Activated platelets mediate inflammatory signaling by regulated interleukin 1β synthesis

Abstract

Platelets release preformed mediators and generate eicosanoids that regulate acute hemostasis and inflammation, but these anucleate cytoplasts are not thought to synthesize proteins or cytokines, or to influence inflammatory responses over time. Interrogation of an arrayed cDNA library demonstrated that quiescent platelets contain many messenger RNAs, one of which codes for interleukin 1β precursor (pro–IL-1β). Unexpectedly, the mRNA for IL-1β and many other transcripts are constitutively present in polysomes, providing a mechanism for rapid synthesis. Platelet activation induces rapid and sustained synthesis of pro–IL-1β protein, a response that is abolished by translational inhibitors. A portion of the IL-1β is shed in its mature form in membrane microvesicles, and induces adhesiveness of human endothelial cells for neutrophils. Signal-dependent synthesis of an active cytokine over several hours indicates that platelets may have previously unrecognized roles in inflammation and vascular injury. Inhibition of β3 integrin engagement markedly attenuated the synthesis of IL-1β, identifying a new link between the coagulation and inflammatory cascades, and suggesting that antithrombotic therapies may also have novel antiinflammatory effects.

Quantification of ADP and ATP receptor expression in human platelets

“…Compared with buffy coat, P2X 1 in platelets was much higher than that in buffy coat (P < 0.0001) and P2Y 1 in platelets was lower than that in buffy coat (P < 0.05). In buffy coat (n ¼ 3), P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 11 , P2Y 12 , P2Y 13 , P2X 1 , P2X 4 and P2X 7 could be detected, but P2X 1 , P2X 4 and P2X 7 were present in low levels (Fig. 1b).…”

“…In platelets (n ¼ 9), P2Y 12 , P2X 1 and P2Y 1 were the most abundantly expressed mRNAs, while P2Y 2 , P2Y 4 , P2Y 6 , P2Y 11 , P2Y 13 , P2X 4 , and P2X 7 had extremely low expression levels (Fig. 1a).…”

“…Oligonucleotide primers and TaqMan probes were designed using the Primer Express software, based on sequences from the GenBank database. Primer and probe sequences have previously been reported in Wang et al [22] except P2Y 12 and P2Y 13 ( Table 1). Each primer pair was selected so that the amplicon spanned an exon junction if present, to avoid amplification of genomic DNA.…”

“…These P2 receptors include two subgroups: fast, ionotropic P2X receptors and P2Y receptors, which are G protein-coupled receptors. At least seven subtypes of P2X (P2X 1À7 ) and seven subtypes of P2Y (P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 11 , P2Y 12 and P2Y 13 ) have been identified in human tissue.…”

“…Platelets have no ability to produce new mRNA due to their lack of a nucleus. It was recently demonstrated that activated platelets translate constitutive mRNAs into proteins [13][14][15]. Activation of platelets does not appear to decrease their life span [16][17][18], and this may be related to functional mRNAs in platelets.…”