Stimulus responses and amyloid precursor protein processing in DAMI megakaryocytes

Area of Science:

• Cell Biology
• Neuroscience
• Hematology

Background:

• Platelets contain amyloid precursor protein (APP) and its fragments, implicated in Alzheimer's disease (AD) due to A beta deposition.
• Activated platelets release APP, suggesting a role in A beta generation and AD pathogenesis.

Purpose of the Study:

• To investigate APP processing and content in megakaryocytic cells (DAMI cells) and human platelets.
• To compare APP translocation and release mechanisms in resting and activated DAMI cells versus platelets.

Main Methods:

• Western blotting, immunoprecipitation, and metabolic labeling (35S-methionine) to analyze APP in DAMI cells.
• Flow cytometry to assess plasma membrane-bound APP and CD63.
• Monitoring calcium concentration and membrane potential changes upon thrombin activation.

Main Results:

• Resting DAMI cells express granule membrane proteins (APP, CD63) on their surface, unlike platelets.
• Thrombin activation of DAMI cells and platelets causes dose-dependent increases in calcium and membrane potential changes.
• Megakaryocytes synthesize APP, which is extensively degraded before platelet formation, with APP being slightly higher in molecular weight.

Conclusions:

• Megakaryocytes, the precursors of platelets, synthesize and extensively process APP.
• DAMI cells exhibit distinct APP localization compared to platelets, with surface expression in resting states.
• Understanding APP processing in megakaryocytes and platelets is crucial for investigating Alzheimer's disease.