Autoinhibitory regulation of S100A8/S100A9 alarmin activity locally restricts sterile inflammation
Thomas Vogl, … , Thomas Pap, Johannes Roth
Thomas Vogl, … , Thomas Pap, Johannes Roth
Published April 3, 2018
Citation Information: J Clin Invest. 2018;128(5):1852-1866. https://doi.org/10.1172/JCI89867.
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Research Article Autoimmunity Inflammation

Autoinhibitory regulation of S100A8/S100A9 alarmin activity locally restricts sterile inflammation

Abstract

Autoimmune diseases, such as psoriasis and arthritis, show a patchy distribution of inflammation despite systemic dysregulation of adaptive immunity. Thus, additional tissue-derived signals, such as danger-associated molecular patterns (DAMPs), are indispensable for manifestation of local inflammation. S100A8/S100A9 complexes are the most abundant DAMPs in many autoimmune diseases. However, regulatory mechanisms locally restricting DAMP activities are barely understood. We now unravel for the first time, to our knowledge, a mechanism of autoinhibition in mice and humans restricting S100-DAMP activity to local sites of inflammation. Combining protease degradation, pull-down assays, mass spectrometry, and targeted mutations, we identified specific peptide sequences within the second calcium-binding EF-hands triggering TLR4/MD2-dependent inflammation. These binding sites are free when S100A8/S100A9 heterodimers are released at sites of inflammation. Subsequently, S100A8/S100A9 activities are locally restricted by calcium-induced (S100A8/S100A9)2 tetramer formation hiding the TLR4/MD2-binding site within the tetramer interphase, thus preventing undesirable systemic effects. Loss of this autoinhibitory mechanism in vivo results in TNF-α–driven fatal inflammation, as shown by lack of tetramer formation in crossing S100A9–/– mice with 2 independent TNF-α–transgene mouse strains. Since S100A8/S100A9 is the most abundant DAMP in many inflammatory diseases, specifically blocking the TLR4-binding site of active S100 dimers may represent a promising approach for local suppression of inflammatory diseases, avoiding systemic side effects.

Authors

Thomas Vogl, Athanasios Stratis, Viktor Wixler, Tom Völler, Sumita Thurainayagam, Selina K. Jorch, Stefanie Zenker, Alena Dreiling, Deblina Chakraborty, Mareike Fröhling, Peter Paruzel, Corinna Wehmeyer, Sven Hermann, Olympia Papantonopoulou, Christiane Geyer, Karin Loser, Michael Schäfers, Stephan Ludwig, Monika Stoll, Tomas Leanderson, Joachim L. Schultze, Simone König, Thomas Pap, Johannes Roth

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Figure 6

Proposed structural modeling of S100A9 homodimer interaction with TLR4/MD2.

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Proposed structural modeling of S100A9 homodimer interaction with TLR4/M...
(A) Modeling of the S100A9 peptides 63–79 hTLR4/MD2 complex in ribbon representation showing a close-up view with the putative interaction aa (labeled in gray for S100A9 aa and red for MD2-specific aa) as indicated. The model is based on the crystal structure of the TLR4/MD complex (PDB ID 3FXI), with LPS being omitted and the coordinates of peptides 63–79 being taken from PDB ID: 1IRJ. (B) Model of the potential binding site of S100A9 homodimer and TLR4/MD2 showing a number of contact aa summarized in Table 1. (C) Close-up view of B focused on the S100A9 EF-hand II, MD2 binding region. (B and C) Model is based on the crystal structures of S100A9 (PDB ID: 1IRJ, chains G and H) and of the human TLR4/MD2 complex (A chain of TLR4 and C chain of MD2) with LPS being omitted. The side chains of S100A9 aa are labeled in gray or brown and those of TLR4/MD2 in red. (D) Structural modeling of S100A8/S100A9 heterodimer (PDB ID 1XK4, chains E and G) interaction with TLR4/MD2 confirms identical binding regions for the homodimer S100A9 as well as for the heterodimer. Molecular modeling and graphics preparation were performed using Cluspro and PyMOL software packages.