Platelets are small anucleate blood cells that play a critical role in preventing blood loss, but also contribute to clot formation that can cause heart attacks and strokes, two leading causes of morbidity and mortality in the world.  The response of platelets to injury is controlled by the opposing activities of receptors found on their surface that either promote or prevent platelets from becoming sticky and forming blood clots. Triggering receptor expressed on myeloid cells-like transcript-1 (TLT-1) is platelet membrane receptor, which has been characterized and identified to play an important role in platelet biology.  TLT-1 is exclusively expressed on megakaryocytes and platelets, sequestered in a-granules and rapidly translocates to the surface of platelets upon activation.  By linking fibrinogen and modulating calcium signalling, but also by displaying anti-inflammatory properties, TLT-1 appears to play an important role in maintaining vascular homeostasis, regulating both adhesion, aggregation and inflammation at sites of vascular injury and infection.  Recent findings from our group have demonstrated that TLT-1 is a more sensitive marker of platelet and megakaryocyte activation than P-selectin, which can be detected in both the core and shell of thrombi in vivo.  This opens the possibility of TLT-1 being utilized as a biomarker for early detection of platelet activation in various pathologies, including coronary artery disease and deep vein thrombosis.

 

The central aim of this PhD proposal is to determine the functional and biochemical roles of TLT-1 in haemostasis and thrombo-inflammatory responses.  Determining how TLT-1 controls platelet stickiness has important implications for understanding why we bleed and form clots.  It will also shed new light on how platelets interact with neutrophils during mechanical injury and vascular inflammation.  This PhD project is divided into three areas of investigation.  The first aim is to determine the molecular mechanism by which TLT-1 signals and is compartmentalized in mouse and human platelets and megakaryocytes.  This will be achieved using pharmacological inhibitors, including the 17-mer peptide LR17, which has been shown to compete with TLT-1 for its ligand.  Von Willebrand Factor (VWF) blocking peptides will be used to examine VWF-mediated TLT-1 signalling events.  The second aim will be to determine the biological function of TLT-1 in regulating platelet production, clearance and functional responses through the use of a TLT-1 knockout (KO) mouse model.  The third aim will be to establish the consequences of TLT-1 deficiency on haemostasis, thrombosis and platelet-neutrophil interactions, following injury and inflammation.  Intravital microscopy will be used to monitor platelet production in vivo. Thrombosis in vivo and platelet-neutrophil interactions will be monitored following laser- and ferric chloride-induced vascular injury.  Sepsis models, including intraperitoneal lipopolysaccharide injection and caecal lining injury using caecal ligation and puncture (CLP) will be performed in order to determine the involvement of TLT-1 in these systemic and local process.

Findings from this proposal will open a new area of anti-platelet therapy, leading to a better understanding of the molecular mechanisms regulating platelet reactivity and identify novel signalling pathways that could be targeted in the treatment of cardiovascular disease.

Directeur de thèse : Alexandra Mazharian / Pierre mangin

Me contacter pierre.mangin@efs.sante.fr