In vitro, ex vivo and in vivo analysis of TGFbeta-induced podosomes in aortic endothelial cells – VASCULOSOMES

Scientific background and objectives

Podosomes are adhesive actin-based microdomains of the plasma membrane located at the ventral side of the cell. Like focal adhesions, numerous structural proteins and signalling components are found at podosomes. However, podosomes differ from classical adhesion structures by their molecular composition, their high turnover driven by a strong actin polymerisation activity and by the presence of metalloproteases around the actin core. Podosomes are found in a restricted number of cell types, cells of the monocytic lineage such as phagocytes, immature dendritic cells and osteoclasts, where they are now well characterised. We have discovered that aortic endothelial cells can also form podosomes when exposed to physiological TGFb concentrations and, focusing our research on this theme, we have kept the leadership in this field. The inducible nature of podosomes in this model and the specificities of the vessel, provides us with a unique opportunity: to study their formation and functional significance in situ in living tissues. Our research programme aims at understanding the role played by podosomes at the vessel level. The first goal of this ambitious project has now been achieved. We have brought evidence for the occurrence of podosomes in living aortic vessel segments exposed to exogenous TGFb. These podosomes degrade the underlying basement membrane (notably the collagene IV network). In this project, we will set up experiments which will enable us to bring evidence for the occurrence of podosomes in vivo, in response to endogenous TGFb release. We will then attempt to understand the consequences of these events in terms of vascular pathophysiology.
Endothelial cells are at the core of many physiological and pathological processes, in which TGFb plays a pivotal role, and this justifies a thorough understanding of the role of podosomes in endothelial cell functioning. Importantly, a number of pathological conditions affecting cells of the myelo-monocytic lineage appear to be associated with a lack of podosomes. Likewise, we wish to establish whether or not some vascular diseases are associated with a lack or to an excess of podosome forming endothelial cells, to determine if alterations in TGFb signalling correlate with endothelial podosome formation capacities. Thus, increasing our knowledge of these structures, notably their characteristics and the mechanisms which regulate their assembly and disassembly, is relevant in order to elaborate novel therapeutic strategies in the long term.