Cytokine Biology Research

Professor Carolyn Geczy

This laboratory investigates novel mechanisms of inflammation. The major thrust of the research during 2008 was in three main areas, some of which overlap. Only key findings are described below.
(i) Characterising the roles of inflammation-associated S100 proteins, S100A8, S100A9 and S100A12, how they are regulated, and structure-function studies to determine functionally-active domains in these proteins, and how divalent cations or post-translational modifications modify functions.
(ii) Regulation of mast cell function
(iii) Mechanisms that regulate thrombus formation.

We described a new mechanism that reduces inflammation and may modulate blood flow in inflamed vessels. We found that S100A8 and S100A9 rapidly scavenge nitric oxide (NO). Because S-nitrosylation is a process that is precisely regulated by the local environment around particular cysteine residues and by structure, few proteins are targets of this modification. This was the first demonstration of S-nitrosylation of a protein generated as a consequence of activation events in acute and chronic inflammation. It is important because S100A8-SNO is a relatively stable NO adduct and it can transnitrosylate hemoglobin, indicating a role in blood vessel homeostasis and NO transport, particularly as S100A8 and S100A9 are expressed in neovessels in vivo, and are induced by proinflammatory mediators in microvascular endothelial cells in vitro. S100A8-SNO also suppressed mast-cell activation and leukocyte adhesion and extravasation in the microcirculation.
We identified new functions for S100A12. We find it expressed by macrophages and eosinophils in human asthmatic lung, but not normal lung, and showed that S100A12 can activate mast cells and potentiate the degranulation induced by conventional activation by IgE and allergen. Because of its elevated expression in non-allergic inflammatory diseases, we propose that S100A12 may initiate inflammation by activating mast cells, and propagate this by inducing of key mediators that influence leukocyte migration and endothelial cell adhesion. Moreover, in addition to S100A12’s ability to provoke monocyte migration, we found that it also sequesters mast cells in vivo. We mapped the active domain of this protein and using mutational analysis identified the amino acids that are essential for its chemotactic activity, and its ability to activate/recruit mast cells in vivo. These are the first studies of their kind and describe a potential amplification pathway in asthma and innate immunity that may represent a key therapeutic target, and further development is underway.

Using reagents that we developed to measure levels of S100s in human blood serum and other sources, we found that sputum levels of S100A12 represent a potential marker of eosinophilic asthma, that serum and mucosal S100A8/S100A9 and S100A12, are elevated at diagnosis in children with inflammatory bowel disease and are expressed in the inflamed gastric mucosa of Helicobacter pylori-infected children.
We identified new ways in which human monocytes are activated to express tissue factor (TF) that activates blood coagulation and initiates thrombus formation in cardiovascular disease. We found that the acute-phase reactant, C-reactive protein, contributes to the hypercoagulable state in patients with coronary artery disease. We also initiated a new area of research into serum amyloid A (SAA), another acute phase reactant and important in the pathogenesis of Alzheimer’s disease, rheumatoid arthritis and cardiovascular disease where it deposits in lesions and when modified, promotes progression. We found that SAA potently and rapidly induces monocyte/macrophage TF, and can potentiate coagulation within 2 hours of stimulation. Some of the signaling pathways involved were characterized. We found SAA rapidly induced numerous proinflammatory genes, particularly TNF, IL-6 and IL-1. We showed that SAA is a prothrombotic and proinflammatory mediator in acute coronary syndromes. We are currently investigating ways in which SAA regulates endothelial cell function and how proinflammatory, prothrombotic effects of SAA may be suppressed.