Lipopolysaccharide Is a Direct Agonist for Platelet RNA Splicing

Abstract

Platelets express TLR4 receptors, but its ligand LPS does not directly activate thrombotic functions nor, obviously, transcription by these anucleate cells. Platelets, however, store information that changes their phenotype over a few hours in the form of unprocessed RNA transcripts. We show even low concentrations of LPS in the presence of soluble CD14 initiated splicing of unprocessed IL-1β RNA, with translation and accumulation of IL-1β protein. LPS was a more robust agonist for this response than thrombin. Platelets also contained cyclooxygenase-2 pre-mRNA, which also was spliced and translated after LPS stimulation. Flow cytometry and immunocytochemistry of platelets extensively purified by negative immunodepletion showed platelets contained IL-1β, and quantitative assessment of white blood cell contamination by CD14 real time PCR confirms that leukocytes were not the IL-1β source, nor were they required for platelet stimulation. LPS did not initiate rapid platelet responses, but over time did prime platelet aggregation to soluble agonists, induced actin rearrangement, and initiated granule secretion with P-selectin expression that resulted the coating of quiescent leukocytes with activated platelets. LPS is a direct agonist for platelets that allows these cells to directly participate in the innate immune response to bacteria.

Platelets mediate increased endothelium permeability in dengue through NLRP3-inflammasome activation

“…It is known that activated platelets mediate inflammatory and immune responses using a variety of mechanisms, including release of stored cytokines and synthesis of others, among them IL-1b. 17,18,27 Our results indicate that DV induces platelets to synthesize IL-1b. A previous report from our group demonstrates that increased IL-1b in dengue patients correlates with thrombocytopenia.…”

“…8,27 The ability of platelets to splice premRNA and synthesize IL-1b by translating the mature mRNA transcript has been well demonstrated in vitro. 17,18 Most recently, synthesis of IL-1b by platelets in vivo has been reported in mice with Figure 1. IL-1b synthesis in DV-infected platelets and platelets from healthy volunteers.…”

“…16 The ability of activated platelets to splice constitutive introncontaining IL-1b pre-RNA to produce mature IL-1b mRNA and synthesize IL-1b has been previously demonstrated. [17][18][19] Nevertheless, the mechanisms involved in IL-1b processing and secretion by platelets remains elusive. It has been previously shown that lipopolysaccharide (LPS)-stimulated platelets release IL-1b packaged into microparticles (MPs).…”

Platelets in infectious disease

“…LPS activates human platelets both in vitro and during in vivo settings, where healthy volunteers are challenged with low doses of LPS, although activation patterns are variable. [22][23][24] However, murine platelets exposed to LPS have demonstrated increased adherence to fibrinogen despite no increase in activation, a lack of fibrin clot formation, and no evidence of degranulation by electron microscopy. Interestingly, LPS has also been shown to lead to pre-mRNA splicing and protein synthesis, 24 alterations in surface CD40L, 25 and trafficking of platelets to the pulmonary capillaries in murine models of endotoxemia.…”

Platelet hyaluronidase-2: an enzyme that translocates to the surface upon activation to function in extracellular matrix degradation

“…Platelet TLR4, for instance, can bind bacterial lipopolysaccharide, whereas TLR9 expressed on activated platelets can mediate bacterial DNA sequestration. 26,27 In this article, we define a novel mechanism by which platelets modify the ECM. We demonstrate that after activation, platelets degrade the proinflammatory matrix by using HYAL2.…”