ABSTRACT
S100A8/A9 is an endogenous alarmin secreted by myeloid cells during many acute and chronic inflammatory disorders. Despite increasing evidence of the proinflammatory effects of extracellular S100A8/A9, little is known about its intracellular function. Here, we show that cytosolic S100A8/A9 is indispensable for neutrophil post-arrest modifications during outside-in signaling under flow conditions in vitro and neutrophil recruitment in vivo, independent of its extracellular functions. Mechanistically, genetic deletion of S100A9 in mice (Mrp14−/−, functional S100a8/a9−/−) caused dysregulated Ca2+ signatures in activated neutrophils resulting in reduced Ca2+ availability at the formed LFA-1/F-actin clusters with defective β2 integrin outside-in signaling during post-arrest modifications. Consequently, we observed impaired cytoskeletal rearrangement, cell polarization and spreading, as well as cell protrusion formation in Mrp14−/− compared to WT neutrophils, making Mrp14−/− cells more susceptible to detach under flow, thereby preventing efficient neutrophil recruitment and extravasation into inflamed tissue.
One-sentence summary intracellular S100A8/A9 is indispensable for firm leukocyte adhesion under flow
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
New text added for revision in red (Result, Discussion, Figure Legend and Method sections); Fig.3I revised and updated with more data and changed representative images (western blot); Fig.4 revised and result section on Fig.4 updated to add colocalization analysis between S100A8/A9 and LFA-1 nanoclusters (Fig.4K and 4L new). Method section, figure legend and discussion for Fig.4K and 4L updated; Fig.5A and 5D updated to add colored line legend; Supplementary Fig. 3e and 3G updated to add colored line legend; Gene locus name (S100a8/a9) changed to lowercase letters in abstract; Supplemental files updated and Supplementary Videos added; Reference list updated (nr.#19 is now published)
