Session Type: Abstract Submissions
Session Time: 5:15PM-5:45PM
Methods: Oligomers of recombinant as well as native S100A12 were isolated from serum samples and freshly isolated human granulocytes after cross-linking. Eluted S100A12 oligomers from patients’ serum were further applied to size exclusion chromatography. TLR4/MD2-binding assay and surface plasmon resonance assays were performed to investigate ligand-receptor interactions. Monocytic cells lines and primary human monocytes were used for stimulation experiments using defined S100A12 complexes.
Results: Here we demonstrate that binding and signaling of S100A12 through TLR4 is dependent on the protein’s arrangement into a hexameric quarternary structure. Hexameric S100A12 triggers pro-inflammatory cytokine production by human monocytes and TLR4-expressing cell lines, which is sensitive to TLR4 and CD14 but not MD2 blockade. Importantly, the arrangement of S100A12 into its hexameric structure appears to depend on extracellular Ca2+ and Zn2+ion strengths. While S100A12-hexamers are not detectable inside human granulocytes, these protein complexes can be found in and isolated from human serum specimens, particularly sera obtained from patients with auto-inflammatory disease.
Conclusion: Our data demonstrate that extracellular ion levels can serve as a molecular switch rendering a protein with non-inflammatory cell-intrinsic function into a pro-inflammatory DAMP. Hexameric S100A12 complexes are responsible for the pro-inflammatory functions of the protein. A detection system specifically quantifying its hexameric forms in human serum will improve the performance of S100A12 biomarker assays. Specific blockade of hexameric S100A12 may provide a novel therapeutic target.
Disclosures: The authors declare no conflict of interest. The described findings and principles are part of an international patent application (WO2016/178154A1).
To cite this abstract in AMA style:Kessel C, Fuehner S, Zimmermann B, Holzinger D, Wittkowski H, Hinze C, Foell D. An extracellular ionic milieu renders human granulocytic S100A12 into a pro-inflammatory TLR4-binding alarmin [abstract]. Arthritis Rheumatol. 2017; 69 (suppl 4). http://acrabstracts.org/abstract/an-extracellular-ionic-milieu-renders-human-granulocytic-s100a12-into-a-pro-inflammatory-tlr4-binding-alarmin/. Accessed August 16, 2017.
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