Nanoscale imaging of CD47 informs how plasma membrane modifications shape apoptotic cell recognition

Area of Science:

• Cell Biology
• Immunology
• Biophysics

Background:

• CD47 acts as a
• don't eat-me
• signal, preventing phagocytosis by macrophages via SIRPα (Signal Regulatory Protein Alpha).
• The mechanism by which apoptosis-induced plasma membrane changes abrogate CD47 function and expose
• eat-me
• signals like phosphatidylserine and calreticulin remains unclear.

Purpose of the Study:

• To investigate the relationship between plasma membrane alterations during apoptosis, the distribution of CD47 and
• eat-me
• signals, SIRPα binding, and macrophage-mediated phagocytosis.
• To elucidate how CD47 mobility and accessibility are affected by apoptosis and membrane changes.

Main Methods:

• Super-resolution microscopy (STORM) for high-resolution imaging of cell surface molecules.
• Single-particle tracking to analyze molecular dynamics.
• Investigating the impact of lipid bilayer modifications (e.g., cholesterol levels) and integrin affinity on CD47 behavior.

Main Results:

• Apoptosis leads to calreticulin clustering in blebs and increased CD47 mobility.
• CD47 mobility is influenced by integrin affinity, but SIRPα binding is not directly affected.
• Cholesterol destabilization disrupts CD47/SIRPα interaction, and SIRPα fails to recognize CD47 on apoptotic blebs.
• Plasma membrane disorganization, potentially causing CD47 conformational changes and inaccessibility, is key to initiating phagocytosis.

Conclusions:

• Plasma membrane lipid bilayer disorganization during apoptosis is central to abrogating CD47's
• don't eat-me
• signal.
• Inaccessibility of CD47, possibly due to conformational changes induced by membrane alterations, facilitates phagocytosis.
• Understanding these mechanisms provides insights into immune evasion strategies and potential therapeutic targets.