Eicosanoids and Proteomics in Rheumatic Diseases

ROLE OF THE INDUCED PGE2 PATHWAY IN CHRONIC INFLAMMATION

Microsomal prostaglandin E synthase (mPGES1) catalyzes the formation of prostaglandin (PG) E2 from cyclooxygenase derived PGH2. This enzyme is induced during inflammation and evidently linked to inflammatory conditions like joint inflammation (arthritis) and fever but also to other conditions such as stroke, cancer and breathing dysfunctions. A major goal in our group is to further characterize this enzyme on its molecular level as well as its role in diseases. In collaboration with NovaSAID we are also investigating inhibitors of mPGES1, which we believe can become a new generation anti-inflammatory drug with fewer side effects than traditional NSAIDs.
Prostaglandins belong to the family of eicosanoids which consists of fatty acid derived biologically potent metabolites. The two major pathways are the 5-lipoxygenase (5-LO) pathway, which produces leukotrienes and the cyclooxygenase (Cox) -1/2 pathway forming prostaglandins. The widely used non-steroidal anti-inflammatory drugs (NSAIDs) exert their actions by targeting Cox-1/Cox-2 with different specificities. There are several prostaglandins produced from Cox-derived PGH2 catalyzed by specific terminal PG synthases such as prostacyclin (PGI2), thromboxane (TxA2), PGF2a, PGE2 and PGD2. Through their respective receptors, these metabolites mediate biological effects like platelet aggregation (TxA2), vasodilation (PGI2) or inflammation (PGE2). There are three described enzymes that catalyze the formation of PGE2 from PGH2. Of these, only microsomal prostaglandin E synthase-1 (mPGES1) is inducible and studies using knock-out mice have shown that mPGES1 inhibition can be useful treating arthritis, fever, anorexia, atherosclerosis, stroke and cancer. Notably, unprovoked these mice are healthy [1].

In collaboration with NovaSAID AB, we are currently investigating the anti-inflammatory effects of mPGES1 inhibitors in various in vivo models of experimental arthritis as well as in relevant cellular in vitro systems. In patients, we have characterized the PGE2 pathway in rheumatoid arthritis and myositis and investigated the effect of anti-TNFa blockers or orally administrated corticosteroids on the expression of respective enzymes. Interestingly, the PGE2 pathway remains overexpressed in the synovial membrane and in muscles despite such treatments [2] [3] ,suggesting that PGE2 may still be formed and thus able to sustain inflammation. We are also studying the structure-function relationships of this enzyme and recently we described the 3D structure of mPGES1 [4]. We have now intensified our work characterizing the enzyme for better understanding of the mechanism of catalysis and to define substrates and inhibitors binding surfaces. This part of the project will provide useful information optimizing lead compounds and to understand their mechanisms of action.

PROTEOMICS
We are also interested in studying rheumatic diseases by means of proteomics. We have recently described a quantitative mass-spectrometry based method allowing for relative quantification of both soluble and integral membrane proteins [5]. We are now aiming for defining antigens for autoantibodies in RA, myositis and SLE. Work is also in progress for identification of peptides bound to the major histocompatibility complex (HLA-D) isolated from antigen presenting cells in the affected joints. Characterization of autoantigens will provide better understanding of autoimmune diseases and may open for the development of new treatment options.