β Protein precursor expression in human platelets and a megakaryocyte cell line: Possible implications for the origin of cerebral amyloidosis in Alzheimer's disease

J. E. Gardella, G. A. Gorgone, P. C. Munoz, J. Ghiso, B. Frangione, P. D. Gorevic

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

BACKGROUND: The origin of the amyloid beta protein (Aβ) that is the main constituent of amyloid fibrils occurring in the senile plaques and cerebrovasculature of individuals afflicted with Alzheimer's Disease, Down's Syndrome, Hereditary Cerebral Hemorrhage with Amyloidosis-Dutch Type, and Sporadic Cerebral Amyloid Angiopathy, is central to the pathogenesis of these disorders. Evidence exists to support a neuronal and/or a vascular origin. We have reported that platelets may serve as one possible source of the Aβ sequence via an intact, membrane-associated Beta Protein Precursor (βPP) which is encoded by a platelet transcript (BBRC 173:1292-1298, 1990). EXPERIMENTAL DESIGN: Immunoaffinity chromatography and western blotting of extracted cellular proteins, polymerase chain reaction amplification of βPP mRNA, fluorescence activated flow cytometric analysis, and confocal scanning laser microscopy have been employed to characterize the presence and distribution of thrombocytic βPP. RESULTS: Immunoblot analysis with antibodies specific for the carboxyl-terminal end of βPP indicates that platelets and the Dami megakaryocyte cell line express membrane-associated species of intact βPP ranging in molecular weight from 110 to 140 kilodaltons (kd), as well as carboxyl-terminal reactive forms ranging from 16 to 22 kd. Thrombin stimulation of platelets induces the release of five soluble βPP species, which possess apparent isofocusing points in the range of 4.1-5.5. By contrast, extracts of peripheral blood mononuclear cells enriched by ficoll centrifugation, endothelial cells and a B cell line were not immunoreactive by western blot, even though βPP transcripts could be amplified by polymerase chain reaction. The distribution of platelet βPP was localized by flow cytometric analysis and scanning laser microscopy, using fluorescein-labeled antibodies. Study of the subcellular distribution of platelet βPP indicates that these translation products are accumulated in discrete foci throughout the thrombocyte, possibly corresponding to secretory granules. CONCLUSIONS: The size of the carboxyl-terminal forms of βPP indicate that the Aβ sequence is present as a membrane associated constituent in unstimulated platelets, and may represent alternative pathways of βPP processing. Cleavage or other abnormal processing of platelet- associated βPP in Alzheimer's disease provides one mechanism whereby cerebral amyloid might derive from the circulation.

Original languageEnglish
Pages (from-to)303-313
Number of pages11
JournalLaboratory Investigation
Volume67
Issue number3
StatePublished - 1992
Externally publishedYes

Keywords

  • Amyloid β-protein precursor
  • Platelet

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