Shear-Sensitive Regulation of Neutrophil Flow Behavior and Its Potential Impact on Microvascular Blood Flow Dysregulation in Hypercholesterolemia

Abstract

Shear stress-induced pseudopod retraction is an anti-inflammatory measure that minimizes neutrophil activity and is regulated by membrane cholesterol. We tested the hypothesis that a hypercholesterolemic impairment of shear mechanotransduction alters the neutrophil flow behavior leading to microvascular dysfunction. We examined the shear effects on the flow behavior of human leukocytes. When subjected to shearing during cone-plate viscometry, leukocyte suspensions exhibited parallel time-dependent reductions in viscosity and pseudopod activity. Shear-induced reductions in suspension viscosity were attenuated by membrane cholesterol enrichment. We also showed that enhanced pseudopod activity of leukocyte suspensions in 10% hematocrit significantly (P<0.05) raised the flow resistance of microvascular mimics. These results implicate an impaired neutrophil pseudopod retraction response to shear in hypercholesterolemic microvascular dysfunction. We confirmed this using near-infrared diffuse correlation spectroscopy to assess skeletal muscle blood flow regulation in the hindlimbs of mice subjected to reactive hyperemia. Using a custom protocol for the mouse, we extrapolated an adjusted peak flow and time to adjusted peak flow to quantify the early phase of the blood flow recovery response during reactive hyperemia when shear mechanobiology likely has a maximal impact. Compared with mice on normal diet, hypercholesterolemic mice exhibited significantly (P<0.05) reduced adjusted peak flow and prolonged time to adjusted peak flow which correlated (r=0.4 and r=-0.3, respectively) with neutrophil shear responsiveness and were abrogated by neutropenia. These results provide the first evidence that the neutrophils contribute to tissue blood flow autoregulation. Moreover, a deficit in the neutrophil responsiveness to shear may be a feature of hypercholesterolemia-related microvascular dysfunction.