Cholesterol redistribution within human platelet plasma membrane: evidence for a stimulus-dependent event

Area of Science:

• Cell Biology
• Membrane Biophysics
• Biochemistry

Background:

• The plasma membrane bilayer's lipid distribution is crucial for platelet function.
• Cholesterol's role in membrane dynamics and platelet activation is not fully understood.

Purpose of the Study:

• To investigate the distribution and movement of lipids, particularly cholesterol, within human platelet plasma membranes.
• To determine if platelet activation by agonists like collagen or ADP induces changes in lipid localization.

Main Methods:

• Utilized fluorescent lipid analogs: NBD-phosphatidylethanolamine, NBD-cholesterol, and cholestatrienol.
• Incorporated probes into platelets via phosphatidylcholine donor vesicles.
• Assessed lipid distribution by quenching fluorescence with dithionite and TNBS; measured endogenous cholesterol accessibility using cholesterol oxidase.

Main Results:

• Collagen or ADP stimulation led to a portion of cholestatrienol and NBD-cholesterol becoming inaccessible to quenching, indicating redistribution.
• Collagen stimulation decreased the accessibility of endogenous membrane cholesterol to cholesterol oxidase.
• NBD-phosphatidylethanolamine showed reciprocal movement into the outer monolayer coincident with cholesterol redistribution.

Conclusions:

• Platelet activation by collagen triggers stimulus-dependent translocation of cholesterol, likely to the inner monolayer.
• This cholesterol movement is accompanied by a reciprocal shift of phosphatidylethanolamine.
• Chaotropic agents inhibited cholestatrienol movement but not phosphatidylethanolamine redistribution, suggesting distinct mechanisms.