Cytosolic S100A8/A9 Regulates Calcium Signaling and Cytoskeletal Dynamics to Promote Neutrophil Recruitment During Inflammation

Core Concepts

Cytosolic S100A8/A9 is indispensable for supplying localized calcium at LFA-1 adhesion clusters, thereby orchestrating cytoskeletal rearrangements critical for neutrophil recruitment and extravasation during inflammation.

Abstract

The study investigates the intracellular functions of the calcium-binding protein S100A8/A9 in neutrophil recruitment during inflammation. Key findings:

Cytosolic S100A8/A9 is crucial for neutrophil adhesion and extravasation in vivo, independent of its extracellular functions.

Loss of cytosolic S100A8/A9 impairs neutrophil spreading, crawling, and post-arrest modifications under flow conditions, without affecting initial β2 integrin activation.

Mechanistically, cytosolic S100A8/A9 regulates the formation and spatial clustering of LFA-1 adhesion complexes, and ensures high local calcium concentrations within these clusters.

The reduced calcium availability at LFA-1 adhesion sites in the absence of S100A8/A9 leads to impaired cytoskeletal rearrangements, including reduced F-actin polymerization, which compromises neutrophil adhesion strengthening and resistance to shear stress.

Cytosolic S100A8/A9 is dispensable for chemokine-induced calcium release from the ER and the initial phase of store-operated calcium entry, but plays a role in stabilizing calcium signaling dynamics within the cell.

In summary, the study uncovers a critical intracellular function of S100A8/A9 in regulating calcium-dependent cytoskeletal dynamics at the site of neutrophil adhesion, which is essential for efficient neutrophil recruitment and extravasation during inflammation.

Stats

Approximately 1-2% of the total cytosolic S100A8/A9 content is secreted upon E-selectin stimulation of neutrophils.
Mrp14-/- mice (S100A8/A9 deficient) show reduced number of adherent neutrophils in inflamed cremaster muscle venules compared to WT mice.
Mrp14-/- neutrophils display impaired spreading, polarization, and protrusion formation under flow conditions on ICAM-1 and CXCL1 coated surfaces.
Mrp14-/- neutrophils show reduced phosphorylation of the focal adhesion proteins Pyk2 and paxillin upon CXCL1 stimulation.
Mrp14-/- neutrophils form fewer LFA-1 nanoclusters and have lower calcium levels within these clusters compared to WT neutrophils.
Mrp14-/- neutrophils exhibit increased frequency and shorter duration of calcium flickers compared to WT neutrophils.

Quotes

"Cytosolic S100A8/A9 is indispensable for firm leukocyte adhesion under flow."
"Cytosolic S100A8/A9 drives neutrophil cytoskeletal rearrangement by regulating LFA-1 nanocluster formation and Ca2+ availability within the clusters."
"Cytosolic S100A8/A9 is crucial for supplying localized calcium at LFA-1 adhesion clusters, thereby orchestrating cytoskeletal rearrangements critical for neutrophil recruitment and extravasation during inflammation."

Key Insights Distilled From

Cytosolic S100A8/A9 promotes Ca2+ supply at LFA-1 adhesion clusters during neutrophil recruitment

by Napoli,M., I... at www.biorxiv.org 04-22-2024

https://www.biorxiv.org/content/10.1101/2024.04.16.589738v1

Deeper Inquiries

How might the insights from this study on the intracellular functions of S100A8/A9 in neutrophils be leveraged to develop novel therapeutic strategies for inflammatory disorders?

The study sheds light on the crucial role of cytosolic S100A8/A9 in regulating calcium supply at LFA-1 adhesion clusters during neutrophil recruitment. This insight could be leveraged to develop novel therapeutic strategies for inflammatory disorders by targeting the intracellular functions of S100A8/A9. For example, modulating the levels or activity of S100A8/A9 within neutrophils could potentially regulate the calcium-dependent post-arrest modifications essential for successful neutrophil recruitment. By understanding the specific mechanisms by which S100A8/A9 influences cytoskeletal dynamics and calcium signaling, researchers could develop targeted therapies that aim to modulate these pathways to control excessive neutrophil recruitment in inflammatory disorders.

What other intracellular signaling pathways or protein interactions might S100A8/A9 be involved in, beyond the regulation of calcium and cytoskeletal dynamics?

Beyond its role in regulating calcium and cytoskeletal dynamics, S100A8/A9 may be involved in various other intracellular signaling pathways and protein interactions. For instance, S100A8/A9 has been implicated in modulating inflammatory responses through interactions with receptors like TLR4 and RAGE. Additionally, S100A8/A9 has been shown to influence microtubule stabilization, vimentin interactions, and F-actin dynamics in different cell types. It may also play a role in regulating cell migration, adhesion, and polarization through interactions with cytoskeletal proteins and signaling molecules. Further research is needed to explore the full extent of S100A8/A9's intracellular functions and its involvement in various signaling pathways beyond calcium and cytoskeletal regulation.

Could the dysregulation of intracellular S100A8/A9 functions contribute to the pathogenesis of autoimmune or other chronic inflammatory diseases characterized by aberrant neutrophil recruitment?

Dysregulation of intracellular S100A8/A9 functions could indeed contribute to the pathogenesis of autoimmune or other chronic inflammatory diseases characterized by aberrant neutrophil recruitment. Given its role in regulating calcium signaling, cytoskeletal dynamics, and integrin activation, aberrant S100A8/A9 function could disrupt the normal processes of neutrophil recruitment and migration. This disruption could lead to excessive or prolonged neutrophil infiltration into inflamed tissues, contributing to tissue damage and chronic inflammation. Understanding how dysregulation of S100A8/A9 impacts these processes could provide insights into the pathogenesis of autoimmune and chronic inflammatory diseases and potentially offer new therapeutic targets for intervention.