HOW PERICELLULAR MATRIX ORCHESTRATES THE ANGIOGENIC-TO-FIBROTIC TRANSITION – ANGIO-FIB

Many diseases are associated with the progressive transformation of vascularized tissue to a fibrotic state. This is accompanied by structural and functional alterations in the microvasculature which can lead to cell death or trigger coping mechanisms such as endothelial-to-mesenchymal transition (EndoMT). While much has been learned about the accumulation of extracellular matrix (ECM) components during the tissue fibrosis, little is known about how the pericellular ECM regulates molecular and cellular signaling events that underlie this conversion. Whereas a variety of receptors can mediate cell binding to the ECM, members of the integrin family are the most extensively studied. Integrins are integral membrane proteins that link the extracellular matrix to the cytoskeleton and regulate cellular function by assembling signaling platforms at their cytoplasmic domain. These adhesion complexes allow cells to integrate multiple extracellular signals and specify the chemical identity, geometry and physical properties of the ECM. Conversely, integrins mediate the cell-driven assembly and remodeling of the ECM having thus a pronounced impact on integrin, growth factor and cytokine signaling.
The overarching goal of this project is to understand how the ECM regulates the balance between angiogenesis and fibrosis and how to tip this balance and avoid a fibrotic state. To this end, we propose to investigate how the composition and mechanobiology of ECM tune cell behavior, leading under certain conditions to an EndoMT. Co-regulatory and counterbalancing effects are crucial to the robustness of biological responses to environmental challenges. We will focus on how a few selected molecular ECM players, known to counterbalance each other’s effects, synchronize and orchestrate the onset of vascular remodeling and fibrosis. The adhesive protein fibronectin (FN) is highly upregulated in early vascular development and in diseased connective tissue. Tenascin-C (TNC) is an adhesion-modulatory ECM component that interacts with FN and appears to function as accomplice in many diseased tissues where the two molecules are co-overexpressed.
Our first Aim addresses the biomechanical properties of the molecules, their inter- and intra-molecular interactions and post-translational modifications. We will elucidate the counteracting roles of FN and TNC on cell traction forces, ECM remodeling and EndoMT, and determine how these effects are modulated by the presence of alternatively spliced (EDA and EDB) domains of FN, for which the physiological roles are still not understood despite major efforts. The functional impact of posttranslational modifications of extracellular domains of FN and TNC will be analyzed, with a focus on extracellular phosphorylation for which little is known to date. Our second Aim is to decipher the roles of conventional and non-conventional (a9b1) integrins in mediating counter regulatory signals from FN and TNC, following our recent observations. This aim will also address the functional impact of phosphorylation of integrin extracellular domains. In our third Aim, the translation of ECM signals to nuclear events will be investigated, with a focus on MKL1 and YAP signaling as key molecular sensors of actin cytoskeletal dynamics that are inhibited by TNC and stimulated by FN. In our fourth Aim we will address using different cellular in vitro and in ex vivo models the impact of relevant signaling systems in a defined TNC context on sprouting angiogenesis and fibrotic responses.
This challenging question is far too great for any one of our laboratories to answer alone, since it requires not only excellent basic sciences, but also transdisciplinary expertise and technologies, including cell biology, molecular biology, mechanobiology, and nanotechnology, state of the art imaging and computational techniques. These are skills that our team combines, particularly in the fields of extracellular matrix (mechano)biology and integrins.