect of decreased alpha-enolase (ENO1) expression on rheumatoid arthritis fibroblasts-like synoviocytes (RA-FLSs) proliferation in response to hypoxia, and elucidate the possible mechanisms involved. METHODS: RA-FLSs and osteoarthritis fibroblasts-like synoviocytes (OA-FLSs) were cultured in tri-gas incubators with different oxygen concentrations (3% O2, 7% O2, and 21% O2). 3% O2 (hypoxia) and 7% O2 conditions simulated intra-articular oxygen concentrations as observed in RA and healthy individual, respectively. 21% O2 represented oxygen condition for normal cell culture. ENO1-knockdown FLSs were established using ENO1-siRNA. The expression level of ENO1 was detected using reverse transcription polymerase chain reaction or RT-PCR and Western blot. Proliferation and apoptosis of RA-FLSs and OA-FLSs were assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium or MTS assay and flow cytometry, respectively. Western blot analysis was used to detect key proteins involved in apoptosis. RESULTS: ENO1 gene expression was remarkably upregulated, as well as its translation into protein, in RA-FLSs and OA-FLSs that were cultured in 3% O2 concentration. RA-FLSs and OA-FLSs that were cultured under hypoxic conditions hyperproliferated compared with similar cells under normaxic conditions. Neither 7% O2 nor 21% O2 condition had any significant effect on ENO1 expression. ENO1-siRNA-transfected FLSs, but not control-siRNA FLSs, showed markedly decreased proliferation. Additionally, ENO1 expression was found to promote significantly higher expression levels of the anti-apoptotic proteins Bcl-2, surviving, and cyclinB1, but inhibited the expression of cleaved caspase3. CONCLUSION: ENO1 may be crucial in the regulation of the proliferation and survival of synovial fibroblasts.

[Association of the PADI4 gene polymorphism and HLA-DRB1 shared epitope alleles with rheumatoid arthritis].

OBJECTIVE: To investigate the association of single nucleotide polymorphisms (SNPs) of the peptidylarginine deiminase IV (PADI4) and HLA-DRB1 shared epitope (SE) alleles with rheumatoid arthritis(RA) in a Chinese population. METHODS: Four exonic SNPs of the PADI4 gene (PADI 4_89*A/G, PADI 4_90*C/T, PADI 4_92*C/G and PADI 4_104*C/T) were genotyped in 67 unrelated patients with RA and 81 healthy controls, using cDNA sequencing and T vector cloning. HLA-DRB 1*01, *04 and *10 subtypes were determined by polymerase chain reaction with sequence specific primers (PCR-SSP). RESULTS: The distributions of the 4 SNPs were different in the two groups, and increased RA susceptibility was significantly associated with the minor alleles of PADI 4_89*G (P was 0.023), PADI 4_90*T (P was 0.004), PADI 4_104*T (P was 0.003), and the haplotypes carrying the 4 minor alleles (P was 0.008). HLA-DRB1 SE alleles are composed of HLA-DRB 1*0101, *0102, *0401, *0404, *0405, *0408, *0409, *0410 and *1001. Individuals carrying the SE alleles were associated with increased RA susceptibility (P was 0.002). Individuals carrying both the SE alleles and minor alleles of the 4 SNPs were more susceptible to RA than individuals carrying neither the minor SNP alleles nor the SE alleles. CONCLUSION: The PADI4 SNPs and haplotypes are associated with RA susceptibility in Chinese. HLA-DRB1 shared epitope is also an important risky factor for RA. There may exist certain synergistic effect between the PADI4 minor alleles and the HLA-DRB1 shared epitope.