The Cycling of Intracellular Calcium Released in Response to Fluid Shear Stress Is Critical for Migration-Associated Actin Reorganization in Eosinophils.

Kiho Son,Amer Hussain,Roma Sehmi,Luke Janssen

doi:10.3390/cells10010157

Abstract

The magnitude of eosinophil mobilization into respiratory tissues drives the severity of inflammation in several airway diseases. In classical models of leukocyte extravasation, surface integrins undergo conformational switches to high-affinity states via chemokine binding activation. Recently, we learned that eosinophil integrins possess mechanosensitive properties that detect fluid shear stress, which alone was sufficient to induce activation. This mechanical stimulus triggered intracellular calcium release and hallmark migration-associated cytoskeletal reorganization including flattening for increased cell–substratum contact area and pseudopodia formation. The present study utilized confocal fluorescence microscopy to investigate the effects of pharmacological inhibitors to calcium signaling and actin polymerization pathways on shear stress-induced migration in vitro. Morphological changes (cell elongation, membrane protrusions) succeeded the calcium flux in untreated eosinophils within 2 min, suggesting that calcium signaling was upstream of actin cytoskeleton rearrangement. The inhibition of ryanodine receptors and endomembrane Ca2+-ATPases corroborated this idea, indicated by a significant increase in time between the calcium spike and actin polymerization. The impact of the temporal link is evident as the capacity of treated eosinophils to move across fibronectin-coated surfaces was significantly hampered relative to untreated eosinophils. Furthermore, we determined that the nature of cellular motility in response to fluid shear stress was nondirectional.

Highlights

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Summary

Introduction

As the positive correlation between eosinophil accumulation in pulmonary tissues and disease severity has been ascertained [4], the past decade has seen the development of several biologics that target interleukin-5 (IL-5), a TH 2 cytokine largely responsible for the mobilization, recruitment, and survival of eosinophils at sites of inflammation [5] Some of these anti-IL-5 clinical trials have reported effective reduction and/or depletion of eosinophils from the blood and airways of severe asthmatic patients [5,6], it has become a point of interest to investigate other factors such as epithelial cell-derived cytokines (IL-25, TSLP) and IL-13-secreting type 2 innate lymphoid cells (ILC2 ) that may contribute significantly to eosinophil migration [5,7,8]. In vivo pre-activation and/or priming of the cells mediated by increased IL-5 levels in asthmatics result in intermediate-activated integrin conformations displayed on the surface [9], resulting in augmented integrin activation; extravasation from circulation; and an overaccumulation of eosinophil populations in respiratory tissues, oftentimes leading to subsequent airway inflammation and obstruction

Methods

Results

Conclusion