CONICET | Buscador de Institutos y Recursos Humanos

Background: In addition to their key role in hemostasis, platelets and megakaryocytes also regulate immune and inflammatory responses, in part through their expression of Toll-like receptors (TLRs). Among the TLRs, TLR3 recognizes double-stranded (ds) RNA associated with viral infection. Thrombocytopenia is a frequent complication of viral infection. However, the expression and functionality of TLR3 in megakaryocytes and platelets is not yet well understood. Objective: To study the expression and functionality of TLR3 in the megakaryocytic lineage. Methods and Results: RT-PCR, flow cytometric, and immunofluorescence assays showed that TLR3 is expressed in CD34+ cells, megakaryocytes, and platelets. Immunoblotting assays showed that stimulation of megakaryocytes with two synthetic agonists of TLR3, Poly(I:C) and Poly(A:U), activated the NF-B, PI3K/Akt, ERK1/2, and p38 pathways. TLR3-megakaryocyte activation resulted in reduced platelet production in vitro and IFN- release through the PI3K/Akt and NF-B signaling pathways. TLR3 ligands potentiated the aggregation mediated by classical platelet agonists. This effect was also observed for ATP release, but not for P-selectin or CD40L membrane exposure, indicating that TLR3 activation was not involved in alpha granule release. In addition, TLR3 agonists induced activation of the NF-B, PI3K/Akt, and ERK1/2 pathways in platelets. Reduction of platelet production and platelet fibrinogen binding mediated by Poly(I:C) or Poly(A:U) were prevented by the presence of an inhibitor of TLR3/dsRNA complex . Conclusions: Our findings indicate that functional TLR3 is expressed in CD34+cells, megakaryocytes, and platelets, and suggest a potential role for this receptor in the megakaryo/thrombopoiesis alterations that occur in viral infections.