Platelet-derived growth factor and transforming growth factor beta synergistically potentiate inflammatory mediator synthesis by fibroblast-like synoviocytes.
BACKGROUND
The objective of this study was to model the effects of transforming growth factor beta (TGF-beta) and platelet-derived growth factor (PDGF), both present in rheumatoid arthritis (RA) synovia, on the behavior of fibroblast-like synoviocytes (FLS) in response to pro-inflammatory cytokine (interleukin (IL)1beta, tumor necrosis factor-alpha (TNFalpha)) challenge.


METHODS
Gene and protein expression by fibroblast-like synoviocytes in vitro was studied by quantitative Polymerase Chain Reaction (qPCR), ELISA and multiplex bead cytokine assays. Intracellular signaling pathway activation was determined by Western blot for phospho-kinases and the use of specific inhibitors.


RESULTS
In combination, TGF-beta and PDGF (2GF) synergistically augmented TNFalpha- or IL1beta-induced matrix metalloproteinase 3 (MMP3), IL6, IL8, and macrophage inflammatory protein 1 alpha (MIP1alpha) secretion by FLS. Other FLS-derived mediators remained unaffected. Individually, neither growth factor significantly potentiated TNFalpha or IL1beta-induced MMP3 secretion, and only slightly enhanced IL6. The effect of 2GF on TNFalpha-induced gene expression was transcriptionally mediated; blocked by imatinib mesylate; and occurred even if 2GF was added as much as four hours prior to TNFalpha. In addition, a 15-minute pulse of 2GF four hours prior to TNFalpha stimulation yielded a synergistic response. The extracellular-signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K) signaling pathways were induced for at least four hours by 2GF, as demonstrated by persistently upregulated levels of phospho-Akt and phospho-ERK. However, pharmacologic inhibitor studies demonstrated that the potentiating action of 2GF was dependent on PI3 kinase only, and not on ERK.


CONCLUSIONS
The combination of PDGF and TGF-beta dramatically potentiates FLS response to cytokines in a receptor-mediated and PI3 kinase-dependent fashion. These data suggest that 2GF contribute to synovitis by directing synovial fibroblasts toward a more aggressive phenotype in response to TNFalpha. Therefore, inhibition of growth factor signaling may constitute a complementary therapeutic approach to cytokine-targeted treatments for RA.
Rosengren
Sanna
S
Division of Rheumatology, Allergy and Immunology, University of California at San Diego School of Medicine, 9500 Gilman Drive, La Jolla, CA 92093-0656, USA.
Corr
Maripat
M
Boyle
David L
DL
D000077214:Becaplermin; D001549:Benzamides; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004357:Drug Synergism; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D000068877:Imatinib Mesylate; D061965:Matrix Metalloproteinase Inhibitors; D020782:Matrix Metalloproteinases / Q000235:genetics / Q000378:metabolism*; D010879:Piperazines / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D011743:Pyrimidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013583:Synovial Membrane / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D001549:Benzamides; D016207:Cytokines; D061965:Matrix Metalloproteinase Inhibitors; D010879:Piperazines; D010982:Platelet-Derived Growth Factor; D047428:Protein Kinase Inhibitors; D020574:Proto-Oncogene Proteins c-sis; D011743:Pyrimidines; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D000077214:Becaplermin; D000068877:Imatinib Mesylate; D020782:Matrix Metalloproteinases