Abstract
Purpose/Objective: Sphingosine kinase (SPHKs), SphK1 and SphK2, have been identified to phosphorylate sphingosine into sphingosine-1- phosphate (S1P). They are involved in a wide variety of cellular responses. S1P acts via S1P Receptors, S1PR1, S1PR2, S1PR3, S1PR4 and S1PR5, all of which can be bound and activated specifically by S1P. A defect either in S1P signalling or S1PRs has been associated with many pathologies. Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by high levels of proinflammatory cytokine production. Elevated SPHK1, S1P, and S1P1 have been reported in RA synovium. S1P signalling via S1P1 promotes synoviocyte proliferation, increases COX-2 expression and prostaglandin E2 production. This study comprehensively evaluated expression of SPHK1/2 and S1PRs in RA patients compare to healthy controls (HC) and osteoarthritis (OA) in peripheral blood (PB) and synovial tissues, respectively.
Materials and methods: mRNA and protein expression of SPHK1/2 and SIPRs were examined in neutrophils, monocytes and T lymphocytes of peripheral blood of 10 HC and RA patients, who met the diagnostic criteria of 2010 ARC / EULAR by QPCR and FACS, respectively. Competitive ELISA assessed SIP in serum of RA patients with remission and relapse and HC. We also performed SPHK 1/2 and SIPRs immunohistochemistry in synovial tissue from 4 RA/ OA patients.
Results: S1P was three times high in RA than those observed in HC, also was statistically higher in RA patient with relapse than remission. Intracellular expression of hSPHK1 in RA patients, with opposed to HC, was up regulated 1.4-folds in monocytes and T- lymphocytes with significance expression in CD4T cells. hS1P1 and hS1P3 exhibited a similar expression were up-regulated in neutrophils, while, hS1P5 was statistical high in T cells. In contrast, hS1P4 was down regulated in all sorted cells particularly in CD4T cells. As opposed to OA synovial tissue, RA synovial tissues were strongly positive for hSPHK1 and hS1P1, 3 expressions. Quantitative analysis showed, SPHK1 and hS1P3 are expressed in lining, sub lining and vascular endothelial layer, while hS1P1 expressed mainly in lining and sub lining layers of the RA synovial tissue compared with OA. Conclusions: These results suggest that SPHKs/S1P and its S1PRs might play a role in RA pathogenesis. The clinical significance of S1P as a biomarker for disease activity deserves further attention.