EVASION

Arterial stiffness and atherosclerosis-related hypercoagulability increase the risk of stroke. Vascular smooth muscle cells (VSMCs) plays a pivotal role in the onset of atherothrombotic diseases. The ability of VSMCs to adapt is related to their high plasticity to reprogram their expression pattern in response to acute stimuli, mainly mediated by ligand-receptor interactions. Increased arterial stiffness and endothelial permeability influence the unidirectional outward convection of soluble substances from the blood across the arterial wall which, in turn, activates VSMC integrin receptors. Activation of mechanotransduction, de-endothelialisation-induced platelet activation and increased tissue factor have been proposed as potential mechanisms but can not explain all the interactions between coagulation and the arterial wall, in particular in age-dependent arterial wall stiffening. Integrin avb3 is expressed at high density on VSMCs and mediates attachment to vitronectin and to all other matrix proteins that display accessible Arg-Gly-Asp motifs. Integrin avb3 has been implicated in the mechanosensitive proliferative response and in the prevention of mechanical stretch-induced apoptosis of VSMCs. Integrin avb3 may also function as a receptor for prothrombin in VSMCs and increased VSMC-supported thrombin generation in response to mechanical forces is abolished by avb3 inhibitors. The main objective of the EVASION project is to gain a better understanding in the triggering mechanisms and the substratum underlying the central role of VSMC-expressed av integrins in linking arterial stiffness with thrombin generation within the vessel wall. Specifically, the project will consist of 4 workpackages: (i) generation of genetically modified mice with cell-specific av integrin mutation including inducible SMC-specific av knock-out and overexpression, and endothelial-specific av knock-out mice (ii) identification of the role of av pathways in VSMCs in arterial elasticity and thrombin generation within the vessel wall by determining the cardiovascular and coagulation phenotypes of av mutant mice at baseline and after induction of hypertension, investigating the cardiac, brain and vascular alterations by positron emission tomography and imaging focused on avb3 integrin and thrombin and by characterizing, using atomic force microscopy, the elasticity of VSMCs (iii) analysis of the impact of cell differentiation on av-mediated functions of VSMCs in stiffness and hemostasis by evaluating the effects of av invalidation or overexpression on serum response factor (SRF)-dependent VSMC differentiation and assessing the cross-talk between av integrin signalling and SRF activity in SRF gain or loss of function mouse models (iv) evaluation of the identified mechanisms in human aortic tissue or VSMCs and assessment of the clinical relevance of drugs targeting the avb3 pathway in the mouse models. The EVASION project is based on the complementary of 2 UMR Inserm (UMR_S 1116 and 698), 1 UMR CNRS (UMR 7588) and 1 research unit from Paris 6 (UR4), spanning a wide range of expertise from basic research, real-time monitoring of cell adhesion to clinical imaging and physiopathology. The consortium will interact with 3 industrial companies specialized in arterial stiffness, coagulation and imaging (Diatecne, Synapse B.V. and Nancyclotep). Strengths of the project will be (i) the integrative approach from transgenic mice to one particular integrin; (ii) the monitoring of thrombin generation directly on micro-samples of arterial tissues; (iii) the assessment of arterial stiffness (from single cell to the arterial wall); (iv) the imaging of the avb3 integrin pathway; and (v) the translational study of avb3 and VSMC differentiation markers from human biopsies. This proposal is expected to introduce new diagnostic and therapeutic approaches for aged individuals with systolic hypertension which drives atherosclerosis, aneurysm formation and other thromboembolic events.