Sphingosine kinase 1/sphingosine 1-phosphate/sphingosine 1-phosphate receptor 1 pathway: A novel target of geniposide to inhibit angiogenesis

Rheumatoid arthritis (RA) is a common inflammatory autoimmune disease characterized by the formation of joint synovitis and pannus. Sphingosine 1-phosphate (S1P) is an important mediator related to angiogenesis, inflammation and autoimmunity. As Geniposide (GE) has potent immuno-modulation function, we investigated the effects on the dynamic balance of angiogenesis-related factors and Sphingosine kinase 1 (SphK1)-S1P-S1P receptor 1 (S1PR1) signal transduction in adjuvant-induced arthritis (AA) rats. The model evaluation was performed from paw swelling degree, arthritis index and movement score. The immunohistochemistry and enzyme-linked immunosorbent assay were used to study the microvascular density (MVD) and pro/anti-angiogenic factors levels. The cell viability was examined by cell counting kit-8 assay. SphK1, S1PR1 mRNA and protein levels in fibroblast-like synoviocytes (FLSs) were detected by quantitative real-time polymerase chain reaction and Western blotting. The results showed that GE can apparently suppressed the inflammatory pathological status. The arthritis index, paw swelling and MVD of AA rats were decreased with dose dependence (⁎P < 0.05, ⁎⁎P < 0.01). In addition, GE can reduce the secretion of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), promote the secretion of endostatin (ES) and inhibit excessive proliferation of FLSs (⁎P < 0.05, ⁎⁎P < 0.01). Importantly, GE can significantly inhibit the activity of SphK1, the level of S1P and the expression of SphK1 and S1PR1 in FLSs (⁎P < 0.05, ⁎⁎P < 0.01). It indicated that GE reduces the activity of SphK1 by restoring the dynamic balance between pro/anti-angiogenic factors, thereby interfering with SphK1-S1P-S1PR1 signal transduction, reducing the formation of synovial microvessels and exerting anti-angiogenesis effect of RA.