G protein-coupled receptors serve as mechanosensors for fluid shear stress in neutrophils

Many cells respond to fluid shear stress but in a cell type-specific fashion. Fluid shear stress applied to leukocytes serves to control pseudopod formation, migration, and other functions. Specifically, fresh neutrophils or neutrophilic leukocytes derived from differentiated HL60 cells respond to fluid shear stress by cytoplasmic pseudopod retraction. The membrane elements that sense fluid shear and induce such a specific response are still unknown, however. We hypothesized that membrane receptors may serve as fluid shear sensors. We found that fluid shear decreased the constitutive activity of G protein-coupled receptors (GPCRs). Inhibition of GPCR constitutive activity by inverse agonists abolished fluid shear stress-induced cell area reduction. Among the GPCRs in neutrophils, the formyl peptide receptor (FPR) exhibits relatively high constitutive activity. Undifferentiated HL60 cells that lacked FPR formed few pseudopods and showed no detectable response to fluid shear stress, whereas expression of FPR in undifferentiated HL60 cells caused pseudopod projection and robust pseudopod retraction during fluid shear. FPR small interfering RNA-transfected differentiated HL60 cells exhibited no response to fluid shear stress. These results suggest that GPCRs serve as mechanosensors for fluid shear stress in neutrophils by decreasing its constitutive activity and reducing pseudopod projection.