Platelets possess functional TGF-beta receptors and Smad2 protein.
TGF-beta1 plays a main role in tissue repair by regulating extracellular matrix production and tissue granulation. Platelets are one of the main sources of this cytokine in the circulation. The aim of this study was to evaluate the presence of the TGF-beta receptors on platelets, the effect of TGF-beta1 on platelet aggregation and the underlying intracellular mechanisms. TGF-beta receptors on platelets were studied by flow cytometry and their mRNA by PCR. Platelet aggregation was assessed by turbidimetric methods and intracellular pathways by Western blot. TGF-beta receptor type II and mRNA codifying for TbetaRI and TbetaRII were found in platelets. We demonstrated that TGF-beta1 did not trigger platelet aggregation by itself but had a modulating effect on ADP-induced platelet aggregation. Either inhibition or increase in platelet aggregation, depending on the exposure time to TGF-beta1 and the ADP concentration used, were shown. We found that platelets possess Smad2 protein and that its phosphorylation state is increased after exposure to TGF-beta1. Besides, TGF-beta1 modified the pattern of ADP-induced tyrosine phosphorylation. Increased phosphorylation levels of 64-, 80- and 125-kDa proteins during short time incubation with TGF-beta1 and increased phosphorylation of 64- and 125-kDa proteins after longer incubation were observed. The modulating effect of TGF-beta1 on platelet aggregation could play a role during pathological states in which circulating TGF-beta1 levels are increased and intravascular platelet activation is present, such as myeloproliferative disorders. In vascular injury, in which platelet activation followed by granule release generates high local ADP concentrations, it could function as a physiological mechanism of platelet activation control.
Lev
P R
PR
Facultad de Medicina, Instituto de Investigaciones Medicas Alfredo Lanari, Universidad de Buenos Aires, Buenos Aires, Argentina. paolal2002@yahoo.com.ar
Salim
J P
JP
Marta
R F
RF
Osorio
M J Mela
MJ
Goette
N P
NP
Molinas
F C
FC
D030201:Activin Receptors, Type I / Q000097:blood* / Q000235:genetics; D000244:Adenosine Diphosphate / Q000494:pharmacology; D001798:Blood Proteins / Q000378:metabolism; D004357:Drug Synergism; D006801:Humans; D008970:Molecular Weight; D010750:Phosphoproteins / Q000097:blood; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000097:blood; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects* / Q000502:physiology; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000097:blood; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000097:blood* / Q000235:genetics; D015398:Signal Transduction; D051899:Smad2 Protein / Q000097:blood*; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000097:blood / Q000494:pharmacology / Q000502:physiology*
D001798:Blood Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; D051899:Smad2 Protein; C508960:TGFB1 protein, human; D053773:Transforming Growth Factor beta1; D019000:Phosphotyrosine; D000244:Adenosine Diphosphate; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II