Date of Award

1-1-2010

Embargo Period

1-1-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology and Immunology

College

College of Graduate Studies

First Advisor

Gary Gilkeson

Second Advisor

Lina Obeid

Third Advisor

James Oates

Fourth Advisor

James Cook

Fifth Advisor

Maria Trojanowska

Abstract

Patients with rheumatoid arthritis (RA) have an over production of pro-inflammatory cytokines, especially TNFα, causing joint erosions and disability in untreated patients. Targeted therapies have had some success but are not without side effects and limitations; additionally, patients become refractory to treatment, and are obligated to use a combination of therapies. Therefore, new therapeutics are necessary. One novel target is sphingolipids, specifically sphingosine kinase 1 (SphK1). Previous research has demonstrated that knockdown/knockout of SphK1 influences the production of inflammatory mediators (i.e. COX-2 and PGE2) in vitro and in vivo. Since sphingosine 1 phosphate (S1P) receptors are upregulated in RA synovium, we propose that modulation of SphK1 will affect disease progression in an hTNFα-induced model of arthritis. With the use of SphK1 activity deficient (SphK1-/-) mice, we investigated lack of SphK1 in arthritis development in vivo. In mice overexpressing hTNFα in the absence of SphK1 (hTNF/SphK1-/-), we observed decreased arthritis score and decreased inflammatory infiltrates and joint erosions in the ankle joints. Additionally, there was a significant decrease in IL-23R+ cells in joints, but an increase in the number of T and B-cells in the spleen of hTNF/SphK1-/- mice. Differential gene expression of hTNF/SphK1-/- compared to control mice revealed an upregulation of IL-6 and SOCS3 transcript levels confirmed by RT-PCR. Upon investigation of active signaling cascades, less COX-2 and mature osteoclasts were found in the ankle joint of hTNF/SphK1-/- mice, yet no differences in MMP-9 production were detected. Since FLS can contribute to joint destruction in RA, we investigated which pathways affected in human and murine FLS upon removal of SphK. Human OA and RA FLS treated with a SphK inhibitor after stimulation with hTNFα had a significant decrease in IL-6 and PGE2 production as well as a decrease in activated ERK1/2. SphK1-/- FLS stimulated with mTNFα had a significant decrease in MMP-1a production as well as a decrease in ERK1/2 and STAT3 activation. Therefore, these data support the hypothesis that genetic and pharmacologic inhibition of SphK can affect inflammation and should be considered a potential therapeutic for RA.

Rights

All rights reserved. Copyright is held by the author.

Download

Share

COinS