Engagement of platelet toll-like receptor 9 by novel endogenous ligands promotes platelet hyperreactivity and thrombosis.
BACKGROUND
A prothrombotic state and increased platelet reactivity are common in pathophysiological conditions associated with oxidative stress and infections. Such conditions are associated with an appearance of altered-self ligands in circulation that can be recognized by Toll-like receptors (TLRs). Platelets express a number of TLRs, including TLR9; however, the role of TLR in platelet function and thrombosis is poorly understood.


OBJECTIVE
To investigate the biological activities of carboxy(alkylpyrrole) protein adducts, an altered-self ligand generated in oxidative stress, on platelet function and thrombosis.


RESULTS
In this study we show that carboxy(alkylpyrrole) protein adducts represent novel unconventional ligands for TLR9. Furthermore, using human and murine platelets, we demonstrate that carboxy(alkylpyrrole) protein adducts promote platelet activation, granule secretion, and aggregation in vitro and thrombosis in vivo via the TLR9/MyD88 pathway. Platelet activation by TLR9 ligands induces IRAK1 and AKT phosphorylation, and it is Src kinase-dependent. Physiological platelet agonists act synergistically with TLR9 ligands by inducing TLR9 expression on the platelet surface.


CONCLUSIONS
Our study demonstrates that platelet TLR9 is a functional platelet receptor that links oxidative stress, innate immunity, and thrombosis.
Department of Molecular Cardiology, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Ave, NB-5, Cleveland, OH 44195, USA.
Soumya
S
Panigrahi
Yi
Y
Ma
Li
L
Hong
Detao
D
Gao
Xiaoxia Z
XZ
West
Robert G
RG
Salomon
Tatiana V
TV
Byzova
Eugene A
EA
Podrez
D000818:Animals; D001792:Blood Platelets / Q000276:immunology / Q000378:metabolism*; D018955:CD36 Antigens / Q000172:deficiency / Q000235:genetics; D002460:Cell Line; D004195:Disease Models, Animal; D017930:Genes, Reporter; D006801:Humans; D007113:Immunity, Innate; D053592:Interleukin-1 Receptor-Associated Kinases / Q000097:blood; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000172:deficiency / Q000235:genetics; D018384:Oxidative Stress; D058539:Phosphatidylinositol 3-Kinase / Q000097:blood; D010766:Phosphorylation; D015539:Platelet Activation; D010974:Platelet Aggregation; D051057:Proto-Oncogene Proteins c-akt / Q000097:blood; D051122:Scavenger Receptors, Class B / Q000172:deficiency / Q000235:genetics; D012709:Serum Albumin / Q000378:metabolism*; D015398:Signal Transduction; D013927:Thrombosis / Q000097:blood* / Q000235:genetics / Q000276:immunology; D013997:Time Factors; D051195:Toll-Like Receptor 2 / Q000172:deficiency / Q000235:genetics; D051216:Toll-Like Receptor 6 / Q000172:deficiency / Q000235:genetics; D051217:Toll-Like Receptor 9 / Q000097:blood* / Q000172:deficiency / Q000235:genetics; D014162:Transfection; D019061:src-Family Kinases / Q000097:blood
D018955:CD36 Antigens; D008024:Ligands; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D012709:Serum Albumin; C495371:TLR9 protein, human; C493486:Tlr2 protein, mouse; C495369:Tlr6 protein, mouse; C495370:Tlr9 protein, mouse; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6; D051217:Toll-Like Receptor 9; D058539:Phosphatidylinositol 3-Kinase; D019061:src-Family Kinases; D053592:Interleukin-1 Receptor-Associated Kinases; D051057:Proto-Oncogene Proteins c-akt