Hjem
Klinisk institutt 2

Midtveisevaluering - Brith Bergum

Hovedinnhold

Abstract

Post translational modifications are a natural way of increasing the protein repertoire, however, some modifications result in the impairment or the loss of a proteins function. Protein carbamylation is a cyanate dependent, non-enzymatic conversion of lysine residues and N terminal amino groups to homocitrulline, and α-carbamyl amino acids. Carbamylation introduced a neutral residue that can result in loss of protein function. Carbamylation occur during the spontaneous decomposition of urea, or by the oxidation of thiocyanate by the neutrophil heme enzyme myeloperoxidase during inflammation.

In our first project we investigated the presence of antibodies against carbamylated proteins in serum from patients with primary Sjögrens Syndrome and healthy controls. We also investigated the prognostic value of anti-CarP antibodies in pSS. Our results show that the prevalence of anti-CarP antibodies are significantly higher in pSS patients that in healthy controls (26.9% vs 6.8%, respectively).  We further investigated the association between clinical manifestations and anti-CarP seropositivity, and found that anti-CarP positivity is significantly associated with higher focus score, presence of GC-like structures, and reduced tear flow. Anti-CarP positive patients were also found to have a higher titer of rheumatoid factor antibodies, increased levels of  β2-microglobulin, IgG and IgM. Anti-CarP, together with cofounders RF antinuclear antibodies, SSA and SSB, predict an increase in the average focus score. Patients with GC-like structures in the minor salivary glands had also a higher level of anti-CarP antibodies. In conclusion, we found that anti-CarP antibodies are generally detected in pSS patients with a more severe disease phenotype. The presence of anti-CarP could also predict the clinical outcome of pSS. Once validated, anti-CarP antibodies in serum could be used to determine disease severity, and identify patients are risk of developing comorbidities.

In project two we investigated the effect of carbamylation on fibrinogen cleavage by thombin, fibrin polymerization and crosslinking by FXIIIa that altogether determine fibrin clot structure and stability.  Our results reveal that carbamylation does not affect thrombin cleavage but alters fibrin polymerization kinetics and impairs cross-linking as well as plasmin-catalyzed clot degradation. Carbamylated fibrin clots showed reduced fiber size and porosity which is associated with decreased mechanical stability. Taken together, carbamylation of fibrinogen is linked to aberrant fibrin clot formation and might be involved in hemostatic disorders associated with chronic inflammatory diseases. While total amounts of fibrinopeptides released by thrombin cleavage of carbamylated and unmodified fibrinogen were comparable, carbamylation resulted in generation of N-terminally carbamylated fibrinopeptide A which was found to be a strong chemoattractant potentially promoting the recruitment of inflammatory cells to sites of fibrin(ogen) turnover.