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Platelets roll on stimulated endothelium in vivo: an interaction mediated by endothelial P-selectin
P S Frenette1, R C Johnson, R O Hynes
1Center for Blood Research, Harvard Medical School, Boston, MA 02115, USA.
Abstract:
P-selectin, found in storage granules of platelets and endothelial cells, can be rapidly expressed upon stimulation. Mice lacking this membrane receptor exhibit a severe impairment of leukocyte rolling. We observed that, in addition to leukocytes, platelets were rolling in mesenteric venules of wild-type mice. To investigate the role of P-selectin in this process, resting or activated platelets from wild-type or P-selectin-deficient mice were fluorescently labeled and transfused into recipients of either genotype. Platelet-endothelial interactions were monitored by intravital microscopy. We observed rolling of either wild-type or P-selectin-deficient resting platelets on wild-type endothelium. Endothelial stimulation with the calcium ionophore A23187 increased the number of platelets rolling 4-fold. Activated P-selectin-deficient platelets behaved similarly, whereas activated wild-type platelets bound to leukocytes and were seen rolling together. Platelets of either genotype, resting or activated, interacted minimally with mutant endothelium even after A23187 treatment. The velocity of platelet rolling was 6- to 9-fold greater than that of leukocytes. Our results demonstrate that (i) platelets roll on endothelium in vivo, (ii) this interaction requires endothelial but not platelet P-selectin, and (iii) platelet rolling appears to be independent of platelet activation, indicating constitutive expression of a P-selectin ligand(s) on platelets. We have therefore observed an interesting parallel between platelets and leukocytes in that both of these blood cell types roll on stimulated vessel wall and that this process is dependent on the expression of endothelial P-selectin.
Insights
Platelets, like leukocytes, roll on blood vessel walls. This rolling depends on endothelial P-selectin, not platelet P-selectin, and occurs even without platelet activation.
Area of Science:
- Hematology
- Immunology
- Cell Biology
Background:
- P-selectin is a membrane receptor found in platelets and endothelial cells, crucial for leukocyte rolling.
- Leukocyte rolling is a key inflammatory process mediated by P-selectin.
Purpose of the Study:
- To investigate the role of P-selectin in platelet rolling on endothelium.
- To determine if platelet P-selectin or endothelial P-selectin mediates platelet rolling.
- To assess the influence of platelet activation on rolling behavior.
Main Methods:
- Fluorescently labeled wild-type and P-selectin-deficient platelets were transfused into recipient mice of either genotype.
- Intravital microscopy was used to monitor platelet-endothelial interactions in vivo.
- Endothelial cells were stimulated with the calcium ionophore A23187.
Main Results:
- Resting platelets from both wild-type and P-selectin-deficient mice rolled on wild-type endothelium.
- Endothelial stimulation significantly increased platelet rolling.
- Platelet rolling velocity was substantially higher than that of leukocytes.
- Platelet interaction with P-selectin-deficient endothelium was minimal, regardless of platelet activation status.
Conclusions:
- Platelets exhibit rolling behavior on endothelium in vivo.
- Endothelial P-selectin is essential for platelet rolling, while platelet P-selectin is not required.
- Platelet rolling is independent of platelet activation, suggesting constitutive expression of P-selectin ligands on platelets.
- Both platelets and leukocytes demonstrate P-selectin-dependent rolling on stimulated vessel walls.