Analysis and identification of citrullinated proteins in Rheumatoid Arthritis and their role in smoking

Hanna Eriksson, Johan Lengqvist, Per-Johan Jakobsson.

Unit of Rheumatology: Lars Klareskog Unit of Respiratory: Medicine: Johan Grunewald, Anders Eklund

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterised by synovial joint inflammation and pannus formation that leads to degradation of cartilage and the underlying bone. The pathogenesis of the disease is poorly understood. It affects 0.5-1 % of the population worldwide, predominately women.
Recent studies, have found autoantibodies against proteins containing the non-standard amino acid citrulline to be strongly associated with RA. These autoantibodies can be detected in up to 80 % of patients with RA with a specificity of nearly 98 %. Among healthy individuals less than 2 % have citrulline specific antibodies. They are today one of the best markers to predict and diagnose arthritis. The existence of citrulline reactive antibodies has been coupled to more active and severe disease. Why these antibodies arise and what role the citrullinated proteins play in arthritis is unknown.
Citrullination is a calcium dependent deimination of arginine residues catalysed by the enzyme peptidylarginine deiminase. Autoantibodies against citrullinated vimentin, filaggrin, alpha enolase, collagen type II and fibrin/fibrinogen have been associated with RA. It is not yet known if any of these proteins is the citrullinated RA-specific autoantigen.

Smoking increases the risk for developing arthritis especially in genetically predisposed individuals. In a study from our laboratory, citrullinated proteins have been detected in cells from bronchoalveolar lavage fluid (BAL) fluid from smokers but not from non-smokers by immunohistochemistry. It is possible that smoking or perhaps inflammation induces post-translational modifications of arginine to citrulline in lungs that may in some individuals trigger a specific immunity to citrullinated proteins. This immune reaction may subsequently contribute to chronic arthritis.

The aim of this project is to identify these citrullinated molecules and analyse citrullinated proteins in RA tissues. Information about what proteins are citrullinated and where, may elucidate the origin and role of them as well as of citrulline specific antibodies in arthritis. Analyses are being performed using one and two-dimensional electrophoresis and mass spectrometry. Citrullinated proteins are detected with citrulline-specific antibodies.

Last updated: 2008-01-10