The septic milieu triggers expression of spliced tissue factor mRNA in human platelets

Abstract

The septic milieu triggers expression of spliced tissue factor mRNA in human platelets. J Thromb Haemost 2011; 9: 748-58.Summary. Background: Activated platelets have previouslyunrecognized mechanisms of post-transcriptional gene expression that may influence hemostasis and inflammation. A novel pathway involves splicing of pre-mRNAs in resting platelets to mature, translatable mRNAs in response to cellular activation. Objectives: We asked if bacterial products and host agonists present in the septic milieu induce tissue factor pre-mRNA splicing in platelets from healthy subjects. In parallel, we asked if spliced tissue factor (TF) mRNA is present in platelets from septic patients in a proof-of-principle analysis. Patients/methods: TF pre-mRNA and mRNA expression patterns were characterized in platelets from septic patients and in platelets isolated from healthy subjects activated with bacteria, toxins and inflammatory agonists. Procoagulant activity was also measured. Results and conclusions: Live bacteria, staphylococcal a-toxin and lipopolysaccharide (LPS) induced TF premRNA splicing in platelets isolated from healthy subjects. Toxin-stimulated platelets accelerated plasma clotting, a response that was blocked by a previously-characterized splicing inhibitor and by an anti-tissue factor antibody. Platelets from septic patients expressed spliced TF mRNA, whereas it was absent from unselected and age-matched control subjects. Tissue factor-dependent procoagulant activity was elevated in platelets from a subset of septic patients. Thus, bacterial and host factors induce splicing of TF pre-mRNA, expression of TF mRNA and tissue factor-dependent clotting activity in human platelets. TF mRNA is present in platelets from some septic patients, indicating that it may be a marker of altered platelet phenotype and function in sepsis and that splicing pathways are induced in this syndrome.

Selective release of circRNAs in platelet‐derived extracellular vesicles

“…Platelets are peculiar in that they are, first, relatively short-lived (~7 days half-life); second, they are the smallest cells of blood, and third, although without a nucleus, they exhibit active RNA metabolism and are translationally active [2–5]. During thrombopoiesis, anucleated platelets are derived from megakaryocytes in the bone marrow and are released into the bloodstream.…”

Platelets in infectious disease

“…For example, in response to in vitro stimulation, LPS, thrombin, bacteria, and bacterial toxins, human platelets process constitutively present tissue facture (TF) pre-mRNA, resulting in a mature TF transcript, synthesis of TF protein, and generation of TF-dependent procoagulant activity. 24 Moreover, platelets from septic patients, but not healthy controls, express the mature, spliced TF mRNA, demonstrating that the septic milieu may alter the platelet transcriptome. 24 Preliminary analyses of next-generation RNA sequencing data ("deep sequencing") performed on platelets from septic patients identified numerous transcripts that are significantly altered compared with matched, healthy control subjects.…”

“…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.…”

Platelets in sepsis — are there any new aspects?

“…According to the authors, platelets from septic patients express mature, spliced TF mRNA revealing that sepsis may alter the platelet transcriptome. Many of these changed transcripts increase host defences to pathogens [20]. In sepsis, alterations in platelet number and function are correlated with a high risk of morbidity and mortality.…”

“…Rondina et al [20] proved that bacterial and host factors induce splicing of TF pre-mRNA, expression of TF mRNA and tissue factor-dependent clotting activity in human platelets. According to the authors, platelets from septic patients express mature, spliced TF mRNA revealing that sepsis may alter the platelet transcriptome.…”