Amyloid beta peptide-activated signal pathways in human platelets.
Amyloid beta peptide (amyloid-beta), which accumulates in the cerebral microvessels in an age-dependent manner, plays a key role in the pathogenesis of cerebral amyloid angiopathy. Platelets are an important cellular element in vasculopathy of various causes. Amyloid-beta may activate or potentiate platelet aggregation. The present study explored the signaling events that underlie amyloid-beta activation of platelet aggregation. Platelet aggregometry, immunoblotting and assays to detect activated cellular events were applied to examine the signaling processes of amyloid-beta activation of platelets. Exogenous amyloid-beta (1-2 microM) potentiated platelet aggregation caused by collagen and other agonists. At higher concentrations (5-10 microM), amyloid-beta induced platelet aggregation which was accompanied by an increase in thromboxane A2 (TxA2) formation. These amyloid-beta actions on platelets were causally related to amyloid-beta activation of p38 mitogen-activated protein kinase (MAPK). Inhibitors of p38 MAPK and its upstream signaling pathways including proteinase-activated receptor 1 (PAR1), Ras, phosphoinositide 3-kinase (PI3-kinase), or Akt, but not extracellular signal-regulated kinase 2 (ERK2)/c-Jun N-terminal kinase 1 (JNK1), blocked amyloid-beta-induced platelet activation. These findings suggest that the p38 MAPK, but not ERK2 or JNK1 pathway, is specifically activated in amyloid-beta-induced platelet aggregation with the following signaling pathway: PAR1 --> Ras/Raf --> PI3-kinase --> Akt --> p38 MAPK --> cytosolic phospholipase A2 (cPLA2)--> TxA2. In conclusion, this study demonstrates amyloid-beta activation of a p38 MAPK signaling pathway in platelets leading to aggregation. Further studies are needed to define the specific role of amyloid-beta activation of platelets in the pathogenesis of vasculopathy including cerebral amyloid angiopathy.
Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
Ming Y
MY
Shen
George
G
Hsiao
Tsorng H
TH
Fong
Hui M
HM
Chen
Duen S
DS
Chou
Chien H
CH
Lin
Joen R
JR
Sheu
Chung Y
CY
Hsu
D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology; D048055:Mitogen-Activated Protein Kinase 8 / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology; D011799:Quinazolines / Q000494:pharmacology; D044463:Receptor, PAR-1 / Q000502:physiology; D044464:Receptor, PAR-2 / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
D016229:Amyloid beta-Peptides; C415424:N3-cyclopropyl-7-((4-(1-methylethyl)phenyl)methyl)-7H-pyrrolo(3, 2-f)quinazoline-1,3-diamine; D011758:Pyrroles; D011799:Quinazolines; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048055:Mitogen-Activated Protein Kinase 8; D048051:p38 Mitogen-Activated Protein Kinases