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Intact Alzheimer amyloid precursor protein (APP) is present in platelet membranes and is encoded by platelet mRNA
J E Gardella1, J Ghiso, G A Gorgone
1Department of Pathology, State University of New York, Stony Brook.
Abstract:
Using antibodies directed against N-terminal and C-terminal epitopes we have immunologically detected APP species in the membrane and saline-soluble fractions of unstimulated platelets, and in the conditioned medium of thrombin-stimulated platelets. These studies demonstrate an intact 140 kD membrane-associated form of APP that is released on degranulation. Evidence that platelets synthesize at least one form of APP (APP751) was obtained by enzymatic amplification of specific mRNA using Polymerase Chain Reaction (PCR) and direct sequence analysis of PCR product. Processing of APP for release may occur via successive C-terminal truncations, and/or by the release and proteolysis of an intact membrane associated form. An intact form of APP in platelets provides a circulating substrate upon which proteases from many tissues may act to produce beta protein (AB) during pathologic conditions.
Insights
Platelets release an intact 140 kD membrane-associated amyloid precursor protein (APP) upon stimulation. This circulating APP may serve as a substrate for beta protein (AB) production in pathological conditions.
Area of Science:
- Biochemistry
- Molecular Biology
- Hematology
Background:
- Platelets are known to play a role in hemostasis and thrombosis.
- Amyloid precursor protein (APP) is implicated in various neurological disorders.
- The presence and processing of APP in platelets are not fully understood.
Purpose of the Study:
- To investigate the presence and characteristics of APP in human platelets.
- To determine if platelets synthesize APP.
- To elucidate the mechanism of APP release from platelets.
Main Methods:
- Immunological detection of APP species using N-terminal and C-terminal antibodies.
- Analysis of APP in platelet membrane and soluble fractions.
- Detection of APP in conditioned medium of thrombin-stimulated platelets.
- Reverse transcription-polymerase chain reaction (RT-PCR) to detect APP mRNA.
- Direct sequence analysis of PCR products.
Main Results:
- An intact 140 kD membrane-associated APP was detected in unstimulated platelets.
- This intact APP form is released from platelets upon degranulation (thrombin stimulation).
- Evidence suggests platelets synthesize at least one form of APP (APP751) via mRNA.
- APP processing may involve C-terminal truncations or release of the intact membrane-associated form.
Conclusions:
- Platelets contain and release an intact, membrane-associated form of APP.
- Platelets possess the machinery to synthesize APP.
- Released platelet APP may act as a substrate for beta protein (AB) production in pathological states.