Angiogenesis is a critical process in the formation of new capillaries and a key participant in rheumatoid arthritis (RA) pathogenesis. Vascular endothelial growth factor (VEGF) stimulation of endothelial progenitor cells (EPCs) facilitates angiogenesis and the progression of RA. Phosphorylation of sphingosine kinase 1 (SphK1) produces sphingosine-1-phosphate (S1P), which increases inflammatory cytokine production, although the role of S1P in RA angiogenesis is unclear. In this study, we evaluated the impact of S1P treatment on VEGF-dependent angiogenesis in osteoblast-like cells (MG-63 cells) and the significance of SphK1 short hairpin RNA (shRNA) on S1P production in an in vivo model. We found significantly higher levels of S1P and VEGF expression in synovial fluid from RA patients compared with those with osteoarthritis by ELISA analysis. Treating MG-63 cells with S1P increased VEGF production, while focal adhesion kinase (FAK) and Src siRNAs and inhibitors decreased VEGF production in S1P-treated MG-63 cells. Conditioned medium from S1P-treated osteoblasts significantly increased EPC tube formation and migration by inhibiting miR-16-5p synthesis via proto-oncogene tyrosine-protein kinase src (c-Src) and FAK signaling in chick chorioallantoic membrane (CAM) and Matrigel plug assays. Infection with SphK1 shRNA reduced angiogenesis, articular swelling and cartilage erosion in the ankle joints of mice with collagen-induced arthritis (CIA). S1P appears to have therapeutic potential in RA treatment.
Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory disease, in which the immune system attacks synovial joint tissues. Interleukin (IL)‐1β is a critical proinflammatory cytokine in RA progression. Sphingosine‐1‐phosphate (S1P), a platelet‐derived lysophospholipid mediator, reportedly regulates osteoimmunology. Here, we investigated how S1P mediates IL‐1β expression in osteoblasts. Our analysis of records from the Gene Expression Omnibus (GEO) database demonstrate higher levels of IL‐1β in patients with RA compared with those with osteoarthritis. Stimulation of osteoblasts with S1P concentration dependently increased mRNA and protein expression of IL‐1β. Elevations in IL‐1β mRNA expression induced by S1P were reduced by the small interfering RNA (siRNA) against the S1P1 receptor. S1P also augmented JAK and STAT3 molecular cascades. We also found that JAK and STAT3 inhibitors and their siRNAs antagonized S1P‐promoted IL‐1β expression. Our results indicate that S1P promotes the expression of IL‐1β in osteoblasts via the S1P1 receptor and the JAK and STAT3 signaling pathways.
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