Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.


Absence of Sphingosine Kinase 1 Alters Erosions in TNF-Alpha Induced Arthritis

Baker,  DeAnna A., Obeid,  Lina M., Gilkeson,  GS

Purpose:

Sphingolipids are constituents of the plasma membrane. Variations in their cellular levels lead to alterations of cellular functions. Sphingosine 1 phosphate (S1P) in vitro is required for TNFa induced production of COX-2 and PGE2. Additionally, stimulation with TNFa and S1P together leads to higher production of COX-2 and PGE2 than either alone. Both sphingosine kinase (SphK) 1 and 2 are upregulated in the rheumatoid synovium compared to osteoarthritis synovium. S1P1R (EDG1), one of the receptors for S1P, is also upregulated in the joints of rheumatoid arthritis patients. Fibroblast-like synoviocytes (FLS), found in the synovial lining, proliferate in response to proinflammatory cytokines and produce COX-2 and PGE2 in response to TNFa and S1P. We hypothesized that S1P, induced by TNFa, is a critical mediator of inflammation and joint damage in the rheumatoid joint. The following experiments were performed to test this hypothesis

Method:

Transgenic hTNFa mice were crossed with SphK1-/- mice and genotyped by PCR. Arthritis in these mice develops independent of antigen, T cells or B cells. The mice were observed weekly for disease activity, while CT images and microarray analysis were used to evaluate disease activity in the joint and evaluate genetic profiles respectively. Mouse synoviocytes were isolated from the knee joints of WT and SphK1-/- mice, cultured, and stimulated with TNFa. OA and RA human synoviocytes were cultured, and stimulated with hTNFa.

Results:

hTNF/Sphk1-/- mice (n=15) had significantly decreased clinical joint disease compared to hTNF/SphK1+/+ mice (n=18), with average arthritis scores of 1+/-0.5 vs. 5+/- 1.2 respectively at 5 months (based on joint swelling and deformity). An erosion Index, measured quantitatively from 3D CT images of the ankles was significantly decreased in hTNF/SphK1-/- mice at 4 and 5 months, with a 2 fold decrease in erosions in hTNF/SphK1-/- vs. hTNF/SphK1+/+ mice. Microarray analysis of ankle joint synovium, with RT-PCR confirmation, demonstrated significant modulation of a cluster of genes regulated by SOCS3 in hTNF/SphK1-/- mice compared to hTNF/SphK1+/+ mice. Synoviocytes from SphK1-/- mice, stimulated with TNFa, produced significantly less IL-6 and PGE2 than synoviocytes from WT mice. Similarly, human RA synoviocytes stimulated with TNFa and treated with a specific SphK inhibitor produced significantly less IL-6 and PGE2 than cells treated with TNFa alone.

Conclusion:

Genetic deletion of SphK1 significantly decreased the severity of hTNFa induced arthritis, decreased erosions and led to upregulation of SOCS3 with impact on expression of SOCS3 related genes. Lack of SphK1 resulted in decreased PGE2 and IL6 production by mouse and human synoviocytes in response to TNFa. These data indicate that S1P plays a key role in TNFa induced joint inflammation and erosions and is a potential target for therapeutic intervention in inflammatory arthritis.

To cite this abstract, please use the following information:
Baker, DeAnna A., Obeid, Lina M., Gilkeson, GS; Absence of Sphingosine Kinase 1 Alters Erosions in TNF-Alpha Induced Arthritis [abstract]. Arthritis Rheum 2009;60 Suppl 10 :1208
DOI: 10.1002/art.26282

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2009 ACR/ARHP