Internalization of Formyl Peptide Receptor in Leukocytes Subject to Fluid Stresses

Abstract

Human leukocytes retract pseudopods under normal physiologic levels of fluid shear stress even in the absence of any other mediator. To gain more detailed understanding of the mechanisms that regulate this cell behavior, we exposed leukocytes to a steady state laminar shear field in a flow chamber and computed the fluid stresses distribution on the surface of individual cells with and without pseudopod. The surface fluid stress distribution on such cell is quite inhomogeneous. We hypothesized that the local fluid stresses on the cell surface serve to regulate pseudopod retraction by way of membrane receptors, especially the formyl peptide receptor (FPR). Comparison of the receptor distribution and the stress distribution over the surface of the cells indicates that the membrane fluid stress alone is not directly correlated with the extent of regional pseudopod retraction, giving further support to the hypothesis that membrane receptors are involved in the mechanotransduction of leukocytes. We observed that after exposure to fluid shear the FPR was internalized to a small intracellular compartment. This internalization appears to be independent of the original location of the receptor on the surface of the cell and the FPR appears to be more derived from multiple locations on the cell, with both higher and lower fluid stresses. The evidence suggests that FPR involvement in the pseudopod-retraction process is not limited to cell surface regions with the highest fluid shear stress, but rather a more global occurrence over the majority of the cell membrane.

Linking the Pathobiology of Hypercholesterolemia with the Neutrophil Mechanotransduction

“…In the case of GPCRs, exposing migrating neutrophil-like cells to parallel plate flow redistributes surface-associated FPRs to a perinuclear compartment in the cytosol [135]. These results suggest that internalization of FPRs under fluid shear stimulation leads to pseudopod retraction by counteracting their constitutive activity which drives pseudopod extension.…”

Fluid Dynamics Analysis of a Novel Micropatterned Cell Bioreactor

“…While the above numerical calculations are based on the orientation of inlet velocity vector being normal to entrance section, as used in a series of flow chambers, 4,11,16,31,40 different orientations of inlet velocity vector have also been applied in other flow chambers. 9,20,27 In this article, the impact of two alternative orientations of inlet velocity vector on flow field has been tested: one is 45°relative to height-direction in x-z plane (Fig.…”

“…Flow chamber is a well-defined in vitro model to mimic the physiological conditions for elucidating the effect of biofluid flow on cellular responses such as cell proliferation, 17,33 apoptosis, 24 differentiation 1,28 migration, 35 adhesion, 29 cell interaction in co-culture, 5 and intra/intercellular signalings. 16,31,40 Flow chamber also serves as a cell/tissue bioreactor in space cell biology to maintain cellular metabolism under microgravity, 32 since the refreshment of culture medium, a conventional procedure under ground-based conditions, becomes complicated and hard to perform in space and should be automatically done via continuous perfusion in a closedloop system. In the past decades, different types of flow chambers or flow-based bioreactors have been developed mainly with parallel-plate flow approach, where cells are seeded on the bottom plate and grown to a confluent monolayer while the medium is driven to flow over cells providing sufficient nutrient supply and mass transportation.…”

“…In previous studies, a few fluid mechanics models were proposed to predict the flow field at the vicinity of curved endothelial cell monolayer in blood vessel, 15,22 and the wall shear stress was found to vary more than 80% across the chamber because of the so-called end effects. 40 Moreover, growing cells are highly sensitive to the alterations of hydrodynamic parameters, for example, alkaline phosphatase activity increases dramatically with shear stress in engineered bone tissue, 3,13,14,16,19,31,40 and intracellular process and cell body respond differentially to various mechanical loadings. 21 Thus, fluid dynamics analysis is a prerequisite to monitor the hydrodynamic parameters, such as flow flux, velocity, and shear stress, and to understand the mechanism of cell mechanotransduction.…”

“…8,15,18,20 For example, intracellular calcium response to shear flow of isolated osteoblasts on micropatterned islands was found to be quite different from that of the osteoblasts in a confluent monolayer. 16,31,40 The shape and size of hydrophilic island designed to confine the spreading configuration and contact area of a cell resulted in distinct phenotypes in apoptosis, differentiation, and proliferation of mesenchymal stem cells. 7 Microfabricating technique with micropatterned cells is especially beneficial for a cell bioreactor used in space life science where the impact of shear flow from continuous perfusion is coupled with the effect of microgravity.…”