Interleukin-18 induces angiogenic factors in rheumatoid arthritis synovial tissue fibroblasts via distinct signaling pathways.
OBJECTIVE
Interleukin-18 (IL-18) is a proinflammatory cytokine implicated in the pathogenesis of rheumatoid arthritis (RA). This study was undertaken to examine the role of IL-18 in up-regulating secretion of the angiogenic factors stromal cell-derived factor 1alpha (SDF-1alpha)/CXCL12, monocyte chemoattractant protein 1 (MCP-1)/CCL2, and vascular endothelial growth factor (VEGF) in RA synovial tissue (ST) fibroblasts, and the underlying signaling mechanisms involved.


METHODS
We used enzyme-linked immunosorbent assays, Western blotting, and chemical inhibitors/antisense oligodeoxynucleotides to signaling intermediates to assess the role of IL-18.


RESULTS
IL-18 significantly enhanced the production of SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, in a time- and concentration-dependent manner. IL-18-induced SDF-1alpha/CXCL12 up-regulation was dependent on JNK, p38 MAPK, phosphatidylinositol 3-kinase (PI3K), and NFkappaB. While IL-18-induced production of SDF-1alpha/CXCL12 was also dependent on protein kinase Cdelta (PKCdelta), production of MCP-1/CCL2 was dependent on PKCalpha, not PKCdelta. Additionally, RA ST fibroblast IL-18-induced MCP-1/CCL2 production was mediated by JNK, PI3K, and NFkappaB. In contrast, IL-18 did not induce secretion of RA ST fibroblast MCP-1/CCL2 or VEGF via p38 MAPK. IL-18-induced RA ST fibroblast production of VEGF was mediated mainly by JNK-2, PKCalpha, and NFkappaB. IL-18 induced phosphorylation of JNK, PKCdelta, p38 MAPK, and activating transcription factor 2 (ATF-2) in RA ST fibroblasts in a time-dependent manner, with JNK-2 being upstream of PKCdelta, ATF-2, and NFkappaB.


CONCLUSIONS
These data support the notion that IL-18 has a unique role in inducing the secretion of angiogenic SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, via distinct signaling intermediates.
Amin
Mohammad A
MA
Department of Internal Medicine, Division of Rheumatology, University of Michigan Medical School, University of Michigan Health System, Ann Arbor, MI, USA. maamin@med.umich.edu
Mansfield
Pamela J
PJ
Pakozdi
Angela
A
Campbell
Phillip L
PL
Ahmed
Salahuddin
S
Martinez
Rita J
RJ
Koch
Alisa E
AE
D051698:Activating Transcription Factor 2 / Q000378:metabolism; D043925:Angiogenesis Inducing Agents / Q000378:metabolism*; D001172:Arthritis, Rheumatoid / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism*; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D020382:Interleukin-18 / Q000502:physiology*; D048688:MAP Kinase Kinase 7 / Q000378:metabolism; D016328:NF-kappa B / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051745:Protein Kinase C-delta / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C497105:ATF2 protein, human; D051698:Activating Transcription Factor 2; D043925:Angiogenesis Inducing Agents; C515255:CXCL12 protein, human; D018932:Chemokine CCL2; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D020382:Interleukin-18; D016328:NF-kappa B; D042461:Vascular Endothelial Growth Factor A; D019869:Phosphatidylinositol 3-Kinases; D051745:Protein Kinase C-delta; D048051:p38 Mitogen-Activated Protein Kinases; D048688:MAP Kinase Kinase 7