Modulation of interleukin-6 and matrix metalloproteinase 2 expression in human fibroblast-like synoviocytes by functional ionotropic glutamate receptors.
OBJECTIVE
Patients with rheumatoid arthritis (RA) have increased concentrations of the amino acid glutamate in synovial fluid. This study was undertaken to determine whether glutamate receptors are expressed in the synovial joint, and to determine whether activation of glutamate receptors on human synoviocytes contributes to RA disease pathology.


METHODS
Glutamate receptor expression was examined in tissue samples from rat knee joints and in human fibroblast-like synoviocytes (FLS). FLS from 5 RA patients and 1 normal control were used to determine whether a range of glutamate receptor antagonists influenced expression of the proinflammatory cytokine interleukin-6 (IL-6), enzymes involved in matrix degradation and cytokine processing (matrix metalloproteinase 2 [MMP-2] and MMP-9), and the inhibitors of these enzymes (tissue inhibitor of metalloproteinases 1 [TIMP-1] and TIMP-2). IL-6 concentrations were determined by enzyme-linked immunosorbent assay, MMP activity was measured by gelatin zymography, and TIMP activity was determined by reverse zymography. Fluorescence imaging of intracellular calcium concentrations in live RA FLS stimulated with specific antagonists was used to reveal functional activation of glutamate receptors that modulated IL-6 or MMP-2.


RESULTS
Ionotropic and metabotropic glutamate receptor subunit mRNA were expressed in the patella, fat pad, and meniscus of the rat knee and in human articular cartilage. Inhibition of N-methyl-D-aspartate (NMDA) receptors in RA FLS increased proMMP-2 release, whereas non-NMDA ionotropic glutamate receptor antagonists reduced IL-6 production by these cells. Stimulation with glutamate, NMDA, or kainate (KA) increased intracellular calcium concentrations in RA FLS, demonstrating functional activation of specific ionotropic glutamate receptors.


CONCLUSIONS
Our findings indicate that activation of NMDA and KA glutamate receptors on human synoviocytes may contribute to joint destruction by increasing IL-6 expression.
Flood
Sophie
S
School of Biosciences, Cardiff University, Museum Avenue, Cardiff, UK.
Parri
Rheinallt
R
Williams
Anwen
A
Duance
Victor
V
Mason
Deborah
D
D000328:Adult; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression; D018698:Glutamic Acid / Q000494:pharmacology; D006614:Hindlimb; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D008592:Menisci, Tibial / Q000737:chemistry / Q000378:metabolism; D008875:Middle Aged; D016202:N-Methylaspartate / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D018092:Kainic Acid Receptors / Q000235:genetics / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism*; D019714:Tissue Inhibitor of Metalloproteinases / Q000378:metabolism; D000097806:GluK2 Kainate Receptor
D002118:Calcium; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D015850:Interleukin-6; D007608:Kainic Acid; D020778:Matrix Metalloproteinase 2; D016202:N-Methylaspartate; D012333:RNA, Messenger; D018092:Kainic Acid Receptors; D018094:Receptors, Metabotropic Glutamate; D019714:Tissue Inhibitor of Metalloproteinases; D000097806:GluK2 Kainate Receptor