The topic platelets / cellular and vascular aspects aims to decipher the cellular and molecular mechanisms regulating the quantity of platelets and their hemostatic functions. Platelets play a key role in stopping bleeding, research within the INSERM unit addresses the different aspects of platelet activation, both the early phases and the more advanced phases such as thrombus formation (figure below).

One of the lines of research focuses on the involvement of the cytoskeleton, signaling proteins and the regulation of calcium signaling (notably Serca3 pumps), in the formation and activation of platelets. The cytoskeleton is an essential actor by its implication on their formation, the morphology of platelets, secretion, … Better understanding, but also defining new actors involved in these mechanisms, are essential issues in particular in pathologies inducing morphological defects (macro- or microplatelets) or the number of platelets (thrombocytopenia) or platelet activation defects. The laboratory uses both megakaryocytes in culture as well as human and mouse platelets and cell lines.

A second line of research concerns the regulation of the quantity of platelets on the periphery. In this theme, our laboratory is particularly interested in the role of sialic acid and the exposure of β-galactose, a senescence signal regulating the clearance of platelets.

An important axis of our research relates to the study of known platelet pathologies such as filaminopathies A, type 2B Willebrand disease or even the study of pathologies associated with unexplained hemorrhagic events. In this context, our objective is to assess and better understand the molecular mechanisms underlying these pathologies. A second part of this axis concerns the monitoring of patients treated with clinical protocols (monitoring of Wiskott-Aldrich patients treated with gene therapy).

To carry out all of these studies, we have multiple models, such as:

– animal models,

– access to patient samples,

– primary cell lines developed in the laboratory,

– our laboratory works in close collaboration with the hospital and clinical research, which is a major advantage in being able to make a link with basic research and clinical research. 

The research projects within this theme are organized around the coagulation cascade (see below) whose main focus is the arrest of bleeding after a vascular breach. Procoagulant molecules are here represented in green.

We are particularly interested in the structure-function relationships of specific hemostatic proteins, mostly those whose absence or modification (e.g. mutations) lead to congenital hemorrhagic disorders. Among these, von Willebrand factor involved in von Willebrand disease, factor VIII in hemophilia A or factor IX in hemophilia B. We are also studying proteins which can be used therapeutically to treat these pathologies such as factor X or factor VIIa.

In order to study these proteins, we are developing, in-house, a number of biological tools such as nanobodies or VHH (single-domain antibodies found in camelids). These nanobodies are extremely useful, both as research tools to better characterize our proteins of interest but also as potential new therapeutics.

Indeed, we are taking advantage of our expertise in hemostasis in order to develop innovative therapies for the treatment of hemorrhagic disorders, whether using gene therapy approaches of through more classical approaches based on protein therapy (nanobodies or engineered coagulation factors).

As an example, in order to treat hemophilia, we have recently developed a new factor VIII molecule with improved pharmacokinetics and reduced immunogenicity properties (see below).

For von Willebrand disease, we are currently developing an ambitious project in the framework of the RHU WillAssistHeart program, coordinated by Pr. Susen (CHU Lille). This project aims to better understand the acquired von Willebrand syndrome, experienced by patients put under mechanical circulatory support devices or patients suffering from severe aortic stenosis. The ultimate goal of the project consists in better answering the hemostatic challenges present in these patients, mainly at the gastro-intestinal level.

The figure below summarizes the current hypothesis of the pathological mechanism involved.

We are working in collaboration with the French Reference Center of von WIllebrand Disease (CRMW) within the framework of the French rare diseases network on hemorrhagic disorders, MHEMO.

Our research projects benefit from funding either private of governmental, ensuring their progress. We also work with national and international collaborators, allowing us to develop our projects efficiently, benefiting from complementary expertise/biological tools not present in our own hands.

Our group is also involved and active with patient’s associations such as the French Hemophilia Association (AFH). Regular laboratory visits/exchanges are organized for the patients.

The research projects within this theme are organized around the natural anticoagulant proteins of the coagulation cascade (represented in red on the figure below). We are not only interested in their anti-coagulant effect per se but also to their cellular effects, allowing them to be molecular players beyond hemostatic processes and in inflammation in particular. The main proteins at the core of our research projects are antithrombin, the protein Z/ZPI complex and the protein C system.

Our previous work, especially on antithrombin, has allowed us to gain significant expertise on Serpins (Serine Protease Inhibitors) (see figure below).

Based on this expertise, we have previously developed the first antidote against fondaparinux, a synthetic pentasacharide that inhibits factor Xa and is used as an anticoagulant drug. This antidote was developed using a modified antithrombin molecule.

Our current projects on Serpins aim to 1) Target antithrombin in order to restore the hemostatic balance in hemophilia and 2) Better understand the structure-function relationships of ZPI, the protein Z-dependent inhibitor which is one of the least known serpins. Our objective consists in better understand ZPI function in inflammatory and thrombotic pathologies but also in hemophilia. For this purpose, we relay partially on the development in our team of nanobodies or VHH (single-domain antibodies found in camelids) directed against this protein.

With regards to the protein C system, our focus is mainly on protein S and we wish to evaluate whether it is possible to modulate the anticoagulant activity of protein S, using nanobodies against this molecule. Also, such nanobodies can help us to better identify the molecular determinants underlying the various functions of protein S.

Beyond the fundamental research projects that we are currently developing, our group has an important clinical activity and we are particularly interested in Congenital Disorders of Glycosylation (CDG) and their associated hemostatic defects. This activity is carried out in the framework of the French Reference Center for CDG, coordinated by Necker Hospital.

All of these projects benefit from national and international collaborations in order to ensure their smooth progression.