Human inflammatory synovial fibroblasts induce enhanced myeloid cell recruitment and angiogenesis through a hypoxia-inducible transcription factor 1alpha/vascular endothelial growth factor-mediated pathway in immunodeficient mice.
OBJECTIVE
Hyperplasia and phenotypic changes in fibroblasts are often observed in chronic inflammatory lesions, and yet the autonomous pathogenic contribution of these changes is uncertain. The purpose of this study was to analyze the intrinsic ability of fibroblasts from chronically inflamed synovial tissue to drive cell recruitment and angiogenesis.


METHODS
Fibroblasts from patients with rheumatoid arthritis (RA) or osteoarthritis (OA), as well as fibroblasts from healthy synovial tissue and healthy skin, were cultured and subcutaneously engrafted into immunodeficient mice. Cell infiltration and angiogenesis were analyzed in the grafts by immunohistochemical studies. The role of vascular endothelial growth factor (VEGF), CXCL12, and hypoxia-inducible transcription factor 1alpha (HIF-1alpha) in these processes was investigated using specific antagonists or small interfering RNA (siRNA)-mediated down-regulation of HIF-1alpha in fibroblasts.


RESULTS
Inflammatory (OA and RA) synovial fibroblasts, compared with healthy dermal or synovial tissue fibroblasts, induced a significant enhancement in myeloid cell infiltration and angiogenesis in immunodeficient mice. These activities were associated with increased constitutive and hypoxia-induced expression of VEGF, but not CXCL12, in inflammatory fibroblasts compared with healthy fibroblasts. VEGF and CXCL12 antagonists significantly reduced myeloid cell infiltration and angiogenesis. Furthermore, targeting of HIF-1alpha expression by siRNA or of HIF-1alpha transcriptional activity by the small molecule chetomin in RA fibroblasts significantly reduced both responses.


CONCLUSIONS
These results demonstrate that chronic synovial inflammation is associated with stable fibroblast changes that, under hypoxic conditions, are sufficient to induce inflammatory cell recruitment and angiogenesis, both of which are processes relevant to the perpetuation of chronic inflammation.
Hospital 12 de Octubre, Madrid, Spain.
Manuel J
MJ
del Rey
Elena
E
Izquierdo
Sergio
S
Caja
Alicia
A
Usategui
Begoña
B
Santiago
María
M
Galindo
José L
JL
Pablos
D000818:Animals; D001172:Arthritis, Rheumatoid / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D016022:Case-Control Studies; D054377:Chemokine CXCL12 / Q000378:metabolism; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000187:drug effects; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology* / Q000637:transplantation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007154:Immune System Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D007279:Injections, Subcutaneous; D051379:Mice; D008819:Mice, Nude; D022423:Myeloid Cells / Q000378:metabolism / Q000473:pathology*; D009389:Neovascularization, Pathologic / Q000378:metabolism / Q000473:pathology*; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology* / Q000637:transplantation; D014183:Transplantation, Heterologous; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D054377:Chemokine CXCL12; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A