Intermittent rolling is a defect of the extravasation cascade caused by Myosin1e-deficiency in neutrophils

Significance Myosin1e is a protein regulating actin cytoskeleton functions, which has not been studied in the context of neutrophil recruitment during inflammation. Using intravital microscopy of inflamed tissue in WT and myosin1e-deficient mice, we show that absence of myosin1e inhibits neutrophil migration out of the blood stream into inflamed tissue. Neutrophils lacking myosin1e show defective actin cytoskeleton polymerization, integrin activation, and aberrant rolling behavior termed “intermittent rolling,” suggesting that myosin1e is important for strengthening adhesive interactions of neutrophils with the vascular endothelium. Our findings are significant as they highlight myosin1e as a critical regulator of inflammatory neutrophil recruitment in vivo. Thus, myosin1e could be a therapeutic target for chronic inflammatory diseases. Neutrophil extravasation is a migratory event in response to inflammation that depends on cytoskeletal dynamics regulated by myosins. Myosin-1e (Myo1e) is a long-tailed class-I myosin that has not yet been studied in the context of neutrophil–endothelial interactions and neutrophil extravasation. Intravital microscopy of TNFα-inflamed cremaster muscles in Myo1e-deficient mice revealed that Myo1e is required for efficient neutrophil extravasation. Specifically, Myo1e deficiency caused increased rolling velocity, decreased firm adhesion, aberrant crawling, and strongly reduced transmigration. Interestingly, we observed a striking discontinuous rolling behavior termed “intermittent rolling,” during which Myo1e-deficient neutrophils showed alternating rolling and jumping movements. Surprisingly, chimeric mice revealed that these effects were due to Myo1e deficiency in leukocytes. Vascular permeability was not significantly altered in Myo1e KO mice. Myo1e-deficient neutrophils showed diminished arrest, spreading, uropod formation, and chemotaxis due to defective actin polymerization and integrin activation. In conclusion, Myo1e critically regulates adhesive interactions of neutrophils with the vascular endothelium and neutrophil extravasation. Myo1e may therefore be an interesting target in chronic inflammatory diseases characterized by excessive neutrophil recruitment.